Bent Lap Fillet Weld Joint for Lower Toe and Root Stress
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Solution Overview
Problem
Lap fillet arc welding joints face challenges in reducing stress concentrations at the weld toe and root portions, especially when gaps are present between metal sheets, which affects the fatigue strength and reliability of the weld.
Innovation Solution
A lap fillet arc welding joint configuration is developed, where the first metal sheet is bent, and the weld bead is formed between the bent region and the second metal sheet, with specific geometrical parameters such as deviation between central axes, joint portion length, and bent angle optimized to minimize stress concentrations. The joint portion length is set to be two times or more of the sheet thickness, and the bent angle is within 10° to 35° to ensure effective stress distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the strength of steel sheets is increased to improve fatigue strength of base metals, then the base metal strength increases, but the fatigue strength of welding members does not necessarily increase due to stress concentration at weld toe portions
Solution Approach 1:
The invention applies local quality by creating a specific geometric configuration at the weld toe portion through bending one steel sheet. The bent configuration locally modifies the stress distribution pattern, transforming the discontinuous outer surface into a more continuous geometry that reduces stress concentration. This local geometric modification addresses the fatigue strength issue without requiring changes to the overall material strength.
Solution Approach 2:
The invention utilizes curvature by bending one steel sheet to create a curved or angled surface at the weld interface. This curvature eliminates the sharp discontinuity between the flat sheet surface and weld metal, creating a more gradual transition that reduces stress concentration at the weld toe portion and improves fatigue strength.
2Reliability
If grinder-finishing is performed to smoothen the outer surface of weld toe portion, then stress concentration factor is reduced and fatigue strength is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The invention applies preliminary action by pre-bending one steel sheet before welding to create the desired geometric configuration. This preliminary shaping eliminates the need for post-weld grinder-finishing operations, as the stress concentration issue is prevented during the forming stage rather than being corrected afterward. This reduces manufacturing complexity while achieving the same fatigue strength improvement.
3Adaptability or versatility
If the central axes of steel sheets in sheet thickness direction deviate from each other, then the welding joint can accommodate misalignment, but significant bending moment is applied to fillet weld causing stress concentration at root portion
Solution Approach 1:
The invention applies local quality by creating a specific bent configuration at one end of the steel sheet that locally compensates for the misalignment between central axes. This localized geometric modification reduces the bending moment transmitted to the fillet weld root portion, thereby reducing stress concentration at this critical location while still accommodating the overall misalignment.
4Productivity
If lap fillet arc welding is performed with steel sheets overlapped and sheet surfaces facing each other, then the welding process is simple and productive, but stress concentration occurs at weld toe and root portions reducing fatigue strength
Solution Approach 1:
The invention applies asymmetry by bending one steel sheet to create an asymmetric configuration at the weld interface, while maintaining the simple lap fillet arc welding process. This asymmetric geometry transforms the stress distribution pattern, reducing stress concentration at critical locations without complicating the welding process itself. The bending operation remains simple, but creates a non-symmetric joint that improves fatigue strength.
Data Source
AI summary
The present invention provides a lap fillet arc welding joint including a first metal sheet, a second metal sheet, and a weld bead. A region of the first metal sheet on one end side is bent. In a first direction, a position of a tip end of the bent region of the first metal sheet overlaps a region of the second metal sheet on one end side. In a second direction, an amount of deviation between a central axis of a region connected to the bent region of the first metal sheet and a central axis of the region of the second metal sheet on one end side is ½ times or less of average sheet thicknesses of the first metal sheet and the second metal sheet. A joint portion length is two times or more of the sheet thickness of the second metal sheet.