Department of Mechanical Engineering, TOBB University of Economics and Technology, Söğütözü, Ankara 06560, Turkey
School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
Philos Trans A Math Phys Eng Sci. 2015 Mar 28;373(2038). doi: 10.1098/rsta.2014.0121.
Two modes of plastic flow localization commonly occur in the ductile fracture of structural metals undergoing damage and failure by the mechanism involving void nucleation, growth and coalescence. The first mode consists of a macroscopic localization, usually linked to the softening effect of void nucleation and growth, in either a normal band or a shear band where the thickness of the band is comparable to void spacing. The second mode is coalescence with plastic strain localizing to the ligaments between voids by an internal necking process. The ductility of a material is tied to the strain at macroscopic localization, as this marks the limit of uniform straining at the macroscopic scale. The question addressed is whether macroscopic localization occurs prior to void coalescence or whether the two occur simultaneously. The relation between these two modes of localization is studied quantitatively in this paper using a three-dimensional elastic-plastic computational model representing a doubly periodic array of voids within a band confined between two semi-infinite outer blocks of the same material but without voids. At sufficiently high stress triaxiality, a clear separation exists between the two modes of localization. At lower stress triaxialities, the model predicts that the onset of macroscopic localization and coalescence occur simultaneously.
在通过涉及空穴成核、增长和聚合的机制导致损伤和失效的结构金属的韧性断裂中，通常会出现两种模式的塑性流动局部化。第一种模式由宏观局部化组成，通常与空穴成核和增长的软化效应有关，在正常带或剪切带中，带的厚度与空穴间距相当。第二种模式是通过内部颈缩过程使塑性应变集中在空穴之间的连接带上的聚合。材料的延展性与宏观局部化处的应变有关，因为这标志着宏观尺度上均匀应变的极限。本文研究的问题是宏观局部化是否先于空穴聚合发生，或者两者是否同时发生。本文使用一个三维弹塑性计算模型，通过在两个无空穴的相同材料的半无限外部块体之间的带中代表双周期空穴阵列，对这两种局部化模式之间的关系进行了定量研究。在足够高的三轴应力下，两种局部化模式之间存在明显的分离。在较低的三轴应力度下，模型预测宏观局部化和聚合的开始同时发生。
