Elsevier

Thin-Walled Structures

Volume 155, October 2020, 106952
Thin-Walled Structures

The collation of impact behaviour of titanium/carbon, aluminum/carbon and conventional carbon fibres laminates

https://doi.org/10.1016/j.tws.2020.106952Get rights and content

Highlights

  • The objective was a comparison of impact resistance of CFRP, CARALL and HTCL.

  • HTCL have at least twice as high impact resistance, in terms of impact energy as CARALL.

  • HTCL have at least six times higher impact resistance, in terms of impact energy than CFRP.

Abstract

Impact resistance is one of the basic properties of thin-walled coating structures that is of vast importance in the aerospace industry. Being able to absorb the energy of impact force, having resistance to puncture and being able to limit internal damage to the structure affect the continued load capacity of the component. Current aerospace designs utilize composite and hybrid materials. The work compares the low-velocity impact resistance of carbon fibres-reinforced polymer, aluminium carbon reinforced aluminium and hybrid titanium carbon laminates. In the assessment measurable, experimental and analytic evaluation criteria for the phenomenon of impact and the reaction of the material to this type of load, based on diverse physical foundations were utilized. It was demonstrated that a laminate based on titanium layers has at least two times higher impact resistance than an aluminium based laminate, and at least six times greater impact resistance than its conventional carbon-epoxy equivalent.

Introduction

Impact resistance, including the ability to absorb impact energy and to be resistant to puncture are basic properties of thin-walled coating structures that are of relevance in the aerospace industry. This mainly applies to such elements as the control surfaces or the fuselage. In addition to macroscopically visible damage, internal damage caused by impact negatively affects the subsequent load-bearing capacity of the structure, especially under compressive and fatigue loads [[1], [2], [3], [4], [5], [6]]. The reduction of compressive strength following impacts reaches up to 40% [7,8] The current trends in aircraft fabrication are the use of poly-fibrous composite materials for extensive fragments of the aircraft skin, due to their low density, high static and fatigue strength and corrosion resistance. However, many studies indicate the limited ability of conventional polymer-fibrous composite materials, including primarily the intensively developed carbon fibre composites (CFRP) [[14], [15], [16]], to absorb both high and low velocity impacts [[9], [10], [11], [12], [13]]. Extensive research has provided evidence that impact loads, especially low-velocity impact, can cause BVID type damage (extensive delamination and matrix cracks) in the structure [11]) or even fibre cracking and perforation [[16], [17], [18]].

Striving to improve the impact resistance of thin-walled skin structures, while maintaining the use of polymer-fibre composites was one of the reasons for the development of innovative metal-fibre laminates (FML), of among others, GLARE® (GLass Aluminium REinforced) and CARALL® (Carbon Reinforced ALuminium Laminates) types [6,[19], [20], [21]]. As demonstrated [[22], [23], [24], [25]], the use of aluminium alloy in combination with a polymer-carbon composite improves the impact resistance of carbon fibre composites, when compared to conventional CFRP composites. Indeed, Caprino et al. [23] revealed that the response of fibreglass-aluminium laminate to complete penetration seems to be better than that of carbon fibre- and GFRPs. Moreover, Bieniaś et al. [24] showed that the global deformation of the laminate may dissipate much more energy in comparison to various other damage types observed in fibre metal laminates. In comparison to conventional CFRP laminates, damage to CARALL was not so critical inside the structures. In addition, Morinare et al. [26] provided an analysis of significance of layering aluminium within polymer-fibre composites with regard to the energy absorption process during impact phenomena. They noted that, in general, metal layers of FML can take up more than 90% of impact energy because the energy is absorbed via membrane deformation. Here, less than 5% of impact absorption was attributed to composite. However, the composite plies contributed to delaying the perforation of aluminium so that more deformation energy is absorbed. In their work, Morinare et al. ascribed a more limited proportion of absorbed energy via aluminium in CARALL laminates because of their higher brittleness (in comparison to GLARE).

The introduction of alternative metal alloys in FMLs has led to the emergence of a new group of hybrid materials, the so-called second generation of Fibre Metal Laminates. The objective of the innovation was to further maximize the strength properties, including impact resistance, but also to secure the corrosion resistance of carbon fibre laminates. Representatives of the second generation of FMLs include laminates that utilize titanium, magnesium alloys and corrosion resistant steels. Of the aforesaid, the titanium containing laminates show great potential [[27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39]]. Reiner et al. [32] described a failure modes in Hybrid Titanium Composite Laminates and explained that a systematic experimental study of different HTCL configurations under tensile loading confirms that the major failure modes are deadhesion between the titanium sheet and the FRP laminate, matrix cracking of the FRP laminate and interlaminar delamination. Veazie et al. [33] were analyzed, experimentally and numerically, the improvement in mechanical properties achieved by the influence of the titanium layer by comparing the uniaxial tensile results of static strength at room temperature. An advanced analysis of Hybrid Titanium Laminates were performed by Le Bourlegat et al. [34] and others [35,36]. According to these studies, the tensile stress, tensile modulus, shear stress, and shear modulus values for titanium/carbon laminates are superior when compared with GLARE® and CARALL® laminates. Moreover, authors concluded that this is an extremely promising material for aerospace and other applications due to its advantageous material properties and excellent damage tolerance characteristics, such as lower crack growth rates and improved toughness.

