Energy absorption and load carrying capability of woven natural silk epoxy–triggered composite tubes

This study investigated the energy absorption response and load carrying capability of woven natural silk/epoxy–triggered composite rectangular tubes subjected to an axial quasi-static crushing test. The rectangular composite tubes were prepared by hand lay-up technique. The tubes consisted of 12, 24, and 30 layers of natural woven silk/epoxy laminate and were 50, 80, and 120 mm long. The crashworthiness of the tubes was evaluated by measuring the specific energy absorption in quasi-static axial compression. Specific energy absorption was obtained from the load–displacement curve during testing. The failure mode of the tubes was analyzed from high resolution photographs obtained. Overall, the tube with 50 mm length and 30 layers showed the best crashworthiness among the tubes. The failure morphology showed that the specimens failed in two distinct modes: local and mid-length buckling. The triggered composite tubes exhibited progressive failure.     

Comparative research on the crashworthiness characteristics of woven natural silk/epoxy composite tubes

This study investigated the energy absorption response of triggered and non-triggered woven natural silk/epoxy composite rectangular tubes subjected to an axial quasi-static crushing test. The rectangular composite tubes were prepared by the hand lay-up technique using 12 layers of silk fabric with a thickness of 1.7 mm and tube lengths of 50, 80, and 120 mm. The parameters measured were peak load, energy absorption, and specific energy absorption (SEA). In both triggered and non-triggered tubes, the SEA values decreased with increasing length of the composite specimen. On the contrary, total energy absorption increased with increasing length of the composite specimen. The peak load in triggered specimens is nearly half of that in non-triggered specimens. Deformation morphology shows that the specimens failed in two distinct modes: local buckling and mid-length buckling. The non-triggered composite tubes exhibited catastrophic failure, whereas the triggered composite tubes only exhibited progressive failure.     

Energy absorption and failure response of silk/epoxy composite square tubes: Experimental

This paper focuses on natural silk/epoxy composite square tubes energy absorption and failure response. The tested specimens were featured by a material combination of different lengths and same numbers of natural silk/epoxy composite layers in form of reinforced woven fabric in thermosetting epoxy resin. Tubes were compressed in INSTRON 5567 with a loading capacity of 30 kN. This research investigates the influence of the wall lengths on the compressive response and also failure mode of the tested tubes are analysed. The load–displacement behaviour of square tubes recorded during the test. Since natural woven silk has been used as textile in centuries but due to rare study of this fabric as reinforcement material for composites, the results of this paper can be considerable. Outcomes from this paper might be helpful to guide the design of crashworthy structures.     

Crashworthiness characteristics investigation of silk/epoxy composite square tubes

This research concentrates on the evaluation of crashworthiness characteristics of natural silk/epoxy composite square tubes energy-absorbers. Composite laminate specimens were subjected to static axial compression load and experimental evaluation of the energy absorption capability of silk/epoxy composite. Specimens were in the form of square cross-sections with the dimension of 80 mm × 80 mm and a radius curvature of 5 mm. The variables in the experiment were the length of the tubes built 50 mm, 80 mm and 120 mm. Meanwhile, the thickness of the walls, consisting of laminates of silk/epoxy of 12, 24 and 30 plies, correspond to equivalent wall thickness of 1.7 mm, 3.4 mm and 4.2 mm, respectively. The parameters measured were the total absorbed energy (E_total), and the crash force efficiency (CFE). E_total is the measure of the amount of energy that the structure can withstand without failure and thus is a measure of its strength, while CFE gives a quantitative indication of the mode of failure of the composites. The mode of failure was observed using photography.     

The Effects of Triggering Mechanisms on the Energy Absorption Capability of Circular Jute/Epoxy Composite Tubes under Quasi-Static Axial Loading

The usage of composite materials have been improving over the years due to its superior mechanical properties such as high tensile strength, high energy absorption capability, and corrosion resistance. In this present study, the energy absorption capability of circular jute/epoxy composite tubes were tested and evaluated. To induce the progressive crushing of the composite tubes, four different types of triggering mechanisms were used which were the non-trigger, single chamfered trigger, double chamfered trigger and tulip trigger. Quasi-static axial loading test was carried out to understand the deformation patterns and the load-displacement characteristics for each composite tube. Besides that, the influence of energy absorption, crush force efficiency, peak load, mean load and load-displacement history were examined and discussed. The primary results displayed a significant influence on the energy absorption capability provided that stable progressive crushing occurred mostly in the triggered tubes compared to the non-triggered tubes. Overall, the tulip trigger configuration attributed the highest energy absorption.     

