Influence of hole eccentricity on failure progression in a double shear bolted joint (DSBJ) Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-22 Alastair M. Croxford, Paul Davidson, Anthony M. Waas
Experimental results on the influence of bolt hole to edge eccentricity for Double Shear Bolted Joints (DSBJ) used to attach fiber reinforced composite laminates are presented. Four different eccentricities of DSBJs were examined and microCT imaging conducted at different stages of the loading history are presented. The macroscopic load-hole elongation results along with the microCT images exhibit a distinct progression of failure which dictate not only the bearing load but also the ultimate load of the joint. The experimental procedure, microCT images and failure progression mechanisms are reported in this paper. The results can serve to develop a mechanism based model of DSBJ failure progression.
An analytical model of square CFRP tubes subjected to axial compression Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-24 Rafea Dakhil Hussein, Dong Ruan, Guoxing Lu
A novel analytical model has been developed to predict the mean crushing force of square carbon fibre reinforced plastic (CFRP) tubes subjected to axial crushing. The model has captured the experimentally observed major energy dissipating mechanisms of CFRP tubes under axial compression, i.e. crack propagation, transverse shearing and friction. Transverse shearing has been taken into account for the first time in this model. Quasi-static compressive tests have been conducted on 16 square CFRP tubes with various side lengths and wall thicknesses to determine their mean crushing forces. The discrepancy between analytically predicted and experimentally measured mean crushing forces of these square CFRP tubes is no more than 7%. Moreover, the proposed analytical model is very simple with only several parameters, which can be determined via relatively simple experimental tests.
Multiscale approach for identification of transverse isotropic carbon fibre properties and prediction of woven elastic properties using ultrasonic identification Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-21 R.D.B. Sevenois, D. Garoz, E. Verboven, S.W.F. Spronk, F.A. Gilabert, M. Kersemans, L. Pyl, W. Van Paepegem
In this work the possibility to reverse engineer the transverse isotropic carbon fibre properties from the 3D homogenized elastic tensor of the UD ply for the prediction of woven ply properties is explored. Ultrasonic insonification is used to measure the propagation velocity of both the longitudinally and transversally polarized bulk waves at various symmetry planes of a unidirectional (UD) Carbon/Epoxy laminate. These velocities and the samples' dimensions and density are combined to obtain the full 3D orthotropic stiffness tensor of the ply. The properties are subsequently used to reverse engineer the stiffness tensor, assumed to be transversely isotropic, of the carbon fibres. To this end, four micro-scale homogenization methods are explored: 2 analytical models (Mori-Tanaka and Mori-Tanaka-Lielens), 1 semi-empirical (Chamis) and 1 finite-element (FE) homogenization (randomly distributed fibres in a Representative Volume Element). Next, the identified fibre properties are used to predict the elastic parameters of UD plies with multiple fibre volume fractions. These are then used to model the fibre bundles (yarns) in a meso-scale FE model of a plain woven carbon/epoxy material. Finally, the predicted elastic response of the woven carbon/epoxy is compared to the experimentally obtained elastic stiffness tensor. The predicted and measured properties are in good agreement. Some discrepancy exists between the ultrasonically measured value of the Poisson's ratio and the predicted value. Nonetheless, it is shown that virtual identification and prediction of mechanical properties for woven plies is feasible.
Low-velocity impact of sandwich beams with fibre-metal laminate face-sheets Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-21 Jianxun Zhang, Yang Ye, Qinghua Qin, Tiejun Wang
Low-velocity impact of fully clamped sandwich beams with fibre-metal laminate face-sheets and metal foam core struck by a heavy mass is investigated. Analytical solutions are developed for the dynamic response of sandwich beams with fibre-metal laminate face-sheets considering the interaction of bending and stretching induced by large deflections. According to the rigid-plastic material approximation with modifications, simple formulae are obtained for the large deflection of sandwich beams with fibre-metal laminate face-sheets. Numerical calculations are carried out, and analytical solutions capture numerical results reasonably. The effects of the composite volume fraction, the ratio of metal layer strength to composite layer strength, and core strength on the structural response are discussed. Using the analytical formulae, optimal design charts are constructed to minimize the mass of sandwich beams. It is demonstrated that the present analytical model can predict the post-yield behavior of sandwich beams with fibre-metal laminate face-sheets reasonably.
Transition from buckling to progressive failure during quasi-static in-plane crushing of CF/EP composite sandwich panels Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-18 Yuan Chen, Lin Ye, Kunkun Fu, Xu Han
Global buckling failure should be avoided when designing a structure with the requirement of crashworthiness performance. This study characterises the quasi-static in-plane crushing of CF/EP composite sandwich panels by tailoring their bevel angles. A finite element model was developed describing the interlaminar and intralaminar damage of a composite sandwich panel; this model was validated by in-plane compression experiments. A numerical analysis and compression experiments were then performed to determine the responses and failure modes in the CF/EP composite sandwich panels with various bevel angles. The results showed that the global buckling-to-progressive failure transition under compression occurred in the composite sandwich panels when the bevel angle reached a critical value. A microscopic analysis showed that the composite sandwich panels with buckling failure behaviours exhibited an apparently classical post-buckling transverse shearing mode, while those with progressive failure presented individual lamina bending with inward and outward fronds. This study provides some useful data for the design of the crashworthiness of a sandwich composite panel by introducing a progressive failure mode.
Analysis of the influence of interphase characteristics on thermal conduction in surface-modified carbon nanotube-reinforced composites using an analytical model Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-18 Hoi Kil Choi, Hana Jung, Yuna Oh, Hyunkee Hong, Jaesang Yu, Eui Sup Shin
In this study, the influence of interphase characteristics on thermal conductivity of carbon nanotube (CNT)-reinforced polymer composites was investigated using a thermal resistance theory-based analytical model. Pristine, nitrogen doped, and carboxyl functionalized CNTs were used to verify the effect of surface modifications. Interfacial thermal conductivities of nanocomposites containing three different CNTs were calculated from non-equilibrium molecular dynamics (NEMD) simulations, to analyze the influence of functionalization on the interphase characteristics. Equilibrium molecular dynamics (EMD) simulations of three different CNTs and epoxy matrix were performed to estimate their effective thermal conductivities. The thermal conductivities of the nanocomposites were predicted by applying the results obtained from the MD simulations in the analytical model. The results predicted by the analytical model show that while thermal conduction in the longitudinal direction of the nanocomposites depends on thermal conductive performance of the CNTs, transverse thermal conductivity could be significantly influenced by the interphase characteristics.
A model for the electrical conductivity variation of molten polymer filled with carbon nanotubes under extensional deformation Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-17 Marjorie Marcourt, Philippe Cassagnau, René Fulchiron, Dimitri Rousseaux, Olivier Lhost, Simon Karam
This work is dedicated to analyzing the variation of conductivity of polymer composites (polystyrene filled with Carbon Nanotubes) under extensional deformation. In a previous work, a conductor-insulator transition has been observed and the predominant role of the polymer dynamics has been brought to light. The evolution of the filler network within a polymer matrix can be described by a kinetic equation that takes into account a structuring mechanism that is controlled by the mobility in the melt matrix and a destruction mechanism that is induced by the extensional deformation. The solution of this equation that describes the filler network at a microscale is used in the percolation law to obtain the macroscopic conductivity of the composite. It turned out that the structuring parameter does not depend on the extensional deformation but only relies on the polymer matrix dynamics. In addition, the breaking parameter only depends on the Hencky strain, whatever the extensional rate. This model has been successfully applied for a large range of filler concentrations and experimental conditions from low to large Weissenberg numbers.
Flexible printed humidity sensor based on poly(3,4-ethylenedioxythiophene)/reduced graphene oxide/Au nanoparticles with high performance Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-15 Rongjin Zhang, Bo peng, Yan Yuan
Wearable and flexible humidity-sensing devices are essential for the real-time monitoring of air humidity in health and environmental applications. We propose a flexible sensor based on a conductive polymer comprising poly(3,4-ethylenedioxythiophene) (PEDOT) and reduced graphene oxide(rGO) to monitor changes in humidity. GO was used as a hard template for the in situ polymerization of EDOT to obtain PEDOT:rGO. Then, PEDOT:rGO-PEI/Au nanoparticles (NPs) ink was prepared through the in situ reduction of Au NPs modified with polyethylenimine (PEI). The ink was printed on the surface of a hydrophilic modified polyethylene terephthalate (PET) substrate using an ink-jet printer to form a specific pattern. After assembly, a PET-based PEDOT:rGO-PEI/Au NPs (PrGANPs) sensor device with high electrical performance, transparency, and sensitivity was obtained for testing at a variety of RH levels. The prepared PET-based PrGANPs sensor printed with 50 layers had a transmittance up to 61% at 500 nm. And the response and recovery times were approximately 20 and 35 s at 98% RH, respectively. Stability was maintained even after bending 200 times, and the sensor could respond within the humidity range of 11%–98% RH, while in response to a wide resistance range of 7.41%–51.60%.
