Failure Analysis and Anisotropy Evaluation of 3D-Printed Tensile Test Specimens of Different Geometries and Print Raster Patterns

Abstract

Anisotropic mechanical properties related to build orientation is a characteristic of parts fabricated with 3D printing technologies. In the development of new materials for 3D printing processes, understanding the effects of 3D printer build orientation and raster pattern on physical property and failure mode differences is extremely important. While there is currently no standard for the evaluation of build orientation-based mechanical performance, such analysis has typically been achieved through the fabrication and scrutiny of tensile and other test coupons which were printed in different build orientations. In some cases, printing specimens in the ZXY (or vertical) build orientation can be difficult due to the capability of a given 3D printer platform. There are also multiple tensile test specimen geometries specified in the ASTM D638 standard for the tensile testing of polymer materials and understanding which specimen geometry works best for 3D printing is not currently well understood. The work presented here explores the effect of tensile test specimen geometry on the anisotropy of mechanical properties related to the build orientation of tensile test specimens. The test coupons were fabricated using a material extrusion 3D printing platform based on fused deposition modeling technology using a grade of acrylonitrile butadiene styrene not typically used in 3D printing in order to simulate the testing of a new material. The effects of raster pattern and the geometric dependence of mechanical property anisotropy were explored, and validation of the use of “faux vertical” specimens in lieu of ZXY-printed specimens was demonstrated. Finally, scanning electron microscopy was used to perform fractography on the various versions of the printed tensile test specimens in order to determine the effect of raster pattern on failure mode.