Elasto-viscoplastic Simulation for Cyclic Stress Assessment
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Solution Overview
Problem
Current methods for determining the maximum acceptable alternating stress in parts subjected to cyclic loading, particularly at high temperatures and frequencies, are inadequate, as they restrict the use of materials and shapes that can withstand such conditions, due to limitations in traditional Goodman diagrams which are based on lower frequency testing.
Innovation Solution
A method that digitally simulates parts using an elasto-viscoplastic (EVP) model to determine the maximum acceptable alternating stress, accounting for both static and alternating stresses, and utilizing a Goodman diagram to assess suitability, allowing for more realistic representation of high-frequency loading conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional Goodman diagrams based on lower frequency testing are used, then the assessment method is simple and well-established, but the results are inaccurate for high-frequency and high-temperature loading conditions
Solution Approach 1:
The patent changes the fundamental parameters of the assessment model by transitioning from static, low-frequency test data to dynamic, high-frequency elasto-viscoplastic simulations. This involves changing the material behavior model from elastic to elasto-viscoplastic, and adjusting the loading frequency parameters to match actual high-frequency operating conditions, thereby resolving the inaccuracy of traditional Goodman diagrams for high-frequency applications
Solution Approach 2:
The patent replaces the traditional mechanical testing-based Goodman diagram approach with a computational simulation system. Instead of relying on physical low-frequency tests, the invention uses digital elasto-viscoplastic simulations to predict material behavior under high-frequency loading, substituting a computational mechanics system for the traditional experimental mechanics approach
2Reliability
If conventional elastic behavior models are used in simulations, then the computational process is simple and fast, but the results do not accurately represent material behavior under high-temperature cyclic loading
Solution Approach 1:
The patent changes the material behavior model parameters from simple elastic properties to complex elasto-viscoplastic properties that account for time-dependent deformation and creep. This involves introducing viscosity parameters and temperature-dependent material properties that accurately represent high-temperature cyclic loading behavior, thereby improving reliability at the cost of increased computational complexity
3Reliability
If the duration of the level period in simulation is too short, then the computational time is reduced, but the assessment does not account for creep phenomena adequately
Solution Approach 1:
The patent applies preliminary action by conducting a sensitivity analysis or pilot simulation to determine the optimal level period duration before performing the full assessment. This allows the simulation to be configured with sufficient duration to capture creep phenomena while avoiding unnecessarily long computational times, balancing reliability and efficiency
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 a more accurate assessment of a part's ability to withstand cyclic loading, enabling the use of materials and shapes that were previously restricted, by accounting for creep and fatigue phenomena and offering results suitable across a wide range of load ratios.
Implementation Method 1
the simulation taking account of an elasto-viscoplastic (EVP) model of behavior for a material constituting the part
Implementation Method 2
accounting for creep and fatigue phenomena
Implementation Method 3
The diagram shows the maximum acceptable alternating stress to which the material may be subjected without breaking as a function of the static stress to which the material is subjected, when the material is subjected to a predetermined number of loading cycles
Data Source
AI summary
A method of determining a maximum acceptable alternating stress at a point of a part subjected to cyclic loading: simulating that the part is subjected to constant loading equal to a threshold value during a level period, and assuming that the part has elasto-viscoplastic behavior; from the results of the simulation, determining a final static stress at the point at the end or after the end of the level period; and for the point under consideration, using a Goodman diagram to determine the maximum acceptable alternating stress, which is determined for a static stress equal to the final static stress; the duration of the level period being equal to the duration of the loading of the testpieces that were used to draw up the Goodman diagram.