Hiroto Shoji

Evaluation method for Charpy impact toughness of laser welds based on lateral contraction analysis

An evaluation of Charpy impact toughness of the weld metal for laser beam welds is often impossible due to occurrence of fracture path deviation (FPD) from the weld metal into base steel. Therefore, the improved toughness evaluation method using side-grooved specimen instead of normal specimen has been suggested for preventing FPD. However, for a pre-qualification of the toughness of laser welds, the toughness value obtained with side-grooved specimen should be corrected to the toughness value of normal Charpy specimen. In this study, the method for correction of side-grooved Charpy energy for laser welds to normal Charpy impact toughness suggested by Hagihara et al. (Q J Jpn Weld Soc 25: 165–172, 2007) is advanced by means of FE analysis with focus on the deformation behaviors associated with strength mismatch. Furthermore, the distinctive strength mismatch of laser welds on lateral contraction of Charpy specimen has been analyzed by means of the Weibull stress approach. The applicability of the advanced engineering method is demonstrated by comparing experimental result, whereas the further verification should be accumulated.

Simulation-based method for hierarchal material design to improve ductile crack growth resistance of structural component

The purpose of this study is to propose a method to correlate micro-structural characteristics of two-phase steel with structural performance in terms of ductile crack growth resistance (R-curve). For this purpose, a meso-scopic simulation method is proposed to predict two types of ductile properties of two-phase steel that control the R-curve from micro-structural characteristics. The R-curve of three-point bend specimen with fatigue pre-crack predicted by a macro-scopic simulation method that we have proposed, in which these two types of ductile properties obtained by the proposed meso-scopic methods are implemented, is in good agreement with experimental result.