An experimental study on the effect of failure trigger mechanisms on the energy absorption capability of CFRP tubes under axial compression

The energy absorption characteristics of graphite/epoxy tubes of circular cross sections, subjected to quasi-static axial compression, were experimentally investigated. Tubes with chamfered-ends, inward-folding or outward-splaying crush-caps, or combined (chamfered-end and crush-cap) failure trigger mechanisms, were investigated to identify the optimal configuration that would result in the lowest initial peak load while providing the highest possible specific energy absorption (SEA). The chamfer failure trigger proved to be the most effective at lowering the initial peak load while yielding a high SEA. The inward-folding crush-caps were more effective than the outward-splaying crush-caps in terms of decreasing the initial peak load and increasing the SEA. These results were significantly affected by the corner radii of the crush-caps: the smaller the radius the higher the initial peak load and the SEA. It was determined that combining a chamfered tube with an inward-folding crush-cap yielded the lowest initial peak load and the highest SEA.     

Experimental investigation into dynamic axial impact responses of double hat shaped CFRP tubes

This paper aims to explore the dynamic responses and crashing characteristics of double hat shaped tubes made of weave carbon fiber reinforced plastic (CFRP). Experimental investigations were carried out into three different thicknesses and lengths of the composite tubes fabricated by the bladder molding process. Three distinct failure modes, classified as progressive end crushing, mid-length collapse and overlap opening, were observed in the dynamic crushing tests. Unlike continuous splaying fronds observed in the quasi-static tests, dynamic tests exhibited a number of fragment segments in the progressive end crushing mode. It is shown that the ply number was a critical parameter affecting the failure mode and energy absorption capability. The increase in ply number led to increases in the peak load and specific energy absorption (SEA); whereas the tubal length seemed insensitive to energy absorption capability. Compared to the quasi-static cases, the dynamic impact tests resulted in the higher peak load (increased from 46 % to 125 %) and lower SEA (reduced from 21 % to 33 %) for the tested tubes.     

Composite sandwich structures with nested inserts for energy absorption application

Polymer composite sandwich structures are promising candidate structures for reducing vehicle mass, thereby improving the fuel economics. Nonetheless, to fully explore this material as the primary structure and energy absorber in vehicles, it is important to understand the energy absorption capability of this material. Hence, in the present work, comprehensive experimental investigation on the response of composite sandwich structures to quasi-static compression has been carried out. The crashworthiness parameters, namely the peak force, absorbed crash energy, specific absorbed energy, average crushing force and crush force efficiency of various types of composite sandwich structures were investigated in a series of edgewise axial compression tests. The tested composite sandwich specimens were fabricated from glass and carbon fiber with epoxy resin. Four distinct modes of failure were observed and recorded. The primary mode of failure observed was progressive crushing with high energy absorption capability. The optimized design in this study had a specific energy absorption capability of 47.1 kJ/kg with a good crush force efficiency of 0.77, higher than conventional metals.     

玻璃/环氧圆柱管能量吸收细观机理

研究了玻璃纤维增强环氧圆柱管轴向撞击和准静态压缩下的能量吸收特性。总结了稳态压缩的三种宏观破坏模式,即层束弯曲、局部屈曲和横向剪切。从细观角度出发,详细研究了不同宏观破坏模式的复合材料圆柱管的能量耗散机理,并比较了吸能能力。随着铺设角度增大,能量吸收机理由基体控制向纤维与基体共同控制转化,因此能量吸收逐渐增大。本文还比较了撞击和准静态下能量吸收的特点。     

Advanced composite sandwich structure design for energy absorption applications: Blast protection and crashworthiness

This paper describes an experimental investigation on the response of composite sandwich structures with tubular inserts to quasi-static compression. The performance parameters, namely the peak load, absorbed crash energy, specific energy absorption; average crushing load and crush force efficiency were evaluated. The composite sandwich specimens were fabricated from glass fiber, polystyrene foam and epoxy resin. The primary mode of failure observed was progressive crushing with the composites exhibiting high energy absorption capabilities and high crushes force efficiency. The mechanism of progressive crushing of the sandwich structures and its relation to the energy absorption capabilities was deliberated. Furthermore, a statistical analysis was performed to investigate the effects of the design variables and also to determine if there were interactions between these variables. Such information is vital in the design of polymer composite sandwich structures as energy absorbers.     

GFRP约束微珠泡沫柱准静态受压性能

本研究对2根微珠泡沫柱及5根玻璃纤维复合材料(GFRP)约束微珠泡沫组合柱开展准静态轴压试验,探讨了GFRP层数、横向纤维与纵向纤维比例、泡沫密度等参数对组合柱极限承载力和吸能效应的影响,并与静态试验结果进行对比,研究不同加载速率对构件受压性能的影响规律.结果表明:准静态压缩作用下GFRP层数和泡沫密度的增加均提高了构...     

