This paper investigates void growth and coalescence in porous ductile solids under dynamic loading condition. A physical definition for the onset of void coalescence in porous ductile solids under dynamic loading is proposed. The onset is deemed to occur when the third invariant of the tensorial form of the Hill–Mandel condition attains a zero value. The definition allows for systematic investigations on the effects of dimensionless stress rate and stress state, defined by the stress triaxiality and Lode parameter , on the onset of void coalescence micromechanical analyses. The analyses reveal that the critical macroscopic effective strain for the onset of void coalescence displays an increasing–decreasing transition trend as the dimensionless stress rate increases, for all levels of and considered. The macroscopic effective strain at the transition is identified as the “ductile–brittle” transition strain. The dimensionless stress rate at which the transition strain occurs is found to be relatively constant. A mapping in the space for , representative of a generalized uniaxial tension typical in spall fracture experiments, is established which depicts regions where coalescence and non-coalescence can take place, as well as the ductile–brittle regions demarcated by a ductile–brittle transition curve. The results also show that the critical void volume fraction and macroscopic effective strain at the onset of void coalescence are insensitive to inertia at high stress triaxialities at .

中文翻译：

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多孔延性固体中动态空洞聚结的开始


本文研究了动态加载条件下多孔延性固体中的孔隙增长和聚结。提出了动态载荷下多孔延性固体中空洞聚结开始的物理定义。当希尔-曼德尔条件的张量形式的第三个不变量达到零值时，就认为发生了这种情况。该定义允许系统研究无量纲应力率和应力状态（由应力三轴性和 Lode 参数定义）对空洞聚结微机械分析开始的影响。分析表明，对于所有水平和考虑的情况，随着无量纲应力率的增加，空隙合并开始的临界宏观有效应变呈现出增加-减少的转变趋势。转变处的宏观有效应变被确定为“延性-脆性”转变应变。发现发生转变应变的无量纲应力速率是相对恒定的。建立了空间中的映射，代表散裂断裂实验中典型的广义单轴张力，它描绘了可以发生聚结和非聚结的区域，以及由延性-脆性转变曲线划分的延性-脆性区域。结果还表明，空隙合并开始时的临界空隙体积分数和宏观有效应变对高应力三轴度下的惯性不敏感。