Welded Joint Fatigue Life Evaluation with Cut-Plane Traction Stress
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Solution Overview
Problem
Current methods for fatigue life evaluation of welded structures are empirical and lack reliability due to stress/strain singularity at joint locations, making it challenging to accurately calculate stress and strain using modern analytical and computer methods.
Innovation Solution
A unified method involving finite element modeling, stress/strain calculation using cut-plane traction stress methods, and integrated fatigue evaluation procedures that account for different types of welds and load conditions, including non-proportional multiaxial loads, to determine fatigue life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If modern analytical and computer methods are used to calculate stress or strain at joint locations, then computational capability is improved, but stress or strain singularity at joint locations makes reliable calculation impossible
Solution Approach 1:
The patent extracts the singularity problem from the joint location by introducing a cut-plane that passes through the joint, separating the singular stress field into manageable traction components that can be calculated reliably using finite element methods
Solution Approach 2:
The patent introduces a cut-plane as an intermediary construct that mediates between the singular joint region and the surrounding structure, allowing stress/strain calculation through traction components on the cut-plane rather than directly at the singular joint location
2Ease of manufacture
If empirical methods are used for fatigue evaluation of welded structures, then simplicity is improved, but reliability and accuracy of fatigue life prediction deteriorate
Solution Approach 1:
The patent changes the fundamental parameters used in fatigue evaluation from empirical stress concentrations to physically-based traction components and strain energy density, maintaining computational feasibility while dramatically improving prediction reliability
Solution Approach 2:
The patent creates a unified fatigue evaluation procedure that works across different weld types, joint configurations, and loading conditions through a single theoretical framework based on strain energy density, replacing multiple empirical methods with one universal approach
3Productivity
If conventional finite element computational results are used directly, then computational efficiency is improved, but mesh-sensitivity causes unreliable stress/strain values at joint locations
Solution Approach 1:
The cut-plane serves as an intermediary that transforms mesh-sensitive joint stresses into mesh-insensitive traction components, allowing direct use of conventional finite element results while eliminating mesh-sensitivity through the post-processing approach
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
This approach provides accurate and mesh-insensitive stress/strain calculations, enabling reliable fatigue life estimation for welded structures under various load conditions, improving design and evaluation processes.
Implementation Method 1
calculating a distribution of structural strain experienced within the given structure using Hooks law in response to a determination that the stress is less than yield strength of material
Data Source
AI summary
Due to geometric discontinuities introduced by welding and joining processes, stresses or strain cannot be calculated reliably calculated using modern analytical and computer methods as result of stress or strain singularity at joint locations, which leads to severe mesh sensitivity. Design and fatigue evaluation of these structures remain empirical. This disclosure addresses mesh insensitivity of stress/strain calculations for welded structures through a cut-plane traction stress method through a novel post processing of conventional finite element computation results, as well as provides a unified fatigue evaluation procedure for fatigue design and structural life evaluation for both low-cycle and high cycle fatigue regime subjected to either proportional or non-proportional multiaxial fatigue loading, as well as a simple and reliable method for treating spot welds.