汽车碰撞砼护拦过程的数值模拟

将汽车与砼护拦简化为刚体，给出了描述碰撞过程中车辆三维空间运动的Ｅｕｌｅｒ－Ｌａｇｒａｎｇｅ方程－微分代数方程组，采用半显式外插方法求解上述方程组。数值计算得出的车辆各方向上的最大平均加速度、最大侧倾角、最大俯仰角、车轮沿护拦面的最大爬升值及车辆脱离护拦时的弹出角等结果是从乘员风险和车辆轨迹等多角全面评估砼护拦的安全性能的重要依据。针对美国ＮｅｗＪｅｒｃｙ型砼护拦的实际算例与文献结果吻合较好。     

POST-BUCKLING AND IMPERFECTION SENSITIVITY OF A COLUMN WITH AN EQUILATERAL TRIANGULAR CROSS-SECTION IN THE PLASTIC RANGE

The asymmetric initial post-buckling corresponding to the lowest bifurcation load andthe imperfection sensitivity are analysed in detail for a compressed simply supported column with anequilateral triangular cross-section in the plastic range.The effect of elastic unloading is taken into ac-count in the analysis.The asymptotic relations,including high order terms,among the load,the am-plitude of imperfection and the amplitude of the bifurcation mode are realized.The results show thatthe maximum supported load is very sensitive to imperfection.     

玻璃纤维增强聚氨酯泡沫塑料的压缩力学性能研究

本文研究了两种不同密度的玻璃纤维增强聚氨酯泡沫塑料在准静态压缩下的力学性能。给出了与相应密度的普通泡沫塑料力学性能的比较，实验结果表明：两种增强泡沫塑料在压缩载荷作用下，具有不同于普通泡沫塑料的应力－应变特性，压缩模量和强度一般均有不同程度的提高，而且对相同纤维含量的增强泡沫塑料来说，密度较高的材料增强效果较好。     

混凝土层裂强度测量的新方法

提出了利用Hopkionson压杆测量混凝土层裂强度的新实验方法:用高聚物材料取代传统的金属材料透射杆,混凝土试件为细长杆,由于高聚物波阻抗比混凝土小,试件中压缩波在试件/吸收杆界面反射后形成拉伸波使试件产生层裂破坏,通过吸收杆上透射波形可以确定混凝土层裂强度。由于波在粘弹性材料中的弥散效应,吸收杆中透射波形会发生变化,但三维有限元分析表明,在利用吸收杆上透射波确定混凝土层裂强度时弥散产生的影响可以忽略。按照一维特征线理论,可以由吸收杆上的应变波形确定出混凝土材料的层裂强度。     

On the Lagrange problem about the optimal form for circular hollow columnsSur le problème de Lagrange de la forme optimale d'une colonne circulaire aux parois minces

A new approach to the problem of finding the form of the strongest clamped circular column with thin walls of fixed volume and height is proposed. The same model describes also the form of the horizontal beam with rectangular vertical sections of a fixed height and variable widths. The existence and the uniqueness of the optimal column are proved here for the first time and the optimal form is found. To cite this article: Yu.V. Egorov, C. R. Mecanique 331 (2003).     

Disk-shaped compact tension test for asphalt concrete fracture

A disk-shaped compact tension (DC(T)) test has been developed as a practical method for obtaining the fracture energy of asphalt concrete. The main purpose of the development of this specimen geometry is the ability to test cylindrical cores obtained from in-place asphalt concrete pavements or gyratory-compacted specimens fabricated during the mixture design process. A suitable specimen geometry was developed using the ASTM E399 standard for compact tension testing of metals as a starting point. After finalizing the specimen geometry, a typical asphalt concrete surface mixture was tested at various temperatures and loading rates to evaluate the proposed DC(T) configuration. The variability of the fracture energy obtained from the DC(T) geometry was found to be comparable with the variability associated with other fracture tests for asphalt concrete. The ability of the test to detect changes in the fracture energy with the various testing conditions (temperature and loading rate) was the benchmark for determining the potential of using the DC(T) geometry. The test has the capability to capture the transition of asphalt concrete from a brittle material at low temperatures to a more ductile material at higher temperatures. Because testing was conducted on ungrooved specimens, special care was taken to quantify deviations of the crack path from the pure mode I crack path. An analysis of variance of test data revealed that the prototype DC(T) can detect statistical differences in fracture energy resulting for tests conducted across a useful range of test temperatures and loading rates. This specific analysis also indicated that fracture energy is not correlated to crack deviation angle. This paper also provides an overview of ongoing work integrating experimental results and observations with numerical analysis by means of a cohesive zone model tailored for asphalt concrete fracture behavior.     