Preparation of poly (propylene carbonate)/graphite nanoplates-spherical nanocrystal cellulose composite with improved glass transition temperature and electrical conductivity Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-14 Shaoying Cui, Pingfu Wei, Li Li
Poly(propylene carbonate) (PPC) is a new attractive biodegradable polymers synthesized from inexhaustible carbon dioxide and propylene epoxide, but shows low glass transition temperature (Tg) and poor mechanical properties, which greatly limits its practical applications and industrialization development. To improve Tg and the practicability of PPC, in this work, graphite nanoplates-spherical nanocrystalline cellulose (GNP-SNCC) hybrids, which were bonded by both physical and chemical forces, were prepared by ball milling from graphite and microfibrillated cellulose, and the structure formation as well as properties of PPC/GNP-SNCC composites were studied. The results showed that the improved interfacial interactions between GNP-SNCC and PPC, and the rigid two-dimensional structure of GNP-SNCC were beneficial for the constraint of PPC molecular chains, thus significantly improving Tg and the mechanical properties of PPC matrix, e.g. Tg increased from 34.0 °C of neat PPC to 51.3 °C, and the yield strength increased from 27 MPa to 52.8 MPa. Moreover, facilitated by SNCC, a conductive pathway of GNP was effectively constructed, leading to the great increase in the electrical conductivity of PPC/GNP-SNCC composite. The composite with 10 wt% (5.71 vol%) graphite showed 9 orders of magnitude higher than that of PPC/graphite composite with the same graphite content, and the percolation threshold was drastically decreased from 15 to 5 wt% (8.56–2.85 vol%).
Preparation of β-cyclodextrin reinforced waterborne polyurethane nanocomposites with excellent mechanical and self-healing property Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-14 Ting Wan, Dajun Chen
Cyclodextrin is an eco-friendly material with extensive application range. In this work, polyethylene glycol (PEG) modified β-cyclodextrin (CD) was added to a self-healing waterborne polyurethane (SHWPU) through a simple solution blending method. The morphologies, chemical structures, emulsion stability, thermal behavior, mechanical and self-healing properties of the SHWPU/CD nanocomposites were investigated. The results indicated that CDs were well dispersed in the SHWPU matrix and the blended emulsions were stable. The thermal stability of the SHWPU was improved by the addition of CD. When the mass fraction of CD was lower than 5%, the mechanical and self-healing property of the nanocomposites were obviously improved, which indicates the CD modified SHWPU can find potential applications in durable coatings and adhesives in areas, such as textile, wood, aerospace and infrastructure.
A highly stretchable carbon nanotubes/thermoplastic polyurethane fiber-shaped strain sensor with porous structure for human motion monitoring Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-13 Xiaozheng Wang, Hongling Sun, Xiaoyan Yue, Yunfei Yu, Guoqiang Zheng, Kun Dai, Chuntai Liu, Changyu Shen
Hydrated aramid nanofiber network enhanced flexible expanded graphite films towards high EMI shielding and thermal properties Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-13 Yuhang Liu, Kaiyi Zhang, Yanling Mo, Li Zhu, Bowen Yu, Feng Chen, Qiang Fu
Expanded graphite (EG) films are known for high electric and thermal transportation properties, due to light oxidation preparation process compared with chemical converted graphene (cGE) films. However, the poor mechanical properties and brittle nature are the major limitations for commercial applications. To meet this challenge, in this work, hydrated aramid nanofiber (HANF) with excellent mechanical properties and flexibility is introduced into EG films to enhance their mechanical properties and flexibility. As a result, only the adding of 2 wt% HANF can endow EG films with good flexibility. The best comprehensive property is achieved by adding 10% HANF (EG-10). Compared with the pure EG films (EG-0), a 223% improvement of tensile strength from 7.5 Mpa to 24.2 Mpa and a 660% enhancement of elongation at break from 0.371% to 2.82% are observed for EG-10. Besides, EG-10 maintains good electric and thermal conductivities of 215 S cm−1, 208 W m−1 K−1. Moreover, the EMI shielding property of 34.9 dB is realized when the film thickness reaches only 30 μm. The EG/HANF films can be used up to the temperature of 300 °C and show good flame resistance compared with adding other polymers thanks to the good stability of HANF. And, the excellent flexibility can be maintained even after 1000 times direct folding. The comprehensive properties of light weight films, together with their advantages of simple, cheap and facile large-scale preparation process endow the films with promising applications in next generation foldable electronic devices.
Lightweight and strong microcellular injection molded PP/talc nanocomposite Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-13 Guilong Wang, Guoqun Zhao, Guiwei Dong, Yue Mu, Chul B. Park
Lightweight is of great significance for reducing material and energy consumptions. Microcellular injection molding is an advanced technology for fabricating lightweight plastic structural components, but the deteriorated mechanical performance is a big challenge. In this study, we reported a facile and scalable way to fabricate the lightweight and strong microcellular polypropylene/talcum (PP/talc) component. Both PP/talc microcomposite and PP/talc nanocomposite were prepared by the twin-screw compounding, and the SEM images show a uniform dispersion of talc. The DSC analysis results demonstrate that either the micro or nano talc is very effective in promoting the crystallization of PP. The rheological tests show that both the micro talc and the nano talc lead to obviously enhanced viscoelastic properties of the PP melt, while the effect of the nano talc is much more pronounced than that of the micro talc. Thanks to the enhanced crystallization and improved viscoelastic behavior, both the microcomposite foam and the nanocomposite foam shows much refined cellular structure than the pure PP foam. The PP/talc microcomposite foam shows significantly improved strength but seriously deteriorated toughness, compared with the pure PP foam. In contrast, the PP/talc nanocomposite foam shows simultaneously improved strength, rigidity and toughness. Notably, the tensile toughness and the Gardner impact toughness of the PP/talc nanocomposite foam are dramatically enhanced by 226.1% and 166.2%, respectively. Taking into account the flexible and scalable features of the processing methodology, the lightweight and strong PP/talc nanocomposite foam shows a promising future to replace the solid structural components in many industrial applications such as automotive and consumer electronics.
Novel self-healing CFRP composites with high glass transition temperatures Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-11 Lisha Zhang, Xuanzhe Tian, Mohammad H. Malakooti, Henry A. Sodano
Carbon fiber reinforced polymer (CFRP) composites were fabricated using a novel intrinsically healable isocyanurate-oxazolidone (ISOX) thermosetting matrix. After multiple delamination events, repeatable strength recovery of the composites has been demonstrated with a first healing efficiency up to 85% after thermal treatment. The healing mechanism results from transformation of the isocyanurate with epoxide groups to yield new oxazolidone rings at the fracture surface. This novel ISOX polymer utilizes commercial diglycidyl ether of bisphenol F (DGEBF) and toluene diisocyanate to produce a high cross-link density thermoset with a glass transition temperature (Tg) up to 285 °C, and 99.5% of the composite weight remains at 300 °C. The strength and stiffness of the composites are comparable with an engineering grade polymer matrix composite typically used in aerospace applications and the thermal stability places the materials in the polybismaleimide performance region although with greater toughness. This polymer exhibits the highest Tg of any self-healing material reported and is composed of low cost reactants, which gives the polymer great potential to function as a major component of an advanced structural composite for extreme environments.
The effect of double grafted interface layer on the properties of carbon fiber reinforced polyamide 66 composites Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-10 Jinchuan Chen, Huajie Xu, Chuntai Liu, Liwei Mi, Changyu Shen
Given the advantages of polyethyleneimine (PEI) for interface modification of carbon fiber reinforced polyamide 66 composite (CF/PA66), an effective method was developed to fabricate CNT@PEI-CF. The XPS results confirmed CNT@PEI-CF was covered with a double grafted layer. Interface stability investigated showed thermal stability (under injection molding temperature, about 270 °C) and structural stability of CNT@PEI-CF/PA66 interface were both improved, but PA66 crystallization behavior affected by CNT@PEI-CF was identical with that of pure PA66. The contact angle tests exhibited that its compatibility with PA66 was also enhanced. Its interfacial shear strength, composite tensile strength and elastic modulus increased by 64.74%, 27.58% and 22.68% compared with that of untreated-CFs and composite, respectively. These best mechanical properties were ascribed to the formation of “fish-scale” layers on pull-out fibers resulted from CNT@PEI-CF modification. It could be concluded that CNT@PEI-CF would not only enhance its composite mechanical properties, but also exhibit much fiber pull-out and avoid the catastrophic failure for CNT@PEI-CF/PA66 composites. This CF surface modification study would be beneficial to expand application of thermoplastic composite with reusability.
