ABSTRACT Void nucleation, growth and coalescence have been identified as the leading cause of ductile damage in metallic materials. To understand the underlying deformation and damage mechanisms, extensive theoretical, experimental and simulation efforts have been attempted on spherically voided metals. In this work, molecular dynamics simulations are performed to analyze the uniaxial straining deformation behaviours of both single-crystal and nanotwinned copper materials embedded with a preexisting spheroidal void. The coupling effects among twin boundary, spheroidal void aspect ratio and orientation on unidirectional elastoplastic behaviours are systematically examined. The dislocation-induced plastic deformation mechanism is also examined and compared with the one due to a perfectly spherical cavity. Simulation results show that elastic modulus increases with both spheroidal void aspect ratio and orientation. So do the yield stress, the first peak stress and the plasticity index. Another peak stress exists for most cases, except for a prolate void embedded in nanotwinned specimens. The slope between peak stresses decreases with both the spheroidal aspect ratio and orientation. The incorporation of a twin boundary results in lower elastic modulus, higher yield strength and smaller plasticity index. For an oblate void, the twin boundary gives rise to more severe strain softening behaviour. The dislocation extraction algorithm illustrates that the continuous nucleation, propagation and reaction of dislocations emanated from both the void front and twin boundary are responsible for the ductile damage of spheroidally voided crystals. The lower dislocation densities found in nanotwinned specimens indicate the desired suppression effects of twin boundary on dislocation activities.

中文翻译：

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空隙形状和取向对球状空隙单晶和纳米孪晶铜弹塑性的影响

摘要 空隙成核、生长和聚结已被确定为金属材料延性损伤的主要原因。为了理解潜在的变形和损伤机制，已经对球形空隙金属进行了大量的理论、实验和模拟工作。在这项工作中，进行了分子动力学模拟以分析嵌入预先存在的球状空隙的单晶和纳米孪晶铜材料的单轴应变变形行为。系统地研究了孪晶边界、球体空隙纵横比和取向对单向弹塑性行为的耦合效应。还检查了位错引起的塑性变形机制，并将其与完美球形腔引起的塑性变形机制进行了比较。模拟结果表明，弹性模量随着球状空隙纵横比和取向而增加。屈服应力、第一个峰值应力和塑性指数也是如此。大多数情况下存在另一个峰值应力，除了嵌入在纳米孪晶样本中的长条形空隙。峰值应力之间的斜率随着球体纵横比和取向而减小。双边界的结合导致较低的弹性模量、较高的屈服强度和较小的塑性指数。对于扁圆孔，孪晶边界会产生更严重的应变软化行为。位错提取算法表明，从空隙前沿和孪晶边界发出的位错的连续成核、传播和反应是造成球状空隙晶体韧性损伤的原因。