Development of simplified evaluation method of brittle crack arrest toughness on small-scale bending test in steels

摘要

The priority items in the safety evaluation of steel structural components generally include an ability to arrest crack propagation, which is necessary to prevent a catastrophic failure even if a brittle fracture occurs. The 'double integrity' concept of brittle crack initiation control and arrest has been considered to be an effective and rational methodology for several decades. The wide plate tensile test such as ESSO test is one of the major methods for evaluating brittle crack arrest toughness of steel plates. Although ESSO test makes it possible to accurately evaluate arrest toughness which indicates the Arrhenius type temperature dependence, it is not suitable for quality assurance test at mass production of steel plates due to its high economical cost and long lead-time. Thus, a number of studies has attempted to establish simplified evaluation method of brittle crack arrest toughness for many years. Generally, bending test is certainly one of the most hopeful methods since it does not require a relatively high test load. However, the phenomenon that brittle crack propagates at extremely high speed in bending condition becomes highly complicated. When brittle crack propagates at almost the same speed as stress wave in bending condition, stress distribution is the middle of the initial state and fully reallocated state by the static equilibrium. It is not easy to make out the detail only by theoretical consideration. In this study, by performing the dynamic elasto-plastic FEA in various test designs based on SEN(B) test, the authors calculated the stress distribution at the crack tip and developed a new test design suitable for evaluating arrest toughness. Moreover, the authors investigated the correlation between the result of ESSO tests and that of the developed tests and presented its applicability.