Numerical investigation of CTOD estimation methods for laser welds

This paper proposes an estimation method for crack tip opening displacement (CTOD) in laser welds. The theoretical model for CTOD estimation developed by Dugdale and Bilby et al. (DBCS model) was used for laser-welded plates. The yield stress of the laser weld metal and narrow hard zone width affected the CTOD, and the correction of yield stress by using the DBCS model to obtain a suitable CTOD estimation was investigated. To apply the DBCS model to CTOD estimation for laser welds, an equivalent yield stress concept was proposed. The equivalent yield stress was affected by the strength mismatch ratio and hard zone width, because the yield stress of the laser weld metal decreases with the constraint loss caused by the plastic deformation that occurred in the base metal. The predicted CTOD from the value of applied load obtained using the proposed estimation method agrees well with experimental critical CTODs for laser welds of both 780 and 520 MPa class structural steel.