Bent Metal Sheet Indentation Band for Fatigue Crack Suppression
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Solution Overview
Problem
Existing methods for suppressing fatigue crack growth in bent metal sheet portions are either costly, limited in applicability, or reduce productivity due to the need for multiple molds, restricted applicability to specific shapes, or require processing in sealed containers to prevent material scattering.
Innovation Solution
Applying plastic strain orthogonally to the valley line direction of bent metal sheet portions using needle peening with an impact pin, forming an indentation band that generates compressive residual stress, thereby suppressing fatigue crack growth without altering the bending angle or increasing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two-step bending process is used to suppress crack generation, then fatigue life is improved, but manufacturing cost increases due to requiring two types of molds
Solution Approach 1:
The patent applies preliminary bending before the final bending operation. The preliminary bending creates initial deformation that prepares the material for the final bending, allowing crack suppression without requiring separate molds for each step. This preliminary action modifies the stress distribution in advance, enabling the use of a single mold for the final operation while still achieving improved fatigue life.
2Reliability
If shot peening is used to enhance yield stress, then fatigue strength is improved, but processing requires sealed container to prevent scattering
Solution Approach 1:
The patent replaces the shot peening process with a mechanical bending process. Instead of using projection material and sealed containers, the invention uses controlled bending operations that directly apply mechanical stress to the metal sheet. This substitution eliminates the need for complex sealed processing equipment while achieving similar or better fatigue strength improvement through stress redistribution.
3Reliability
If air-type hammer peening is used to close fatigue crack, then crack growth is suppressed, but productivity decreases due to whole bend inner side receiving impact
Solution Approach 1:
The patent applies local quality by targeting specific regions during bending rather than treating the entire bend inner side. The preliminary bending and final bending operations are designed to concentrate stress modification in critical areas where cracks are most likely to initiate and propagate. This localized approach suppresses crack growth effectively while maintaining high productivity by avoiding unnecessary processing of non-critical areas.
4Reliability
If impact pin with large tip radius is used for peening, then crack suppression is achieved, but bending angle expands and part deformation occurs
Solution Approach 1:
The patent controls the parameters of the bending operation to achieve crack suppression without excessive deformation. By carefully controlling the bending radius, applied force, and number of passes during preliminary and final bending, the invention modifies stress distribution to suppress cracks while maintaining precise control over the final bending angle. This parameter optimization allows effective crack suppression without the need for oversized impact pins that would cause part deformation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively improves the fatigue life of automotive parts with bent metal sheet portions by preventing crack growth in the valley line direction while maintaining productivity and avoiding deformation or scattering issues.
Implementation Method 1
applying a plastic strain at least in a range from a bending start point to a bending end point on a bend inner side of the bent portion in a direction orthogonal to a valley line direction of the bent portion
Implementation Method 2
generate a compressive residual stress
Implementation Method 3
forming an indentation band which is a series of indentations on the bend inner side of the bent portion by a needle peening treatment using an impact pin
Implementation Method 4
generate a compressive residual stress
Data Source
AI summary
A metal sheet bent portion fatigue crack growth suppressing method suppresses a growth of a fatigue crack generated in a bent portion formed by bending a metal sheet, and includes applying a plastic strain at least in a range from a bending start point to a bending end point on a bend inner side of the bent portion in a direction orthogonal to a valley line direction of the bent portion at an interval equal to or larger than a sheet thickness of the metal sheet in the valley line direction so as to generate a compressive residual stress.