冲击加载下样品软回收过程中的侧向稀疏效应

通过数值模拟, 计算冲击加载下样品经历一维应变加载过程和侧向稀疏过程产生的塑性功, 给出试样内部从冲击加载开始到进入回收桶前全过程的应力随时间变化的历程。结果表明:侧向稀疏过程开始后，样品在径向汇聚波的作用下受循环拉、压载荷作用，拉压循环的振幅在中等冲击压力下达到最大。如果振幅超过了材料的层裂强度，样品中心将发生拉伸破坏不能完整回收。侧向稀疏与一维应变加载产生的塑性功之比随冲击速度的增加而减小。在冲击速度为某临界值时，侧向稀疏产生的塑性功与一维应变加载产生的塑性功相等。在一定的冲击速度下，采用低初始屈服应力的材料可减轻侧向稀疏效应。对理想塑性材料的理论分析表明，侧向稀疏与一维应变加载产生的塑性功之比随冲击速度与屈服强度比值的增大而减小，与数值模拟结果一致。

Lateral release effect in shock-loaded specimens during soft recovery process

Under shock loading a specimen undergoes a uniaxial-strain loading process and a lateral release process, both of which have an influence on the residual structure, while the influence of the latter is often underestimated or even totally neglected. The plastic work generated in these two processes is calculated in this paper, and the stress history from the beginning of the shock loading to the specimen entering the recovery bin is given. It is found that after the lateral release process begins, the specimen experiences cyclic tension and compression load and the amplitude of the cyclic load reaches its maximum under moderate impact pressure. If the amplitude of the cyclic load is larger than the spall strength, the center of the specimen will be destroyed and the specimen cannot be recovered successfully. The ratio of the plastic work produced during the lateral release to that produced during the uniaxial-strain loading decreases as the impact velocity increases. When the impact velocity reaches a certain critical value, the plastic work produced during the lateral release is equal to that produced during the uniaxial-strain loading. At a certain impact velocity, decreasing the initial yield stress of the materials reduces the lateral release effects. Theoretical analysis of the ideally plastic material shows that the ratio of the plastic work produced during the lateral release to that produced during the uniaxial-strain loading decreases as the ratio of the impact velocity to the yield strength increases, which is consistent with the numerical results.