Crushing response of foam-filled conical tubes under quasi-static axial loading

Foam-filled thin-walled tubes are considered to be desirable energy absorbers under axial loading due to their higher energy absorption compared with empty tubes. This paper treats the axial crushing and energy absorption response of foam-filled conical tubes under quasi-static axial loading, using non-linear finite element models. Influence of important parameters such as wall thickness, semi-apical angle and density of foam filler was investigated and the results highlight the advantages of using foam-filled conical tubes as energy absorber. Results also indicate that the crush and energy absorption performances of conical tubes are significantly enhanced by foam filling. The primary outcome of the study is new research information and development of empirical relations which will facilitate the design of foam-filled conical tubes as energy absorbers in impact applications.     

Experimental and analytical assessment of axial crushing of circular hybrid tubes under quasi-static load

In the present article, axial crushing behavior of circular aluminum/glass–epoxy hybrid tubes is studied experimentally and analytically. 48 quasi-static axial crushing experiments are carried out on bare metal and hybrid tubes to evaluate the effect of different parameters such as metal and composite wall thicknesses and stacking sequence of composite layers on the crashworthiness characteristics. The specimens are made in two types of layups including angle ply pattern [±θ]_s and multi angle ply pattern (different ply angles). The experimental results reveal that stacking sequence has a considerable effect on crashworthiness characteristics, for example for layup [90/0/0/90], the absorbed energy is more than three times of aluminum tube with the same aluminum wall thickness. Also the aforementioned layup has better energy absorption compared to [90/90/90/90] which has been previously proposed as the best layup.     

Crushing and energy absorption performance of different geometrical shapes of small-scale glass/polyester composite tubes under quasi-static loading conditions

This paper presents the quasi-static crushing performance of nine different geometrical shapes of small-scale composite tubes. The idea is to understand the effect of geometry, dimension and triggering mechanism on the progressive deformation of small-scale composite tubes. Different geometrical shapes of the composite tubes have been manufactured by hand lay-up technique using uni-directional E-glass fabric (with single and double plies) and polyester resin. Dedicated quasi-static tests (144 tests) have been conducted for all nine geometrical shapes with different t/D (thickness–diameter) ratios and two triggering profiles (45° chamfering and tulip pattern with an included angle of 90°). From this unique study, it was found that the crushing characteristics and the corresponding energy absorption of the special geometrical shapes are better than the standard geometrical shapes such as square and hexagonal cross sections. Furthermore, the tulip triggering attributed to a lower peak crush load followed by a steady mean crush load compared to the 45° chamfering triggering profile which resulted into a higher energy absorption in most of the geometrical shapes of the composite tubes.     

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.     

Crushing behaviour of composite hemispherical shells subjected to quasi-static axial compressive load

This paper examines the effects of composite constituents and geometry on the energy absorption capability of composite hemispherical shells. To examine the effects of matrix types on their energy absorption capability, glass fibre/epoxy and glass fibre/polyester hemispherical shells were fabricated. While glass fibre/epoxy and carbon fibre/epoxy hemispherical shells were fabricated to investigate the effect of fibre reinforcements. Effect of aspect ratio (R/t) was also examined and the results were presented. The results obtained showed that the energy absorption capability of the hemispherical shells significantly affected by the composite constituents as well as R/t ratio.     

A numerical study on the quasi-static axial crush characteristics of square aluminum–composite hybrid tubes

In this paper, we describe a numerical investigation on the quasi-static axial crush performance of aluminum–composite hybrid tubes containing a filament-wound E-glass fiber-reinforced epoxy over-wrap around square aluminum tubes. The fiber orientation angle in the overwrap was varied between [±30°] and [90°] with respect to the tube’s axis. The quasi-static axial crush resistance of the hybrid tubes are compared in terms of the maximum load, mean crush load, crush energy and specific energy absorption. The deformation modes of these tubes are also described. An empirical equation is proposed for predicting the mean crush force of hybrid tubes.     

