Abstract Residual tensile strength (hereinafter abbreviated as ‘residual strength’) is a critical fail-safe consideration but has rarely been reported in the case of shallow pre-cracked structures. When the pre-crack depth is shallower than a critical value, the residual strength of cylindrical specimens made of interstitial-free steel exhibits a plateau identical to the tensile strength of smooth specimens, and with a rupture occurred far away from the pre-cracked cross-section. According to the damage characteristics by microscopic observation and the plastic strain distribution by kernel average misorientation measurement, such a situation exists when the physical meaning of residual strength changes from fracture instability to plastic instability. The corresponding mechanism, with the assistance of finite element analysis, is ascribed to the following: 1. The plastic strain localization induced by shallow cracks preferentially hinders plastic instability in the pre-cracked cross-section rather than promotes fracture instability at the crack tip because the high fracture toughness makes shallow cracks remain non-propagating or stable-propagating at least until plastic instability occurs; 2. Whether a shallow crack strengthens or weakens the pre-cracked cross-section depends on the integrated factors of the effective area of cross-section for bearing load narrowed by the crack depth (negative effect), the strain hardening and damage initiation in near crack-tip region affected by gradient plasticity (positive or negative effect), and uniform plasticity in remote crack-tip region alleviated by plastic strain localized near the crack tip (positive effect). Then, the above features are defined as the ‘shallow crack effect’ in the residual strength issue. To incorporate this problem in design, a residual strength diagram considering physical meanings of residual strength and corresponding damage characteristics is suggested. It helps to estimate the trend of residual strength from the perspective of plastic strain localization. Finally, influential factors on the ‘shallow crack effect’ in the residual strength issue are discussed.

中文翻译：

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浅裂纹对残余抗拉强度评估的影响：由延性金属制成的有限尺寸结构中的无害且稳定的裂纹

摘要 残余抗拉强度（以下简称为“残余强度”）是一个关键的故障安全考虑因素，但在浅层预开裂结构的情况下鲜有报道。当预裂纹深度小于临界值时，由无间隙钢制成的圆柱试样的残余强度与光滑试样的抗拉强度相同，并且断裂发生在远离预裂纹交叉处-部分。根据显微观察的损伤特征和核平均取向误差测量的塑性应变分布，当残余强度的物理意义从断裂不稳定转变为塑性不稳定时，就会出现这种情况。相应的机理，在有限元分析的帮助下，归因于以下几点： 1. 由浅裂纹引起的塑性应变局部化优先阻碍预裂纹截面的塑性失稳，而不是促进裂纹尖端的断裂失稳，因为高断裂韧性使浅裂纹保持不扩展或稳定传播至少直到发生塑性不稳定；2. 浅裂纹对预开裂截面的增强或减弱取决于裂纹深度缩小的承载载荷有效截面面积（负效应）、近处的应变硬化和损伤萌生等综合因素。裂纹尖端区域受梯度塑性影响（正面或负面影响），远程裂纹尖端区域的均匀塑性被裂纹尖端附近的局部塑性应变缓解（正面效果）。然后，上述特征被定义为残余强度问题中的“浅裂纹效应”。为了在设计中解决这个问题，提出了考虑剩余强度物理意义和相应损伤特征的剩余强度图。有助于从塑性应变局部化的角度估计残余强度的趋势。最后，讨论了残余强度问题中“浅裂纹效应”的影响因素。