Optical excitation thermography for twill/plain weaves and stitched fabric dry carbon fibre preform inspection Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-12 Hai Zhang, François Robitaille, Christian U. Grosse, Clemente Ibarra-Castanedo, Jaime Ocana Martins, Stefano Sfarra, Xavier P.V. Maldague
Multi-failure analysis of composite Isogrid stiffened cylinders Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-09 Ming Li, Hualin Fan
Adopting filament winding and co-curing technique, carbon fiber reinforced composite (CFRC) Isogrid stiffened cylinders (ISCs) were designed and manufactured. Revealed by experiments, CFRC ISC has multi-failure modes, including material failure, global instability, local buckling, rib crippling and end delamination. Failure criteria for the first four failure modes were proposed and applied to predict the failure load of specific ISC. Skin thickness, cell dimension, rib height, rib thickness and end strengthening scheme jointly decide the failure pattern and failure load of the ISC. Failure maps were deduced to figure out the optimizing route for lightweight design of ISC. Wrapped ends were suggested to restrict the end delamination failure mode which results in rather low and uncertain load carrying capacity.
Novel dielectric BN/epoxy nanocomposites with enhanced heat dissipation performance for electronic packaging Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-09 Dongju Lee, Seyong Lee, Segi Byun, Kyung-Wook Paik, Sung Ho Song
Two-dimensional hexagonal boron nitride (h-BN) has excellent and useful mechanical and thermal properties, and can be used as a novel filler to enhance the thermal conductivity of polymer composites. We prepared exfoliated h-BN nanoplatelets (BNNP) with hydroxyl functional groups using a hydroxide-assisted ball milling process, and demonstrated the enhanced thermal conductivity of its epoxy nanocomposites. The prepared BNNP are highly soluble and retain their in-plane structure. The dielectric constant and dielectric loss of the nanocomposites increase with the addition of BNNP owing to interfacial polarization by the large surface area of BNNP and the ionic and electronic relaxation polarizations by the surface functional groups on the BNNP. Notably, the thermal conductivity of the epoxy nanocomposites with 10% mass fraction of BNNP was 0.57 W/m·K, which is 2.85-times higher than that of neat epoxy. Finally, compared with neat epoxy, BNNP nanocomposite exhibits excellent heat dissipation capability in flat chip packaging. This enhanced performance is ascribed to the high quality and dispersion of the BNNP and their strong interfacial bonding with the epoxy matrix, which is produced by the hydroxyl functional groups on the BNNP. The overall results suggest that BNNP nanocomposites have strong potential for application as electronic packaging materials.
Numerical analysis of viscoelastic process-induced residual distortions during manufacturing and post-curing Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-08 Maria Benavente, Lionel Marcin, Alice Courtois, Martin Lévesque, Edu Ruiz
Degree of cure- and temperature-dependent elastic and viscoelastic models were implemented into ABAQUS to compute the geometrical distortion developed during the RTM manufacturing and post-curing of asymmetric plates and corner shaped parts. Comparisons between the predicted and experimental geometrical distortion for an asymmetric plate reinforced with 3D interlock woven fabric are presented. The results showed that the parts can experience creep behavior when submitted to free-standing post-curing, increasing the total geometrical distortion up to 30 %%, depending on post-curing cycle and part geometry. The numerical results of this work demonstrate that a temperature-dependent viscoelastic model is needed to accurately predict the geometrical distortion evolution developed during cure cycles where post-curing processes are involved.
Structural health monitoring of fibre metal laminates under Mode I and II loading Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-08 Björn Bosbach, Christoph Ohle, Bodo Fiedler
Delamination is one of the most common defects in FRP and occurs due to low interlaminar strength. Such defects are difficult to detect and lead often to catastrophic failure of the composite. In this work a new approach of a multi-functional FML for structural applications is investigated. The interlaminar fracture toughness is determined and the capacitance change between the metal plies during crack propagation is measured in-situ. The metal sheet component undergoes a chemical pre-treatment by nanoscale sculpturing before manufacturing by resin transfer moulding, to prevent adhesive failure of the interfacial metal/matrix bond.The experimental test results show high potential for detecting defects in FMLs. Delamination, which occurs between the glass fibre/matrix interface, can be electrically detected using the capacitance measurement. The fracture surface of the pre-treated metal sheet demonstrates that the adhesive bond between the cubical hook-like surface structure of the aluminium and the matrix remains intact.
Chemorheological study and in-situ monitoring of PA6 anionic-ring polymerization for RTM processing control Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-08 Abderrahim Maazouz, Khalid Lamnawar, Mohamed Dkier
The main objective of this work was an experimental investigation making it possible to monitor, as well as achieve a deeper understanding of, the structural evolution of polyamide-6 as a thermoplastic-based composite matrix. Polyamide-6 from anionic ring-opening polymerization (AROP) of ε-caprolactam was chosen as a model matrix. Throughout this work, various formulations of PA with anionic polymerization from caprolactam were studied depending on different activator/catalyst pairs, concentrations and combinations. Moreover, chemorheological properties were first determined ex-situ by rheology coupled with FTIR and microdielectrometry. The extent of the reaction conversion was thus obtained and subsequently modeled. The formed PA6 matrix materials were fully characterized in terms of their viscosimetric properties and molar masses. In a second step, a hybrid extrusion resin transfer molding machine (T-ERTM) with an instrumented mold was designed for the in-situ monitoring. Thereby, specific dielectric sensors were used to follow the different processing steps for the manufacturing of complex and continuous glass fiber-reinforced parts. Furthermore, the reaction kinetics in competition with the crystallization were probed and quantified as a function of the processing parameters (mold temperature, times given for impregnation, time for demolding etc.). Calibration curves were obtained in which the ionic conductivity was correlated to the change of viscosity determined previously from ex-situ measurements. Indeed, a processing window was proposed for each PA6 system to ensure a good preform impregnation. Interestingly, the apparent conversion calculated from the online dielectric measurements corroborated the ex-situ values obtained from chemorheological studies. The viscosity and conversion evolution were then tracked in the mold. Based on the present findings and for the optimal formulation, a Time-Temperature-Transformation (TTT)-equivalent diagram was established from online measurements and related to the reactive processing to get a better handle on the PA6-based composite.
Introducing Cryomilling for Reliable Determination of Resin Content and Degree of Cure in Structural Carbon Fibre Reinforced Thermoset Composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-06 Nessa Fereshteh-Saniee, Neil Reynolds, Catherine A. Kelly, Peter R. Wilson, Mike J. Jenkins, Ken N. Kendall
A novel material preparation method is presented that facilitates accurate measurement of the degree of cure and resin content within carbon fibre reinforced polymer composites (CFRPs). When using conventional specimen preparation for standard thermal analysis, it is demonstrated that the experimentally-obtained enthalpy of reaction and resin content varies significantly between analyses. Measurement uncertainties arise because small specimen volumes are extracted from materials that exhibit both macroscopic inhomogeneity and physical discontinuities. To address this issue, representative sample volumes of aligned CFRPs were first cryogenically milled to develop a homogeneous powder before smaller specimens were extracted. The variation in obtained enthalpy of reaction between analyses was reduced from 23% (for conventional specimen extraction) to 1% following cryomilling. The accuracy in measurement of degree of cure for the compression moulding parts was improved 7 times. Further, subsequent FTIR analysis proved that cryomilling did not affect the final chemical structure of the cured material.
Effect of interface on composites made from DREF spun hybrid yarn with low twisted core flax yarn Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-04 Mahadev Bar, Apurba Das, R. Alagirusamy
In the present work, the influence of interface and hybrid yarn structure on flax-PP based unidirectional composite properties have been studied thoroughly. Flax-PP based core-sheath structured DREF spun hybrid yarns are manufactured after varying the core yarn twist and sheath percentage at three different levels and using MAgPP treated and untreated flax yarn as core. These hybrid yarns are consolidated to manufacture unidirectional composite samples and the resultant composites are tested accordingly. It is observed that MAgPP treatment of the core flax yarn improves the tensile and flexural properties of the hybrid yarn reinforced unidirectional composites while impact strength decreases after the treatment. A negative impact on the tensile and flexural properties of the unidirectional composite samples is observed with increasing core twist and sheath content of the reinforcing hybrid yarn. The impact strength of the composite samples increases for similar changes in hybrid yarn parameters.
