Micromechanical modeling of irreversible thermal strain

Abstract

Warping and delamination in material extrusion additive manufacturing (MatEx) parts are well documented and irreversible thermal strain (ITε) has also recently been reported. As parts are built up as a collection of roads, they are analogous to fiber reinforced composites. However, the lack of bonding between the matrix, air, and the reinforcing phase, polymer roads, necessitates the development of a micromechanical model for these parts. In this work, a micromechanical model for MatEx parts is developed to describe bulk part behavior that incorporates void fraction, road morphology, and bonding between and within layers. Previous work suggested ITε occurred within roads. Combining stress accumulation within roads with the micromechanical model successfully predicted ITε and provided a rationale for ITε dependence on both layer thickness and raster angle. These results show ITε can be predicted and, therefore, controlled, making MatEx part annealing more feasible and opening the possibility of one-way shape memory in parts. Additionally, the micromechanical model developed can be used to explain bonding limitations in MatEx based on road and bond geometry.