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.     

顶板垮落诱发瓦斯灾害的理论分析

利用热力学、摩擦学、燃烧学等原理，研究了岩石摩擦、撞击过程中的能量转化关系及岩石表面升温机理，建立了岩石升温的数学模型，分析了引起瓦斯燃烧的条件，得出了岩石摩擦、撞击过程中引起表面升温的主要因素为岩石相互作用的摩擦生热、岩石变形引起的应变能升温和岩石破坏释放能量升温．研究表明：岩石碰撞升温通过热对流作用引起周围瓦斯-空气混合气体的温度升高，如果瓦斯-空气混合气体原始温度上升到瓦斯着火温度，时间大于瓦斯爆炸的感应期，就会引燃引爆瓦斯．     

空难的应急处置及伤员急救

本文根据空难中机场相关单位与航空公司的应急处置及驻地医院对伤者的急救及部分伤员的临床资料进行了较完整的初步分析,并针对诸如航空公司运控系统、机场指挥中心、急诊医院医护人员的明确分工等问题展开讨论。充分认为：对出现空难后,对大批空难伤员,现场的应急救援争分夺秒、行之有效的救援工作十分重要,同时可为后续的治疗赢得时机,并对提高多发性创伤救治成功率具有极其重大的作用。     

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.     

竹增强环氧乙烯基树脂的制备及性能研究

和传统的钢护拦相比较,竹片增强复合材料护拦具有重量轻、成本低、耐腐蚀、环境友善和可再生性等优点。但是竹纤维表面的复杂成分,影响了复合材料的界面性能。本文利用竹片作为增强材料,采用真空辅助成型方法制备了竹片增强环氧乙烯基树脂复合材料,研究了表面改性和铺层数对竹复合材料弯曲强度和冲击韧性的影响,并对单向复合材料的冲击断面破坏方式进行了分析。结果表明,在不同铺层结构条件下,用经过碱与硅烷偶联剂改性处理过的竹条制备的复合材料的弯曲强度分别提高了31.95%、46.72%、29.58%,冲击韧性分别提高了25.62%、29.74%、28.61%,而且单向复合材料的弯曲和冲击性能最佳。当单向复合材料中的竹片铺层为15层时,其冲击吸收功为13.55J,拉伸强度为270MPa,弯曲强度为340MPa,在主要性能上能满足公路防撞护栏对其原料Q-235B钢的要求;通过扫描电镜分析发现,竹片增强复合材料防撞护栏材料的防撞机理表现为竹纤维抽拔断裂、基体断裂、纤维/基体界面脱黏以及剪切分层。本文的结果对复合材料公路防撞护栏的制备有一定的指导作用。     

Investigating driver injury severity patterns in rollover crashes using support vector machine models

Rollover crash is one of the major types of traffic crashes that induce fatal injuries. It is important to investigate the factors that affect rollover crashes and their influence on driver injury severity outcomes. This study employs support vector machine (SVM) models to investigate driver injury severity patterns in rollover crashes based on two-year crash data gathered in New Mexico. The impacts of various explanatory variables are examined in terms of crash and environmental information, vehicle features, and driver demographics and behavior characteristics. A classification and regression tree (CART) model is utilized to identify significant variables and SVM models with polynomial and Gaussian radius basis function (RBF) kernels are used for model performance evaluation. It is shown that the SVM models produce reasonable prediction performance and the polynomial kernel outperforms the Gaussian RBF kernel. Variable impact analysis reveals that factors including comfortable driving environment conditions, driver alcohol or drug involvement, seatbelt use, number of travel lanes, driver demographic features, maximum vehicle damages in crashes, crash time, and crash location are significantly associated with driver incapacitating injuries and fatalities. These findings provide insights for better understanding rollover crash causes and the impacts of various explanatory factors on driver injury severity patterns.     

基于碰撞安全性的泡沫铝填充矿用救生舱优化及性能分析

为提高矿用救生舱的碰撞安全性,设计一种泡沫铝填充矿用救生舱。利用ANSYS Workbench的参数优化模块,以舱体的加速度、变形及吸能大小为优化目标,对舱体的结构参数和泡沫铝的材料性能参数进行优化。对优化后的泡沫铝救生舱的碰撞安全性进行分析,结果表明泡沫铝救生舱在质量和最大等效应力均有所降低的前提下,泡沫铝救生舱碰撞时的最大变形和最大加速度得到显著降低并且舱体吸收的能量得到大幅提升,证明泡沫铝填充救生舱具有更佳的碰撞性能可以提高其安全性。     

热成型技术在提高汽车偏置碰性能中的应用

为了提高某车型的偏置碰性能,采用LS-DYNA分析软件,对该车型偏置碰性能进行仿真优化。在保证周边车身零件的搭接关系不变的前提下,在前纵梁Kickdown区域使用热成型板。结果显示:前隔板侵入量减小,保证了车内乘员在偏置碰中的生存空间,提高了车身偏置碰安全性能。     

Evaluation of the predictability of real-time crash risk models

The primary objective of the present study was to investigate the predictability of crash risk models that were developed using high-resolution real-time traffic data. More specifically the present study sought answers to the following questions: (a) how to evaluate the predictability of a real-time crash risk model; and (b) how to improve the predictability of a real-time crash risk model. The predictability is defined as the crash probability given the crash precursor identified by the crash risk model. An equation was derived based on the Bayes’ theorem for estimating approximately the predictability of crash risk models. The estimated predictability was then used to quantitatively evaluate the effects of the threshold of crash precursors, the matched and unmatched case-control design, and the control-to-case ratio on the predictability of crash risk models. It was found that: (a) the predictability of a crash risk model can be measured as the product of prior crash probability and the ratio between sensitivity and false alarm rate; (b) there is a trade-off between the predictability and sensitivity of a real-time crash risk model; (c) for a given level of sensitivity, the predictability of the crash risk model that is developed using the unmatched case-controlled sample is always better than that of the model developed using the matched case-controlled sample; and (d) when the control-to-case ratio is beyond 4:1, the increase in control-to-case ratio does not lead to clear improvements in predictability.