Dynamic and Quasi-Static Fracture Behavior of Two Thermosetting Polymers for Additive Manufacturing

Abstract

This study examines the fracture behavior of two thermosetting polymer resins for additive manufacturing (AM) and specifically presents the role of print orientation on the quasi-static and dynamic fracture responses of DA-3 resin printed via digital light processing (DLP) and PM-EM828 resin printed via stereolithography (SLA). A unique long-bar apparatus is used to launch a striker at the opposite end of a notched and pre-cracked specimen to create a dominantly Mode-I (opening) fracture event. Digital image correlation (DIC) is used in conjunction with ultra-high-speed imaging to capture the evolving displacement fields ahead of the crack tip. The elastodynamic solution for a stationary crack is used to determine the critical stress intensity factor (SIF), and the asymptotic steady-state dynamic crack solution is used to examine propagation behavior. These results are compared to quasi-static experiments of the same material and similar geometries on a standard load frame. Both DA-3 and PM-EM828 exhibited higher quasi-static fracture toughness values than critical dynamic stress intensity values, although the PM-EM828 demonstrated less rate dependence on fracture toughness than DA-3. Overprinting the last two layers of the weakest DA-3 orientation proved to enhance isotropy of DLP 3-dimensional (3D) printed DA-3 plaques while PM-EM828 plaques 3D printed by SLA did not show significant anisotropy.