Fatigue Life Prediction of Lattice Structures Using a Strain-Life Method Based on an Equivalent Solid Model

Abstract

In this study, an efficient fatigue life estimation approach is proposed based on an equivalent solid model, along with two stress concentration factors, instead of a lattice model to simplify simulations for the strain-life method. One of the stress concentration factors accounts for the stress concentrations at the strut joints in lattice structures without any manufacturing effect, while the other accounts for the stress concentrations due to surface defects on the struts introduced by the additive manufacturing process. A simple solid cell, for which the dimensions are the same as those of the lattice cell, is first used to estimate the fatigue life of the bulk material used in the additive manufacturing process using the Brown-Miller strain-life method. Combinations of two stress concentration factors were then utilized to predict the fatigue life of the lattice structure from the equivalent solid model. Using this approach, computationally expensive lattice structure simulations were eliminated, and the fatigue life of the lattice structure was predicted directly from the bulk material fatigue life estimation. The proposed approach was applied to different lattice types made of Ti-6Al-4V alloy using the laser-powder bed fusion additive manufacturing process. The fatigue life results estimated using the proposed approach were in good agreement with the experimental fatigue life results reported in the literature.