Multiobjective crashworthiness optimization design of functionally graded foam-filled tapered tube based on dynamic ensemble metamodel

Foam-filled thin-walled structures have recently gained attention with increasing interest due to their excellent energy absorption capacity. In this study, a new type of foam-filled thin-walled structure called as functionally graded foam-filled tapered tube (FGFTT) is proposed. FGFTT consists of graded density foam and thin-walled tapered tube. In order to investigate the energy absorption characteristics of FGFTTs, the numerical simulations for two kinds of FGFTTs subjected to axial dynamical loading are carried out by nonlinear finite element code LS-DYNA. In addition, a new kind of multiobjective crashworthiness optimization method employing the dynamic ensemble metamodeling method together with the multiobjective particle swarm optimization (MOPSO) algorithm is presented. This new kind of multiobjective crashworthiness optimization method is then used to implement the crashworthiness optimization design of FGFTTs. Meanwhile, the crashworthiness optimization designs of FGFTTs are implemented by using traditional multiobjective crashworthiness optimization method, which employs metamodels such as polynomial response surface (PRS), radial basis function (RBF), kriging (KRG), support vector regression (SVR) or the ensemble with the static design of experiment (DOE). Finally, by comparing the optimal designs of FGFTTs obtained by using the new multiobjective crashworthiness optimization method and the traditional one, the results show that the proposed new crashworthiness optimization method is more feasible.     

Optimization design of corrugated beam guardrail based on RBF-MQ surrogate model and collision safety consideration

As the main safety facility on the highway, a guardrail system is very essential for the highway traffics safety. In this paper, the Finite Element (FE) models of the vehicle and the corrugated beam guardrail system were created. Two types of widely used corrugated beam semi-rigid guardrails were simulated, which were the W-beam guardrail and the Thrie-beam guardrail. The collision between the corrugated beam guardrail systems and the vehicle body was analyzed. In the collision process, the snagging effect of the post to the vehicle body was also concerned. Under the considerations of the collision safety and the mechanism of the snagging effect, the multiobjective optimization problem was defined with dimensional sizes of guardrails to be the design variables. And the radial basis function (RBF) was applied to construct the regression models of the analytical objective, which increased the accuracy of fitting. The Pareto set and the optimal solution were obtained. After the optimization design, the W-beam guardrail and Thrie-beam guardrail were both greatly improved, that increased the collision safety between the corrugated beam guardrail and the vehicle body. This kind of analytical method can also be used for the crashworthiness optimization between any other cars and guardrails.     

Multiobjective crashworthiness optimization of multi-cornered thin-walled sheet metal members

Plastic deformation of structures absorbs substantial kinetic energy when impact occurs. Therefore, energy-absorbing components have been extensively used in structural designs to intentionally absorb a large portion of crash energy. On the other hand, high peak crushing force, especially with regard to mean crushing force, may lead to a certain extent and indicate the risk of structural integrity. Thus, maximizing energy absorption and minimizing peak to mean force ratio by seeking for the optimal design of these components are of great significance. Along with this analysis, the collapse behavior of square, hexagonal, and octagonal cross-sections as the baseline for designing a newly introduced 12-edge section for stable collapse with high energy absorption capacity was characterized. Inherent dissipation of the energy from severe deformations at the corners of a section under axial collapse formed the basis of this study, in which multi-cornered thin-walled sections was focused on. Sampling designs of the sections using design of experiments (DOE) based on Taguchi method along with CAE simulations was performed to evaluate the responses over a range of steels grades starting from low end mild steels to high end strength. The optimization process with the target of maximizing both specific energy absorption (SEA) and crush force efficiency (CFE), as the ratio of mean crushing load to peak load, was carried out by nonlinear finite element analysis through LS-DYNA. Based on single-objective and multi-objective optimizations, it was found that octagonal and 12-edge sections had the best crashworthiness performance in terms of maximum SEA and CFE.     

Quasi-static axial compression of concentric expanded metal tubes

Previous studies have demonstrated that the failure mechanism and energy absorption capacity of expanded metal tubes strongly depends on the orientation of the cells. This paper presents an experimental investigation on the collapse of concentric expanded metal tubes subjected to quasi-static axial compression. Square tubes with two different cell orientations are tested to failure, and the energy absorption characteristics are calculated. The results show that the combination of cell geometries lead to a complex buckling mode interaction, which enhances the energy absorption capacity of expanded metal tubes.     

某微车正面碰撞模拟仿真与优化

近几年我国微型客车行业得到了很大发展,随着我国正面碰撞法规—CMVDR的颁布,为了通过法规规定,各个车企纷纷加大研发力度。微型客车的发展不仅仅是数量的增加,更应该把重点放在提高汽车的安全性能方面,尤其是放在提高微型客车的正面碰撞安全性能。在此背景下,对国内某款微型客车为研究对象,对其与正面刚性墙碰撞的过程进行了有限元模拟仿真。通过对比计算机模拟结果与实车试验结果,验证此模型准确性,同时针对车身薄弱环节提出改进方案,并且进行前后方案对比,最终确定改进方案。     

Comparisons of honeycomb sandwich and foam-filled cylindrical columns under axial crushing loads

