The Effects of Nanostructure upon the Dynamic Ductile Fracture of High Purity Copper
The Effects of Nanostructure upon the Dynamic Ductile Fracture of High Purity Copper
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DOI：
10.1016/j.proeng.2017.08.078
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
Sarah Ward;C. Braithwaite;A. Jardine
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文献类型：
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作者：
Sarah Ward;C. Braithwaite;A. Jardine
动态断裂是一个非常重要的物理过程。然而，材料的纳米结构，包括晶格和晶粒结构，以及它们各自的缺陷，对这些事件的影响还没有很好的理解。韧性断裂被广泛认为是通过孔洞的成核、生长和合并而形成失效面。在晶界处形成空隙，并且在这些空隙的中心经常发现杂质和第二相颗粒，这表明它们参与成核过程。在不存在杂质的纯金属中，空穴成核过程尚不清楚，尽管理论表明位错及其亚结构的重要性。位错参数的基础上的塑性行为的相关材料，这往往是高度应变率相关的，在铜的情况下，也是历史dependent.Here，我们描述的实验，研究环断裂OFHC铜，在应变率约104 s-1。诊断包括高速摄影、激光测速和碎片的软捕获。观察到断裂处的碎片和应变的数量随着施加的应变速率而增加，这表明延展性随着速率而增加。在施加载荷期间，由于环与驱动器圆柱体的相互作用，碎片的横截面发生了显著变化，这表明存在强烈的三轴应力状态，其中应变率可能高于根据激光测速数据的周向膨胀估计的应变率。断裂表面显示宏观尺度的表面拓扑结构，并显示出几种不同的断裂机制的证据，在整个故障平面。断裂表面的长度尺度为数十微米及以下的量级，这表明低于材料晶粒尺寸的结构主导所观察到的行为。
Dynamic fracture is a fundamentally important physical process. However, the effect of material nanostructure, including both lattice and grain structure, and their respective defects, on such events is not well understood. Ductile fracture is widely accepted to proceed through the nucleation, growth and coalescence of voids to form a failure plane. The formation of voids at grain boundaries is established, and impurities and secondary phase particles are often found at the centre of these voids suggesting their involvement in the nucleation process. In a pure metal, where impurities are absent, the void nucleation process is unclear, although theories suggest the importance of dislocations and their substructures. Dislocation parameters are underpinned by the plasticity behaviour of the relevant material, which is often highly strain rate dependent, and in the case of copper, is also history dependent.Here, we describe experiments that study the ring fragmentation of OFHC copper, at strain rates around 104s-1. Diagnostics include high speed photography, laser velocimetry, and soft capture of fragments. The number of fragments and strain at fracture was observed to increase with the applied strain rate, suggesting an increase in ductility with rate. The cross-section of the fragments changed significantly during the applied loading, due to interaction of the ring with the driver cylinder, suggesting a strongly tri-axial stress state, where the strain rate is likely to be higher than that which was estimated, based on circumferential expansion from laser velocimetry data. The fracture surfaces displayed macroscale surface topology, and showed evidence of several different fracture mechanisms across the failure plane. The length scales of the fracture surfaces were to the order of tens of microns, and below, suggesting that structures below the grain size of the material are dominating the observed behaviour.