Tailoring swelling to control softening mechanisms during cyclic loading of PEG/cellulose hydrogel composites Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-07 A. Khoushabi, C. Wyss, B. Caglar, D. Pioletti, P.-E. Bourban
One of the novel approaches for discogenic lower back pain treatment is to permanently replace the core of the intervertebral disc, so-called Nucleus Pulposus, through minimally invasive surgery. Recently, we have proposed Poly(Ethylene Glycol) Dimethacrylate (PEGDM) hydrogel reinforced with Nano-Fibrillated Cellulose (NFC) fibers as an appropriate replacement material. In addition to the tuneable properties, that mimic those of the native tissue, the surgeon can directly inject it into the degenerated disc and cure it in situ via UV-light irradiation. However, in view of clinical applications, the reliability of the proposed material has to be tested under long-term fatigue loading. To that end, the present study focused on the characterization of the fatigue behavior of the composite hydrogel and investigated the governing physical phenomena behind it. The results show that composite PEGDM-NFC hydrogel withstands the 10 million compression cycles at physiological condition. However, its modulus decreases by almost 10% in the first cycle and then remains constant, while cyclic loading does not affect the neat PEGDM hydrogel. The observed softening behavior has similar characteristics of the Mullins effect. It is shown that the reduction of modulus is due to the gradual change of NFC network, which is highly stretched in the swollen state. Moreover, the swelling degree of the matrix is correlated to the extent of softening during cyclic loading. Consequently, softening can be minimized by lowering the swelling of the composite hydrogel.
Scalable one-step synthesis of hydroxylated boron nitride nanosheets for obtaining multifunctional polyvinyl alcohol nanocomposite films: Multi-azimuth properties improvement Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-08 Wei Cai, Bibo Wang, Yongqian Shi, Ying Pan, Junling Wang, Weizhao Hu, Yuan Hu
Introducing hydroxyl (OH) groups onto the surface of chemically inert hexagonal boron nitride (h-BN) is conducive to the exfoliation and functionalization of h-BN, meanwhile could enhance the intermolecular forces with polymer as well. However, chemical inertness generated by partially ionized B-N bonds makes the introduction of OH groups still remains a challenge. Here, we reported a scalable one-step thermal calcination method for the fabrication of OH-functionalized h-BN nanosheets (OH-BN). Then, transparent, strong, and flexible as well as flame retardant nanocomposite films of as-prepared OH-BN and PVA were prepared through a aqueous solution casting technique. Due to hydrogen-bond self-assembly and crystalline-region self-relief, elongation at break, tensile strength, and Young's modulus of PVA nanocomposite film were simultaneously increased by 109.3%, 73.6%, and 144.4% with as low as 0.2 wt % OH-BN. Besides, the self-stiffness phenomenon that damages the material elasticity during dynamic service process of PVA nanocomposite films was effectively hindered. Meanwhile, the superior visible light transmittance and higher absorption quality to UV-light were also confirmed, which promoted its practical use in artificial cornea materials. Attributing to the well-dispersed state and layered structure, incorporated OH-BN presented a barrier function to suppress the delivery of thermal degradation products of PVA matrix, thus enhancing thermal stability and fire safety. Herein, we come to a conclusion that the scalable one-step synthesis of OH-BN and environmentally friendly fabrication of PVA/OH-BN nanocomposite films as well as excellent properties greatly contribute to the development of the practical application of h-BN nanosheets, thus obtaining multifunctional composite materials.
Cavitation-crazing transition in rubber toughening of poly(lactic acid)-cellulose nanocrystal composites Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-06 Joseph K. Muiruri, Songlin Liu, Wern Sze Teo, Jayven Chee Chuan Yeo, Warintorn Thitsartarn, Chaobin He
In this work, the mechanism behind rubber toughening of poly(lactic acid)/cellulose nanocrystal-g-rubber-g-poly(D-lactide) (CNC-rDx-PDLA) composites was elucidated through systematic study of the effects of rubber segment content (length) in CNC-rDx-PDLA nanofillers and the nanofiller concentrations on the deformation behavior of the nanocomposites. It was shown that with an increase of rubber segment length and rubber filler concentration, the elongation at break of the resulting composites increased. Moreover, a dramatic increase in elongation at break (from 20% to 200%) was observed when the rubber segment content (length) in the CNC-rDx-PDLA nanofillers was increased from 52 to 68%. Cavitation mechanism was found dominant when the rubber segment content in the nanofillers was 52% and below, whereas, stable crazes were formed and followed by fibrillation when the rubber segment content in the nanofillers was increased to 68%, which was evident by small angle X-ray scattering (SAXS) study and scanning electron microscopy (SEM) analysis. The existence of a transition from cavitation to crazing in the composite systems could be attributed to a more mobile rubber phase because of longer rubber chain length. Our study suggests that the effective toughening mechanism for thermoplastics such as PLA is crazing induced plastic deformation.
Prediction and validation of electromagnetic performance of curved radar-absorbing structures based on equivalent circuit model and ray tracking method Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-05 Dae-Sung Son, Jong-Min Hyun, Jung-Ryul Lee
In this study, an equivalent circuit model and ray tracking method were used to predict the electromagnetic characteristics of curved radar-absorbing structures (RASs) applied with a frequency selective surface (FSS). After performing an electromagnetic analysis of FSS using a unit cell model, an equivalent circuit model reflecting the characteristics of the FSS was constructed. The equivalent circuit model of the FSS was applied to an equivalent circuit model for the RAS to evaluate the absorption performance as a function of the curvature and incident angle. Electromagnetic characteristics of the curvature structure were predicted by estimating the path of the electromagnetic wave using the ray tracking method. The calculated results were compared with the experimental results using free space measurements. Through this study, it was possible to estimate an equivalent circuit model reflecting the electromagnetic characteristics of the RAS with respect to the incident angle and curvature of the FSS. In addition, the electromagnetic performance of the entire curved structure was evaluated using the ray tracking method.
Analysis of the effect of manufacturing imperfections in the elastic properties of platelet nanocomposites Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-05 J.M. Munoz-Guijosa, G. Fernández-Zapico, H. Akasaka, E. Chacón
We have developed and validated a conceptually simple model capable of predicting the macroscale elastic properties of a platelet nanocomposite. The model allows for studying the individual and combined effect of the parameters with influence on those properties, namely nanofiller weight fraction, misalignment, dispersion quality, size distribution and nanofiller-matrix interfacial characteristics. The model shows a very good correlation with experimental results. The interfacial characteristics under different strain states are evaluated at the nanoscale by means of a cohesive model which considers out-of-plane strains and angular distortions, so that the full, strain-dependent elastic tensor can be calculated, allowing for homogenization and subsequent study of the effect of filler orientation, dispersion quality and size distribution on the elastic properties at the macroscale. The use of a low complexity nanoscale model allows us to conceptually and quantitatively explain the causes underlying the divergences between the expected and experimental macroscale material stiffness experimentally found by different researchers.
Geometrical deviation analysis of CFRP thin laminate assemblies: Numerical and experimental results Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-05 Andrea Corrado, Wilma Polini, Luca Sorrentino, Costanzo Bellini
During the cure process, the anisotropic characteristics of composite material, combined with high temperature and high pressure to which the material is subjected, cause the development of residual stresses. Consequently, laminate deformations arise and dimensional and geometrical requirements are not reached. Laminate deformations transfer into product distortions through assembly process. Distortions result in uncertainty in the performance of manufactured goods and they require effective management to ensure correct performance.The present work shows a numerical approach suitable to determine the geometrical deviations of an assembly constituted by thin laminates in composite material. The proposed model considers the geometrical deviations of the assembly parts, due to the manufacturing process, the assembly sequence and the presence of adhesive to put together the parts.The proposed model was experimentally verified by considering a T-shaped assembly constituted by flat and L-shaped components. The obtained results show a good agreement with the experimental ones.
Study the mechanism that carbon nanotubes improve thermal stability of polymer composites: An ingenious design idea with coating silica on CNTs and valuable in engineering applications Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-04 Yihe Wang, Xingna Qiu, Junping Zheng
Silica nanotubes (SNTs) were coated on the surface of carbon nanotubes (CNTs) to form SNTs@CNTs core–shell hybrids, which is an ingenious and rigorous method to study the effect of CNTs for improving thermal stability of composites. SNTs@CNTs, CNTs, SNTs were introduced to silicone rubber (SR) and the different composites were tested and analyzed. The difference in the properties of SR-based composites leads us to get the specific mechanism that CNTs improve thermal stability of composites. This work reveals the mechanism on CNTs improving thermal stability of composites systematically and detailedly for the first time. The theoretical research provides an efficient guideline for further studying CNTs to improve properties of composites. Moreover, SNTs@CNTs/SR composites are also valuable in engineering applications. Experimental results show that the properties of SNTs@CNTs/SR are much better than CNTs/SR. Especially the initial thermal degradation temperature (Ti) of SNTs@CNTs/SR composites is 41 °C higher than that of SR.
