Residual Stress Calculation in Metal Sheets With Spin History Tracking
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Solution Overview
Problem
Existing methods for measuring residual stress in metal sheets with multiple phases or during deformation are inaccurate, especially when significant deformation occurs or rigid body motion is involved, and finite element analysis is difficult to apply accurately due to reliance on precise input values and complex deformation conditions.
Innovation Solution
A method and device that acquire deformation, strain, and spin histories to calculate residual stress distribution by setting measurement points, updating stress sequentially, and converting to a global coordinate system, using digital image correlation and material constitutive laws to align stress directions accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If measurement methods using X rays or supersonic waves are used, then non-destructive stress measurement is achieved, but accurate measurement is impossible for metal sheets with two or more types of phases
Solution Approach 1:
The patent replaces physical measurement methods (X-ray diffraction, supersonic wave measurement) with a computational mechanics approach. By using digital image correlation to obtain deformation history and applying constitutive laws to calculate stress, the method eliminates the limitation of physical measurement techniques that assume material uniformity, enabling accurate stress calculation for multi-phase materials.
2Loss of information
If stress is sequentially calculated using strain history and material constitutive law, then stress history during deformation can be acquired, but coordinate system deviation occurs in cases of significant deformation or rigid body motion
Solution Approach 1:
The patent introduces a global coordinate system that remains fixed throughout the deformation process, separate from the moving material coordinate system. By transforming stress components from the material coordinate system to the global coordinate system using rotation matrices derived from digital image correlation measurements, the method maintains accurate stress direction information even during significant deformation or rigid body motion.
3Manufacturing precision
If finite element analysis is used to estimate residual stress, then residual stress distribution can be calculated, but high accuracy is difficult to achieve due to sensitivity to input values and complex deformation conditions
Solution Approach 1:
The patent extracts only the essential information needed for stress calculation from the complex finite element analysis framework. By using digital image correlation to directly measure deformation history at measurement points and applying constitutive laws locally, the method eliminates the need for complex global models, boundary condition specifications, and material property databases required by finite element analysis, while achieving comparable or superior accuracy.
4Measurement precision
If measurement is performed at one specific point, then stress at that point is determined, but repeated measurements are necessary to obtain residual stress distribution
Solution Approach 1:
The patent divides the measurement area into multiple measurement points, each with its own set of measurement marks. By applying digital image correlation to capture the deformation of all measurement points simultaneously in a single measurement session, the method obtains the complete residual stress distribution in one operation, eliminating the need for repeated single-point measurements.
Data Source
AI summary
A calculation method of a residual stress distribution calculates a distribution of residual stress generated in a metal sheet subjected to plastic deformation and includes: a step of acquiring a deformation history on a surface of a deformable portion of a metal sheet in a deformation process of plastically deforming the metal sheet and acquiring a strain history and a spin history generated in the deformable portion from the acquired deformation history on the surface; a step of sequentially updating stress in a material coordinate system of each of measurement points set in the deformable portion of the metal sheet from the start to the end of deformation in the deformation process; and a step of converting the stress in the material coordinate system of each of the measurement points at the end of deformation into stress in a global coordinate system and calculating the residual stress distribution.