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.     

Simulation of progressive damage development in braided composite tubes under axial compression

A continuum damage mechanics based model for composite materials (CODAM), which has been implemented as a user material model in an explicit finite element code (LS-DYNA), is used to capture the complete tensile and compressive response of a braided composite material. Model parameters are related to experimentally observed behaviour to ensure a physical basis to the model and a crack band scaling approach is used to minimize mesh sensitivity (or lack of objectivity) of the numerical results. The predictive capability of the model is validated against the results from dynamic tube crush experiments. The damage propagation, failure morphology and energy absorption predictions correlate well with the experimental results.     

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.     

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.     

三维编织复合材料面内刚度和强度性能研究

以修正的经典层合板理论为基础, 分析三维编织复合材料的力学性能。在单胞的长度方向积分和平均, 预测编织结构复合材料的有效弹性模量; 采用蔡-胡多项式失效准则, 得到三维编织复合材料的强度性能。另外, 进行编织结构复合材料的力学性能实验, 探讨纺织工艺参数, 如纤维编织角、横向编织角、轴向纱数与编织纱数之比、纤维体积含量等对力学性能的影响, 理论预报和试验结果进行对比, 发现该力学模型能较好地预报三维编织复合材料的刚度和强度性能。      

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.     

On the Collapse of Cotton/Epoxy Tubes under Axial Static Loading

Experimental quasi-static crushing tests and finite element analysis have been carried out for unidirectional filament wound laminated cotton/epoxy tubes. The work focuses on three main factors, which considerably affect the axial collapse load of unidirectional natural composite tubes. These factors are structural geometry, fibre diameter and fibre orientation. Cotton/epoxy tubes with different diameters (50, 70, 90, 110 and 130 mm) were examined and tested. The fibre orientation angles were 80 and 90°. The initial geometric imperfections are measured using the computerised Mistral coordinate measuring machine. The numerical prediction was obtained using commercially available finite element software. A limited agreement between the experimental and computational results was obtained. For all structures considered classical axial collapse eigenvalues were computed. The initial failure crush load computed from the finite element simulation model has been compared with the experiments.     

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 tube geometry and ply-angle on energy absorption of a circular glass/epoxy crush tube – A numerical study

The superior specific energy absorption characteristics of long fiber composite structures as compared to aluminum and steel are well established. Due to cost and time involved in testing of composites, it is imperative to develop numerical solution of the crushing phenomenon. The work presented here reports work to better understand the energy absorption characteristics of glass–fiber circular crush tubes. The effect of tube diameter and ply orientation on the energy absorption has been extensively investigated. Numerical results are compared with experiments performed elsewhere and the correlation between the two is encouraging.     

立体多向编织结构对复合材料性能的影响

本文采用1×1,1×2和1×3三种不同的编织结构对轴向增强和非增强三维多向编织复合材料的性能进行了研究。对编织复合材料的拉伸强度、刚度和弯曲强度、刚度进行了实验分析。结果表明;三维编织复合材料具有良好的性能。编织结构对复合材料性能有较大的影响。纤维表面编织角和纤维体积比是影响复合材料性能的重要结构参数。通过轴向加入非编织增强纤维,使编织复合材料的拉伸强度和模量,弯曲强度和模量有了较大改善。      

立体多向编织结构对复合材料性能的影响

本文采用1×1,1×2和1×3三种不同的编织结构对轴向增强和非增强三维多向编织复合材料的性能进行了研究。对编织复合材料的拉伸强度、刚度和弯曲强度、刚度进行了实验分析。结果表明;三维编织复合材料具有良好的性能。编织结构对复合材料性能有较大的影响。纤维表面编织角和纤维体积比是影响复合材料性能的重要结构参数。通过轴向加入非编织增强纤维,使编织复合材料的拉伸强度和模量,弯曲强度和模量有了较大改善。     

Analysis of Crushing Response of Composite Crashworthy Structures

The paper describes quasi-static and dynamic tests to characterise the energy absorption properties of polymer composite crash energy absorbing segment elements under axial loads. Detailed computer tomography scans of failed specimens are used to identify local compression crush failure mechanisms at the crush front. The varied crushing morphology between the compression strain rates identified in this paper is observed to be due to the differences in the response modes and mechanical properties of the strain dependent epoxy matrix. The importance of understanding the role of strain rate effects in composite crash energy absorbing structures is highlighted in this paper.     

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。     

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。      

Axial capacity and crushing behavior of metal–fiber square tubes – Steel,stainless steel and aluminum with CFRP

Composite metal-carbon fiber reinforced polymer (CFRP) tubes combine the benefits of the high strength to weight ratio of the fiber/resin composite and the stable, ductile plastic collapse mechanism of the metal, to form a composite tube with high strength and energy absorption capability. This paper investigates the axial capacity and crushing behavior of square hollow section (SHS) tubes composed of composite steel-CFRP, stainless steel-CFRP and aluminum-CFRP. Experiments of tubes with different metal SHS geometries and two different matrix layouts of carbon fibers are described, and a general theory to predict the compression buckling, axial capacity, axial collapse and mean crush load of metal–fiber square tubes is developed and validated against the experimental results. It is shown that carbon fiber may be successfully externally bonded to metal SHS, and such application may be provided to improve the performance of existing structures, or to design new structures with enhanced strength-weight and energy absorption-weight ratios. Comparisons are made between the performance of the different types of metals, SHS geometries and carbon fiber matrix layouts.     