The formation of atomic-level interfacial layer and its effect on thermal conductivity of W-coated diamond particles reinforced Al matrix composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-03 Zifan Che, Jianwei Li, Qingxiao Wang, Luhua Wang, Hailong Zhang, Yang Zhang, Xitao Wang, Jinguo Wang, Moon J. Kim
Out-of-autoclave scarf repair of interlayer toughened carbon fibre composites using double vacuum debulking of patch Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-03 H.M. Chong, S.L. Liu, A.S. Subramanian, S.P. Ng, S.W. Tay, S.Q. Wang, S. Feih
Interlayer particle toughened carbon fibre composites play an integral role in the lightweight design of primary aerospace structures. We investigate an out-of-autoclave method using double vacuum debulking (DVD) to perform in-situ soft patch repairs. Utilizing the DVD process decreases the porosity of the co-cured film adhesive and patch from 4.7% to 0.4%, thereby increasing the flexural and interlaminar shear strength of 1D repair laminates by 30% to levels equal to autoclave cured laminates. In contrast, the higher void content did not significantly affect straight (2D) and round (3D) scarf repair strengths. 3D repairs showed significantly improved strength recovery compared to 2D repairs due to the stress shedding in the hoop direction. Finally, DVD process parameters may be optimized to reduce repair time by increasing the temperature and ramp rates while reducing the soak times, with no detrimental effects on porosity or strength observed.
Enhanced Thermal Conductivity of Polyethylene/Boron Nitride Multilayer Sheets through Annealing Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-03 Shu-Ya Yang, Yan-Fei Huang, Jun Lei, Lei Zhu, Zhong-Ming Li
Polyethylene/hexagonal boron nitride (PE/h-BN) composite sheets with enhanced thermal conductivity were fabricated through annealing a multilayered structure of alternating high density PE (HDPE)/h-BN composite and low density PE (LDPE) layers. Multilayer sheets possess a relatively low initial content filler, and after thermal annealing at 200 °C, the PE molecules in the composite layers diffused into neighboring layers. As a result, the h-BN concentration in the composite layers increased with the annealing time, resulting in the formation of thermal conduction pathways and enhancement of the final thermal conductivity. When the volume content of h-BN was 5.97 vol.%, the through-plane thermal conductivity of the annealed specimen was 1.37 W m-1K-1, which showed an enhancement of ∼180% compared to the value of the neat composite with the same content of randomly dispersed h-BN. Our work suggests that this facile method is promising for the development of high-performance thermally conductive products.
An energy-efficient composite by using expanded graphite stabilized paraffin as phase change material Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-03 Xi Guo, Shaodi Zhang, Jinzhen Cao
Thermal energy storage (TES) composites were prepared by employing expanded graphite (EG) stabilized paraffin as phase change material (PCM) and wood flour/ high density polyethylene (WF/HDPE) as matrix. The morphology and structure of EG and form-stable phase change material (FSPCM) were investigated by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and mercury intrusion porosimetry. The fabricated TES composites with different FSPCM types and contents were characterized by differential scanning calorimetry (DSC), thermogravimetric (TG), infrared thermography and laserflash thermal analysis. Physical and mechanical strength were also evaluated. The results showed that: (1) the EG had abundant pores and most of the pores were below 26 μm, the EG stabilized paraffin material showed perfect stability without any chemical reactions; (2) thermal performance indicated that the TES composites had efficient temperature-regulated ability, but thermal durability need to be further enhanced; (3) addition of paraffin and EG destroyed the interface bonding of the TES composites and mechanical properties appeared slight decrease; (4) the satisfying thermal performance and acceptable mechanical property indicating the TES composites can be used as building material for temperature conditioning.
Mechanical properties and strain monitoring of glass-epoxy composites with graphene-coated fibers Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2018-01-02 Haroon Mahmood, Lia Vanzetti, Massimo Bersani, Alessandro Pegoretti
An engineered interphase can improve the mechanical properties of epoxy/glass composites simultaneously inducing a piezoresistive response. To prove this concept, E-glass fibers were coated with graphene oxide (GO) by electrophoretic deposition, while reduced graphene oxide (rGO) coated fibers were obtained by subsequent chemical reduction. The fiber-matrix interfacial shear strength measured by the single-fiber fragmentation test increased for both GO and rGO coated fibers. Unidirectional composites with a high content of both uncoated and coated fibers were produced and mechanically tested under various configurations (three-point bending, short beam shear and mode-I fracture toughness, creep). Composites with coated fibers performed similarly or better than composites prepared with uncoated fibers. Finally, composites with rGO coated fibers were tested for their piezoresistive response under both static and dynamic conditions. The electrical resistance changed proportionally to applied strain thus confirming the possibility of using composites with rGO coated fibers as strain sensors in load-bearing components.
Role of lignin nanoparticles in UV resistance, thermal and mechanical performance of PMMA nanocomposites prepared by a combined free-radical graft polymerization/masterbatch procedure Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-29 Weijun Yang, Marco Rallini, De-Yi Wang, Daqian Gao, Franco Dominici, Luigi Torre, José M. Kenny, Debora Puglia
In the present work, the preparation of lignin nanoparticles (LNP) reinforced PMMA nanocomposites, obtained by combining solvent-free radical polymerization, micro extrusion and hot press methods through a masterbatch approach, was reported. Results from Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and Gel Permeation Chromatography (GPC) evidenced the successful grafting of LNP on MMA, confirmed by the higher glass transition temperatures observed by DSC in LNP grafted PMMA (PMMA-g-LNP) systems. Microstructural characterization confirmed good LNP dispersion in PMMA, achieved by means of the adopted masterbatch procedures. Furthermore, results from optical, thermal and mechanical characterization of the resulted PMMA nanocomposites confirmed improved hardness values, enhanced UV resistance, better thermal and scratch resistance for PMMA/LNP nanocomposites, opening the possibility of using these systems in many different sectors, such as automotive, flooring, acrylic glasses and lenses.
Effect of post curing temperature on mechanical properties of a flax fiber reinforced epoxy composite Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-29 Charlotte Campana, Romain Leger, Rodolphe Sonnier, Laurent Ferry, Patrick Ienny
Achieving a complete curing of biocomposites without damaging fibers is very challenging. This study assesses the impact of processing upon the mechanical properties of a unidirectional flax reinforced epoxy composite and identifies which component (resin, reinforcement or interphase) is the most sensitive to post-curing at high temperature (100, 120 or 150°C). Post-curing temperature had a limited impact on the composite mechanical behavior excepted at 150°C where ultimate stress and strain decreased drastically while the stabilized modulus slightly increases. Post curing is responsible of a slight decrease of the matrix tensile properties attributed to the polymer oxidation but cannot explain on its own the evolution of the composite behavior. Interfacial adhesion played a minor role in the composite behavior probably due to its intrinsic weakness. Finally, the flax fabric was highlighted to be the component most sensitive to thermal treatment thus governing the drop in the composite mechanical properties.
An experimental study of water diffusion in carbon/epoxy composites under static tensile stress Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-28 Corentin Humeau, Peter Davies, Frédéric Jacquemin
The coupling between tensile stress and water diffusion in composites represents a major issue in many marine applications. Even if these two behaviours are well documented as separate subjects, there are still very few data on fully coupled mechanisms. The aim of this study is to understand what governs the coupled behaviour, by investigating the water diffusion in carbon/epoxy. The coupling is first evaluated on neat resin samples to characterise the matrix behaviour. Then the study focuses on composites with two types of woven fibre orientation: one at ±45°, in order to understand the coupling effects on materials loaded away from the reinforcement direction and another quasi-isotropic to obtain properties along the fibres. For each material the same approach was applied: first, the tensile behaviour, damage development and water diffusion were studied uncoupled. Then, semi-coupled effects were investigated. The final part of the paper combines both behaviours as fully coupled phenomena.