Effect of aluminum closed-cell foam filling on the quasi-static axial crush performance of glass fiber reinforced polyester composite and aluminum/composite hybrid tubes

The effect of Al closed-cell foam filling on the quasi-static crushing behavior of an E-glass woven fabric polyester composite tube and thin-walled Al/polyester composite hybrid tube was experimentally investigated. For comparison, empty Al, empty composite and empty hybrid tubes were also tested. Empty composite and empty hybrid tubes crushed predominantly in progressive crushing mode, without applying any triggering mechanism. Foam filling was found to be ineffective in increasing the crushing loads of the composite tubes over the sum of the crushing loads of empty composite tube and foam. However, foam filling stabilized the composite progressive crushing mode. In empty hybrid tubes, the deformation mode of the inner Al tube was found to be a more complex form of the diamond mode of deformation of empty Al tube, leading to higher crushing load values than the sum of the crushing load values of empty composite tube and empty metal tube. The foam filling of hybrid tubes however resulted in axial splitting of the outer composite tube due to the resistance imposed by the foam filler to Al tube inward folding and hence it was ineffective in increasing crushing load and SAE values over those of empty hybrid tubes.     

On the effect of geometrical designs and failure modes in composite axial crushing: A literature review

Composite materials have been known for its low density, ease in fabrication, high structural rigidity, and wide range applications, i.e. aeronautic applications and automotive industry. Due to this, extensive studies had been conducted to evaluate its axial crushing ability to replace metallic materials. In this paper, it reviewed the usage of fibre reinforced plastic composite (FRP) as an energy absorption application device. Failure modes and geometrical designs such as shapes, geometry and triggering effect have been studied where these factors affected on peak load and specific energy absorption significantly. Accordingly, numerical analysis for axial crushing of affected factors had been simulated to predict the failure mechanisms of FRP composites.     

Response of pultruded composite tubes subjected to dynamic and impulsive axial loading

The energy absorption of circular pultruded composite tubes subjected to axial crush load, transmitted by a small attached mass accelerated by means of an explosive load is presented in this paper. Different masses of explosive are used to provide a range of transmitted impulse and crushed distance of the pultruded composite tubes. The influence of the mass of the explosive on the tube response is investigated with regard to crushed distance, the average crushing force and the specific energy absorption (SEA). The crushing distance increases with increasing transmitted impulse. The results and failure mode are also compared with compression tests carried out on a servo-hydraulic machine (type: MTS-309).     

Investigating the quasi-static axial crushing behavior of polymeric foam-filled composite pultrusion square tubes

The capability of structures to absorb large amounts of energy is a crucial factor, particularly for structural components of vehicles, in reducing injury in case of collision. In this study, an experimental investigation was conducted to study the crashworthiness of polymeric foam-filled structures to the pultruded square cross-section E-Glass fiber-reinforced polyester composite tube profiles. Quasi-static compression was applied axially to composite tubes to determine the response of the quasi-static load displacement curve during progressive damage. Three pultruded composite tube wall thicknesses at different sizes were examined, and the effects of crushing behavior and failure modes were analyzed and discussed. Experimental results indicated that the foam-filled profile is superior to the non-filled foam composite tube profile in terms of the capacity to absorb specific energy.     

薄壁开孔圆管在轴向荷载作用下的理论研究

研究薄壁开孔圆管的轴向耐撞性有助于其在缓冲、吸能领域的广泛应用。通过分别考虑开孔区域和未开孔区域的能量吸收特征并引入材料的应变强化效应,根据塑性铰理论建立了轴向荷载下开孔圆管轴对称压溃模式的理论模型,得到了弯曲应变能、拉伸应变能、平均压溃力、比吸能的解析表达式。分析结果表明:该理论模型的预测结果与数值和实验结果相吻合;正则化平均压溃力会随半皱褶长细比的降低而显著增加;单层孔数对正则化平均压溃力的影响会随管壁厚度的增加或孔半径的减小而降低;比吸能可通过减少单层孔数或减小孔半径提高。     

On the response of thin-walled CFRP composite tubular components subjected to static and dynamic axial compressive loading: experimental

In this work the crushing response and crashworthiness characteristics of thin-wall square FRP (fibre reinforced plastic) tubes that were impact tested at high compressive strain rate are compared to the response of the same tubes in static axial compressive loading. The material combination of the tested specimens was carbon fibres in the form of reinforcing woven fabric in epoxy resin, and the tested tubes were constructed trying three different laminate stacking sequences and fibre volume contents on approximately the same square cross-section. Comparison of the static and dynamic crushing characteristics is made by examining the collapse modes, the shape of the load–displacement curves, the peak and average compressive load and the absorbed amount of crushing energy in both loading cases. In addition, the influence of the tube geometry (axial length, aspect ratio and wall thickness), the laminate material properties-such as the fibre volume content and stacking sequence-and the compressive strain rate on the compressive response, the collapse modes, the size of the peak load and the energy absorbing capability of the thin-wall tubes is extensively analysed.     

