Method of peening lap fillet welded joint and welded structures

A welded structure having a lap fillet welded joint, comprising a plurality of knocking mark groups in which a plurality knocking marks run at an angle relative to a welding direction across a weld toe of the lap fillet welded joint, wherein

• the knocking marks have a curvature radius in a cross section perpendicular to the weld line direction of 0.05 mm to 0.50 mm, and
• each knocking mark group is partially superimposed on an adjacent knocking mark group while, except for the superimposed part, an end part in a direction orthogonal to a welding direction of the knocking mark group is separated from an end part in the direction orthogonal to the welding direction of the adjacent knocking mark group.

A method of peening a lap fillet welded joint, comprising knocking a weld toe of the lap fillet welded joint using a knocking pin attached to a tip of a knocking tool, wherein

• the knocking pin has, on its tip, a curvature radius in a vertical cross section in a direction orthogonal to a welding direction of 0.05 mm to 0.50 mm and equal to or less than a curvature radius of the weld toe,
• the knocking pin is knocked while the knocking pin is oscillated in the direction orthogonal to the welding direction across the weld toe and moved in the welding direction,
• the knocking pin has an oscillation width around the weld toe at least twice a width of a knocking mark per knock point, and in a knocking region determined according to the oscillation width of the knocking pin, end parts in a direction orthogonal to the welding direction of knocking marks, which are located at a widthwise edge of the knocking region and partially superimposed on each other, are separated from each other in the direction orthogonal to the welding direction, or, knocking marks located at the widthwise edge of the knocking region are contacted with each other in the welding direction at three knock points or less.