Amir Kamali

Grade:  Master

Thesis Title:

Estimation of fatigue lifetime for Stainless Steel 316 produced by SLM method using continuum damage mechanics

Year: Sept. 2016- Jun. 2019.

Abstract:

Selective Laser Melting (SLM) is one of the additive manufacturing methods that is widely used in various industries, including automotive, turbine, medical and decorative applications. This research studies the prediction of failure in fatigue loading for 316 stainless steel produced by SLM using continuum damage mechanics. Empirical experiments are carried out on 316 stainless steel parts produced by SLM. Based on empirical observations, samples produced by SLM method show a semi-crisp behaviour due to high thermal gradients and inherent imperfections in the laser melting process. Experimental tests are used to investigate simple tensile test and low cycle fatigue loading. The tests are done on two sample groups. The first group is stainless steel 316, which is manufactured using traditional methods and is known as "Stainless Steel 316 under primary cold work". The second group is the stainless steel 316 produced by the SLM method, which is referred to in this research as "Stainless Steel 316 Printed". By experimental tests, parameters related to mechanical properties, isotropic and kinematic hardening and damage parameters are extracted for both sample groups. In numerical analysis, an algorithm for solving equations is introduced and then implemented in the commercial non-linear finite element software Abaqus/ Explicit through a VUMAT subroutine. Subsequently, the VUMAT subroutine has been verified for various loading conditions. The two-scale damage model is applied to predict the behaviour of the material in the fatigue loading. Extracting the S-N curve and obtaining the fatigue life of the components in cyclic loading, is the results of this research. The results show that the fatigue life in samples taken by the SLM method is lower than the samples that product in the traditional methods.

Keywords:  Selective laser melting, continuum damage mechanics, 316 stainless steel, fatigue.