编织复合材料圆管准静态轴向压缩吸能特性的试验研究

通过二维三向编织复合材料圆管的轴向准静态压缩试验, 分析了编织复合材料圆管的压缩破坏机理和吸能特性, 并探讨了编织参数对吸能特性的影响。试验中观察到4种破坏模式: 分瓣破坏、 局部屈曲、 块状断裂和突发破坏。在纤维体积分数相同的情况下, 随着编织层数的增加和编织角的减小, 圆管的吸能能力有所提高。二维三向编织复合材料圆管是一种较好的吸能材料, 具有较高的单位质量吸能特性。      

Influence of forming effects on the axial crush response of hydroformed aluminum alloy tubes

The impact behaviour of tubular hydroformed axial crush tubes is examined. The results of dynamic axial crush tests performed with both non-hydroformed and hydroformed AA5754 aluminum alloy tubes were compared to predictions from finite element models. Explicit dynamic finite element simulations of the hydroforming and crash events were carried out with particular attention to the transfer of forming history from the hydroforming simulations to the crash models. The values of tube thickness, work hardening, and residual stresses at the end of the hydroforming simulations were used as the initial state for the crash models. In general, simulations performed using the von Mises yield criterion with isotropic material behaviour gave reasonable predictions when compared to experimental data. It was found that it was important to account for the forming history of the hydroforming operation in the axial crush models. The results showed that work hardening resulting from hydroforming is beneficial to increasing the energy absorption during crash, whereas thickness reduction decreased the energy absorption. Residual stresses had little effect on the energy absorption characteristics. It was also shown that the energy absorption characteristics of tubes with the same mass could vary greatly by adjusting the geometry of the tube and the amount of work hardening experienced by the tube during hydroforming.     

Finite element modelling of the progressive crushing of braided composite tubes under axial impact

Composite tubular structures are of interest as viable energy absorbing components in vehicular front rail structures to improve crashworthiness. Desirable tools in designing such structures are models capable of simulating damage growth in composite materials. Our model (CODAM for COmposite DAMage), which is a continuum damage mechanics based model for composite materials with physically based inputs, has shown promise in predicting damage evolution and failure in composites. In this study, the model is used to simulate the damage propagation, failure morphology and energy absorption in triaxially braided composite tubes under axial compression. The model parameters are based on results from standard and specialized material testing and a crack band scaling law is used to minimize mesh sensitivity (or lack of objectivity) of the numerical results. Axial crushing of two-ply and four-ply square tubes with and without the presence of an external plug initiator are simulated in LS-DYNA. Refinements over previous attempts by the authors include the addition of a pre-defined debris wedge, a distinguishing feature in tubes displaying a splaying mode of failure, and representation of delamination using a tiebreak contact interface that allows energy absorption through the un-tying process. It is shown that the model adequately predicts the failure characteristics and energy absorption of the crushing events. Using numerical simulations, the process of damage progression is investigated in detail and energy absorptions in different damage mechanisms are presented quantitatively.     

Stochastic simulations of square aluminium tubes subjected to axial loading

Stochastic simulations of square aluminium tubes of 6060 T6 aluminium alloy subjected to axial crushing have been performed and compared to an experimental program carried out previously at SIMLab. The main variables during testing were the extrusion length, the wall thickness of the extrusions and the impact velocity of the impactor. Three different buckling modes were observed: progressive buckling, transition from progressive to global buckling and global buckling. Progressive buckling was primarily observed in the short specimens, while increasing the length a transition mode took place. However, for the thick-walled tubes a direct global buckling mode was found. In the present study, it has been investigated if geometric imperfections modelled by assumed Gaussian random fields could explain the experimentally observed behaviour. Variation of the random field parameters by use of a factorial design resulted in variations in especially the buckling modes and consequently the average force, and the same buckling modes found in the experiments were obtained in the simulations. For the chosen model, the shape of the geometric imperfections seemed to be more important than the amplitude. Further, simulations of profiles with three different lengths subjected to impacts at two different velocities were performed. The estimated probability for progressive buckling to appear decreased as the length increased, while the change in velocity had minor effects for the chosen parameter range.     

