Fracture Determination Method for Metal Structures
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Solution Overview
Problem
Conventional methods for determining fracture risk in metal structures during deformation, such as in automotive collision or press forming, struggle to accurately assess the risk when the structure transitions from a plastic to an elastic state, leading to inaccurate fracture predictions.
Innovation Solution
A fracture determination method and apparatus that simulate deformation sequences using finite element methods, allowing for accurate fracture risk assessment by extracting and analyzing deformation states at arbitrary steps, including those where the structure returns from a plastic to an elastic state, using stress and strain calculations to determine fracture limits and risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional fracture prediction methods are used, then fracture risk can be evaluated in simple deformation cases, but accurate fracture determination becomes difficult when the metal structure returns from plastic state to elastic state
Solution Approach 1:
The invention changes the evaluation parameter from stress-based criteria to plastic strain-based criteria. By using equivalent plastic strain as the fracture evaluation parameter and comparing it with the formation limit diagram, the method remains accurate whether the material is in elastic or plastic state, and regardless of deformation path complexity.
Solution Approach 2:
The invention performs preliminary calculation of the formation limit diagram based on material properties before the actual fracture evaluation. This pre-computed limit diagram serves as a reference for comparing equivalent plastic strain at any deformation stage, enabling accurate fracture risk assessment without recalculating complex stress states.
2Ease of manufacture
If stress-based fracture criteria are used, then fracture limit can be determined in proportional deformation, but the method becomes complicated when deformation path changes
Solution Approach 1:
The invention transitions from stress-based parameters to strain-based parameters for fracture evaluation. The equivalent plastic strain accumulates along the deformation path and can be directly compared with the formation limit diagram, providing both simplicity and reliability regardless of whether the deformation path is proportional or non-proportional.
Solution Approach 2:
The invention creates a formation limit diagram that represents the material's fracture boundary in strain space. This diagram serves as a universal reference that can be applied to any deformation scenario, eliminating the need to recalculate fracture limits for different deformation paths.
3Measurement precision
If conventional methods evaluate fracture margin by distance to non-proportional formation limit value, then fracture risk can be assessed, but the calculation becomes complicated and time-consuming
Solution Approach 1:
The formation limit diagram is pre-calculated based on material properties before any specific deformation analysis. This diagram contains all necessary fracture limit information for different strain paths, allowing rapid comparison with actual equivalent plastic strain during deformation without time-consuming recalculations.
Solution Approach 2:
By using equivalent plastic strain as the evaluation parameter instead of stress components, the invention simplifies the fracture assessment to a single scalar comparison against the formation limit diagram, dramatically improving calculation efficiency while maintaining accuracy.
Data Source
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AI summary
A fracture determination method for determining a fracture of a metal structure includes: a deformation analyzing step of performing deformation analysis from start of deformation to end of deformation of the metal structure; and a fracture determination step of extracting a fracture determination target portion from a deformation state of the metal structure obtained in the deformation analyzing step, and when the extracted fracture determination target portion has returned from a plastic state to an elastic state, given that a stress when the portion returned to the elastic state is (x, y) = (σ2, σ1) (maximum principal stress: σ1, minimum principal stress: σ2) on a (x, y) coordinate plane and performing fracture determination of the fracture determination target portion using a re-yield stress determined by an intersection between a straight line satisfying a relation y = (σ1/σ2)x and an yield curve obtained from the plastic state of the fracture determination target portion, and in the fracture determination step, a fracture limit stress determined by an intersection between the straight line satisfying the relation y = (σ1/σ2)x and a fracture limit stress line of the fracture determination target portion is obtained, a fracture limit equivalent plastic strain corresponding to the fracture limit stress and an equivalent plastic strain corresponding to the re-yield stress are obtained using an equivalent stress-equivalent plastic strain curve, and a fracture risk of the fracture determination target portion is calculated using the fracture limit equivalent plastic strain and the equivalent plastic strain. Fracture determination can be performed with high accuracy even when the fracture determination target portion has returned from a plastic state to an elastic state.