中文摘要：

为了讨论率敏感材料软钢钢梁受矩形脉冲载荷作用下的动力响应问题，通过直接离散有限变形弹塑性连续体最小加速度原理中的Lee泛函得到基本控制方程，并将包含应变率的Cowper-Symonds方程嵌入应力-应变关系方程，使该计算模型计及材料的应变率效应，因而能够准确描述钢梁受爆炸和冲击载荷作用下的动力响应问题。该计算模型的有效性通过与通用有限元程序ABAQUS比较而得到了验证，并进一步与已有的刚塑性解做了对比。利用该计算模型进行数值计算，分析了均布和集中脉冲载荷作用下钢梁动力响应的应变率效应，结果发现对于钢梁存在新的异常行为响应模式，应变率导致异常区域偏移和扩大，已有的刚塑性解在一定载荷强度范围内不能准确预报钢梁的实际位移。

英文摘要：

In order to better understand the dynamic behavior of rate sensitive material and structure, a computational model for the dynamic response analysis of a mild steel beam subjected to square pulse loading is presented, which is derived through discretizing directly the Lee functional to be applied in the minimum principle of acceleration of elastic-plastic continua at finite deformation. Since the strain rate dependent Cowper-Symonds equation is integrated into stress-strain relation equations, the effects of strain rate could be taken into account, and the dynamic response of steel beam under explosion and impact load could be predicted accurately. The validity of the model is verified by simulated results from the general-purpose finite element program ABAQUS and further compared with the rigid-plastic solutions. Based on numerical simulation of this model, the effect of strain rate on dynamic response of steel beam under uniformly distributing and concentrate pulse loads is discussed in detail. The nu- merical results show that there is a novel response mode of abnormal behavior of the steel beams, the abnormal window is shifted and enlarged, and the actual permanent deflection of steel beam cannot be predicted by previous rigid-plastic model in certain range of load magnitude.