Effects of initial imperfections on out-of-plane deformation and residual stress produced by welding

Abstract

In this paper, the effects of initial imperfections (deflection and residual stress), which are necessarily produced when the steel plates are manufactured, on the out-of-plane deformation and residual stress generated by welding were elucidated from the results of the large deformation thermal elastic-plastic FEM (Finite Element Method) modeling. Residual stress, which was generated when the steel plates were manufactured, did not influence the out-of-plane deformation and residual stress produced by welding. However, initial deflection largely influenced the out-of-plane deformation produced by welding. When the temperature history was the same, transient deflection became and maximum at the same time irrespective of the initial deflection shapes. When the initial deflection shape was concave, the out-of-plane deformation became small near the weld line. However, the out-of-plane deformation in the perpendicular direction to the weld line depended on the initial deflection shapes. On the other hand, the out-of-plane displacement generated by welding when initial deflection wound in the welding direction became the smallest. As a result, the out-of-plane deformation remained large because initial deflection remained as it was. When initial deflection wound in the direction perpendicular to the weld line, the out-of-plane deformation largely served to maintain the initial deflection shape. The distribution of residual stress and plastic strain generated by welding was affected by the initial deflection shapes. However, the magnitude was not largely affected.

本報では、鋼板製作時にどうしても起こる初期不整(たわみと残留応力)の、溶接時に発生する面外変形や残留応力に及ぼす影響を、大変形熱弾塑性有限要素法モデリングの結果から明らかにした。鋼板の製作時に生じた残留応力は、溶接により生じる面外変形や残留応力には影響しなかった。しかし、初期たわみは溶接時に生じる面外変形に大きく影響した。温度履歴が同じであれば、過渡的なたわみは初期たわみ形状には無関係に、同時に最大値をとった。初期たわみが凹面の場合には、面外変形は、溶接ライン近傍で小さくなった。しかし、溶接ラインに垂直方向での面外変形は初期たわみ形状に依存した。一方、初期たわみ傷が溶接ラインに一致している時は、溶接により発生する面外変形は最小になった。その結果、初期たわみがそのまま残っているので、面外変形は大きなままに残った。初期たわみ傷が溶接ラインに垂直方向にある時は、面外変形は初期たわみ形状をほとんどそのままの状態に残した。溶接により発生した残留応力と塑性ひずみの分布は、初期たわみ形状の影響を受けた。しかし、その程度は大きくはなかった。