Crashworthiness of helicopter subfloor structures

To improve a helicopter design concept, which meets structural and crashworthiness requirements, a research program is undertaken to study the energy absorption capability of a subfloor structure. In particular, crash tests are performed on the subfloor structure and on the intersection elements, which are components of the structure and can create high deceleration peak loads at the cabin floor level causing dangerous inputs to the occupants. Then the structures are analysed by a commercial explicit finite element code, PAM-CRASH, using detailed geometrical models, suitable materials models and the appropriate definition of contact forces and rivets. The analysis shows that the load-shortening diagrams present a good correlation to the experimental data and that the structural collapse predictions correspond closely to the observed behaviour during the experimental tests. Consequently the finite element analysis can be used to aid the designers in evaluating the crashworthiness of different structural concepts and can therefore be an important mean of reducing development costs.     

单胞及多胞铝合金薄壁梁吸能特性研究

对单胞、方孔多胞及蜂窝多胞三种薄壁梁进行了不同碰撞形式的仿真计算;利用台车碰撞试验台对蜂窝铝与方管铝薄壁梁结构的变形模式和变形量进行分析。结果显示,在相同的初始碰撞动能情况下,方孔多胞结构的压溃量最小,且以叠缩压溃的稳定变形模式进行;而在压溃量相同时,方孔多胞结构的吸能量最大,碰撞过程的材料利用率最高,其碰撞力峰值与均值差别最小。因此,方孔多胞薄壁梁应用于车身结构可以显著提高车辆的耐撞性能。     

Numerical investigation of a crash test of a composite helicopter subfloor structure

Composite energy-absorbing aircraft structures are being studied within a European Commission research programme (CRASURV – Design for Crash Survivability). One of the aims of the project is to evaluate the current capabilities of crashworthiness simulation codes for modelling future composite primary structures. In this paper, a detailed analysis is presented of a generic module of a composite helicopter subfloor structure, subjected to crash loading. The analysis is performed with the explicit finite element code PAM-CRASH and is compared with the results of a drop test. It has been found that pre-test simulations with only coupon data as input are capable of providing a reasonable overall representation, but to closely match the behaviour of the test, a significant amount of post-test work is required. The calibration of the post-failure material properties proved to be more crucial than the behaviour up to initial failure. The representation of fabric materials was found to be inadequate and a new fabric material model is under development as a result. The importance of modelling frictional effects was highlighted, and a mesh density study showed the model to be robust over a range of mesh densities.     

Crushing of soft-core sandwich profiles: experiments and analysis

The present paper investigates the mechanics of the crushing of sandwich profiles through component testing and theoretical analysis. Experiments were run showing that the underlying folding mechanism of sandwich profiles is very different from that of solid-section thin-walled structures. In particular, the shear behavior of the core material was found to strongly influence the mechanics of energy absorption. The analysis focuses on the crushing behavior of double-cell profiles that are made of soft-core hybrid stainless steel assembly (HSSA) sheets. Both material and structural tests were performed. It is demonstrated that the shear strength of the HSSA fiber core is small as compared to the face sheet properties. When subjected to bending, the core deformed in the shear mode, whereas the facings bent independently. Based on this mechanism, a new shear-folding model for sandwich profiles is derived, incorporating the “shear crushing” of the sandwich core material. Theoretical predictions of the mean crushing force based on the present model compared very well with the experimental data.     

A computational approach for prediction of the damage evolution and crushing behavior of chopped random fiber composites

A computational model is developed, by implementing the damage models previously proposed by authors into a finite element code, for simulating the damage evolution and crushing behavior of chopped random fiber composites. Material damages induced by fiber debonding and crack nucleation and growth are considered. Systematic computational algorithms are developed to combine the damage models into the constitutive relation. Based on the implemented computational model, a range of simulations are carried out to probe the behavior of the composites and to validate the proposed methodology. Numerical examples show that the present computational model is capable of modeling progressive deterioration of effective stiffness and softening behavior after the peak load. Crushing behavior of composite tube is also simulated, which shows the applicability of the proposed computational model for crashworthiness simulations.     

