硬さ試験による炭素鋼の局所力学特性の推定と配管溶接部への適用

抄録

Recent surge for seismic resistance requires an evaluation for welded pipes under mechanical conditions including plastic deformation. Although the welded metal and the heat affected zone have different mechanical properties compared with those of the base material, these local characteristics are difficult to measure. Indentation test is one of the possible solutions for evaluating local mechanical properties including plastic stress-strain response, however, there are many experimental difficulties for the measurement. The present study aims to modify the method simple and convenient using an observation of dents similar to the conventional hardness testing. The modified method was applied to weld joints of piping steels and utilized to investigate the influence of local mechanical properties of the weld metal on the surrounding stress distribution. The piping steels exhibit remarkable yield elongation under the lower yield point, which is not taken into account in the indentation tests measuring the local mechanical properties. Stress-strain response was evaluated under the tensile test using a digital image correlation technique, by which local and bulk strains could be obtained simultaneously. Based on the result, limitations of the indentation method were discussed.