混凝土单轴受拉的非局部本构模型

混凝土受拉本构行为存在很强的局部软化现象,使得单轴受拉试验无法给出应力-应变关系,而只能给出应力-位移关系。本文根据内变量理论和等效应变假设建立了基于真实应变的混凝土单轴受力本构方程,并根据Weibull分布可以描述混凝土等脆性材料断裂过程的试验现象,建立了关于弹性应变的损伤演化规律。然后,通过假设平均应变与真实弹性应变的函数关系,在应力-平均应变的本构关系中采用平均弹性应变以描述其非局部行为,而在材料的损伤演化规律中采用真实弹性应变以描述其局部行为,由此建立了单轴受拉荷载条件下的非局部本构模型。最后,对一个单调受拉试验和一个反复受拉试验的仿真结果表明所提出的非局部本构模型可以准确地模拟试验结果。     

单向连续竹纤维增强聚合物的拉伸性能

描述了一种单向连续竹纤维增强聚合物试件的制作工艺过程:研究了该型竹纤维增强复合材料的拉伸力学性能。将该性能与单向连续玻璃纤维增强聚合物的拉伸力学性能进行了比较,发现竹纤维增强聚合物的拉伸模量要明显高于玻璃纤维增强聚合物的对应值,而其拉伸强度和玻璃纤维增强聚合物的相当。同时发现竹纤维增强聚合物的纵向延展性较小,呈现一次性单界面脆性断裂状况,相对地,连续玻璃纤维增强聚合物的拉伸断裂是多次多界面分段断裂。     

Numerical simulation: The dynamic behavior of reinforced concrete plates under normal impact

This investigation deals with the use of the finite element method on the reinforced concrete structural dynamic response and failure behavior when subjected to the projectile impacts of different velocities, using the test conducted in [S.J. Hanchak, M.J. Forrestal, E.R. Young, J.Q. Ehrgott, Perforation of concrete slabs with 48 MPa (7 ksi) and 140 MPa (20 ksi) unconfined compressive strengths, Int. J. Impact Eng. 12 (1992) 1–7]. The Johnson–Holmquist concrete material constitutive law model is employed to simulate the large strains, high strain states and high pressures to which the concrete is subjected. The projectile impact velocity ranges from 381 m/s to 1058 m/s. Numerical simulations demonstrate that the Johnson–Holmquist concrete material constitutive model can describe the different failure modes without any predefined defects in the element mesh, and normally obtain good agreement between the numerical simulations and test results.     

土中爆炸冲击混凝土道面的数值模拟

炸药在多相介质中的爆炸是气态爆轰产物和固态介质之间的耦合作用问题，对其进行数值模拟一般不考虑炸药而直接将爆轰压力加在介质上，而耦合方法对炸药和其周围的介质进行离散，炸药和介质采用统一的控制方程，通过界面条件实现相互作用。任意拉格朗日欧拉（Arbitary Lagrangian and Eularian）法，是最近兴起的适用于计算固体大变形问题的数值计算方法。将其引入爆炸力学计算，可以避免由于物质的大变形引起的单元畸变和计算困难。同时混凝土的损伤模型，更加符合混凝土在高应变率加载条件下的力学特性和破坏机理。将这三种方法引入数值模拟，计算结果与相关试验结果有较好的吻合。