Functionalized graphene as an effective antioxidant in natural rubber Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-28 Lin Zhang, Hongqiang Li, Xuejun Lai, Xiaofeng Liao, Jing Wang, Xiaojing Su, Heng Liu, Wenjian Wu, Xingrong Zeng
To improve the thermo-oxidative aging resistance of natural rubber, a kind of functionalized graphene (FGE) was prepared by grafting 2-tert-butyl-6-(3-tertbutyl-2-hydroxy-5-methylphenyl) methyl-4-methylp-henyl acrylate (GM) onto graphene oxide (GO) using (3-mercaptopropyl) trimethoxysilane as bridging agent. In comparison to GO, FGE appeared more curled surface and reached the higher water contact angle of 134o. By latex-mixing method, the uniformly dispersed FGE endowed NR vulcanizates with obviously improved thermal stability. Importantly, the NR/FGE nanocomposites exhibitd excellent thermo-oxidative aging resistance, which was attributed to not only the synergistic antioxidative effect of hindered phenol groups and thioether bonds, but also the barrier role of graphene sheets to oxygen. Our findings provide a new strategy to prepare functionalized graphene as effective antioxidant for rubber and other polymer materials.
Cellulose/Graphene Bioplastic for Thermal Management: Enhanced Isotropic Thermally Conductive Property by Three-Dimensional Interconnected Graphene Aerogel Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-28 Li Chen, Xingshuang Hou, Na Song, Liyi Shi, Peng Ding
Environment-friendly cellulose bioplastic is a promising material to replace fossil-fuel plastic for the more sustainable future. In present study, we reported a functional cellulose bioplastic that can be used for thermal management. The cellulose bioplastic was easily fabricated by impregnating three-dimensional graphene aerogel (GA) into the cellulose solution and then hot-pressed. The cellulose/GA composites exhibited enhanced isotropic thermal conductivity and good mechanical performance. The thermal conductivity of the cellulose/GA composite was 0.67 W⋅m-1⋅K-1 in vertical direction increasing by 219% and 0.72 W⋅m-1⋅K-1 in parallel direction, increasing by 44% respectively. Meanwhile, the hardness of the composites reached to 148 MPa and the Young's modulus is 2.3GPa, superior to those of most common plastics, such as Nylon and Polymethyl methacrylate (PMMA). The integrated performance of the composites could be attributed to the formation of efficient thermally conductive network and the good adhesion between the graphene cell wall and the cellulose.
Mechanical response of multi-layer bacterial cellulose nanopaper reinforced polylactide laminated composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-27 Martin Hervy, Jonny J. Blaker, Ana Letícia Braz, Koon-Yang Lee
In this study, we investigated the mechanical response of polylactide (PLLA) reinforced with multiple layers of BC nanopaper. Laminated composites consisting of 1, 3, 6 and 12 sheet(s) of BC nanopaper were produced. It was observed that increasing the number of BC nanopaper led to an increase in the porosity of the resulting BC nanopaper-reinforced PLLA laminated composites. The tensile moduli of the laminated composites were found to be ∼12.5 – 13.5 GPa, insensitive to the number of sheets of BC nanopaper in the composites. However, the tensile strength of the laminated composites decreased by up to 25% (from 121 MPa to 95 MPa) when the number of reinforcing BC nanopaper sheets increased from 1 to 12 sheets. This was attributed to the presence and severity of the scale-induced defects increased with increasing BC nanopaper sheets in the PLLA laminated composites.
Constructing hierarchical polymer@MoS2 core-shell structures for regulating thermal and fire safety properties of polystyrene nanocomposites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-27 Keqing Zhou, Gang Tang, Rui Gao, Hailin Guo
Two dimensional MoS2 acting as reinforcing fillers had attracted intense interests in recent years. However, the homogeneous dispersion of MoS2 nanosheets in polymer matrix and exact interface control were still difficult to achieve due to potent van der Waals forces and surface inactiveness. In this work, hierarchical polystyrene@MoS2 core-shell structures were constructed by combining latex technology and self-assembly of oppositely charged MoS2 nanosheets onto the surface of polystyrene spheres. The formed core-shell structures were characterized by X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy and further employed as reinforcing fillers in a host polystyrene matrix by solvent blending method. It was clearly observed that the construction of polystyrene@MoS2 core-shell structures not only improved the dispersion of MoS2 in the matrix and the interfacial adhesion between MoS2 and polystyrene, but also obviously improved the thermal stability and fire safety of polystyrene. The method proposed here had proved to be an efficient and facile approach to fabricate polymer/MoS2 nanocomposites with good dispersion and markedly improved properties.
Surface Engineered Poly(dimethylsiloxane)/Carbon Nanotube Nanocomposite Pad as a Flexible Platform for Chemical Sensors Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-27 Yunjung Hwang, Jeong Yong Park, Chang-Soo Lee, Oh Seok Kwon, Sung-Hoon Park, Joonwon Bae
This study demonstrated the sensing performance of surface-patterned poly(dimethylsiloxane) (PDMS)/carbon nanotube (CNT : 3∼5 wt %) nanocomposite pads. PDMS/CNT nanocomposite pads as a flexible sensing platform were prepared by employing a series of techniques: 3-roll milling for mixing, 2-roll for pad formation, and imprinting for pattern development. Then, tailored surface engineering strategy was introduced. First, the silane coupling agent was incorporated to improve the surface compatibility of the nanocomposite pads. The change in surface property was monitored by shift in contact angle from 132 to 141 degree. Subsequently, the beta-cyclodextrin (CD) molecules were introduced as a sensing medium through a simple bio-conjugation reaction. The nanocomposite pads showed a sensitive response to methylparaben (MePRB), a representative preservative for cosmetics through host-guest interactions between CD and MePRB in the range of 1 to 100 nmol. Owing to the surface hydrophobicity of the nanocomposite pads, the sensor was found most effective under nonpolar solvents. The feasibility of surface engineered PDMS/CNT pad as a flexible sensor was demonstrated by measurement after 50 times manual bending. This study can be a useful example for the application of nanocomposites that show unique surface structure and properties.
Insights from in-situ x-ray computed tomography during axial impregnation of unidirectional fiber beds Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-27 Natalie M. Larson, Frank W. Zok
In-situ x-ray computed tomography during axial impregnation of unidirectional fiber beds is used to study coupled effects of fluid velocity, fiber movement and preferred flow channeling on permeability. In order to interpret the experimental measurements, a new computational tool for predicting axial permeability of very large 2D arrays of non-uniformly packed fibers is developed. The results show that, when the impregnation velocity is high, full saturation is attained behind the flow front and the fibers rearrange into a less uniform configuration with higher permeability. In contrast, when the velocity is low, fluid flows preferentially in the narrowest channels between fibers, yielding unsaturated permeabilities that are lower than those in the saturated state. These insights combined with a new computational tool will enable improved prediction of permeability, ultimately for use in optimization of composite manufacturing via liquid impregnation.
Experimental investigation of intra-tow fluid storage mechanisms in dual-scale fiber reinforcements Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-24 Mathieu Imbert, Sebastien Comas-Cardona, Emmanuelle Abisset-Chavanne, David Prono
Fiber reinforcements used for structural RTM applications feature dual-scale porous microstructures. During injections, these microstructures induce intra-tow resin storage that affects, significantly in fast curing cases, the distribution of temperature, viscosity and degree of cure. Storage is considered permanent in the literature; however, to optimize the process, a finer understanding of the storage and release mechanisms is required. To reach this goal, an experimental program has been implemented. Based on the injection of colored model and UV-curing fluids, the distribution of the colorant during the injection has been studied in a quantitative manner at the macroscopic and microscopic scales. It has been observed that storage is transient and that the release rate depends on the average FVF, the fiber orientation and the architecture of the reinforcement. Furthermore, the local intra-tow flow mechanisms have been identified. Finally the overall/tow permeability ratio has been identified as a good indicator to classify storage trends.
