Kazem malikipour

Grade:  Ph.D.

Ph.D. Thesis:

High cycle fatigue analysis of SLM manufactured AISI 316 parts using the numerical and experimental methods

Year:  Feb.  2015 -Feb. 2021.

Abstract:

Despite significant improvements in the mechanical and metallurgical properties of additively manufactured metallic components, the fabricated parts may suffer from low fatigue properties due to the microstructure internal defects such as porosity. This study attempts to evaluate the high cycle fatigue (HCF) behavior of the additively manufactured specimens using damage mechanics approach in Meso-scale. While, The Chaboche-Lemaitre damage model is used to simulate the evolution of stress-induced damage, the damage growth caused by plastic flow at the stress concentration domain around the internal defects is modelled using the Lemaitre damage model. The HCF and uniaxial tensile tests of AISI 316 L parts, utilizing the technology of selective laser melting (SLM), are carried out to identify the models’ material constants. Agreement between experimental fatigue life and numerical fatigue life prediction based on real SLMed part’s microstructure image captured by optical microscope demonstrate the capability of the numerical model. In addition, with the development of a parametric numerical model, the effect of stress triaxiality, external HCF loading, and void geometric parameters including ligament length to average voids size ratio, void aspect ratio, and void size on the damage growth and coalescence of two-void cluster embedded in representative volume element (RVE) have been investigated. The results show that increasing the triaxial stress from 0.5 to 2.1 leads to a severe decrease in ligament load carrying capacity and eventually voids coalescence through an increase in von Mises stress around the micropores.

Keywords: Selective laser melting, High cycle fatigue, Damage mechanics, Porosity modeling, Microvoids coalescence.