For the conventional thin-walled energy absorber, the energy dissipation during a collision is concentrated in relatively narrow zones. This means that a great deal of material does not participate in the plastic deformation or enter the large plastic deformation stage. To expand the plastic deformation zones and improve the energy absorption efficiency, the authors presented a new type of honeycomb sandwich circular column. This innovative energy absorber is a composite structure composed of two circular aluminum tubes filled with core shaped as a large-cell honeycomb lattice. In this paper, six different honeycomb sandwich circular columns were investigated numerically. Comparisons of the interaction effect between tubes and filler, the deformation modes and the energy absorption abilities of these columns were conducted. The results were as following. The kagome sandwich column had the best energy absorption capability, followed by the columns sandwiched with triangle, hexagon lattices. In addition, foam-filled columns with different adhesive conditions were also simulated and compared with the honeycomb sandwich columns. It was found that increasing the adhesive strength improved the energy absorption and changed the deformation mode of the foam-filled columns. Furthermore, comparison showed that the honeycomb sandwich columns had higher specific energy absorption capability than the foam-filled tubes except for the strong bonded case. The kagome sandwich column performed best in crashworthiness, followed by triangle sandwich column.     

Identification of a new failure criterion for toughened epoxy adhesive

The increasing use of structural adhesive in industry leads to the need of a detailed failure criterion. In this paper, a structural adhesive especially designed for automotive crashworthiness applications named BETAMATE 1496V™ is studied. The authors propose a new failure criterion based on an equivalent failure strain which evolves with the triaxiality stress ratio and the strain rate. This criterion is identified by means of new measurement techniques on a large range of strain rates and for different loadings like tensile, shear and compressive.     

Aortic injuries in newer vehicles

The occurrence of AI was studied in relation to vehicle model year (MY) among front seat vehicular occupants, age ≥ 16 in vehicles MY ≥ 1994, entered in the National Automotive Sampling System Crashworthiness Data System between 1997 and 2010 to determine whether newer vehicles, due to their crashworthiness improvements, are linked to a lower risk of aortic injuries (AI). MY was categorized as 1994–1997, 1998–2004, or 2005–2010 reflecting the introduction of newer occupant protection technology. Logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals for the association between AI and MY independent of possible confounders. Analysis was repeated, stratified by frontal and near lateral impacts. AI occurred in 19,187 (0.06%) of the 31,221,007 (weighted) cases, and contributed to 11% of all deaths. AIs were associated with advanced age, male gender, high BMI, near-side impact, rollover, ejection, collision against a fixed object, high ΔV, vehicle mismatch, unrestrained status, and forward track position. Among frontal crashes, MY 98–04 and MY 05–10 showed increased adjusted odds of AI when compared to MY 94–97 [OR 1.84 (1.02–3.32) and 1.99 (0.93–4.26), respectively]. In contrast, among near-side impact crashes, MY 98–04 and MY 05–10 showed decreased adjusted odds of AI [OR 0.50 (0.25–0.99) and 0.27 (0.06–1.31), respectively]. While occupants of newer vehicles experience lower odds of AI in near side impact crashes, a higher AI risk is present in frontal crashes.     

Crashworthiness of straight section hydroformed aluminium tubes

There exists considerable motivation to reduce vehicle weight through the adoption of lightweight materials, such as aluminium alloys, while maintaining energy absorption and component integrity under crash conditions. The interaction between tube hydroforming and behaviour during crash events was studied using lightweight automotive structural members. Dynamic crush tests were performed on 400 mm length sections of both non-hydroformed and hydroformed EN-AW 5018 aluminium alloy tubes. The force versus crush distance data from 76.2 mm diameter non-hydroformed tubes was compared with results from 76.2 mm square cross-section hydroformed tubes of 2.0 and 3.5 mm initial tube thicknesses. The hydroforming operation was performed using a high-pressure process in which the corner radius of the tube cross-section was varied. 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 the tube thickness, work hardening, residual stress, and damage level at the end of the hydroforming simulation were used as the initial state for the crash model. The Gurson–Tvergaard–Needleman constitutive model was used to account for damage based on void nucleation, growth, and coalescence. Numerical predictions of the force versus crush distance response were compared to experimental data. The results have demonstrated that it is important to account for thickness changes and work hardening from previous forming operations, in simulating crash events. The energy absorbing capabilities of the hydroformed aluminium tubes decreased with sharper corner radius due to increased thinning of the material during the hydroforming process. It was found that the simulations slightly over-predicted the mean crush force compared to the experimental data.     

Closed form implementation of an N-point unequally spaced approximation of vehicle shortening applied to various force-shortening models

Force-shortening models have been ubiquitously utilized for the quantification of dissipated energy for motor vehicles involved in real world collisions. Inherent in the use of force-shortening models is the necessity for modeling of the shortening geometry. The methodologies presented in the subject study increase the utility of force-shortening models beyond the traditional three, four or six-point equally spaced approximations and the recently published N-point equally spaced approximation of a continuum motor vehicle shortening profile. Closed form solutions for the four most commonly utilized force-shortening models incorporating an N-point unequally spaced linearly interpolated model of the shortening geometry are provided. The specific solutions for the three, four and six point models are also presented.