3D-printed polymers exhibit a strength size effect

Abstract

This study is an investigation on the size dependence of strength of a 3D printed acrylic polymer. 3D printed beams are used in three-point bend fracture experiments. Three print modes of the PolyJet process are used to manufacture beams of dimensions commonly considered in 3D printed structures (1–5 mm). It is found that for that range of dimensions, the fracture response is in the nonlinear size-strength domain and specimens neither follow the limiting linear elastic fracture mechanics nor the strength criterion. Consequently, strength and toughness are size dependent. Moreover, a strong interaction between specimen dimensions and print layer thickness was found. A size threshold exists below which there appears to be an interaction between specimen dimensions and print layer thickness, and for specimens of dimension below that threshold exhibit a declining strength with size. From the present experiments, the size threshold is estimated to be 50 times the print layer thickness. The finding of a maximum strength relative to geometric dimensions should be accounted for in designing with 3D printed materials.