Synthesis and characterization of beeswax-tetradecanol-carbon fiber/expanded perlite form-stable composite phase change material for solar energy storage Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-23 Fei Cheng, Ruilong Wen, Xiaoguang Zhang, Zhaohui Huang, Yaoting Huang, Minghao Fang, Yan'gai Liu, Xiaowen Wu, Xin Min
In this study, beeswax-tetradecanol/expanded perlite composited with carbon fiber (BW-TD-CF/EP) composite phase change materials (CPCMs) have been prepared via vacuum impregnation method for solar energy utilization. The chemical compatibility, microstructure and thermal properties of CPCMs are characterized and measured, which proves that it is no chemical interaction among the raw materials but physical combination and BW-TD-CF is sufficiently absorbed into the EP porous structure with no leakage even in the molten state. According to differential scanning calorimeter (DSC) results, BW-TD-CF/EP composite melts at 34 °C with high enthalpy value of 178.7 kJ/kg, while thermal cycling measurements show that the form-stable composite PCM has adequate stability after being subjected to 200 melting/freezing cycles. Morever, thermal conductivity of BW-TD/EP composite is enhanced from 0.443Wm−1K−1 to 1.245Wm−1K−1 by adding CF. In result, the form-stable composite PCMs have more appropriate thermal properties and better thermal stability in building for solar energy utilization.
Comparative Investigation on Combustion property and Smoke Toxicity of Epoxy Resin Filled with α- and δ-MnO2 Nanosheets Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-23 Wei Wang, Yongchun Kan, Kim Meow Liew, Lei Song, Yuan Hu
Manganese dioxide (MnO2) as a promising green material has attracted widely attention in virtue of its outstanding chemical and physical properties. Herein, MnO2 nanosheets with α- and δ- crystal structures were used to comparatively study the influence of crystal structures on the fire resistance of EP resin. Cone calorimeter results confirmed that δ-MnO2 nanosheets achieved better improvements than α-MnO2 nanosheets in reducing the PHRR and THR values as well as suppressing smoke release during combustion process. Moreover, Raman data and SEM tests showed that δ-MnO2 nanosheets could effectively promote the char dense of char residues of EP composites. TG-IR results also indicated that the pyrolysis toxic products were significantly decreased after the incorporation of δ-MnO2 nanosheets. By the way, the mechanical property of EP/δ-MnO2 2% composites had no obvious reduction compared with pristine EP resin, which would not restrict the application of EP resin in fields requiring high mechanical properties.
Ductility and pseudo-ductility of thin ply angle-ply CFRP laminates under quasi-static cyclic loading Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-21 J.D. Fuller, M.R. Wisnom
The quasi-static loading-unloading performance of thin ply carbon-epoxy [±265]s,[±275]s[±265]s,[±275]s and [±265/0]s[±265/0]s laminates is presented. Consistent experimental results allow the reduction in laminate modulus to be evaluated using three different methods: secant modulus of each loading cycle; a secant modulus up to a constant stress, and the initial tangent modulus of reloading. It is shown, via all three methods, that these layups can undergo multiple cyclic loadings and display excellent retention of stiffness. The [±265/0]s[±265/0]s layup displays a limited modulus reduction, despite the gradual failure of the 0°0° layers. The [±θ5]s[±θ5]s specimens do not display any decrease in initial modulus and effectively suppress damage accumulation (shown via X-ray CT imaging), which both suggest that the stress-strain behaviour of these layups is ductile, rather than pseudo-ductile.
Impact resistance of shear thickening fluid/Kevlar composite treated with shear-stiffening gel Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-20 Qianyun He, Saisai Cao, Yunpeng Wang, Shouhu Xuan, Pengfei Wang, Xinglong Gong
In this work, shear-stiffening gel (STG) was introduced into shear thickening fluid (STF)-impregnated-Kevlar® woven fabric (Kevlar/STF) to improve the impact resistance. The STF filled within the yarns of Kevlar and the STG covered the Kevlar/STF to form Kevlar/STF/STG composite. The STG in the Kevlar/STF/STG not only protected STF but also improved the impact resistance of the fabric because of its excellent shear-stiffening characteristics. A series of experiments including the yarn pull-out test, the split Hopkinson pressure bar impact test, rod penetration test, and knife cutting test were carried out to verify the enhancement effect. The improvement mechanism of the impact resistance for the Kevlar/STF/STG was studied. Under the similar anti-impact performance, the Kevlar/STF/STG possessed lower weight than the Kevlar and its strong impact resistance originated from the synergetic effect among the STF, STG and Kevlar. Therefore, the Kevlar/STF/STG exhibited broad potential in the soft body armor.
Identification of the Anisotropic Elastic and Damping Properties of Complex Shape Composite Parts Using an Inverse Method Based on Finite Element Model Updating and 3D Velocity Fields Measurements (FEMU-3DVF): Application to Bio-based Composite Violin Soundboards Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-20 Romain VIALA, Vincent PLACET, Scott COGAN
Inverse methods have been used for decades to identify material properties, in parallel, or as a substitution for direct methods. Although it has proven a useful method for many types of materials and simple geometrical shapes, it has barely been used on complex shape parts. This is the main objective of the non-destructive method proposed in this study. The proposed inverse approach, based on both vibrational experiment data and Finite Element Model Updating (FEMU), is successfully applied to a violin soundboard made of flax-epoxy composite. Results show that, by minimizing the discrepancy between the experimental and numerical data, three rigidities and three loss factors can be determined simultaneously. The identified values of the constitutive elastic moduli and longitudinal loss factor are in agreement with those determined using quasi-static tests and dynamic mechanical analysis.
Interaction of textile variability and flow channel distribution systems on flow front progression in the RTM process Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-19 C. Kracke, A. Nonn, C. Koch, M. Nebe, E. Schmidt, S. Bickerton, T. Gries, P. Mitschang
The high volume production of carbon fibre reinforced plastics needs cost efficient and robust processes. This paper investigates the influence of local textile variation on flow front progression in resin transfer moulding (RTM). To quantify the textile variation, the textile has been tested with laser triangulation, to achieve the thickness profile map of the flat textile preform. This preform is placed in a transparent flow visualisation tool and an oil is injected into the mould via two different flow channel distribution systems. The flow front progression of the fluid is continuously measured from both sides with two cameras. Furthermore, to demonstrate the influence of defects like folds from the draping process on the local filling behaviour, the textile is prepared with an artificial fold, made of additional non-crimp fabric (NCF) strips. The results show how different defects in the textile influence the local filling behaviour and how the additional flow channel distribution system can decrease the effect of these defects.
A multi-pattern compensation method to ensure even temperature in composite materials during microwave curing process Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-18 Jing Zhou, Yingguang Li, Nanya Li, Shuting Liu, Libing Cheng, Shaochun Sui, James Gao
Microwave curing technologies have many advantages in manufacturing fiber reinforced polymer composite materials used in aerospace products, compared with traditional autoclave curing technologies. However, the uneven electromagnetic field of microwave in the cavity of the curing chamber results in uneven temperature on the surface of composite laminates during curing, which has been a major obstacle in industrial applications worldwide. Existing methods attempted to solve the problem by the random superposition of uneven electromagnetic fields, but the results were still not satisfactory to meet the high quality requirements of aerospace parts. This paper reveals the one-to-one correspondence between heating patterns of composite parts and microwave curing system settings, and reports a new concept to solve this problem by continuously monitoring and compensating the uneven temperature distribution in real-time. Experimental results from both fiber optical fluorescence sensors and infrared thermal imagers showed significant improvement in temperature uniformity compared with existing methods.
Fabrication and properties of novel porous CuAlMn shape memory alloys and polymer/CuAlMn composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-16 Xiangwei Ji, Qingzhou Wang, Fuxing Yin, Chunxiang Cui, Puguang Ji, Gangling Hao
Novel porous CuAlMn shape memory alloys (SMAs) with interconnected pores and polystyrene/CuAlMn composites with uniformly distributed polystyrene were successfully fabricated via sintering-dissolution and sol-gel methods. Properties tests indicated that the porous CuAlMn SMAs had excellent compression energy absorption and damping properties. Compared with porous CuAlMn SMAs, polystyrene/CuAlMn composites had higher compression strength and damping capacity, which had been ascribed to the hindering effect of polystyrene on the collapse of pores and the superposition of multiple damping sources, respectively. The addition of mica or graphite sheets in polystyrene could remarkably improve the elastic modulus, damping as well as storage modulus of the polystyrene/CuAlMn composites. The associated mechanisms were discussed.
