A Proposal of the Crack Tip Opening Displacement Calculation Formula and Its Conversion Factor to J-Integral in C(T) Specimens

Abstract

The crack tip opening displacement (CTOD) concept describing cleavage embrittlement failure proposed by Wells is an important technology supporting the reliability of steel structures around the world. In 2002, ASTM E1290, Standard Test Method for Crack-Tip Opening Displacement (CTOD) Fracture Toughness Measurement, proposed a CTOD calculation formula based on a J-integral different from the previous integral that reflected the work-hardening characteristics and was triggered by the appearance of a case where evaluation values significantly different from the conventional British Standard (BS) formula are given. The authors attempted to construct an accurate CTOD calculation formula by performing actual measurements in CTOD experiments and systematic numerical analyses. Detailed observation of the plastic deformation mode in the ligament demonstrates the validity of the plastic hinge model that BS has adopted to date. In 2016, it was possible to propose a highly accurate formula that considers the work-hardening characteristics for edge-cracked bending test piece specimens and is adopted into the Japanese and ISO standard. Here, the outline of the CTOD calculation formula for the compact specimen (denoted as C(T)) constructed in the same manner will be described. The authors also suggested that the CTOD and J-integral conversion factor can be expressed in a simpler form than the form indicated by ASTM E1820, Test Method for Measurement of Fracture Toughness. In this study, we discovered that the same conversion factor can be applied to a compact specimen, which is quite reasonable considering the energy release rate of the J value.