45钢柱壳爆炸膨胀断裂的SPH模拟分析

金属柱壳爆炸膨胀断裂存在拉伸、剪切及拉剪混合等多种断裂模式，目前其物理机制及影响因素还不清晰。本文中采用光滑粒子流体动力学方法（smoothed particle hydrodynamics， SPH）对45钢柱壳在JOB-9003及RHT-901不同装药条件下的外爆实验进行了数值模拟，探讨柱壳在不同装药条件下发生的剪切断裂、拉剪混合断裂模式及其演化过程，模拟结果与实验结果一致。SPH数值模拟结果表明:在爆炸加载阶段，随着冲击波在柱壳内、外壁间来回反射形成二次塑性区，沿柱壳壁厚等效塑性应变演化呈凸形分布，壁厚中部区域等效塑性应变较内、外壁大；在较高爆炸压力（JOB-9003）作用下，柱壳断裂发生在爆轰波加载阶段，损伤裂纹从塑性应变积累较大的壁厚中部开始沿剪切方向向内、外壁扩展，形成剪切型断裂模式；而在RHT-901空心炸药加载下，虽然裂纹仍从壁厚中部开始沿剪切方向扩展，但随后柱壳进入自由膨胀阶段，未断区域处于拉伸应力状态，柱壳局部发生结构失稳，形成类似“颈缩”现象，裂纹从剪切方向转向沿颈缩区向外扩展，呈现拉剪混合断裂模式。拉伸裂纹占截面的比例与柱壳结构失稳时刻相关。可见，柱壳断裂演化是一个爆炸冲击波与柱壳结构相互作用的过程，不能简单将其作为一系列膨胀拉伸环处理。

An investigating on explosive expanding fracture of 45 steel cylinders by SPH method

The expanding fracture of ductile alloy cylinder subject to the explosion includes multiple fracture modes, such as tensile, shear, and mixed tensile-shear fracture. The mechanism and the factors influencing the fracture processes are still enigmatic and far from understood. In this paper, the smoothed particle hydrodynamics (SPH) method is used to simulate the explosion experiment of 45 steel cylinders shell with different charges of JOB-9003 and RHT-901. The shear fracture, tension-shear mixed fracture modes and the evolution process of cylindrical shell with different charges are discussed. The simulation results are consistent with the experimental trend. The SPH results show that due to the propagation and reflection of shock wave between the inner and outer surfaces of cylinder during the loading stage of detonation wave, the distribution of equivalent plastic strain on wall-thickness of the cylinder is a convex shape, i.e. the strain in the middle of wall-thickness is larger than that of in the inner and outer walls; when loading by a higher explosive pressure (JOB-9003), the fracture cracks initiate from the middle of wall-thickness, and then develop to the inner and outer walls along the direction of maximum shear in loading stage, showingthe shear fracture mode. However, under the loading caused by charge RHT-901 with relatively low pressure, although the crack still starts from the middle of wall-thickness and propagates along the shear direction, the shear crack could not grow through the section of the wall completely in the loading stage; then the cylinder experiences the stage of free expansion, the stress state of unbroken zone changes into triaxial tensile stress state and the structural instability, similar to “necking” occurs in the unbroken zone. Consequently, the cracks turn from the shear direction to the necking zone along the radial direction, showing the mixed tensile-shear fracture mode. The proportion of tension and shear cracks is related to the occurrence time of structural instability. The results show that the explosion expanding-fracture process of a metal cylinders involves the interaction between shock wave and cylinder structure, and cannot be treated as that of a series of expansion rings.