Thermal annealing induced enhancement of electrical properties of a Co-continuous polymer blend filled with carbon nanotubes Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-04 Haixin Zhang, Jianwen Chen, Xihua Cui, Yuexin Hu, Liangcai Lei, Yutian Zhu, Wei Jiang
In the current study, it is found that the electrical properties of a co-continuous polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend containing with conductive multi-wall carbon nanotubes (MWCNTs) can be remarkably improved via the thermal annealing treatment. Utilizing the on-line (rheometer and optical microscope) and off-line (transmission electron microscopy) instruments, the evolution of the morphology and microstructure of PS/PMMA/MWCNTs composites are visualized. It is observed that thermal annealing can induce the coalescence of small phases into the more perfect co-continuous phase structure, which can significantly improve the electrical properties of the composites. Moreover, the re-aggregation of MWCNTs under thermal annealing also helps to improve the electrical properties of the composites. Furthermore, it is worth to note that parts of MWCNTs can be enriched at the interface of a co-continuous PS/PMMA blend to build up the conductive network during the thermal annealing, which further enhances the electrical properties of the composites.
Towards aerospace grade thin-ply composites: Effect of ply thickness, fibre, matrix and interlayer toughening on strength and damage tolerance Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-04 J. Cugnoni, R. Amacher, S. Kohler, J. Brunner, E. Kramer, C. Dransfeld, W. Smith, K. Scobbie, L. Sorensen, J. Botsis
Thin-ply composites represent a promising approach to further improve the performance of carbon fibre composite structures thanks to their ability to delay the onset of matrix cracking and delamination up to the point of fibre dominated failure. However, this increased strength comes with a more brittle failure response which raises concerns on damage tolerance. Thus a careful material optimization is needed to address this trade-off. In this work, eight different formulations of thin-ply composites ranging from low modulus to high modulus carbon fibres are evaluated to understand the effects of the fibre and matrix constituents on the onset of damage and strength in unnotched tensile (UNT) tests of quasi isotropic laminates for ply thicknesses between 300 and 30 microns. The obtained experimental data are combined in master curve diagrams for simplified material selection process. It is observed that certain thin-ply composites with a ply thickness t < 134 um can reach UNT strength corresponding to or approaching the ultimate strain of the fibres as well as UNT stress at onset of damage as high as 92% of the latter. Based on this knowledge, a novel aerospace grade toughened thin-ply composite system is developed which can reach a quasi-isotropic UNT strength above 1 GPa (>95% of the fibre strain). The newly developed composite is further optimized to improve damage tolerance by toughening the resin and selected interfaces. The effect of those modifications on damage tolerance are evaluated through compression strength after impact (CAI) tests and open hole tensile tests (OHT). It is found that an optimized interlayer toughened thin-ply composite based on 68 microns plies of intermediate modulus fibre can reach both outstanding strength properties with comparable or better CAI and OHT strength compared to current aerospace grade composites.
Synergetic enhancement of mechanical and electrical strength in epoxy/silica nanocomposites via chemically-bonded interface Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-04 He Li, Feihua Liu, Huidong Tian, Chuang Wang, Zihao Guo, Peng Liu, Zongren Peng, Qing Wang
While the incorporation of the inorganic fillers into polymers is envisioned to improve the properties of polymers, the organic–inorganic interface in the nanocomposite plays a prominent role in the modulation of the electrical, mechanical and thermal properties. Here, the epoxy chain-grafted silica nanoparticles were prepared and utilized as the fillers in epoxy matrix. The multiple physical properties such as the tensile strength, the elongation at break, the glass transition temperature, the dielectric strength of the nanocomposites with epoxy chain-grafted silica are simultaneously improved in comparison with those of the neat epoxy and the nanocomposites with unmodified silica. Moreover, substantial reductions in the water absorption ratio, dielectric loss and electric conductivity are obtained in the nanocomposites filled with epoxy-grafted silica even at relatively low filler loadings. These results verify the critical role of the chemically-bonded interface between organic and inorganic phases in determining the mechanical and dielectric strength of the polymer nanocomposites. The interaction zone models for the interface between nanoparticle and polymer matrix have been proposed to rationalize the experimental results.
Buckling load prediction of grid-stiffened composite cylindrical shells using the vibration correlation technique Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-01 Davoud Shahgholian Ghahfarokhi, Gholamhossein Rahimi
The vibration correlation technique (VCT) is one of the most important nondestructive methods to calculate the buckling load of imperfection sensitivity in thin-walled structures. VCT is widely used for beam and plate structures, but the technique is still under development for thin-walled shells. In this paper, an experimental and numerical validation of VCT approach was presented and discussed for the prediction of the buckling load of the grid-stiffened composite cylindrical shells loaded in compression. From the experimental point of view, three specimens were fabricated using a new silicone rubber mold, and specially-designed filament winding setup. The modal behavior of the grid-stiffened composite cylindrical shells was investigated by exciting the structures using modal hammer method in different applied compression load. Then, the variation of the first natural frequency of vibration with the applied compressive load was measured up to buckling during testing. Furthermore, a series of Finite Element Models (FEMs), including nonlinear effects such as geometric and thickness imperfection, are carried out in order to characterize the variation of the natural frequencies of vibration with the applied load and also compare it with the experimental results. Finally, the buckling test was performed to validate the experimental and numerical results of VCT approach. The results showed that the difference between the predicted buckling load using the VCT approach on the experimental results and numerical results with an experimental buckling load is 3.1% and 5.0%, respectively. Also, the current VCT approach has a very good correlation for grid-stiffened composite cylindrical shells when the maximum applied load is higher than 68% of the experimental buckling load.
Effects of aspect ratio and crystal orientation of cellulose nanocrystals on properties of Poly(vinyl alcohol) composite fibers Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-31 Shikha Shrestha, Francisco Montes, Gregory T. Schueneman, James F. Snyder, Jeffrey P. Youngblood
This work reports a study on the effects of different types and aspect ratios of cellulose nanocrystals (CNCs) on properties of poly (vinyl alcohol) (PVA) composite fibers. CNCs were extracted from wood pulp and cotton and reinforced into PVA to produce fibers by dry-jet-wet spinning. The fibers were collected as-spun and with first stage drawing up to draw ratio 2. The elastic modulus and tensile strength of the fibers improved with increasing CNC content (5–15 wt. %) at the expense of their strain-to-failure. It was also observed that the mechanical properties of fibers reinforced with cotton CNC were higher than the fibers with wood CNC at the same amount of CNCs due to their higher aspect ratio. The degree of orientation along the spun fiber axis was quantified by 2D X-ray diffraction. As expected, the CNC orientation correlates to the mechanical properties of the fibers. Micromechanical models were used to predict the fiber performance and compare with experimental results. Finally, surface and cross-sectional morphologies of fibers were analyzed by scanning electron microscopy and optical microscopy.
Compression properties of composite laminates reinforced with rectangular z-pins Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-31 Julian Hoffmann, Gerhard Scharr
This paper presents an experimental study investigating the static and fatigue compression properties of unidirectional and quasi-isotropic carbon fiber/epoxy laminates reinforced with rectangular and circular z-pins. The insertion of z-pins did not affect the compression modulus of the specimens, but all z-pinned laminates demonstrated a significantly reduced compression strength compared to unpinned specimens. Rectangular z-pins that were aligned lengthwise to the fiber direction of the laminate ply were observed to cause minor microstructural damages, such as in-plane fiber waviness. Therefore, the use of rectangular z-pins led to a minor reduction of the compression strength in both unidirectional and quasi-isotropic laminates. Especially for a small number of load cycles, the insertion of z-pins resulted in a decrease in the fatigue performance of the tested unidirectional and quasi-isotropic laminates. Since this deterioration was primarily caused by the initial knockdown of the static compression strength of the z-pinned laminates, rectangular z-pins showed superior fatigue performance in both unidirectional and quasi-isotropic laminates.
Fabrication of epoxy functionalized MWCNTs reinforced PVDF nanocomposites with high dielectric permittivity, low dielectric loss and high electrical conductivity Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-09-01 Saddiqa Begum, Hameed Ullah, Ayesha Kausar, Mohammad Siddiq, Muhammad Adeel Aleem
Nanocomposites of Polyvinylidene Flouride (PVDF) with Multi-walled Carbon Nanotubes (MWCNTs) possess excellent thermal, piezoelectric and conductive behaviors. However, the potential of MWCNTs as filler in polymer composites is hampered by their poor dispersion into the matrix, corresponding to the strong inter-tubular and weak inter tubular-polymer chain interactions. This issue is successfully overcome by utilizing di-glycidyl ether of bisphenol-A (DGEBA) grafted MWCNTs (DG-MWCNTs) as reinforcement in PVDF matrix. To synthesize the desired nanocomposites, the easier to manipulate, solution casting technique was employed. The resulting PVDF/DG-MWCNTs nanocomposites have different loadings of filler ranging from 1.0 wt% to 10 wt%, and have shown variation in the phase transformation from α-phase to β-phase along with improvements in thermal and dielectrical behaviors. It was revealed by the impedance spectroscopy (IS) that the reinforcement of PVDF with DG-MWCNTs leads to an increase in the dielectric permittivity. This increase was found higher enough to reach up to ∼5288 (at ∼100 Hz) and 214 (at ∼102 Hz) for filler loading of 10 wt %. The increase is several hundreds of magnitude i.e., ∼204 at ∼102 Hz higher than the PVDF matrix, while retaining a low level conductivity (4.18 × 10−6 S/cm). This enhancement in the dielectric permittivity is attributed to the strong interfacial interaction between PVDF and DG-MWCNTs, and was explained by the Maxwell-Wagner-Sillar (MWS) effect.
