Similarity between shallow notch and crack effects on structural strength governed by global plastic instability

抄録

Previous conclusions of the crack-like notch in small-scale yielding are invalid for shallow notches with extensive plasticity. This article focused on the global plastic instability that occurs independently under plane strain condition without the assistance of the pre-crack propagation. The boundary condition, geometrical configuration, and elastic-plastic fields that dominate the overall work hardening in notched and cracked cross-sections were considered based on finite element analysis. From the perspective of asymptotic and phenomenological analysis, this article suggested that a crack-like notch should satisfy the following requirements: (1) Structural strength should be independent of notch geometry, except for the notch depth; (2) Elastic-plastic fields in the notched cross-section should be broadly convergent to those in the pre-cracked cross-section; (3) The damage phenomenon should be similar. The underlying reason of crack-like notches existing in extensive plasticity is the gradient distribution of elastic-plastic fields near the notch root or crack tip may result in the same overall work hardening in the notched and pre-cracked cross-sections. This concept was verified on Interstitial-free steel, which is a typical strain hardening ferrite steel with the excellent ductility and the simple metallurgical microstructure. Also, the significance of notch geometrical factors (notch root radius, and opening angle) for shallow crack-like notches was simply discussed.