Bioinspired mechanical and thermal conductivity reinforcement of highly explosive-filled polymer composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-15 Guansong He, Jiahui Liu, Feiyan Gong, Congmei Lin, Zhijian Yang
The low mechanical and thermal conductivity property of polymer bonded explosives (PBX) could greatly restrict its further practical application. In this study, inspired by mussels, a facile and noncovalent modification for three carbon nanofillers including multiwalled carbon nanotubes (CNTs), graphene and graphene nanoplates (GNPs), was adopted by the self-polymerization of dopamine. Next, in-depth characterizations, including SEM, TEM, FTIR, FT-Raman and TGA, confirmed that the carbon nanofillers were successfully coated by a dense graphite-like structure polydopamine (PDA) without destroying the original structures, through the oxidation of dopamine at room temperature. The polydopamine-coated nanofillers (pFillers) were further incorporated into PBX matrix. Compared to neat PBX and PBX/carbon nanocomposites, the PBX/pFillers nanocomposites exhibited improved tensile and compression strength, creep resistance, and thermal conductivity. The work presented herein greatly broadens the application scope of the bioinspired dopamine, and will be potential of interest to the communities in highly particle-filled polymer composites.
Development of biocomposites from denim waste and thermoset bio-resins for structural applications Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-13 Robin Temmink, Behnaz Baghaei, Mikael Skrifvars
This paper examines the use of post-consumer denim fabric in combination with thermoset bio-resins in composite manufacturing for structural applications. Bio-epoxy and acrylated epoxidized soybean oil resin (AESO) were used as bio-resins with four different manufacturing techniques in order to create a wide scope of possibilities for research. The four techniques are: compression moulding (COM), vacuum infusion (VAC), resin transfer moulding (RTM) and hand lay-up (HND). The bio-resins were compared to a conventional polyester resin, as this is highly used for structural applications. To determine suitability for structural applications, the biocomposites were tested for their mechanical and thermal properties. Fabricated composites were characterised regarding porosity, water absorption and analysed through microscopic images of the composite. Results show both bio-epoxy and AESO are suitable for use in structural applications over a range of manufacturing techniques. Furthermore, biocomposites from bio-epoxy are superior to those from AESO resin. The conventional polyester has shown to be unsuitable for structural applications.
Healing Mechanisms Induced by Synergy of Graphene-CNTs and Microwave Focusing Effect for the Thermoplastic Polyurethane Composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-11 Yunbo Luan, Feilong Gao, Yongcun Li, Jinglei Yang, Yinchun Hu, Zhangxin Guo, Zhihua Wang, Aijuan Zhou
Healing is a vital factor of polymer materials. Herein, an investigation on the healing performance of Graphene-CNTs reinforced thermoplastic polyurethane (TPU) composites induced by microwave was carried out. The results show that the graphene sheet and CNTs formed a combined structure of Graphene-CNTs. This Graphene-CNTs may have a synergy effect on the coupling between microwave and Graphene-CNTs on the interface, and promote the fully healing of damaged composites. The tensile strength of the healed composites even exceeds the value of the virgin specimens. Simultaneously, there is a microwave focusing effect within the region of crack, and on the surfaces of graphene or CNTs that exposed on the fracture surfaces. This effect will also promote the healing of damaged composites, and can realize the preferential healing of crack as compared with the non-damaged regions. These results may help us to get a deeper understanding of healing mechanisms of some thermoplastic composites.
Tailoring Viscoelastic Response, Self-heating and Deicing Properties of Carbon-Fibre Reinforced Epoxy Composites by Graphene Modification Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-08 Jamal Seyyed Monfared Zanjani, Burcu Saner Okan, Panagiotis-Nektarios Pappas, Costas Galiotis, Yusuf Ziya Menceloglu, Mehmet Yildiz
Vacuum infusion process was employed for the fabrication of carbon fiber reinforced polymeric composites modified by graphene. Three different methods were utilized for the incorporation of graphene into the CFRP composites. In the first and second approaches, graphene were respectively electrosprayed on the surface of carbon fibers as interface modifiers and dispersed into the epoxy resin to improve the matrix properties. The third method includes the concurrent usage of both treatments just mentioned above. The viscoelastic behavior of composites was examined by dynamical mechanical testing at different temperatures, frequencies and graphene integration configurations. In addition, the effect of graphene on the electrical conductivity, thermal diffusivity and electro-thermal performance of composites was also studied in detail. The results indicated that the FRP composites gain multi-functionality while preserving their mechanical integrity for all graphene integration configurations with significant improvements when graphene is used simultaneously as the interface modifier and the matrix reinforcement.
Exploring the pseudo-ductility of aligned hybrid discontinuous composites using controlled fibre-type arrangements Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-08 J. Finley, H. Yu, M.L. Longana, S. Pimenta, M.S.P. Shaffer, K.D. Potter
Pseudo-ductility presents a potential means for preventing catastrophic failure in composite materials; large deformations will prevent brittle fracture and provide warning before final failure. This work explores how the pseudo-ductility and strength of aligned hybrid discontinuous composites can be controlled by manipulating the arrangement of different fibre types. Aligned carbon/glass hybrid specimens with different fibre arrangements are manufactured and tested using a modification to the High Performance Discontinuous Fibre (HiPerDiF) method. Experimental results are complemented by an improved virtual testing framework, which accurately captures the fracture behaviour of a range of hybrid discontinuous composite microstructures. With a randomly intermingled fibre arrangement as a baseline, a 27% 27 % increase in strength and a 44% 44 % increase in pseudo-ductility can be achieved when low elongation fibres are completely isolated from one-another. Results demonstrate that the HiPerDiF method is the current state-of-the-art for maximising the degree of intermingling and hence the pseudo-ductility of hybrid composites.
Design and synthesis of wool-like Co-Mg compound@NiMoO4 nanosheet material for high performance supercapacitors Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-07 Yu Zhang, Wei-dong Xue, Huan Yin, Dong-xu He, Rui Zhao
We have elaborated nanocomposite electrodes, which were designed and synthesized via facile hydrothermal with further annealing processes of NiMoO4 nanosheets on cobalt and magnesium double hydroxide (DH) growing directly on Ni foam. The integrated electrode (the optimum hydrothermal time 6h) designed according to this structural pattern, had an excellent electrochemical performance along with a high areal-specific capacitance of 6.50 F cm-2 at 5 mA cm-2and retained 56% at 60 mA cm−2, the capacitance of the electrode material remained 74% after 5000 cycles at 40 mA cm-2. The Co-Mg compound@NiMoO4 and activated carbon were assembled into an asymmetric supercapacitor (Co-Mg compound@NiMoO4//AC), which allowed the feasible voltage could reach 1.6V and a high energy density of 57 Wh kg-1 at the power density of 0.4 kW kg-1. The Co-Mg compound@NiMoO4//AC also showed significant cyclic stability with the capacitance retention of 87% after 5000 cycles.
THE electric field alignment of short carbon fibres to enhance the toughness of epoxy composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-07 Anil R. Ravindran, Raj B. Ladani, Shuying Wu, Anthony J. Kinloch, Chun H. Wang, Adrian P. Mouritz
An investigation is presented on increasing the fracture toughness of epoxy/short carbon fibre (SCF) composites by alignment of SCFs using an externally applied alternating current (AC) electric field. Firstly, the effects of SCF length, SCF content and AC electric field strength on the rotation of the SCFs suspended in liquid (i.e. uncured) epoxy resin are investigated. Secondly, it is shown the mode I fracture toughness of the cured epoxy composites increases with the weight fraction of SCFs up to a limiting value (5 wt.%). Thirdly, the toughening effect is greater when the SCFs are aligned in the composite normal to the direction of crack growth. The SCFs increases the fracture toughness by inducing multiple intrinsic and extrinsic toughening mechanisms, which are identified. Based on the identified toughening mechanisms, an analytical model is proposed to predict the enhancement to the fracture toughness due to AC electric field alignment of the SCFs.