Crashworthiness characteristics of a carbon fiber reinforced dual-phase epoxy–polyurea hybrid matrix composite

The crashworthiness characteristics of rectangular tubes made from a Carbon-fiber reinforced Hybrid-Polymeric Matrix (CHMC) composite were investigated using quasi-static and impact crush tests. The hybrid matrix formulation of the CHMC was created by combining an epoxy-based thermosetting polymer with a lightly crosslinked polyurea elastomer at various cure-time intervals and volumetric ratios. The load–displacement responses of both CHMC and carbon-fiber reinforced epoxy (CF/epoxy) specimens were obtained under various crushing speeds; and crashworthiness parameters, such as the average crushing force and specific energy absorption (SEA), were calculated using subsequent load–displacement relationships. The CHMC maintained a high level of structural integrity and post-crush performance, relative to traditional CF/epoxy. The influence of the curing time and volumetric ratios of the polyurea/epoxy dual-hybridized matrix system on the crashworthiness parameters was also investigated. The results reveal that the load carrying capacity and total energy absorption tend to increase with greater polyurea thickness and lower elapsed reaction curing time of the epoxy although this is typically a function of the loading rate. Finally, the mechanism by which the CHMC provides increased damage tolerance was also investigated using scanning electron microscopy (SEM).     

Effect of triggering and polyurethane foam-filler on axial crushing of natural flax/epoxy composite tubes

In this study, empty and polyurethane-foam filled flax fabric reinforced epoxy composite tubes were longitudinally crushed under quasi-static compression. The effects of foam-filler (density of 160 kg/m³, two diameters of 64 and 86 mm), tube thickness (2, 4 and 6 plies of laminate), and triggering (45° edge chamfering) and the combination of triggering and foam-filler on the crushing characteristics and energy absorption capacity of these tubes were investigated. The test results indicate that the observed primary failure mode was progressive crushing for all the specimens. Foam-filled tubes have better crashworthiness than empty tubes in total absorbed energy, specific absorbed energy and crush force efficiency. The presence of triggering has no significant effect on total absorbed energy and specific absorbed energy of the empty tubes. However, the crush force efficiency of triggered tube is significantly larger compared to the non-triggered one. In addition, the triggering minimises the force variation of the tubes from the average crush force and in turn a more stable progressive crushing is achieved. The foam-filled and triggered tubes have better crashworthiness than the empty tubes in all the aspects. Compared with either triggered or foam-filled tubes, the triggered and foam-filled tubes have larger values in average crush load and crush force efficiency. In terms of total absorbed energy and specific absorbed energy, the triggered and foam-filled tubes have values always larger than those of the tubes with triggering only, but these values are either larger or smaller than the tubes with foam-filler only.     

Effect of fiber orientation on energy absorption characteristics of glass cloth/epoxy composite tubes under axial quasi-static and impact crushing condition

The collapse characteristics and energy absorption capability of composite tubes made of 759/5224 woven glass cloth/epoxy with different fiber orientations were studied in the present article under axial quasi-static and impact crushing condition. The effects of fiber orientation and loading condition on the crushing modes and energy absorption capability were discussed in detail. The fiber orientation could be found to have significant influences on energy absorption performance. Based on results, the energy absorption capability could be improved by selecting proper fiber orientation. The energy absorption capability in impact crushing tests could be found to be slightly lower than that in quasi-static crushing tests.     

Experimental and numerical investigation of the crushing response of an open section composite energy absorbing element

The quasi-static crushing response of carbon epoxy composite hat-shaped crush elements is described herein. A steeple-type triggering mechanism was used to ensure the specimens exhibited a continuous stable crushing mode of failure. The explicit finite element software PAM-CRASH was used to predict the crushing failure of these energy absorbing elements. A four-layer, stacked-shell model of the composite hat-shaped element, after calibration against experimental test data, was found to be capable of closely approximating the failure modes and provide agreement with the load vs. displacement behaviour observed during the experiments. The predicted steady state load and specific energy absorption were respectively within 1.5 and 0.2% of the experimental average. With further validation, the developed stacked-shell methodology could help provide a predictive tool to characterise the energy absorption of open section crush elements and significantly reduce the cost associated with an extensive experimental material characterisation test program.     

