Abstract
The improvement in the fracture toughness Jc of a material in the ductile-to-brittle transition temperature region due to compressive residual stress (CRS) was considered in this study. A straightforward fracture prediction was performed for a specimen with mechanical CRS by using the T-scaling method, which was originally proposed to scale the fracture stress distributions between different temperatures. The method was validated for a 780-MPa-class high-strength steel and 0.45% carbon steel. The results showed that the scaled stress distributions at fracture loads without and with CRS are the same, and that Jc improvement was caused by the loss in the one-to-one correspondence between J and the crack-tip stress distribution. The proposed method is advantageous in possibly predicting fracture loads for specimens with CRS by using only the stress–strain relationship, and by performing elastic-plastic finite element analysis, i.e., without performing fracture toughness testing on specimens without CRS.
Highlights
It is well known that some types of preloading improve the apparent fracture toughness of cracked structures
One of the successful approaches for predicting the increase in the fracture toughness of a specimen by using a mechanically introduced compressive residual stress (CRS) is a local approach proposed by Yamashita et al [14]; the local approach [15,16] was originally developed to explain three characteristics exhibited by the cleavage fracture toughness Jc of ferritic materials in the ductile-to-brittle transition temperature (DBTT) region: (i) temperature dependence [17,18,19,20], (ii) test-specimen-size dependence [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36], and (iii) large scatter [15,37]
The proposed method was validated for a 780-MPa-class high-strength steel (HT780) and 0.45% carbon steel (JIS S45C) for predicting the minimum fracture load observed in the fracture toughness tests
Summary
It is well known that some types of preloading improve the apparent fracture toughness of cracked structures. One of the successful approaches for predicting the increase in the fracture toughness of a specimen by using a mechanically introduced CRS is a local approach proposed by Yamashita et al [14]; the local approach [15,16] was originally developed to explain three characteristics exhibited by the cleavage fracture toughness Jc of ferritic materials in the ductile-to-brittle transition temperature (DBTT) region: (i) temperature dependence [17,18,19,20], (ii) test-specimen-size dependence [21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36], and (iii) large scatter [15,37] These studies determined that the local approach is suitable for the prediction of increase in a specimen’s fracture toughness, and the Weibull stress without and with CRS is found to be the same.
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