April 12, 2023 at 4:41 amJared McFaddenSubscriber
I am trying to do a fatigue analysis on two models but am getting results that seem incorrect. Both models use the same part with same S-N data but one has a larger load applied, about 2x more than the other. I created an ASCII file for both that put the load history as a ratio of the maximum load. The issue is that the results of the model with the smaller load are saying that the fatigue life is less, which I know is incorrect. I have attached the load history plot and the result for both loads. I tried changing settings in the fatigue tool and noticed that changing the "infinite life" setting is the only one that makes a difference. Would the fact that the load history for the smaller load having a higher frequency than the other be the reason for these seemingly incorrect results? The images are in order of: small load result, small load history, large load result, large load history.
Thank you for any help!
April 12, 2023 at 1:17 pmVinayak VipradasAnsys Employee
Results for multiple frequency cases will use the number of cycles last defined S-N data point for undefined, low-stress values. Extrapolation of the S-N data curve outside your data points is not done. So at high frequencies, there will be many cycles per second so a shortened life could be predicted if your S-N data does not cover appropriate stress range.
The infinite life setting is used to reduce the effect that small stress cycles have on the calculated fatigue damage. For non-constant amplitude loading, cycles with very small alternating stresses can over predict the fatigue damage. For example, with non-constant amplitude proportional loading, the history data may produce many cycles with near zero alternating stress. These near zero stress cycles should produce negligible fatigue damage. It is extremely conservative to assume that the life associated with these stress cycles is 1e6 cycles.
For more information about fatigue life results, please refer to the following resources:
Fatigue Results (ansys.com)
Frequency-Based Fatigue using Harmonic Analysis in Ansys Mechanical — Lesson 4 - YouTube
April 12, 2023 at 2:31 pmJared McFaddenSubscriber
Thank you for your response! I noticed that my S-N curve did not cover all stress values experienced by the part at the lower load level so I added more data points to encapsulate all stress values. Even with doing this I was given the same result. I increased the infinite life value but all that does is increase the fatigue life by whatever factor the infinite life is increased by. Also, the fatigue life for the lower load case is showing the entire part as one single fatigue life value. I am really confused as to why my results are the way they are so any explanation would be great!
April 13, 2023 at 1:36 amtaylor godivaSubscriber
a problem that is really hard to find an answer to. I asked for help from a @Geometry Dash Scratch teacher I know. I believe there will be the answer that we all want!
- You must be logged in to reply to this topic.
Boost Ansys Fluent Simulations with AWS
Computational Fluid Dynamics (CFD) helps engineers design products in which the flow of fluid components is a significant challenge. These different use cases often require large complex models to solve on a traditional workstation. Click here to join this event to learn how to leverage Ansys Fluids on the cloud, thanks to Ansys Gateway powered by AWS.
Earth Rescue – An Ansys Online Series
The climate crisis is here. But so is the human ingenuity to fight it. Earth Rescue reveals what visionary companies are doing today to engineer radical new ideas in the fight against climate change. Click here to watch the first episode.
Subscribe to the Ansys Blog to get great new content about the power of simulation delivered right to your email on a weekly basis. With content from Ansys experts, partners and customers you will learn about product development advances, thought leadership and trends and tips to better use Ansys tools. Sign up here.
- Solver Pivot Warning in Beam Element Model
- Saving & sharing of Working project files in .wbpz format
- Understanding Force Convergence Solution Output
- An Unknown error occurred during solution. Check the Solver Output…..
- What is the difference between bonded contact region and fixed joint
- User manual
- The solver engine was unable to converge on a solution for the nonlinear problem as constrained.
- whether have the difference between using contact and target bodies
- material damping and modal analysis
- Colors and Mesh Display
© 2023 Copyright ANSYS, Inc. All rights reserved.