In term of impact behaviour Nakatani et al. [37] state that FMLs with titanium exhibit two modes of impact response. The titanium layer on the non-impacted side remains intact after impact, and small interlaminar delamination appears in the composite layer. Also, a single crack is induced in the titanium layer on the non-impacted side, and interlaminar delamination in the GFRP layer occurs. Jakubczak [38] demonstrated that titanium and glass fibre HTGLs are characterized by significant impact resistance, as demonstrated by the criteria of transferred forces, absorption energy, permanent deformation and propagating damage, including the lack of susceptibility to the initiation of perforation in the energy range of up to 30 J. However, it should be noted that both researchers deal with glass fibre composites. Li et al. [39] presented the issue of the effect of the type of fibres in titanium-based FMLs on impact of different speed ranges. The authors disclosed that the deformation and failure modes depend on the type of fibre-based composite layer incorporated. Bernhardt et al. [40] were tested the impact response of Titatnium-Graphite laminates. The analysis was characterized by two modes of failure which differed by failure or nonfailure in tension of the bottom titanium ply. The ductility of titanium caused buckling by yielding whereas the brittle adjacent composite ply lead to fracture. The maximum failure force of the material correlated well with the previously reported static flexural data, and the material outperformed the commonly used graphite/epoxy. Reiner et al. [41] presented an experimental and numerical study on low-velocity impact responses on hybrid titanium composite laminates. Authors concluded that the main failure modes are experimentally and numerically found to be debonding between titanium and composite, matrix cracking and interlaminar delamination. The principal energy-absorbing mechanism is plastic dissipation of the two titanium sheets. Above were also presented and modelled in detailed in Ref. [35].

Nevertheless, regardless of the components used in laminar structures, the phenomena of inter-laminar damages induced by impact and non-destructive approaches needed to detect the damage are significant. Among others Riccio et al. [42,43] presented a numerical and experimental studies about structural behaviour under dynamic loading of composites, but also the impact-induced intra-laminar and inter-laminar damage in laminated composites were deeply described. Authors have shown that fully characterization of the damage evolution and different phases of the damage formation of composites is possible to detect and predict by modeling. Shi et al. [44] shown modeling of the impact damage of composite laminates in the form of intra- and inter-laminar cracking. Moreover, The various damage mechanisms introduced during the impact event were observed by non-destructive technique (NDT) X-ray radiography and were successfully captured numerically by the proposed damage evolution model. Sellitto et al. [45] have shown the global buckling phenomenon and the progressive fibre-matrix damage of composites by using a compressive mechanical test. Non-destructive techniques, such as lock-in thermography and ultrasounds, have been used by authors to detect the damage status of composite. Gaudenzi et al. [46] have evaluated the ultrasonic testing, optical thermography and sonic infrared for the inspection of composite laminates with barely visible impact damage. Finally, they have carried out a comparison amongst their capabilities for such an application.

Considering that numerous literature reports exist on the impact resistance of carbon /polymer composites, information is limited in the scope of aluminium/carbon laminates, and is residual in the area of titanium/carbon laminates. Furthermore, it was noted significant deficiencies in the application of consistent assessment criteria and in the direct comparison of resistance to impact of these materials. Hence, in presented work, the impact resistance of selected materials was analyzed based on predefined and unified criteria for assessing the material reaction to this type of load. Moreover, the collation was performed based on diverse physical foundations in order to quantitatively and qualitatively compare the resistance to low-velocity impact of carbon fibre-reinforced polymer, carbon reinforced aluminium and innovative hybrid titanium carbon laminates.

Section snippets

Materials

The subjects of research were three different types of composites: hybrid titanium carbon laminate (HTCL), hybrid aluminium carbon laminate (CARALL) and conventional carbon/epoxy composite (CFRP). The laminates were manufactured with unidirectional carbon/epoxy prepreg (Hexcel, USA), based on AS7J high-strength carbon fibre with M12 epoxy resin system (single layer thickness was 0.125 mm). The nominal fibre content of prepreg after curing was about 60 vol.%. Additionally, for FMLs, commercially

Force - time relation

Fig. 1 presents the relationship of force and time during impact (f-t) in the energy range of 2.5–30 J for conventional carbon-epoxy composites, and aluminum/carbon-epoxy and titanium/carbon-epoxy laminates.

The experimental f-t curves for the CFRP composite and CARALL and HTCL laminates can be divided into three main stages (Fig. 1 b), including: system stabilization stage (I), the stage of increase in force over time (II) and the stage of decrease in force over time (III). Stage I lasts some

Summarizing

The objective of the present study was a quantitative and qualitative comparison of resistance of carbon fibres-reinforced polymer, and its further improvements such as aluminum carbon reinforced and hybrid titanium carbon laminates, to low velocity impact. Based on the analyzes and comparison of the results, can be concluded that:

  • -

    force curves - CFRP composite time, as well as that of the CARALL and HTCL laminates indicate significant differences in the process of load increase during impact.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This research was funded by the National Science Centre (Poland), grant number UMO-2018/31/D/ST8/00865.

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