Development of a novel fatigue damage model with AM effects for life prediction of commonly-used alloys in aerospace

In the aerospace industry, more and more alloy parts with requirements of complex geometry and light weight are fabricated by additive manufacturing (AM) process, which has significant influence on their high-cycle fatigue properties. However, so far no work has been done to predict fatigue life of AM alloy parts through the damage mechanics based method. In this paper, a novel fatigue damage model with AM effects is proposed to address the issue, in which laser power, scan speed, hatch spacing and powder layer thickness are integrated in terms of the volumetric energy density, and the material parameters are calibrated with reported experimental data for the damage-coupled elastoplastic constitutive equations. After that, a good agreement is achieved numerically between the present theoretical model and published experimental results. Then the three most commonly-used alloy (SS316L, Ti6Al4V and AlSi10Mg) parts fabricated by AM process are studied in detail to investigate their several important characteristics, including the variation of fatigue life with the volumetric energy density, the variation of damage evolution rate with fatigue life subject to different volumetric energy densities, the relations between Young's modulus and fatigue life, and so on. Finally, several recommendations are presented for selection of the commonly-used AM alloy parts in aerospace, based on the engineering requirements and economy consideration.