Meandering Weld Toe Geometry for Thin High-Strength Steel Joints
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Solution Overview
Problem
Existing techniques for improving fatigue strength in welded joints of thin steel sheets with high tensile strength (780 MPa or more) are ineffective, as they fail to adequately address the dominance of fatigue crack initiation life over crack propagation life in these thin structures.
Innovation Solution
A welded joint design featuring a pair of steel base materials with sheet thicknesses between 0.4 to 4.0 mm and a weld metal with a specific toe shape, characterized by peaks and valleys with controlled distances and numbers, along with a Vickers hardness ratio and aluminum content to enhance fatigue strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional welding techniques are used on thin high-strength steel sheets, then the welding process is simple, but the fatigue strength is insufficient due to dominant crack initiation life
Solution Approach 1:
The weld toe is designed with a meandering pattern featuring peaks and valleys instead of a straight configuration. This curved, undulating structure redistributes stress along the weld toe, preventing stress concentration at single points and thereby improving fatigue strength in thin high-strength steel sheets where crack initiation is the dominant failure mode.
Solution Approach 2:
The weld toe structure incorporates localized peaks and valleys with specific geometric characteristics (average distance between peak and valley ≤3.0mm, average number of peaks and valleys between 2-30 per 15mm). These local structural variations create a controlled stress distribution pattern that addresses the specific fatigue problem of thin high-strength steel sheets without requiring complex overall welding procedures.
2Duration of action of moving object
If the weld metal meanders with peaks and valleys, then the fatigue crack initiation life is extended, but the manufacturing precision requirement increases
Solution Approach 1:
The invention specifies quantitative parameters for the meandering weld toe structure: average distance between peak and valley points of 3.0mm or less, and average number of peaks and valleys between 2-30 per 15mm length. These parameter ranges provide clear manufacturing targets that balance fatigue performance improvement with achievable manufacturing precision, allowing standard welding processes to produce the required geometry.
Data Source
AI summary
A welded joint comprising: a pair of steel base materials having a sheet thickness of 0.4 to 4.0 mm, and at least one of which has a tensile strength of 780 MPa or more; and a weld metal that welds the pair of steel base materials, wherein, when the weld metal is seen in plan view, a weld toe of the weld metal has peaks and valleys, an average distance in a direction orthogonal to a weld line direction between a top point of a peak and a bottom point of a valley that are adjacent to one another is 3.0 mm or less, and an average number of a total of peaks and valleys, at which the distance in the direction orthogonal to the weld line direction between the top point of the peak and the bottom point of the valley that are adjacent to one another is 0.1 mm to 3.0 mm, is 2 to 30/15 mm, and an automobile component having the welded joint.