The role of defects and critical pore size analysis in the fatigue response of additively manufactured IN718 via crystal plasticity

The inherent defects associated with materials produced by selective laser melting (SLM) limits their usage in safety- critical applications. In ourwork, a crystal plasticity (CP) based framework is developed to identify the critical porosity characteristics, which quantifies the limiting scenarios of fatigue crack initiation at a pore rather than the crystallographic features. 3D virtual microstructures are developed based on the characterization of SLM IN718 for use in the CP simulations. Damage indicator parameters, such as the plastic strain accumulation, elastic stress anisotropy, resolved shear stress and triaxiality, obtained from the CP simulations are used to identify the most probable locations of crack initiation. Pores are explicitly added to the microstructure instantiations in a systematic manner by varying the size, location, and proximity between pores. The critical pore size is defined as the size beyond which the location of crack nucleation transitions from crystallographic features to the pore vicinity, which is determined to be 20 mu m in the material of interest with an average grain size of 48 mu m. This work is beneficial in qualifying SLM materials given the natural porosity inherent to the manufacturing process, by reducing the number of fatigue experiments. (c) 2018 Elsevier Ltd. All rights reserved.