Abstract Introducing crack-like notches is essential for investigating the mechanical properties of pre-cracked structures because fatigue pre-cracking occasionally fails to ensure some rigorous investigation conditions. However, the results obtained by previous studies related to crack-like notches under small-scale yielding are invalid for shallow notches with extensive plasticity, particularly when plastic instability instead of unstable crack propagation governs the structural strength. This study focused on the plastic instability occurring under the plane strain condition without the assistance of pre-crack propagation. The boundary condition, geometric configuration, and elastoplastic fields dominating the overall work hardening in notched and cracked cross-sections were considered in finite element analyses. From the perspective of asymptotic and phenomenological analysis, this study proposes that a shallow crack-like notch should satisfy the following requirements: (1) the structural strength should be independent of the notch geometry, except for the notch depth; (2) the elastoplastic fields in the notched cross-section should be broadly convergent to those in the pre-cracked cross-section; (3) the failure mode characterized by damage pattern should be similar. The underlying reason for crack-like notches existing in extensive plasticity is that different elastoplastic field gradients close to the notch root or crack tip may still result in the same overall work hardening in notched and pre-cracked cross-sections. This concept was experimentally verified using interstitial-free steel, which is a typical strain-hardening ferrite steel with excellent ductility and simple metallurgical microstructure. The generality of the identification method and the significance of influential factors for shallow crack-like notches are discussed in this study.

中文翻译：

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塑性失稳引起的结构破坏中浅缺口与浅裂纹的等效性

摘要 引入类裂纹缺口对于研究预开裂结构的力学性能是必不可少的，因为疲劳预开裂有时无法确保一些严格的研究条件。然而，先前关于小尺度屈服下裂纹状缺口的研究结果对于具有广泛塑性的浅缺口是无效的，特别是当塑性不稳定而不是不稳定的裂纹扩展控制结构强度时。本研究侧重于在没有预裂纹扩展帮助的情况下在平面应变条件下发生的塑性不稳定性。在有限元分析中考虑了边界条件、几何构型和弹塑性场，这些场在缺口和有裂纹的横截面中主导整体加工硬化。本研究从渐近和唯象分析的角度，提出浅裂纹状缺口应满足以下要求：（1）结构强度应与缺口几何形状无关，缺口深度除外；(2) 缺口截面的弹塑性场应与预开裂截面的弹塑性场大致收敛；(3)以损伤模式为特征的失效模式应相似。裂纹状缺口存在于广泛塑性中的根本原因是缺口根部或裂纹尖端附近的不同弹塑性场梯度仍可能导致缺口和预裂纹横截面中相同的整体加工硬化。使用无间隙钢对这一概念进行了实验验证，是一种典型的应变硬化铁素体钢，具有优良的延展性和简单的金相组织。讨论了浅裂纹状缺口识别方法的通用性和影响因素的意义。