铺层顺序对复合材料薄壁圆管轴向压溃吸能特性的影响研究

采用仿真和试验相结合的方法探讨复合材料薄壁圆管在准静态轴向压缩载荷下的失效吸能特性和吸能机理。首先,建立复合材料薄壁圆管"层合壳"有限元模型,通过显式动力学方法求解其在准静态轴向载荷下的压溃失效力学行为。仿真与试验结果在圆管轴向压溃变形过程、初始峰值载荷、平均压溃载荷及比吸能等主要吸能参数上具有很好的一致性,验证了"层合壳"复合材料圆管有限元模型和建模方法的有效性。其次,采用解析模型与仿真分析方法分别对[0/90]_3s、[0/90/0₂/90₂]_s、[0₃/90₃]_s三种不同铺层顺序的复合材料圆管的屈曲载荷与吸能特性进行了对比,进一步分析了铺层顺序对圆管失效吸能特性的影响。研究表明,0°与90°铺层交替程度对复合材料圆管的吸能特性影响较大,保证纤维失效方式在结构宏观失效中占主导地位能够提高材料失效吸收能量。     

Axial crush and bending collapse of an aluminum/GFRP hybrid square tube and its energy absorption capability

In this paper, energy absorption capability of axial crush and bending collapse of aluminum/GFRP hybrid tubes were investigated. Glass fiber–epoxy composite prepregs were wrapped around an aluminum tube and then cured completely in the autoclave under the recommended cure cycle. Bonding process between composite and aluminum tubes was performed by excess resin extracted from the composite tube during curing process. For comparing energy absorption characteristics of the hybrid tube with those of pure aluminum and composite tubes, tests were performed using specimens made of an aluminum alloy and a composite material, respectively.

Failure mechanisms of the hybrid tube under the axial compressive load and the bending load were experimentally investigated. For calculating energy absorption capability of axial crush and bending collapse behaviors of the hybrid tube, the modified plastic hinge collapse model and the modified Kecman's model for hybrid tube were suggested, respectively. Two suggested models for the hybrid tube showed a good agreement with the experimental results.     

圆-方异形截面复合材料管件物能量吸收机制

圆形截面复合材料管件物的能量吸收性能比方形截面管件物更加优越,但具有平整表面的方形管件物更容易与其他部件相装配,即方管在实际运用中更具优势。结合圆形与方形管件物的各自优势,以碳纤维为增强体,环氧树脂为基体,利用编织成型方法以及真空辅助树脂传递成型技术制备出编织角度为15°和60°的3类复合材料圆-方形管件物,编号为T15-15、T15-60及T60-60。通过准静态压缩实验研究了3类管件物的能量吸收性能,发现通过合理的编织角设计,可以利用周向纤维限制轴向中央裂纹的扩展,使复合材料内部更多的纤维发生断裂,从而提高纤维增强复合材料管件物的能量吸收性能。最终制备了集高能量吸收性能与易装配性于一身的圆-方异形截面复合材料管件物。     

粉煤灰空心球/Al复合泡沫材料准静态力学性能及本构模型

为研究粉煤灰空心球/Al(Fly ash cenosphere/aluminum syntactic foam,FAC/Al)复合泡沫材料静力性能,采用万能试验机对铝基复合泡沫材料进行了准静态轴向压缩性能试验,考察了不同空心球平均粒径(分别为150、200和300 μm)对铝基复合泡沫材料变形失效模式及力学性能的影响,并获取了具有不同空心球粒径的复合材料在准静态下的应力-应变曲线,在此基础上分析了空心球粒径大小对复合材料能量吸收性能的影响。试验结果表明,在准静态荷载作用下,随着空心球粒径的增大,复合材料的压缩屈服强度、吸能能力及理想吸能效率有着明显的降低。此外,在获得的应力-应变曲线基础上,采用最小二乘法拟合得到了铝基复合泡沫在准静态荷载作用下的本构方程,并对其进行了验证,结果表明该方程具有较好的拟合度。      

Static and high-rate loading of single and multi-bolt carbon–epoxy aircraft fuselage joints

Single-lap shear behaviour of carbon–epoxy composite bolted aircraft fuselage joints at quasi-static and dynamic (5 m/s and 10 m/s) loading speeds is studied experimentally. Single and multi-bolt joints with countersunk fasteners were tested. The initial joint failure mode was bearing, while final failure was either due to fastener pull-through or fastener fracture at a thread. Much less hole bearing damage, and hence energy absorption, occurred when the fastener(s) fractured at a thread, which occurred most frequently in thick joints and in quasi-static tests. Fastener failure thus requires special consideration in designing crashworthy fastened composite structures; if it can be delayed, energy absorption is greater. A correlation between energy absorption in multi-bolt and single-bolt joint tests indicates potential to downsize future test programmes. Tapering a thin fuselage panel layup to a thicker layup at the countersunk hole proved highly effective in achieving satisfactory joint strength and energy absorption.