Modeling the Axial Splitting and Curling of Metal Tubes under Crush Loads

Plastic deformation and splitting are two important mechanisms of energy dissipation when metal tubes undergo axial crushing. Isotropic J2 plasticity theory combined with a failure criterion is used to model axial splitting and curling of metal tubes undergoing axial crush. The proposed material model is implemented within a finite element (FE) framework using the user material subroutine VUMAT option available in the commercial code ABAQUS. Experimental results from literature are used to validate the model. The predicted splitting and curling patterns as well as the load-displacement response agree well with the experimental observations. The present material model is also used to predict the number of axial cracks in splitting the tube.     

Experimental testing and phenomenological modelling of the fragmentation process of braided carbon/epoxy composite tubes under axial and oblique impact

A new simulation technique is presented for the phenomenological modelling of stable fragmentation in fibre reinforced composite structures under dynamic compressive loading. An explicit crash code is used for implementation of a hybrid modelling technique, in which two distinct material models act simultaneously. The first model is implemented in a multi-layered shell element and uses a unidirectional composites fracture criterion to predict potential ply fracture mechanisms on a macroscopic scale. This model is, however, unable to represent the complex localised fracture mechanisms that occur on a meso (sub-ply) scale under compression fragmentation loading. Therefore, a second constitutive model is added to capture the energy absorbing process within the fragmentation zone, utilising an Energy Absorbing Contact (EAC) formulation between the composite structure and the impacting body. The essential benefits of the procedure are that it requires minimal input data that can be obtained from simple fragmentation tests, and that the procedure is computationally efficient enabling application to large scale industrial structures. The EAC theory is discussed, together with the required material model parameters. A series of dynamic axial and oblique impact tests and simulations of cylindrical continuous carbon fibre reinforced composite tubes have been performed to validate the approach. Furthermore, the application to more complex load cases including combinations of fragmentation and global structural fracture have also shown a good correlation with test results.     

Ellipticity Ratio Effects in the Energy Absorption of Axially Crushed Composite Tubes

In this paper, the influence of ellipticity ratio on energy absorption capability and load-carrying capacity of woven roving wrapped composite elliptical tubes has been investigated both experimentally and numerically. A series of experiments was conducted for composite elliptical tubes with ellipticity ratios (a/b) ranging from 1 to 2. Typical failure histories of their failure mechanism are presented and discussed. The experimental data are correlated with predictions from a finite element model. Load-deformation curves and deformation histories of typical specimens are presented and discussed. For all specimens considered, classical axial collapse eigenvalues were computed. The results showed that the ellipticity ratio significantly influenced the energy absorption capabilities as well as the load-carrying capacity. Tubes with ellipticity ratios of a/b 1.25 and 2.0 displayed the highest normalised specific energy absorption capability. A reasonable agreement between the experimental and computational results was obtained for the critical crush load.     

三维编织复合材料弹道侵彻准细观层次有限元计算

三维编织复合材料相比于层合复合材料有较高的层间剪切强度和断裂韧性,因而具有更高的冲击损伤容限。用钢芯弹对三维编织复合材料作弹道贯穿测试,得到弹体的入射速度和剩余速度,并考察侵彻破坏模式。目前对三维编织复合材料弹道侵彻性能计算主要建立在连续介质假设上,从真实细观结构计算三维编织复合材料弹道冲击性能尚有一定难度,用三维结构复合材料的纤维倾斜模型在准细观结构层次上分解三维编织复合材料,就其中的一块倾斜单向板作弹道侵彻有限元计算,由弹体动能损失得到贯穿整个复合材料靶体后弹体的剩余速度。有限元计算及与弹道测试结果的比较证明在准细观层次上计算三维编织复合材料弹道冲击性能的有效性。      

三维四向编织复合材料宏观有限元模型冲击损伤仿真及试验验证

三维编织复合材料作为整体编织材料,能够克服层合复合材料层间强度低、易分层的缺陷,相对于金属材料,还具有质量轻、高比刚、高比强度以及良好的抗冲击性能、较高的损伤容限,在汽车、高铁、航海、航空及航天领域中具有广泛应用前景。使用空气炮发射系统开展了钢珠以约210 m/s速度冲击三维四向编织复合材料平板的不同位置试验,基于宏观观察和细观观测,分析了三维编织复合材料在受到钢珠高速冲击下的破坏模式和破坏机制。此外,本文建立了三维四向编织复合材料宏观连续介质损伤（CDM）有限元模型,其中模型计算剩余速度和试验测得剩余速度误差在5%以内,试验和数值模拟的破坏形貌也高度一致,验证了所建立的宏观CDM有限元模型的有效性。