Multifunctional performance of a carbon fiber UD lamina electrode for structural batteries Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-30 Wilhelm Johannisson, Niklas Ihrner, Dan Zenkert, Mats Johansson, David Carlstedt, Leif E. Asp, Fabian Sieland
In electric transportation there is an inherent need to store electrical energy while maintaining a low vehicle weight. One way to decrease the weight of the structure is to use composite materials. However, the electrical energy storage in today's systems contributes to a large portion of the total weight of a vehicle. Structural batteries have been suggested as a possible route to reduce this weight. A structural battery is a material that carries mechanical loads and simultaneously stores electrical energy and can be realized using carbon fibers both as a primary load carrying material and as an active battery electrode. However, as yet, no proof of a system-wide improvement by using such structural batteries has been demonstrated. In this study we make a structural battery composite lamina from carbon fibers with a structural battery electrolyte matrix, and we show that this material provides system weight benefits. The results show that it is possible to make weight reductions in electric vehicles by using structural batteries.
Quantifying fibre reorientation during axial compression of a composite through time-lapse X-ray imaging and individual fibre tracking Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-30 Monica Jane Emerson, Ying Wang, Philip John Withers, Knut Conradsen, Anders Bjorholm Dahl, Vedrana Andersen Dahl
The sudden compressive failure of unidirectional (UD) fibre reinforced composites at loads well below their tensile strengths is a cause of practical concern. In this respect and more generally, analytical and numerical models that describe composite behaviour have been hard to verify due to a lack of experimental observation, particularly in 3D. The aim of this paper is to combine fast in-situ X-ray computed tomography (CT) with advanced image analysis to capture the changes in fibre orientation in 3D during uninterrupted progressive loading in compression of a UD glass fibre reinforced polymer (GFRP). By analysing and establishing correspondence between a sequence of time-lapse X-ray CT images of the composite, we are able for the first time to follow each fibre and quantify the progressive deflection that takes place during axial compression in the steps leading up to fibre micro-buckling and kinking. Even at just 25% of the failure load, fibres have started to tilt in approximately the direction of the ultimate kink band. The rate of tilting increases as the composite approaches the collapse load. More generally, our approach can be applied to investigate the behaviour of a wide range of fibrous materials under changing loading conditions.
A novel model for determining the fatigue delamination resistance in composite laminates from a viewpoint of energy Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-30 Yu Gong, Libin Zhao, Jianyu Zhang, Ning Hu
A previous study indicated that the normalized fracture controlling parameter (strain energy release rate G normalized by fatigue delamination resistance Gcf) in the Paris-type law has advantages of lower exponents and data scatter to evaluate the fatigue delamination growth (FDG) behaviour. To accurately determine the critical Gcf, which characterizes the real changing resistance against delamination growth, a novel model is proposed from a viewpoint of energy. This model also allows the judgement on the numerical equivalence between the Gcf and fracture toughness Gc in a simple way. Well-designed delamination tests under mode I loading were carried out to validate the model. Significant R-curve effects on the FDG behaviour due to fiber bridging and the bridging difference between static and fatigue delamination at the same delamination length were observed. The calculated result of Gcf has a really good agreement with that obtained by the compliance method, which indicates that fatigue delamination resistance can be accurately determined by using the present model.
Modelling process induced deformations in 0/90 non-crimp fabrics at the meso-scale Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-31 Adam J. Thompson, Bassam El Said, Jonathan P-H. Belnoue, Stephen R. Hallett
The manufacture of non-crimp fabric composites typically requires the forming and consolidation of the reinforcement material. During this process the material is subjected to complex loading where the coupling of tensile, bending, shear and compressive forces result in deformations to the internal architecture of the textile. To determine the extent of these deformations a numerical modelling method has been developed to capture the kinematic behaviour of non-crimp fabric textiles. This method focuses on capturing the interactions between the fibrous tows and the stitch yarns which bind the tows together. Through modelling at a level of detail in which the meso-scale interactions are explicitly present, the macro-scale behaviour of the material proceeds naturally within the model, negating any requirement for detailed characterisation of the physical material. This also enables a detailed description of the internal architecture of the deformed fabric to be extracted for analysis or further modelling. The present study explores the method's ability to capture both local and global deformations which occur in non-crimp fabrics, specifically to capture the onset of deformations that appear due to tow-stitch interactions and the forming and compaction of multiple layers. Comparison with experimental results show good agreement for both meso-scale deformations, resulting from multi-layer compaction, and global in-plane shear deformations induced through forming over complex tooling.
Design of shape-memory materials based on sea-island structured EPDM/PP TPVs via in-situ compatibilization of methacrylic acid and excess zinc oxide nanoparticles Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-29 Chuanhui Xu, Wenchao Wu, Zhongjie Zheng, Zhiwei Wang, Jiada Nie
Development of electrically conductive structural BMI based CFRPs for lightning strike protection Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-29 Z.J. Zhao, G.J. Xian, J.G. Yu, J. Wang, J.F. Tong, J.H. Wei, C.C. Wang, P. Moreira, X.S. Yi
In the present paper, bismaleimide resin (BMI) based carbon fiber reinforced composite (CFRP) with remarkable lightning strike protection (LSP) capability was developed. A light weight conductive veil was prepared and interleaved to CFRP with the through thickness conductivity of 27.9 S/m, while its static mechanical strength was unaffected. We prove that the through thickness conductive pathways made CFRP to disperse the lightning current more effectively; reducing the lightning damage toward the inner part of the CFRP. The deepening Joule heat was proved to be the major reason of the penetrating structure failure. Comparing to the state-of-art metal sacrifice layer for LSP, the through thickness conductive CFRP has lighter weight and similar LSP capability, without compromising the mechanical strength.
Electrically insulating, layer structured SiR/GNPs/BN thermal management materials with enhanced thermal conductivity and breakdown voltage Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-29 Chang-Ping Feng, Shen-Shen Wan, Wei-Chun Wu, Lu Bai, Rui-Ying Bao, Zheng-Ying Liu, Ming-Bo Yang, Jun Chen, Wei Yang
Layer structured high-performance thermal management materials via integrating the advantages of boron nitride (BN, electrically insulating) and graphene nanoplateles (GNPs, highly thermally conductive) as fillers were realized by a facile and scalable strategy. Outstanding thermal conductivity (TC) of 8.45 W m−1 K−1, the highest value among reported electrically insulating polymer-based materials, excellent electrical insulation (breakdown voltage∼5.33 kV/mm; volume resistance ∼1012Ωcm) and superior electromagnetic interface shielding performance are achieved at a filler loading of 17.88 vol%. Moreover, the mechanical properties and hardness are also in quite good range. Thus, a promising method is provided for large scale production of superior thermal management materials.
Graphitic carbon nitride (g-C3N4) Interfacially Strengthened carbon fiber epoxy composites Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-29 Bo Song, Tingting Wang, Honggang Sun, Hu Liu, Xianmin Mai, Xiaojing Wang, Li Wang, Ning Wang, Yudong Huang, Zhanhu Guo
In-situ synthesis of C3N4 on the carbon fiber surface was reported for enhancing interfacial properties of carbon fiber reinforced epoxy resin composite. The formed C3N4 on the carbon fiber surface can greatly increase the roughness, polar functional groups and wettability of carbon fiber surface, thereby leading to significant enhancement of interfacial properties of composites. After modification, interlaminar shear strength (ILSS) and interfacial shear strength (IFSS) of carbon fibers composites are increased from 44.3 to 60.7 MPa and from 43.1 to 75.9 MPa, respectively. Moreover, the surface free energy of carbon fibers is increased by 65.6%. The improved interfacial properties endow carbon fiber composites with better mechanical properties, leading to an increased tensile strength of composites from 1063 to 1279 MPa and total absorbed energy of impact experiment from 1.22 to 1.75 J. Meanwhile, the dynamic mechanical properties and hydrothermal aging resistance are also enhanced significantly. The storage modulus increases from 64.3 to 74.1 GPa. The markedly enhancement of interfacial mechanical properties and mechanical properties could be attributed to the improved resin wettability, enhanced mechanical interlocking and increased chemical bonding induced by the existence of C3N4 on the carbon fiber surface.