Crashworthiness design optimization using successive response surface approximations

 Finite Element (FE) method is among the most powerful tools for crash analysis and simulation. Crashworthiness design of structural members requires repetitive and iterative application of FE simulation. This paper presents a crashworthiness design optimization methodology based on efficient and effective integration of optimization methods, FE simulations, and approximation methods. Optimization methods, although effective in general in solving structural design problems, loose their power in crashworthiness design. Objective and constraint functions in crashworthiness optimization problems are often non-smooth and highly non-linear in terms of design variables and follow from a computationally costly (FE) simulation. In this paper, a sequential approximate optimization method is utilized to deal with both the high computational cost and the non-smooth character. Crashworthiness optimization problem is divided into a series of simpler sub-problems, which are generated using approximations of objective and constraint functions. Approximations are constructed by using statistical model building technique, Response Surface Methodology (RSM) and a Genetic algorithm. The approximate optimization method is applied to solve crashworthiness design problems. These include a cylinder, a simplified vehicle and New Jersey concrete barrier optimization. The results demonstrate that the method is efficient and effective in solving crashworthiness design optimization problems. Received: 30 January 2002 / Accepted: 12 July 2002 Sponsorship for this research by the Federal Highway Administration of US Department of Transportation is gratefully acknowledged. Dr. Nielen Stander at Livermore Software Technology Corporation is also gratefully acknowledged for providing subroutines to create D-optimal experimental designs and the simplified vehicle model.     

泡沫铝填充在轿车B柱中的侧面耐撞性研究

为了提高轿车侧面耐撞性,设计耐撞性能强的B柱成为主要课题之一.目前的优化方法很难将B柱侵入量和侵入速度同时控制在理想范围内.因此,提出泡沫铝材料填充在汽车B柱内代替B柱加强板的方法,缓冲侧面碰撞冲击.通过建立泡沫铝有限元模型与材料特性分析,确定仿真泡沫铝主要材料参数.进而根据中国新车评价规程C-NCAP要求,建立轿车整车侧面碰撞有限元模型,采用LS-DYNA软件进行仿真分析.结果表明,泡沫铝填充后的B柱侵入量和侵入速度都有明显降低.泡沫铝材料塑性变形和整体弯曲变形能够吸收1.51kJ的能量,是B柱加强板的3倍.填充泡沫铝前后仿真结果表明,轿车B柱填充泡沫铝是一种提高轿车侧面耐撞性的方法.     

端部方锥形薄壁构件的抗撞性尺寸优化

基于显式有限元技术,采用响应面法,以结构的比吸能为优化函数,以提高车辆吸能原件的抗撞性为目的,研究正方形截面金属薄壁构件的端部锥形尺寸对抗撞性的影响.经过数值分析,得出端部为方锥形的正方形截面薄壁构件的比吸能关于锥形长度和小锥边长的变化规律,这些规律可以用于实际吸能原件的设计,为进一步研究奠定基础.     

汽车碰撞中触发机械的参数化研究

讨论轿车车身安全性设计中触发机械的设计方法。研究了V型槽、角台和圆孔三种不同几何形状触发机械的设置方法 ,针对每种几何形状 ,探讨了不同大小的设计参数对变形模态和碰撞力峰值的影响。     

Neural network systems to reproduce crash behavior of structural components

The use of neural networks as global approximation tool in crashworthiness problems is here investigated. Neural networks are not only asked to return some meaningful indices of the structural behavior but also to reproduce load-time curves during crash phenomena. To contain the number of examples required for the training process, parallel subsystems of small neural networks are designed. Design points for the training process are obtained by explicit finite element analyses performed by PAMCRASH. The settlement of the points in the design domain is defined using a maximum distance concept. The procedure is applied to different typical absorption structures made of aluminum alloy: riveted tubes, honeycomb structures, longitudinal keel beam and intersection elements of helicopter subfloors.