Investigation of the response to low velocity impact and quasi-static indentation loading of particle-toughened carbon-fibre composite materials

This work investigates damage caused by low velocity impact and quasi-static indentation loading in four different particle-toughened composite systems, and one untoughened system. For impact tests, a range of energies were used between 25 and 50 J. For QSI, coupons were interrupted at increasing loading point displacement levels from 2 to 5 mm to allow for monitoring of damage initiation and propagation. In both loading cases, non-destructive inspection techniques were used, consisting of ultrasonic C-scan and X-ray micro-focus computed tomography. These techniques are complemented with instrumentation to capture force–displacement data, whereby load-drops are associated with observed damage modes. Key results from this work highlight particular issues regarding strain-rate sensitivity of delamination development and an earlier onset of fibre fracture associated with particle-toughened systems. These issues, in addition to observations on the role of micro-scale events on damage morphology, are discussed with a focus on material development and material testing practices.     

Robustness study on the behaviour of top-hat thin-walled high-strength steel sections subjected to axial crushing

A robustness study on the behaviour of top-hat thin-walled high-strength steel sections from different batches subjected to dynamic axial crushing has been performed. The robustness was investigated by considering 25 components produced from five different material batches. The variation of material properties within and between the batches was characterised by use of tensile tests. A 3D scanner was used in order to study the geometric imperfections of the profiles. The components were crushed in a kicking machine at an impact velocity of 10 m/s with an impacting mass of 985 kg. Fracture was observed in all the components, but the extent of fracture varied from batch to batch and seemed to be positively correlated to the material strength and negatively correlated to the material ductility. The mean force varied significantly within each batch, while the variation in the batch mean of the mean force was relatively small compared to the variations in the batch means of the material strength and thickness.     

The quasi-static and blast loading response of lattice structures

A range of metallic lattice structures have been manufactured using the selective laser melting (SLM) rapid manufacturing technique. The lattice structures were based on [±45°] and [0°, ±45°], unit-cell topologies. Initially, the structures were loaded in compression to investigate their progressive collapse behaviour and associated failure mechanisms. Tests were then undertaken at crosshead displacement rates up to 3 m/s in order to characterise the rate-dependent properties of these architectures. A series of blast tests were then undertaken on a ballistic pendulum in order to investigate the behaviour of lattice structures under these extreme loading conditions.     

Effect of anisotropy,kinematic hardening,and strain-rate sensitivity on the predicted axial crush response of hydroformed aluminium alloy tubes

There exists considerable motivation to reduce vehicle weight through the adoption of lightweight materials while maintaining energy absorption and component integrity under crash conditions. Aluminium and magnesium alloys, advanced high-strength steels, and composites are all proposed candidates for replacing mild steel in automotive structures. It was of particular interest to study the crash behaviour of lightweight tubular hydroformed structures. Thus, the current research has studied the dynamic crush response of hydroformed Al–Mg–Mn aluminium alloy tubes using both experimental and numerical methods. The research focused on axial crush structures that are designed to absorb crash energy by progressive axial folding. The main experimental parameter that was varied during the hydroforming process was the corner-fill radius of the tube. Numerical studies were carried out using explicit dynamic finite element models incorporating advanced constitutive material models to capture the measured forming and crash history. A constitutive model was implemented in the finite element models combining the Johnson–Cook strain-rate sensitivity model, a non-linear isotropic-kinematic hardening model, and the Yld2000-2d anisotropic model. Each effect was isolated, and it was shown that strain-rate sensitivity slightly increased the energy absorption capabilities while kinematic hardening and anisotropy effects decreased the energy absorption capabilities during axial crush. When including all three effects, the predicted energy absorption was less than the response predicted from simulations performed using the von Mises yield criterion and in reasonable agreement with measured data. It is recommended that a combined constitutive model be utilized for the study of materials that show sensitivity to the Bauschinger effect, strain-rate effects, and anisotropy.