Functional polycarbonates for improved adhesion to carbon fibre Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-29 Jan Henk Kamps, Christina Scheffler, Frank Simon, Ruud van der Heijden, Nikhil Verghese
In order to improve the fibre-matrix interaction in carbon fibre reinforced composites the polycarbonate (PC) matrix polymer was modified by the introduction of ethyl-3,5-dihydroxybenzoate as reactive sequences in the polycarbonate backbone. This promising strategy can be considered as an alternative approach to the modification of the carbon fibre surface to control and tailor the adhesion between carbon fibres and polymer matrix. The modification of the polycarbonate demonstrated improved adhesion to carbon fibre in pressed films, which was observed with microscopy-ATR-FTIR and SEM when compared to unmodified polycarbonate. Single fibre pull-out testing subsequently confirmed the improved adhesion, demonstrating higher interfacial shear strenght for the functionalized polycarbonate.
Thermo-mechanical coupling analysis of transient temperature and rolling resistance for solid rubber tire: Numerical simulation and experimental verification Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-29 Fanzhu Li, Feng Liu, Jun Liu, Yangyang Gao, Yonglai Lu, Jianfeng Chen, Haibo Yang, Liqun Zhang
The achievement of low rolling resistance and long-term durability of tires on various vehicles is of great challenge. Tire performances heavily depend on rubber properties; however, the thermo-mechanical coupling characteristics of rubber composites are complicated rendering the design of high-performance tires time-consuming and costly. In our research, the transient temperature and rolling resistance of a solid rubber tire were performed based on the thermo-mechanical coupling approach and nonlinear viscoelastic theory by using finite element method. Particular attention was paid to the strain cycles as the tire rolling on the road presents non-sinusoidal deformation. First, a static three dimensional tire-road contact analysis was conducted to obtain the principal strain cycles. Second, the 100th-order Fourier sine series was used to approximate the strain amplitude. Third, the heat generation rate proportional to the product of the loss modulus and the square of strain amplitude was calculated. The loss modulus was updated as a function of strain amplitude, temperature and frequency. Loss modulus softening effect was also considered. A practical method was proposed to compute the rolling resistance and transient temperature distributions by establishing a 2-D axisymmetric model. A rubber rolling tester was used to verify the numerical results. The comparison between numerical data and test data reveals that the proposed analytical method is a reliable approach to predict rolling resistance and transient temperature distribution for rubber tires. At last, the dependence of rolling resistance and heat build-up on thermal conductivity and loss factor were investigated by the parametric numerical experiments.
Natural weathering of hemp fibers reinforced polypropylene biocomposites: Relationships between visual and surface aspects, mechanical properties and microstructure based on statistical approach Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-27 Célia Badji, Joana Beigbeder, Hélène Garay, Anne Bergeret, Jean-Charles Bénézet, Valérie Desauziers
Two natural weathering of neat polypropylene (PP) and hemp fibers reinforced PP biocomposites were investigated. The objective was to emphasize the relationships between the properties of materials according to the fiber loading and the weathering time in order to bring new insights of degradation mechanisms understanding. For this purpose, a Principal Component Analysis (PCA) method was applied to the dataset. The treatment carried out by isolating materials loaded by the three different hemp fiber rates particularly outstand the link between mechanical properties and products issued from oxidation. The close correlation between whitening parameter and C=C bond level also confirmed the lignin degradation way. Finally, depending on the weathering duration, the properties characterized either fiber loading or weathering state (unweathered or weathered) whereas mechanical performance differentiated the three different non-weathered samples whatever the exposure time.
A rigid thick Miura-Ori structure driven by bistable carbon fibre-reinforced polymer cylindrical shell Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-27 Zheng Zhang, Weili Ma, Helong Wu, Huaping Wu, Shaofei Jiang, Guozhong Chai
Origami, the art of folding paper, has inspired the development of rigid foldable structures for various applications in aerospace, biomedical, and packaging applications. In order to drive and control origami structure with thick panels, a novel rigid Miura-Ori structure with bistable anti-symmetric carbon fibre reinforced polymer (CFRP) shells was proposed in this paper. Based on the membrane hinge technique, a theoretical model of the Miura-Ori structure with thick panels combined with bistable CFRP shells was established based on the principle of minimum potential energy. Bistable CFRP shells were used as the connection and driving parts of the whole structure instead of thin-walled materials or hinged structures. Finite element simulations were conducted to explore the deformations and trigger forces. The coincident boundary conditions were provided, which were the same as those used in the compression tests using the universal tensile testing machine. Experiments were conducted to validate the simulation results. The results showed that there is good agreement between the simulation and experimental results, indicating that the bistability of the origami structure is achieved under the control of the CFRP cylindrical shells.
Recyclable and heat-healable epoxidized natural rubber/bentonite composites Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-25 Chuanhui Xu, Rui Cui, Lihua Fu, Baofeng Lin
Carbon fibre reinforced thermoplastic composites developed from innovative hybrid yarn structures consisting of staple carbon fibres and polyamide 6 fibres Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-24 M.M.B. Hasan, S. Nitsche, A. Abdkader, Ch Cherif
With the increased demand and usage of carbon fibre reinforced composites (CFRP), effective methods to reuse waste carbon fibres (CF), which are recoverable either from manufacturing waste or from end-of-life components, are attracting growing attention. In this paper, the development of innovative core-sheath hybrid yarn structures consisting of staple CF and polyamide 6 (PA 6) fibres of 60 mm lengths using a DREF-3000 friction spinning machine with varying machine parameters, such as core to sheath ratio and suction air pressure, is described. Furthermore, uni-directional (UD) CFRP were manufactured based on the developed hybrid yarns, and the influence of the processing parameters on tensile properties and CF content of the composites was analysed. UD composites manufactured from the developed hybrid yarns possess approximately at least 86% of the tensile strength and Young's modulus of composites produced from virgin CF filament yarn.
Comparison of different surface treatments of carbon fibers used as reinforcements in epoxy composites: Interfacial strength measurements by in-situ scanning electron microscope tensile tests Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-22 Yu Liu, Delong He, Ann-Lenaig Hamon, Benhui Fan, Paul Haghi-Ashtiani, Thomas Reiss, Jinbo Bai
In-situ characterization of the fiber/matrix interfacial failure behavior at microscopic scale is important to optimize the fiber surface treatment and to design high performance composites. In this study, in-situ tensile tests in scanning electron microscope (SEM) were used to investigate the interfacial adhesion strength of epoxy composites reinforced by four kinds of carbon fibers (CF)—raw CF, desized CF, carbon nanotube-grafted CF (CNT-CF) and oxidized CNT-CF. The crack initiation position and fracture failure mode were well recorded. The strains and the interfacial adhesion strength were obtained for these four kinds of composites. It was found that the interfacial strength decreased from 53 MPa to 48 MPa after removing the sizing on carbon fiber surface. However, by grafting CNTs on the CF surface, the interfacial strength reached 55 MPa and was further increased to 58 MPa after a simple thermal oxidation treatment. Moreover, energy dispersion X-ray analysis (EDX) was carried out using scanning transmission electron microscopy (STEM). The EDX mapping demonstrated that oxygen aggregated at the interfaces of raw CF/epoxy and oxidized CNT-CF/epoxy. Thus, a combination of CNT grafting with chemical functionalization should be necessary to achieve high performance carbon fiber reinforced polymer composites.
Mechanical reinforcement in poly(propylene carbonate) nanocomposites using double percolation networks by dual volume exclusions Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-21 Shanshan Lin, Benke Li, Tingting Chen, Wei Yu, Xianhong Wang
Poly(propylene carbonate) (PPC) nanocomposites with poly(lactic acid) (PLA) and sepiolite nanofibers (NF) double percolation networks were prepared according to the dual volume exclusions principle. A two-step melt mixing with annealing process was adopted to construct the double percolation networks, which were verified by rheological and morphological characterization. The formation of double percolation networks structure effectively increased both the mechanical properties and heat resistance of PPC due to the greatly improved efficiency of the formation of force transferring network of NF. As a result, the PPC/PLA/NF ternary nanocomposites with double percolation networks exhibited elastic modulus about three orders higher than that of the pure PPC at 100 °C. The thermal deformation temperature, evaluated from the modulus at the glass transition of pure PPC (0.1 GPa), was found to be above 100 °C.
Influence of chitin nanocrystals on the dielectric behaviour and conductivity of chitosan-based bionanocomposites Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-21 A.M. Salaberría, R. Teruel-Juanes, J.D. Badia, S.C.M. Fernandes, V. Sáenz de Juano-Arbona, J. Labidi, A. Ribes-Greus
A series of bionanocomposite films based on chitosan, reinforced with chitin nanocrystals, were developed, and assessed in terms of dielectric behavior and conductivity by using an experimental methodology that allows avoiding the conductivity contribution and the exclusion of contact and interfacial polarization effects. The dielectric relaxations at low and high frequency and temperatures were modeled by Havriliak-Negami functions. Below the glass transition temperature (Tg), the γ and β relaxations were observed, which were related to intramolecular and non-cooperative segmental movements. At higher temperatures, an intermolecular and cooperative macromolecular movement, related to the glass transition, gave rise to α-relaxation. In addition, two over-Tg ρI and ρII relaxations were found, which were related to the displacement of dipoles in the disordered structure of bionanocomposites. The addition of chitin nanocrystals did not affect the apparent activation energy Ea of the γ-relaxation. However, it decreased the Ea of the β-relaxation and increased the free volume at temperatures in the vicinities of the α-relaxation. Finally, the electric conductivity of the bionanocomposites was lower than that of neat chitosan and chitin due to the interaction between the -OH and -NH2 groups that reduced the ionic mobility, along with the increase of free volume, with the subsequent separation of phases.
