Closed-Section Frame Member for Buckling-Resistant Energy Absorption
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Solution Overview
Problem
Existing frame members, particularly those made from high-strength steel sheets, face challenges in achieving both weight reduction and sufficient energy absorption efficiency due to issues with elastic buckling and fracture during axial loading, which limits their ability to absorb impact energy effectively.
Innovation Solution
A frame member with a closed cross-section design, featuring flat parts with controlled width and hardness standard deviation ratios, where the Vickers hardness of the thickness middle portion is 300 Hv or greater, and the width of the reference flat part is 2.0 times or less the effective width, and the standard deviation ratio of hardness frequency distribution in the surface layer portion to the thickness middle portion is greater than 1.0, to prevent elastic buckling and fracture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the member thickness is reduced to achieve weight reduction, then the weight decreases, but the energy absorption efficiency and resistance to elastic buckling deteriorate
Solution Approach 1:
The invention applies local quality by creating a non-uniform hardness distribution within the steel sheet thickness direction. The surface layer portion has a different hardness (higher) compared to the thickness middle portion, forming distinct hardness zones. This local differentiation allows the surface layer to resist buckling while the inner portion maintains ductility for energy absorption, resolving the contradiction between weight reduction and energy absorption efficiency.
Solution Approach 2:
The invention changes the physical parameter of hardness distribution within the material. By controlling the hardness values at different thickness positions (surface layer vs. middle portion) and their standard deviation ratios, the material properties are optimized to simultaneously achieve thin-section capability and high energy absorption performance, overcoming the traditional trade-off between thickness and strength.
2Strength
If high-strength steel sheet is used to increase proof stress, then the proof stress increases, but the energy absorption efficiency deteriorates due to fracture during bellows deformation
Solution Approach 1:
The invention applies local quality by creating a non-uniform hardness distribution within the steel sheet thickness direction. The surface layer portion has a different hardness (higher) compared to the thickness middle portion, forming distinct hardness zones. This local differentiation allows the surface layer to resist buckling while the inner portion maintains ductility for energy absorption, resolving the contradiction between weight reduction and energy absorption efficiency.
Solution Approach 2:
The invention changes the physical parameter of hardness distribution within the material. By controlling the hardness values at different thickness positions (surface layer vs. middle portion) and their standard deviation ratios, the material properties are optimized to simultaneously achieve thin-section capability and high energy absorption performance, overcoming the traditional trade-off between thickness and strength.
3Ease of manufacture
If the width of flat part is increased to reduce manufacturing complexity, then the manufacturing ease improves, but elastic buckling occurs more easily
Solution Approach 1:
The invention applies local quality by creating a non-uniform hardness distribution within the steel sheet thickness direction. The surface layer portion has a different hardness (higher) compared to the thickness middle portion, forming distinct hardness zones. This local differentiation allows the surface layer to resist buckling while the inner portion maintains ductility for energy absorption, resolving the contradiction between weight reduction and energy absorption efficiency.
Data Source
AI summary
Provided is a frame member formed by cold-pressing a steel sheet. The frame member has a closed cross section portion in which a cross section perpendicular to a longitudinal direction is a closed cross section, and the closed cross section portion has at least one flat part having a radius of curvature larger than a maximum external dimension of the cross section. A Vickers hardness of a thickness middle portion in a reference flat part is 300 Hv or greater, a width of the reference flat part is 2.0 times or less the effective width, and a standard deviation ratio obtained by dividing a standard deviation of hardness frequency distribution in a surface layer portion in the reference flat part by a standard deviation of hardness frequency distribution in the thickness middle portion in the reference flat part is greater than 1.0.