Efficient characterization on the interlayer shear strengths of 3D printing polymers

Abstract

Shear strength measurement becomes increasingly important because three-dimensional (3D) printing materials are used in load-bearing structures subjected to a combined normal and shear stress state. Hence, this paper presents a combined experimental and numerical investigation of the interlayer shear strength measurement approach, and its application to four kinds of 3D printing polymers including acrylonitrile butadiene styrene (ABS), polycarbonate (PC), and polylactic acid (PLA) made with fused deposition modeling (FDM), and polyamide 12 (PA12) made with selective laser sintering (SLS). First, a traditional Iosipescu shear specimen was employed to validate the uniform shear strain field using digital image correlation. Second, a new necking-shaped shear specimen was proposed to measure the shear strength efficiently with the aid of an effective alignment assistant beam. Third, 3D finite element analysis was conducted to highlight the stress comparisons of the Iosipescu shear specimen and the necking-shaped shear specimen. In order to quantify the anisotropic strengths, three kinds of shear specimens with different build directions were designed and tested. The results demonstrated that the minimum shear strength of a 3D printing polymer specimen was the interlayer shear strength when the shear force was acting along the printing surface. Our measurement was consistent with the shear strength measurements of the same type of 3D printing PA reported by other researchers. Moreover, our measurement was more conservative and accurate due to the pure shear stress state of all specimens.