Highly sensitive and stretchable graphene-silicone rubber composites for strain sensing Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-21 Heng Yang, XueFeng Yao, Zhong Zheng, LingHui Gong, Li Yuan, YaNan Yuan, YingHua Liu
Flexible strain sensors made by conductive elastomer composites have attracted increasing attention. In this paper, the electromechanical properties of graphene-silicone rubber nanocomposites are studied systematically. First, the conductive nanocomposites composed of graphene and silicone rubber are prepared by means of co-coagulation, which shows a lower percolation threshold with 1.87 wt% (0.94 vol%). Second, the rubber nanocomposites with different graphene contents exhibit a very high strain sensitivity (gauge factor > 143) and a larger strain sensing range (>170%), also, the good recoverability and reproducibility have been found during the loading-unloading cycle. Finally, the analytical model based on the connectivity of the graphene nanosheets and the viscoelasticity of the rubber matrix is developed to describe the electromechanical properties and explain the ‘shoulder peak’ phenomenon, also a typical application example about monitoring the operate state of the rubber seal is given.
Self-healing improves the stability and safety of polymer bonded explosives Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-20 Xin Huang, Zhong Huang, Jian-Cheng Lai, Lei Li, Guang-Cheng Yang, Cheng-Hui Li
Polymer-bonded explosives (PBXs) are often subjected to different external environmental conditions with various temperature and humidity during long-term storage, transportation, and usage process. The change in temperature and humidity will result in PBXs cracks formation and cause higher risk of explosion evolution when undergoing various stimulus including impact or friction. Herein, a self-healing polymer binder is developed to solve this problem. The fluoropolymer gel binder, a PVDF-co-HFP (copolymer of CH2-CF2 and CF2-CF(CF3))/EMIOTf (1-ethyl-3-methylimidazolium trifluoromethanesulfonate)/graphene ternary composite, has high density, high thermal conductivity, excellent interfacial adhesion property, and exhibits self-healing ability at room temperature. Highly filled PBXs composites with 95% of explosive 2, 6-diamino-3, 5-dinitropyrazine-1-oxide (LLM-105) and 5% of ternary composite are fabricated. The as-prepared PBX samples have high denotation parameter (7800 m s−1), low impact sensitivities (11–12 J), and low friction sensitivity (no sparks was observed even at friction energy load of 0.36 N). More importantly, our PBXs have effective crack healing ability within 48 h at room temperature. Therefore, the stability and safety of PBXs are improved through the self-healing polymer binder. Such PBXs can find widespread application in various military and civil fields.
Counterion design of TEMPO-nanocellulose used as filler to improve properties of hydrogenated acrylonitrile-butadiene matrix Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-19 Shunsuke Fukui, Takuro Ito, Tsuguyuki Saito, Toru Noguchi, Akira Isogai
A viscoelastoplastic stiffening model for plant fibre unidirectional reinforced composite behaviour under monotonic and cyclic tensile loading Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-19 F. Richard, C. Poilâne, H. Yang, F. Gehring, E. Renner
At room conditions and standard strain rate (ε˙∼10−4s−1), unidirectional (UD) plant-based reinforced organic polymers often exhibit nonlinear mechanical behaviour in tension. A viscoelastoplastic model (VEP model) for the simulation of UD plant fibre composite mechanical behaviour in tension, previously validated from twisted flax yarn epoxy composite under room conditions and standard strain rate, is calibrated with new data obtained from flax fibre epoxy composite under repeated progressive loading and a wide range of strain rates (ε˙∼10−3 to 10−7s−1). The VEP model does not reproduce well the experimental observations. There seems to be a lack of stiffening in this phenomenological model.We propose an improved VEP model, developed within the frameworks of thermodynamics and limited to uniaxial tension and infinitesimal strains. An internal variable s representing the stiffening is added to create a VEP-stiffening model. This internal variable represents the coupled effects of reorienting cellulose microfibrils in kink band areas, spiral spring-like extension of cellulose microfibrils, and shear-stress-induced crystallization of the amorphous cellulose of flax fibres. The stiffening phenomenon was considered viscous, without a threshold, and was related to the tension energy in the direction of the fibres. Three viscosity coefficients drive the three phenomena: η (elastic), K (plastic), and Ks (stiffening). In the chosen formalism, this leads to two thermodynamic potentials φVEPs and ΩVEPs in which the stiffening phenomenon is strongly coupled with all the others.This VEP-stiffening model of the UD flax fibre epoxy composite correlates well with experimental observations. The paper also explores the evolution of the three viscous phenomena (elastic, plastic, and stiffening) by simulation of different loading conditions: monotonic, cyclic, and creep.This VEP-stiffening model can easily enrich existing multiaxial models of UD behaviour in the fibre direction. Implemented in a finite element model, it could be used at different length scales to numerically explore the origin of the mechanical behaviour of plant-based reinforced polymers.
The effects of polybenzimidazole and polyacrylic acid modified carbon black on the anti-UV-weathering and thermal properties of polyvinyl chloride composites Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-17 Dandan Jin, Shiai Xu
In this study, the effects of polybenzimidazole (PBI) and polyacrylic acid (PAA) modified carbon black (MCB) on the anti-UV-weathering and thermal properties of PVC composites were investigated. The optimal mass ratios of PBI and MCB to PVC are 0.1 wt% and 0.2 wt%, respectively, and the resultant 1PBI/2MCB/PVC composite membrane with a thickness of about 60 μm can block over 99% of UV light below 380 nm. The UV absorption mechanism was investigated by the optional band gaps (Eg) and the fluorescence spectra. The incorporation of PBI and MCB results in a decrease in Eg, from 4.96 eV for PVC membrane to 2.90 eV for 1PBI/2MCB/PVC composite membrane, and MCB can quench the fluorescence of PBI by photon-induced electron transfer to further protect PVC. The results of accelerated UV-weathering experiment indicate that the incorporation of PBI and MCB can improve the anti-UV-weathering property of PVC. The thermal degradation behaviors of PVC and its composite membranes in air and N2 atmosphere were also investigated. The highest char residue (13.7 wt%) is obtained in 1PBI/2MCB/PVC composite membrane at 800 °C in N2 atmosphere, with an increase of 73.4% compared with that of PVC membrane, which may be because PBI and MCB can synergistically accelerate the carbonization of PVC molecules to rapidly form stable char residue.
Effect of nano-silica filler on microstructure and mechanical properties of polydimethylsiloxane-based nanocomposites prepared by “inhibition-grafting” method Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-18 Jian Liu, Yu Cheng, Kai Xu, Lulu An, Yuhang Su, Xiaohong Li, Zhijun Zhang
Silica/polydimethylsiloxane nanocomposites (denoted as SiO2/PDMS) prepared by physical mixing exhibit poor processing flexibility and strength associated with the high viscosity effect and low addition amount of silica during the fabrication of room-temperature vulcanized PDMS elastomer. Thus a facile and scalable one-step “inhibition-grafting” method was established to graft polydimethylsiloxane (PDMS) onto the surface of DNS-2 (a kind of dispersible nano-silica with network structure) to yield nano-SiO2/PDMS high-performance nanocomposites. Their microstructure and chemical structure were characterized by TEM, GPC, FTIR and TGA. The viscosity and rheological properties were evaluated, and their mechanical properties of the as-prepared nano-SiO2/PDMS elastomers were measured as well. Findings indicate that PDMS chains are grafted on the silica surface via covalent bonding and the chains either grafted on the silica or in free state interpenetrated silica network thereby forming a kind of interpenetrating network. This kind of interpenetrating network and short PDMS chains can provide more crosslinking sites, leading to low viscosity and high mechanical properties of SiO2/PDMS composites. Besides, the nano-SiO2/PDMS elastomers containing over 16 phr (phr: parts of silica per hundred parts of PDMS by weight) of nano-silica exhibit shear thinning behavior, which corresponds to the transformation from Newtonian fluids to non-Newtonian fluids associated with the formation of whole interpenetrating network between nano-silica and PDMS chains. In summary, the nano-SiO2/PDMS elastomers exhibit a low viscosity and good mechanical properties, which is favorable for promoting their applications in the industry of high performance silicone materials.