Fabrication of ZrP nanosheet decorated macromolecular charring agent and its efficient synergism with ammonium polyphosphate in flame-retarding polypropylene Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-05 Huali Xie, Xuejun Lai, Hongqiang Li, Xingrong Zeng
Poor efficiency is one of the biggest challenges for halogen-free flame retardant polymer. Catalyzing the carbonization of polymer itself during combustion is proposed to be a promising way to address this issue. In this work, a novel macromolecular charring agent (MCA) decorated by zirconium phosphate nanosheet named ZrP-d-MCA was synthesized and characterized. Subsequently, it was combined with ammonium polyphosphate (APP) to reduce the flammability of polypropylene (PP). When the contents of ZrP-d-MCA and APP were 5 wt% and 15 wt%, respectively, PP/Zr-d-MCA/APP could reach a limiting oxygen index of 32.5% and achieve UL-94 V-0 rating. Moreover, the bench-scale combustion performance determined by the cone calorimeter was significantly improved. The flame-retardant mechanism of ZrP-d-MCA/APP was revealed: during combustion, ZrP nanosheet could efficiently catalyze the charring reactions of MCA to form closed micro-nano char-cages, in which the degradation products of PP would be trapped and catalyzed into thermostable graphitization char.
The enhancement effect of carbon-based nano-fillers/polyaniline hybrids on the through-thickness electric conductivity of carbon fiber reinforced polymer Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-05 Xiuyan Cheng, Tomohiro Yokozeki, Lixin Wu, Jun Koyanagi, Haopeng Wang, Qingfu Sun
Overall goal of this research is to study the conductivity enhancement effect and its mechanism for different types of carbon-based nano-fillers/conduct polymer hybrids in carbon fiber reinforced polymer (CFRP). Multi-walled carbon nanotubes (MWCNT) /polyaniline (PANI) and graphene oxide (GO) /PANI hybrids were separately dispersed into divinylbenzene (DVB) to make the CFRP composites. The alternating current (AC) electrical conductivity results show that both, the binary MWCNT/PANI and GO/PANI hybrids have significant enhancement on AC conductivity, while MWCNT/PANI gives better improvement over GO/PANI hybrids. The mechanism for the conductivity enhancement was studied by SEM, XRD, UV-Vis and nanoindentor. Circuit models were proposed. The maximum AC conductivity of CFRP made of MWCNT/PANI was measured to be 22.4 S/m, which has been found to be enhanced by more than 3 orders of magnitude compared to CF/DVB. Thus, CF/MWCNT-PANI composites can be considered to be promising candidates for multifunctional material where high conductivity is demanded.
Friction stir welding/processing of polymers and polymer matrix composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-05 Yongxian Huang, Xiangchen Meng, Yuming Xie, Long Wan, Zongliang Lv, Jian Cao, Jicai Feng
Friction stir welding/processing (FSW/P) involving temperature, mechanics, metallurgy and interaction, is a complex solid state joining and processing technology. FSW has been widely applied to join aluminum alloy, titanium alloy and other materials which are difficult to weld by fusion welding. The last scientific study states that FSW has potential to join thermoplastic polymers and polymer matrix composites. In this review, current understanding and development about FSW of thermoplastic polymers and polymer matrix composites, multifunctional composites fabrication as well as dissimilar FSW of metal and polymer are reviewed. Future scientific research and engineering development related to FSW/P of thermoplastic polymers and polymer matrix composites are identified.
Cavitation in epoxies under composite-like stress states Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-05 Anupam Neogi, Nilanjan Mitra, Ramesh Talreja
In a previous study the experimentally observed low strains to transverse tensile failure of unidirectional (UD) polymer matrix composites were explained as an effect of triaxial (composite- like) stress state in the epoxy matrix. Assuming cavitation as an underlying mechanism for brittle cracking under triaxial stress states, a dilatation energy density based criterion was put forth and was shown to predict well the transverse failure of epoxy based UD composites. The assumption of cavitation in the epoxy matrix has hitherto not been supported by a mechanism study. The current study attempts to provide a systematic clarification of the cavitation mechanism by molecular dynamic simulation. By imposing uniaxial, equi-biaxial and equi-triaxial tension on a simulation cell of a crosslinked epoxy, the degrees of cavitation at various stages of the stress- strain response are revealed. The results show that triaxiality of the stress states is a governing factor in cavitation of epoxies.
Reinforcement of Economical and Environment Friendly Acacia Catechu Particles for the Reduction of Brittleness and Curing Temperature of Polybenzoxazine Thermosets Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-05 Abdul Qadeer Dayo, Rui-kun Ma, Sadia Kiran, Abdeldjalil Zegaoui, Wan-an Cai, Ahmer Hussain Shah, Jun Wang, Mehdi Derradji, Wen-bin Liu
The brittleness always remained a major concern for the polybenzoxazine thermosets. Several attempts have been made to overcome the brittleness issue, but all find some kind of sacrificing in other properties. A new and economical approach is presented by the reinforcement of catechin-rich acacia catechu (AC) particles. The micro size AC particles blended with bisphenol-A aniline-based benzoxazine (BA-a) resin and isothermally cured. The terminal –OH groups of produced tannic acid participated in the curing process and helped in the ring opening of BA-a resin. The composites exhibited that the brittleness of polybenzoxazine has been improved by 35%, simultaneously its strength, Youngs’ modulus, stiffness, glass transition temperature, and thermal stabilities are also enhanced. The highest impact strength of the composite is observed on only 4 wt% loading of AC particles and read as 5.2 ± 0.16 kJ/m2, 307.1% higher than the value of neat poly(BA-a).
Process-Induced Fiber Matrix Separation in Long Fiber-Reinforced Thermoplastics Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-05 S. Goris, T.A. Osswald
This work explores the fiber migration during injection molding of long glass fiber-reinforced polypropylene. It was found that the simplified assumption of uniform fiber concentration distribution is inaccurate, and the process causes substantial variations in the fiber concentration along the flow path and through the thickness of injection molded parts. This was tested for a simple plate geometry molded at varying nominal fiber concentrations. The fiber concentration was measured by pyrolysis to obtain a global concentration, and using micro computed-tomography for a through-thickness analysis. Additionally, the fiber concentration at the melt front of partially filled moldings was investigated. A new measurement protocol using micro computed-tomography and digital image processing is proposed to calculate the through-thickness fiber concentration. The results of this study show substantial heterogeneity of the fiber concentration throughout the molded plates. Fibers agglomerated in the core layer with volume fractions up to 1.5 times the nominal fiber concentration.
Highly Sensitive and Stretchable Piezoresistive Strain Sensor Based on Conductive Poly(styrene-butadiene-styrene)/Few Layer Graphene Composite Fiber Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-05 Xingping Wang, Si Meng, Mike Tebyetekerwa, Yilong Li, Jürgen Pionteck, Bin Sun, Zongyi Qin, Meifang Zhu
High stretchability and sensitivity are the major desired requirements of strain sensors for wearable electronics applications, especially in health and medical monitoring. Herein, a highly sensitive and stretchable strain sensor based on conductive poly(styrene-butadiene-styrene)/few layer graphene (SBS/FLG) composite fiber is fabricated through an easy and scalable wet-spinning process. Owing to the super flexibility of SBS matrix and the excellent electrical and mechanical properties of FLG, the SBS/FLG fiber based strain sensor revealed superior performance, including wide workable strain range (>110%), superior sensitivity (gauge factor of 160 at a strain of 50% and of 2546 at a strain of 100%), and durability. Furthermore, the mechanism behind the excellent performances of SBS/FLG fiber based sensors is discussed in detail.
