Crack initiation emerges due to a combination of elasticity, plasticity, and disorder, and it displays strong dependence on the material’s microstructural details. The characterization of the structural uncertainty in the original microstructure is typically empirical and systematic characterization protocols are lacking. In this paper, we propose an investigational tool in the form of the curvature of an ellipsoidal notch: As the radius of curvature at the notch increases, there is a dynamic phase transition from notch-induced crack initiation to disorder-induced crack nucleation. We argue that the this transition may unveil the characteristic length scale of structural disorder in the material. We investigate brittle but elastoplastic metals with continuum, microstructural disorder that could originate in a manufacturing process, such as alloying. We perform extensive and realistic simulations, using a phase-field approach coupled to crystal plasticity, where microstructural disorder and notch width are systematically varied. We identify the brittle-to-quasi-brittle transition for various disorder strengths in terms of the damage and stress evolution. Moreover, we investigate precursors to crack initiation that we quantify in terms of the expected stress drops during displacement control loading.

中文翻译：

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具有结构不均匀性的晶体中的脆性至准脆性转变和裂纹萌生前体

裂纹萌生是由于弹性，可塑性和无序性的结合而出现的，并且显示出对材料微观结构细节的强烈依赖。原始微观结构中结构不确定性的表征通常是经验性的，缺乏系统的表征方案。在本文中，我们提出了一种椭圆形缺口的曲率形式的研究工具：随着缺口的曲率半径的增加，从缺口引起的裂纹萌生到无序诱发的裂纹成核有一个动态的相变。我们认为这种转变可能揭示了材料中结构无序的特征长度尺度。我们研究了具有连续性，微观结构异常的易碎但具有弹塑性的金属，这些金属可能源自制造过程，例如合金化。我们使用与晶体可塑性相耦合的相场方法进行了广泛而逼真的模拟，其中微观结构无序和缺口宽度系统地变化。我们从损伤和应力演化的角度确定了各种无序强度的脆性到准脆性转变。此外，我们研究了裂纹萌生的前兆，我们根据位移控制载荷期间的预期应力降对其进行了量化。