Fracture of Polyjet 3D printed materials: a preliminary investigation

Additive manufacturing (AM), in particular 3D printing, gained a lot of interest in the past few years. This work is focused in particular on the Polyjet 3D process by means of which photo-curable polymers with strongly different physical and mechanical properties can be injected (in the form of liquid droplets) and cured through the use of a UV lamp. In previous works [1,2] we already highlighted the important influence that the interphase between different constituents can have on the viscoelastic properties of the 3D printed composite materials. In view of extending our research beyond small deformations and towards the determination of the fracture properties of Polyjet composites, a preliminary investigation was carried out to characterize the fracture behaviour of base constituents, and to verify the applicability of conventional fracture mechanics approaches to this particular class of AM materials/structures. As a first step, the effect of several parameters on the apparent fracture properties was determined: material composition (rubber content), printing orientation, presence of support material and ageing time. For this study, two polymers were considered: VeroWhitePlus (RGD835) and VeroGray (RGD850). They both share the same glassy matrix, but VeroGray also includes a secondary rubbery phase. Tensile and scratch experiments were performed to evaluate bulk and surface mechanical properties, later to be considered as a basis to analyze fracture data obtained on three point bending notched samples, tested according to ISO 13586 to determine apparent toughness and fracture energy values, KIC and GIC. The applicability of a fracture mechanics framework to these materials was discussed.