Predicting the Compression-After-Impact (CAI) strength of damage-tolerant hybrid unidirectional/woven carbon-fibre reinforced composite laminates Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-02 Haibao Liu, Brian G. Falzon, Wei Tan
The evaluation of Compression-After-Impact (CAI) strength is of great significance in the design of composite aerostructures. This paper presents a model for the numerical simulation of Compression-After-Impact (CAI) of hybrid unidirectional (UD)/woven carbon-fibre reinforced composite laminates. This three-dimensional damage model is based on Continuum Damage Mechanics (CDM) and Linear Elastic Fracture Mechanics (LEFM), and implemented as a user defined material subroutine (VUMAT) in Abaqus/Explicit. This model, which accounts for interlaminar and intralaminar damage, and load reversal, incorporates a non-linear shear profile to account for matrix plasticity. Two different composite laminate lay-ups with varying extent of initial impact damage were tested to validate the computational model and enable a quantitative study of the influence of using woven plies on the surfaces of a laminate. Woven surface plies are often used in composite aerostructures to mitigate damage during drilling and constrain the extent of damage during low velocity impact. Good correlation was obtained between physical testing and simulation results, which establishes the capability of this damage model in predicting the structural response of composite laminates. The fully validated model was used to compare the Compression-After-Impact (CAI) strength of an equivalent unidirectional (UD)-only carbon-fibre reinforced composite laminate. The results showed that the hybrid unidirectional (UD)/woven laminate had a marginally higher strength (+3.3%) than the equivalent unidirectional (UD)-only laminate.
Passive control of wrinkles in woven fabric preforms using a geometrical modification of blank holders Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-12-02 A. Rashidi, A.S. Milani
Textile preforms have become materials of choice in numerous modern industries, partly due to their superior conformability onto complex 3D mould shapes. Maximum formability of this category of composite reinforcements, however, is still limited by defects such as wrinkling, which remains a challenging issue for composite designers during optimization of thermo-stamping operations. The aim of this article is to gain a deeper understanding of the effect of blank holding boundary condition on the extent of wrinkling as well as other local defects such as tow slippage and yarn jamming, and thereby to introduce a passive defect mitigation approach via geometrical modification of the blanks. To verify the applicability of the approach, a series of hemisphere forming experiments under unmodified and modified forming boundary conditions have been performed and compared on both single and multiple ply layups, using a comingled polypropylene/E-glass thermoplastic plain weave.
Transverse shear modulus of unidirectional composites with voids estimated by the multiple-cells model Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-28 Jui-He Tai, Autar Kaw
Voids are inevitably formed as a by-product during manufacturing processes of composite materials and affect many of its mechanical properties including the transverse shear modulus. Although several analytical and empirical models are available for transverse shear modulus, they are based on simple assumptions, and none of them consider the effect of voids. In this work, we estimate transverse shear modulus through a finite element model that uses multiple-cells and three-dimensional analysis. The effect of voids on the transverse shear modulus is studied through a design of experiment approach via three primary parameters: fiber-to-matrix Young’s moduli ratio, fiber volume fraction, and void volume fraction. The results indicate that for allowable void volume fractions, the transverse shear modulus can decrease by as much as 15%, while the fiber volume fraction is the most dominating factor of the three in influencing its value.
Constructing three-dimensionally interwoven structures for ceramic/polymer composites to exhibit colossal dielectric constant and high mechanical strength: CaCu3Ti4O12/epoxy as an example Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-28 Xiaoqiang You, Nan Chen, Guoping Du
Until now, the reported dielectric constants of the ceramic/polymer composites are rather low, even though their corresponding bulk ceramics have colossal dielectric constants. This work demonstrates that ceramic/polymer composites can achieve colossal dielectric constants by constructing three-dimensionally interwoven structures. Furthermore, the ceramic/polymer dielectric composites exhibit high mechanical strength. As an example, CaCu3Ti4O12/epoxy dielectric composites with such interwoven structures are fabricated in this work. The CaCu3Ti4O12/epoxy composites exhibit both colossal dielectric constant and high flexural strength, both of which rapidly increase with the CaCu3Ti4O12 content. When the CaCu3Ti4O12 content is about 57.7 vol.%, the dielectric constant and flexural strength of the CaCu3Ti4O12/epoxy composites are about 1501 at 1 MHz and 118.8 MPa, respectively. Their dielectric constants are much higher than the predicted values by the existing theoretical models for ceramic/polymer dielectric composites. A modified parallel model is proposed to explain the presence of colossal dielectric constants of the ceramic/polymer composites.
Rheological Percolation Behaviour and Fracture Properties of Nanocomposites of MWCNTs and a Highly Crosslinked Aerospace-grade Epoxy Resin System Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-24 Yan Liu, Arthur Wilkinson
The effects of incorporating MWCNT in a high-functionality epoxy resin system are reported. Oscillatory-shear rheology showed as-received MWCNT (AR-MWCNT) to have a low degree of interaction with the resin and consequently G′ values were low, whereas G′ values for functionalized MWCNTs (amino and oxidised) were higher due to increased resin-nanotube interactions. Three approaches used to obtain rheological percolation thresholds showed values to increase in an order reflecting the improved MWCNT dispersion imparted by functionalisation. Analysis using colloidal dispersion theory fitted better with the experimental data than statistical percolation theory, and more closely mirrors the clustering of MWCNT agglomerates to form a percolated network. In fracture studies, toughness decreased with AR-MWCNT addition whereas for functionalised MWCNT addition toughness increased. For AR-MWCNT nanocomposites large agglomerates were formed which reduced toughness. In contrast, functionalised MWCNTs exhibited pull-out and fracture and formed smaller agglomerates which toughened the matrix via crack-deflection and pinning.
Thermal conductivity and mechanical properties of flake graphite/copper composite with a boron carbide-boron nano-layer on graphite surface Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-24 H. Bai, C. Xue, J.L. Lyu, J. Li, G.X. Chen, J.H. Yu, C.T. Lin, D.J. Lv, L.M. Xiong
Graphite/copper composites had attracted significant recent attention for thermal management applications due to their superior thermal properties, low cost and ease of machining. However, achieving the enhancement of mechanical properties of composites with high thermal conductivity remained challenging. In this study, graphite/copper composites had been produced by vacuum hot pressing process, in which the boron carbide-boron coating was synthesized on graphite to improve the mechanical properties of copper matrix composites with high volume fraction of graphite. The resulting composites had superior thermal conductivity (676W/mK, 180% of copper) and apposite coefficient of thermal expansion (7.1ppm/K), which was attributed to the homogeneous dispersion and well-controlled alignment of graphite in the composite. And the results showed that the coating on graphite slightly decreased the thermal conductivity and coefficient of thermal expansion of the composites, but evidently improved the bending strength. The flexural strength raised to 74MPa, 42% increased with that of uncoated composite.
Multi-scale design of novel materials for emerging challenges in active thermal management: open-pore magnesium-diamond composite foams with nano-engineered interfaces Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-24 J.M. Molina-Jordá
Open-pore Mg foams, which have been traditionally discarded for heat dissipation applications given their low thermal conductivity values, can prove appealing materials for active thermal management if they incorporate diamond particles coated with a nano-dimensioned layer of TiC. These composite foam materials can be manufactured by the replication method, conveniently adapted to Mg, that requires a strict multi-scale control: correct distribution of structural constituents (pores, diamond and Mg) on the meso-/micro-scale ensures homogeneity and complete pore connectivity, while a proper nanoscale control of the TiC coating on diamond particles achieves high thermal conductance at the interface between diamond particles and Mg. The manufactured Mg-diamond foam materials attain outstanding thermal conductivity values (up to 82 W/mK) and maximum heat dissipation performance, tested on active convective cooling, almost two times higher than their equivalent magnesium foams and twenty per cent superior to that of conventional aluminium foams.
Dynamic Bridging Mechanisms of Through-Thickness Reinforced Composite Laminates in Mixed Mode Delamination Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-23 Hao Cui, Mehdi Yasaee, Stephen R. Hallett, Ivana K. Partridge, Giuliano Allegri, Nik Petrinic
Delamination resistance of composite laminates can be improved with through-thickness reinforcement such as Z-pinning. This paper characterises the bridging response of individual carbon fibre/BMI Z-pins in mixed mode delamination at high loading rate using a split Hopkinson bar system. The unstable failure process in quasi-static tests, was also captured with high sampling rate instruments to obtain the complete bridging response. The energy dissipation of the Z-pins were analysed, and it was found that the efficacy of Z-pinning in resisting delamination growth decreased with an increase in mixed mode ratio, with a transition from pull-out to pin rupture occurring. The Z-pin efficacy decreased with loading rate for all mode mix ratios, due to the changing in failure surface with loading rate and rate-dependent frictional sliding.
