Application of damage mechanics for fatigue life assessment.

Date of Award


Degree Type


Degree Name



Civil and Environmental Engineering


Engineering, Civil.




Traditional multiaxial fatigue assessment models are based on the definition of an equivalent uniaxial measurement of the stress and strain tensors in the critical region of the studied component. An equivalent uniaxial criterion is then used to assess the fatigue life. In this thesis, we study a new approach based on Continuum Damage Mechanics theory. The introduction of the Continuum Damage Mechanics (CDM) in late 1970s to model fatigue has opened a new arena of research for developing a suitable model for multiaxial fatigue. In CDM, constitutive equations are derived by using internal variables under the framework of the thermodynamics to simulate the degradation of the material responses due to damage causing phenomenon. The main advantage of this approach is that, once the constitutive laws are derived, they can be used to model the damage behavior of the material under different damage causing modes with the appropriate calibration. In this work the locally coupled analysis proposed by J. Lemaitre [1990] has been adopted, as a post-processor of the FE analysis. The SAE1045 HR shaft has been used as the example case for the analysis and the results have been compared with the experimental results of Fash [1985]. This work focuses on the identification of the model parameters as formulated by Lemaitre. It is shown that the initial identification procedure proposed by Lemaitre leads to results poorly correlated with experimental findings. A new methodology for the identification of Lemaitre model parameters is proposed, it uses the Coffin-Manson relation for the uniaxial case. The approach is applied to the SAE1045 HR steel and it is shown that an excellent correlation can be achieved in the uniaxial case. With the calibrated parameters, the model's performance for multiaxial loading has improved. (Abstract shortened by UMI.)Dept. of Civil and Environmental Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2005 .R34. Source: Masters Abstracts International, Volume: 44-01, page: 0452. Thesis (M.A.Sc.)--University of Windsor (Canada), 2005.