Mutiscale modeling of the high cycle fatigue of thermoplastic polymer solids

Details

Supervisors

Issam Doghri

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil mécanicien, à finalité spécialisée

Abstract

Accurate prediction of fatigue failure in thermoplastic polymer solids, especially those produced through additive manufacturing, remains challenging. Traditional models relying on macroscopic fatigue criteria fail to give accurate predictions of teh fatigue lifetime. This study introduces a novel methodology including microstructural details into fatigue predictions, specifically for materials manufactured using the Selective Laser Sintering (SLS) process. The primary contribution is the development of a coupled time and space homogenization method for viscoelastic-viscoplastic (VEVP) composites under cyclic loading. This method demonstrates significant accuracy in predicting the response within material phases at a low computational cost, even for high cycle fatigue (HCF) scenarios. The study utilizes a Representative Volume Element (RVE) modeling approach, assuming that in HCF, the majority of the material volume remains viscoelastic, with viscoplastic deformation accumulating at weak spots, which represent preexisting defects and inhomogeneities of the material. This approach effectively predicts interactions between weak spots and the matrix while maintaining computational efficiency. The proposed model, while not always accurate, showed promising results that suggest it could be applied to a wide range of loading conditions with further refinement. Overall, this work presents a valuable tool for engineers and researchers, far better than the phenomenological and empirical models commonly used in the industry for fatigue life assessment.