Effect of Polycarbonate Film Surface Finish and Plasma Treatment on Mode I and II Fracture Toughness of Interleaved Composite Laminates Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-21 Xin Qian, Oleksandr G. Kravchenko, Diego Pedrazzoli, Ica Manas-Zloczower
Polycarbonate (PC) offers excellent impact resistance, high elongation at break and high glass transition temperature making. Therefore, PC films were used in this work to interleave bi-directional glass fiber (GF)/epoxy composites to study mode I and mode II interlaminar fracture toughness. PC films with smooth and textured surface finish and oxygen plasma treatment were used to examine the effect on composite toughening using double cantilever beam and end notched flexure tests for mode I and II interlaminar fracture toughness characterization, respectively. Increase up to 71% in mode I and 42% in mode II interlaminar fracture toughness for interleaved composites was measured. The morphological observations of fractured surfaces indicate that improved toughness in the case of PC interleaves is related to promoting cohesive-adhesive failure of the film, providing additional energy dissipating mechanisms during delamination propagation. Dynamic mechanical analysis revealed that PC films are able to preserve high operational temperature of composite.
Health monitoring of scarfed CFRP joints under cyclic loading via electrical resistance measurements using carbon nanotube modified adhesive films Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-21 Till Augustin, Julian Karsten, Benedikt Kötter, Bodo Fiedler
This study deals with a structural health monitoring approach for adhesively bonded carbon fiber reinforced polymer joints. A modification of an epoxy based adhesive film with single wall carbon nanotubes allows for electrical resistance measurements through the joint. Cyclic fatigue tests of adhesively bonded scarf joints with simultaneous electrical resistance measurements are conducted to investigate the damage detection and localization of repaired composite parts during operation. The measured electrical resistance changes are compared to results from digital image correlation. Crack initiation and growth can be detected by an increase of electrical resistance. Furthermore, it is possible with parallel oriented ink-jet printed circuits to localize the damages occurred.
Electrical and Thermal Conductivities of MWCNT/Polymer Composites Fabricated by Selective Laser Sintering Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-21 Shangqin Yuan, Yun Zheng, Chee Kai Chua, Qingyu Yan, Kun Zhou
Additive manufacturing such as selective laser sintering (SLS) offers the strategies to create 3D complex components with desirable mechanical, electrical and thermal properties using the composite powders as feeding materials. This work proposes a new fabrication approach to preparing carbon nanotube (CNT) composite powders and utilizes them for SLS process. As compared with the hot-compression process, the SLS process could offer an effective method to fabricate the CNT/Polymer composite with electrically conductive segregated structures. At a small loading range of CNTs (<1wt%), the laser-sintered composites exhibit significant improvements in the electrical conductivity up to anti-static and conductive range qualifying the applications in automobile and aerospace. However, the enhancement in thermal conductivity of laser-sintered composites is not comparable with that of hot-compressed ones. The process-structure-property relationships are further investigated to study the different processes induced microstructures and the underlying mechanism of thermal and electrical performances.
Microstructure and synergistic-strengthening efficiency of CNTs-SiCp dual-nano reinforcements in aluminum matrix composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-21 Xin Zhang, Shufeng Li, Deng Pan, Bo Pan, Katsuyoshi Kondoh
In this study, reinforcements of carbon nanotubes (CNTs) and silicon carbide particle (SiCp) in CNTs-SiCp reinforced aluminum matrix nanocomposites (AMNCs) are studied. The tensile strength of 0.5CNTs-0.5SiCp/Al increase by 94% compared with pure Al reaching 247 MPa, it also has a lifting of 14% and 56% compared with 1.0CNTs/Al and 1.0SiCp/Al. CNT-SiCp reinforcements have the synergistic enhancement effect of 1+1>2 in tensile strength. It is found that SiCp as a dispersed particle around CNTs can inhibit and delay the pulling out and peeling of CNTs to further enhance the strengthening effect of CNTs by pinning effect. Between CNTs and Al matrix, there is a nano-scale reaction transition layer which improves the mechanical properties of AMNCs by strengthening the interfacial bonding. The existences of SiCp inhibit the excessive reaction of the interface, when the tensile strength of AMNCs increases compared with pure Al, the elongation and conductivity have similar maintaining.
Long-term performance of β-nucleated toughened polypropylene-biocarbon composites Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-21 Ehsan Behazin, Arturo Rodriguez-Uribe, Manjusri Misra, Amar K. Mohanty
Thermoplastic polyolefins or TPOs are of widespread use in the automotive industry. In this study, the long-term performance of biocarbon based TPOs is investigated for the first time. The durability of these bio-based composites with and without hindered phenolic antioxidants was investigated under accelerated heat aging for 1000 h. Thermo-oxidative degradation was tracked along the specimen’s thickness using energy dispersive spectroscopy. Performance of the biocomposites was gauged by Izod notched impact and tensile properties. Microstructural changes were monitored by differential scanning calorimetry and dynamic mechanical analysis. While the tensile properties were sufficiently sustained using the antioxidants after this test, the impact strength failed to retain initial values. The morphological changes in the β crystal phase were recognized as the primary factor in reduction of the impact strength of the biocomposites.
A Particular Interfacial Strategy in PVDF/OBC/MWCNT Nanocomposites for High Dielectric Performance and Electromagnetic Interference Shielding Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-21 Xiang-Jun Zha, Jun-Hong Pu, Li-Feng Ma, Ting Li, Rui-Ying Bao, Lu Bai, Zheng-Ying Liu, Ming-Bo Yang, Wei Yang
Multi-walled carbon nanotubes (MWCNTs) were easily dispersed at the interface of polyvinylidene difluoride (PVDF) and ethylene-α-octene block copolymer (OBC) blend by melt compounding and the nanocomposites exhibited enhanced dielectric performance, electromagnetic interference shielding effectiveness (EMI SE) and balanced mechanical performance. Through the simple, efficient and scalable interfacial strategy to disperse MWCNTs at the interface of PVDF and OBC phases, the accumulation of charge carriers at the interfaces and strong interfacial polarization effect can be achieved. At low frequency, PVDF/OBC/MWNCT nanocomposite exhibits high dielectric permittivity (753.8) and low dielectric loss tangent (0.8), offering great potential in energy storage applications. Simultaneously, in X-band range, PVDF/OBC/MWNCT nanocomposite shows high EMI SE of around 34 dB which is higher than the industrial requirement when the content of MWCNTs is as low as 2.7 vol%. This study provides possibilities to realize high-performance polymer nanocomposites via the particular interfacial structure through one-step melt processing.
Impedance spectroscopy as a tool for moisture uptake monitoring in construction composites during service Compos. Part A Appl. Sci. Manuf. (IF 4.075) Pub Date : 2017-11-21 Sotirios A. Grammatikos, Richard J. Ball, Mark Evernden, Ryan G. Jones
This is a first study comparing dielectric spectroscopy and gravimetric measurements of moisture uptake in pultruded glass fibre reinforced polymers (FRPs). Specimens were subjected to sub-Tg hygrothermal aging for 224 days. Impedance spectra in the frequency range 0.1Hz to 10MHz were captured during exposure and compared with gravimetric measurements. Moisture concentration was found to increase the FRP’s dielectric permittivity monotonically and decrease bulk resistance. High quality dielectric data was obtained as moisture uptake is independent of inherent changes suggested by mass loss which compromise gravimetry. Dielectric measurements remained sensitive to moisture despite significant mass loss, which typically distorts the weight gain process complicating the commonly adopted gravimetric methodology. Real-time dielectric measurements were obtained from FRP specimens continuously immersed in water and without making use of any additional sensing elements. The novel approach adopted is of high commercial impact as moisture uptake control is recognized as a significant problem by industry.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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