Topology optimization for crashworthiness of thin-walled structures under axial crash considering nonlinear plastic buckling and locations of plastic hinges

Although topology optimization is established for linear static problems, more effort is required for solving nonlinear plastic problems. A new topology optimization approach with equivalent static loads (ESLs) is suggested to find the optimum topologies and locations of plastic hinges of thin-walled crash boxes by considering crash-induced deformation, the main crash energy-absorbing mechanism. Together with finite element method crashworthiness analyses, considering all nonlinearities with rate-dependent plasticity, the method was developed using an appropriate time-incremental scheme of ESLs without removing any high values of loads. Analyses show that the crash boxes with optimum topologies have energy-absorbing capabilities equivalent to the original structure. The proposed method is evaluated for two crashes: a crash box at low speed and a double cell subjected to high-speed collision. The results indicate that this method captures nonlinear crushing behaviours and accurate locations of plastic hinges where, if proper reinforcements are made, energy absorption can be enhanced.     

Comparative analysis of energy absorption behavior of tapered and grooved thin-walled tubes with the various geometry of the cross section

ABSTRACT

In this paper, Crush force efficiency (CFE), Specific Energy Absorption (SEA), Energy Absorption per Crush Length (E_cl), Maximum and average crush forces of straight and grooved tapered thin-walled tubes with various cross-section shapes (circle, ellipse, square, rectangle, hexagon, and octagon) have been studied. The effects of taper, the groove (as initiator) and their interaction have been presented in the current study using Finite Element Method as a numerical method. The tubes have the same volume, height, average cross-section area, thickness and material and have been subjected to axial and oblique dynamic loading. The results of simulations show that the section's geometry, taper and groove addition have a significant effect on energy absorption behavior and the hexagon cross section have better energy absorption behavior compared with other considered geometries. On the other hand, it was found that the behavior of these structures could improve against dynamic axial and oblique impact loading with the cost-effective geometry modifications. These results could help to improve and choose appropriate energy absorber structure based on desirable crush force and energy absorbing characteristics.     

复合材料波纹梁冲击试验与数值模拟

为了探究复合材料波纹梁的吸能性能,针对铺层形式分别为[(±45)3/(0,90)/(±45)3]、[(±45)8]和[(±45)7]的3种复合材料波纹梁元件,进行了动态冲击试验,得到了吸能载荷-位移曲线,并对其损伤破坏形貌进行了分析。以连续损伤力学为基础,结合改进的Hashin损伤判定准则以及损伤演化规律,提出了针对波纹梁耐撞性损伤分析的刚度退化模型,并基于有限元软件平台开发了适用于波纹梁渐进损伤分析的子程序。对3种不同结构形式的波纹梁进行了渐进失效数值分析,模拟得到了能量评估参数比吸能(SEA)和平均载荷值,并将模拟结果与试验结果进行了对比分析。比较分析了不同薄弱环节复合材料波纹梁的吸能能力。结果表明:波纹梁在冲击载荷作用下发生了渐进压溃失效;平均压溃载荷的相对误差不超过12%,能够满足工程应用要求;薄弱环节的设置需综合考虑复合材料性能和铺层方式等因素。     

Numerical simulation of impact behaviour of structures with response adapted to the intensity of shock

This study presents an alternative approach for the absorption of impact energy that uses the internal pressurization of structures in the framework of a crash‐adaptive response. Numerical simulations were conducted on axial impact of thin‐walled tubular structures with circular cross section that serve as an approximation to a front crash box of a motor vehicle. The main objective of this work consists in studying the effect of internal pressurization of tubular structures in a crashworthiness application, as well as the possibility to obtain a reduction in wall thickness thus improving weight efficiency. A numerical study is presented for an internal pressure of 20 bar and tubular structures of circular section and 1.14 mm thickness. Numerical simulations were performed recurring to LS‐DYNA explicit dynamics software while considering for the material a stainless steel alloy that is a material with interest for crashworthiness applications and manufacturing requisites due to its balance between strength, ductility and energy absorption. The results obtained allow concluding that recurring to internal pressurization it is feasible to reduce the wall thickness and have an impact resistance identical to the original while improving overall efficiency.     

