This content is not included in
your SAE MOBILUS subscription, or you are not logged in.
Advances Relating to Fatigue Calculations for Combined Random and Deterministic Loads
Technical Paper
2014-01-0725
ISSN: 0148-7191, e-ISSN: 2688-3627
Annotation ability available
Sector:
Language:
English
Abstract
Techniques for calculating fatigue life from random structural responses were first proposed in the 60's but these early methods were limited to narrow band responses (ref 1). When used for wide band responses these same techniques could become very conservative. In order to reduce this conservatism much effort was devoted from the 1980's onwards to develop methods that worked more accurately for the wide band situation. Several methods now exist for the wide band case and these typically exist alongside Finite Element (FE) based random analysis tools like Nastran, Ansys or Abaqus to take the PSD's of stress response and return the Rainflow cycle count and fatigue damage (ref 2).
Several problems still exist with todays design methods. Firstly, for large models, these stress transfer functions have to be generated and stored for subsequent use in the fatigue life calculation and these files can be very large. By treating the fatigue life calculation in this way, as a post processing task, the analysis of large models becomes difficult. Secondly, the processing of random stresses within an FE model is problematic when fatigue life is the required result. And thirdly, no practical way exists to simultaneously combine both random and deterministic loads. This is widely required by the test environment standards like MIL-HDBK-810G (ref 3).
This paper will present a review of existing methods, particularly where a design approach has been implemented within an FE environment. This is then followed by details of a new approach, which includes novel procedures for more accurately processing the random stresses, more efficient ways of dealing with large models and new methods for combining deterministic and random loads.
Recommended Content
Technical Paper | Trials and Tribulations of Fatigue Testing of Bearings |
Technical Paper | The Development of Agricultural Equipment Power Take-Off Mechanism |
Technical Paper | Automated Analysis of Automotive Data |
Authors
Citation
Bishop, N., Kerr, S., Murthy, P., and Sweitzer, K., "Advances Relating to Fatigue Calculations for Combined Random and Deterministic Loads," SAE Technical Paper 2014-01-0725, 2014, https://doi.org/10.4271/2014-01-0725.Also In
References
- Bendat , JS Probability functions for random responses NASA report on contract NAS-5-4590 1964
- Bishop N W M and Sherratt F Fatigue life prediction from power spectral density data. Part 1, traditional approaches and Part 2, recent developments Environmental Engineering 2 1989
- MIL-STD-810G Department of Defense Test Methods Standard: Environmental Engineering Considerations and Laboratory Tests 31 October 2008
- Metallic Materials Properties Development and Standardization (MMPDS) DOT/FAA/AR-MMPDS-01 January 2003
- Dowling N. E. Mean Stress Effects in Stress-Life and Strain-Life Fatigue Fatigue 2004: Second SAE Brasil International Conference on Fatigue June 2004 São Paulo, Brasil 14
- Bishop N W M and Sherratt F Finite Element Based Fatigue Calculations NAFEMS book 2000
- CAEfatigue Vibration Quick Reference Guide CAEfatigue Limited www.caefatigue.com 2013
- CAEfatigue Vibration User Guide CAEfatigue Limited www.caefatigue.com 2013
- CAEfatigue Vibration Theory Guide CAEfatigue Limited www.caefatigue.com 2013
- Lambert , R. G. Analysis of fatigue under random vibration The Shock and Vibration Bulletin 55 71 1976