블라스트 처리된 면외거셋 용접이음부의 피로수명 평가

Abstract

Since the late 1980s, the blast treatment has become an important process in the manufacturing of steel structures in Korea, its purpose is to remove the impurities on the surface of steel material and to enhance the adhesiveness of coating. Even though the blast treatment has been generalized, its influence on the fatigue behavior of welding joints has not been considered. In the fatigue test with the blast treated out-of-plane gusset welded joint, it is proved that the fatigue strength has increased by the blast treatment, and it is mainly because of the geometric shape improvement of welded toe and the residual compressive stress introduction. So, it is necessary to evaluate the correlation between the blast treatment condition and the residual compressive stress quantitatively. To study the geometric shape change of welded toe, the flank angle and the curvature radius as well as the change of residual stress were measured along with the blast treatment(BT). The flank angle showed little change, and the curvature radius increased by 15% for BT specimen compared with the as-welded(AW) specimen. It was found that the tensile residual stress was reduced and the residual compressive stress was introduced near the toe by the blast treatment. To evaluate the effect of blast surface treatment on fatigue behavior of welded joints, the fatigue tests were carried out on two types of out-of-plane gusset fillet welded joints, as-welded specimens and blast-treated specimens. The fatigue tests results showed that over 67% increase in fatigue limit was obtained by using blast treatment but in high stress range there was no significant difference in fatigue limit between the as-welded and blast-treated specimen. Mathematical Interpretation was applied to assess effect of stress concentration and residual stress on fatigue limit of out-of-plane gusset welded joints.