All-organic dielectric nanocomposites using conducting polypyrrole nanoclips as filler Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-18 Lin Zhang, Xu Lu, Xinyu Zhang, Li Jin, Zhuo Xu, Z.-Y. Cheng
All-organic nanocomposites using conducting polypyrrole (PPy) nano-clips as fillers and poly(vinylidene fluoride-chlorotrifluoroethylene) (PVDF-CTFE) as the matrix are studied. The nanocomposites with a uniform microstructure were fabricated via a combination of a solution casting and a hot pressing process. Due to the uniform microstructure, the composites exhibit a single glass transition process, whose temperature decreases with increasing PPy content. The dielectric properties of the nanocomposites are systemically studied and analyzed over a wide temperature range from −60 °C to 140 °C and a broad frequency range from 100 Hz to 1 MHz. The nanocomposites have a low percolation threshold (∼7.4 wt.%) and exhibit a high dielectric constant and a low dielectric loss. For the composites with 7 wt.% of PPy at room temperature, the dielectric constant at 1 kHz is 23 times higher than that of the polymer matrix and the dielectric loss over a broad frequency range is less than 0.4 which is lower than the loss reported in other composites with the composition close to the percolation threshold. It is concluded that mixing PPy with P(VDF-CTFE) results in a new relaxation process that dominates the observed dielectric loss at low temperatures including room temperature. It is demonstrated that it is the DC conductivity rather than the dielectric constant that should be used to determine the percolation threshold.
Preparation of carboxylated nitrile butadiene rubber/fly ash composites by in-situ carboxylate reaction Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-18 Shuyan Yang, Ping Liang, Kaihui Hua, Xiaokang Peng, Yanxue Zhou, Zhuodi Cai
Fly ash (FA) is a byproduct of thermal power stations, which causes increasing environment pollutions in the last decade. The incorporation of FA would deteriorate the performance of polymer composites even modified by silane coupling agents. Thereby, the bulk utilization of FA in polymer industry is still a challenge in the world. In this work, by in-situ carboxylate reaction between carboxyl groups of carboxylated nitrile butadiene rubber (XNBR) and FA particles, an immobilized rubber layer is formed on the surface of FA particles, resulting in a better interface adhesion. As a consequence, the tensile strength of XNBR/20FA composite reaches 23.19 MPa, about 44.0% larger than pure XNBR. Even if the incorporation of FA is up to 40phr, the tensile strength is still about 20.60 MPa, about 28.0% larger than pure XNBR, which opens a new approach to lower polymer product cost and solve the environment pollution.
Extremely high thermal conductivity of nanodiamond-polydopamine/thin-layer graphene composite films Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-16 Hui-Ching Yuan, Chi-Young Lee, Nyan-Hwa Tai
The hybrid composite films containing nanodiamonds (ND) coated with polydopamine (pDA) (ND-pDA) and reduced graphene oxide (rGO) converted from graphene oxide (GO) films are designed for achieving extremely high thermal conductivity. The ND-pDA/rGO films are successfully fabricated using the vacuum-filtration process followed by a heat treatment at 800 °C. The thermal conductivities of the films in the in-plane (K//) and through-plane (K⊥) directions are measured by the laser flash method to better understand how the addition of dopamine, the amount of ND-pDA, and the test temperature affect the thermal properties of the hybrid films.The experimental results show that the addition of dopamine results in dense structure of the ND-pDA/rGO hybrid films, which is favorable for phonon transport, and thus remarkably increase the thermal properties of the film. Additionally, films with higher ND-pDA loading possess lower in-plane but higher through-plane thermal conductivity. K// and K⊥ of 1406 and 0.677 W m−1 K−1, respectively, for 20ND-pDA/20rGO measured at 25 °C are achieved. Both the K// and K⊥ of 20ND-pDA/20rGO increase with test temperature. Maintaining such high thermal conductivities at high temperature, the hybrid films are believed to be suitable for lightweight thermal management materials with high heat transfer properties in a specific direction.
Great toughness reinforcement of isotactic polypropylene/elastomer blends with quasi-cocontinuous phase morphology by traces of β-nucleating agents and carbon nanotubes Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-15 Yanhui Chen, Zhiqiang Wu, Qian Fan, Song Yang, Erchao Song, Qiuyu Zhang
Aiming at obtaining the polyolefin blends potentially applied in the field of the super-tough polymer products, in this work, isotactic polypropylene (iPP)/styrene-ethylene-butadiene-styrene block copolymer (SEBS) blends with great impact toughness were successfully fabricated by adding traces of β-nucleating agents (β-NAs) and carbon nanotubes (CNTs). The impact toughness of iPP blends with 30 wt% SEBS was as high as 62.4 kJ/m2, when simultaneously containing 0.1 wt% β-NAs and 0.05 wt% CNTs. Their toughness was about 13.1 kJ/m2 more than iPP blends with 30 wt% SEBS and 0.1 wt% β-NAs, 49.6 kJ/m2 more than iPP blends with 30 wt% SEBS and 0.05 wt% CNTs, and almost 22.3 times of pure iPP. The iPP matrix with abundant self-toughed β-crystals generated by β-NAs, the quasi-cocontiunous morphology of the SEBS dispersed phase as well as some small SEBS droplets induced by CNTs in the iPP matrix, and the good interfacial compatibility between SEBS and the iPP matrix all harmoniously took effect to synergistically enhance the toughness of iPP blends.
Micro-mechanical damage model accounting for composite material nonlinearity due to matrix-cracking of unidirectional composite laminates Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-13 Ghazi A.F. Abu-Farsakh, Haitham M. Al-Jarrah
A new micromechanical damage model for predicting the effect of matrix-cracking on the mechanical behavior of the composite material is proposed. The model is based on the volumetric change that occurred due to the presence of cracks in a composite lamina due to uniaxial off-axis loading. It determines the volumetric crack-density (VCD) by combining the macro-mechanical and micro-mechanical principles. A representative volume-element is proposed that determines the material mechanical properties (E1, E2, G12 and ν 12 ) in terms of crack-density, fiber and matrix properties and initial volume-fraction of fibers. The rule-of-mixture in combination with Halpin-Tsai model is used to determine the mechanical properties of a cracked composite lamina. It has been shown that, matrix-cracking is the main cause for composite-material nonlinearity. Moreover, the model has been shown to give a reliable and reasonable predictions of the VCD and the tangential damage-factor (TDF) for various fiber/matrix systems using the corresponding available data from literature. An alternative secant damage-factor is being proposed, which has a linear relationship with the VCD. In order to validate the model, two composite materials; Boron/Epoxy (Narmco-5505) and Graphite/Epoxy (4617/Modmor-II), have been considered using laminates at different fiber-orientation angles. The maximum volume-crack-density (MVCD) and maximum secant damage-factor (MSDF) are obtained using equations that depend on the fiber-orientation angle and the initial material mechanical properties.
Enhanced fracture toughness in architected interpenetrating phase composites by 3D printing Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-11 Tiantian Li, Yanyu Chen, Lifeng Wang
Interpenetrating phase composite (IPC), also known as co-continuous composite, is one type of material that exhibits an unusual combination of high stiffness, strength, energy absorption, and damage tolerance. Here we experimentally demonstrate that IPCs fabricated by 3D printing technique with rationally designed architectures can exhibit a fracture toughness 16 times higher than that of conventionally structured composites. The toughening mechanisms arise from the crack-bridging, process zone formation and crack-deflection, which are intrinsically controlled by the rationally designed interpenetrating architectures. We further show that the prominently enhanced fracture toughness in the architected IPCs can be tuned by tailoring the stiffness contrasts between the two compositions. The findings presented here not only quantify the fracture behavior of complex architected IPCs but also demonstrate the potential to achieve tailorable mechanical properties through the integrative rational design and the state-of-the-art advanced manufacturing technique.
Largely enhanced mechanical property of segregated carbon nanotube/poly(vinylidene fluoride) composites with high electromagnetic interference shielding performance Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-11 Wan-Cheng Yu, Tao Wang, Guo-Qiang Zhang, Zhi-Guo Wang, Hua-Mo Yin, Ding-Xiang Yan, Jia-Zhuang Xu, Zhong-Ming Li
The potential impact of DGEBA/amine reaction kinetics on interphase formation in glass fiber composites Compos. Sci. Technol. (IF 5.16) Pub Date : 2018-08-11 Gale A. Holmes
A distinctive region known as the fiber-matrix (F-M) interface/interphase (I/I) is formed between the matrix and fiber during composite manufacture. This region is assumed to be created in thermoset matrices by chemistry perturbations induced during the cure reaction. These perturbations occur at the un-sized or sized fiber surface, with the sized surface typically engineered to promote adhesion between matrix and fiber. Given the importance of this region to composite performance, potential chemistry perturbations that may arise are discussed, focusing on epoxy/amine reaction kinetics. These perturbations are linked to morphology changes that arise during fiber fracture. It is hoped that these ideas will facilitate a more complete understanding of the F-M I/I region and promote strategies for developing tougher composites.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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