Welding Residual Stress Field Research Articles

溶接残留応力場における疲労き裂の部分開口モデルによる応力拡大係数範囲算定法の提案とそのき裂伝播挙動の推定

Generally, fatigue crack propagation rate is well put in order by stress intensity range ΔKeff by considering crack closure period in crack opening process. But, in weld residual stress field, it seems that crack propagation behavior can not be exactly expressed in ΔKeff. This would be caused that ΔKeff was calculated by detecting crack full opening point which was able to be well measured experimentally. On the other hand, partially crack opening phenomena, which was presumed theoretically by considering the residual stress distribution in the case of crack laying over the tension and compression stress transition region, has not reflected in ΔK calculation process by this time.In this paper, as mentioned above consideration, calculation method of stress intensity factor in partially crack opening condition was proposed and its model was based on superpose principle of elastic stress. As a result of applying our calculation of stress intensity range ΔKact to evaluate the fatigue crack propagation rate in welded plate, it was made clear that the crack propagation behavior could be put in order well by ΔKact than by ΔKeff.Namely, ΔKact concept would not be only modification of KΔeff, because of applying new calculation technique for partially crack opening model.

Stress Redistribution During Annealing of a Multi-Pass Butt-Welded Pipe

The reduction of welding stresses during some standard post-weld heat treatments (PWHT) is numerically determined for a multi-pass butt-welded pipe made of a micro-alloyed C-Mn steel. Most of the stress reduction is found to occur during heating to the holding temperature. The further reduction obtained during the subsequent holding period is significant only for holding temperatures above 550°C. Both welding stresses and stresses during annealing were calculated by use of the FE-method assuming rotational symmetry. Experiments performed on a welded pipe indicate that the assumption of rotational symmetry is justified for the welding residual stress field, but not for the transient stress field present during welding of each pass.