基于正面碰撞仿真的轿车关重零件分析及改进

建立了某轿车整车及乘员和约束系统的有限元模型,进行100%正面碰撞的数值仿真,通过仿真与试验的加速度曲线对比,验证了有限元模型的有效性.针对车体耐撞性能的不足,通过正交试验构造零件厚度对车体吸能的线性响应面,得到对能量吸收影响显著的关重零件.对关重零件中的前纵梁和前悬挂推力杆采取局部加强和改变形状的改进措施,使传力路线连续.通过整车数值仿真对比,改进方案使关重零件吸能增加,假人头部伤害值降低,说明其车体耐撞性能得到了改善.     

功能梯度金属泡沫填充管在冲击载荷下的高效吸能

研究功能梯度泡沫填充管(FGFTs)在落锤冲击载荷作用下的变形行为和耐撞性。采用液态工艺制备的闭孔泡沫铝、A356合金泡沫和锌泡沫作为轴向梯度填料,用于制备不同构造的单层和多层结构。结果表明,多层泡沫填充管的变形由低强度部位开始,然后通过应力的逐渐增加在高强度部位中扩展。使用更多的A356合金和泡沫铝层可为梯度结构提供更大的比吸能(SEA),而高强度的锌泡沫对碰撞性能没有积极的影响。由泡沫铝和A356合金泡沫组成的梯度结构在准静态和落锤冲击条件下以对称模式发生连续倒塌。使用锌泡沫会引起对称模式和扩展模式倒塌,样品在动态加载下产生更大的局部变形,在准静态加载下产生更大的局部破裂。Al?A356泡沫填充管具有最高的SEA(10 J/g)和最低的初始峰值应力(σmax=10.2 MPa),是最好的轻质耐撞结构。     

Topology optimization for nonlinear dynamic problems: Considerations for automotive crashworthiness

Crashworthiness of automotive structures is most often engineered after an optimal topology has been arrived at using other design considerations. This study is an attempt to incorporate crashworthiness requirements upfront in the topology synthesis process using a mathematically consistent framework. It proposes the use of equivalent linear systems from the nonlinear dynamic simulation in conjunction with a discrete-material topology optimizer. Velocity and acceleration constraints are consistently incorporated in the optimization set-up. Issues specific to crash problems due to the explicit solution methodology employed, nature of the boundary conditions imposed on the structure, etc. are discussed and possible resolutions are proposed. A demonstration of the methodology on two-dimensional problems that address some of the structural requirements and the types of loading typical of frontal and side impact is provided in order to show that this methodology has the potential for topology synthesis incorporating crashworthiness requirements.     

基于LS-DYNA的保险杠耐撞性虚拟试验研究

为提高某轿车保险杠的耐撞性,根据GB17354-1998标准,在LS-DYNA软件中建立虚拟碰撞试验的有限元模型,对不同车体边界条件、材料屈服强度和地面摩擦系数下的主梁和吸能盒变形以及系统内能进行了对比分析,探讨了这些参数对保险杠耐撞性的影响.研究表明:依据实际试验情况,车体边界条件应设为不固定;合理组合主梁和吸能盒的屈服强度可提高保险杠耐撞性;地面摩擦系数增大,保险杠吸能量增加.     

From fundamental understanding to innovative developments of high-performance composites for aerospace application

In framework of the National Key Basic Research Program (973 Program) we focus our attention on R&D of (1) continuous enhancement of composites performance both for new generation and existing materials, (2) cost-effective manufacturing technologies, particularly resin transfer molding (RTM) in conjunction with textile technology, and (3) crashworthy composite structures in design, and manufacturing and simulation methodology for aircrafts composites. Many successful examples stories such as ex-situ concept have been demonstrated that the performance potential of composites could be enhanced and maximized by basically understandirg the complicated multi-scale and multi-dimensional structural characteristics in relation to properties. Based on the concept, graphite composites system with generally high impact damage resistance and balanced processing conditions has being developed consisting of base resins, modifiers and binders/tackifiers.     

基于有限元法和Taguchi方法的移动硬盘耐撞性能稳健设计

运用Taguchi参数设计方法,提出了基于数值模拟的移动硬盘跌落冲击耐撞性能稳健设计方法。以6.3cm(2.5in)移动硬盘为研究对象,建立了基于有限元软件ANSYS/LS-DYNA的移动硬盘跌落冲击三维有限元模型。分析了关键结构参数对移动硬盘耐撞性能稳健性的影响,进行了移动硬盘耐撞性能稳健设计,获得使磁盘盘片接触面等效应力对地面硬度变化具有稳健性的最优参数水平组合,并进行了仿真试验验证分析。该方法为改进设计提高移动硬盘耐撞性能提供了理论依据。