The international community is exploring many potential end uses for polymer additive manufacturing. However, significant issues must be addressed before broad application can occur, in particular understanding the relationships between materials, processes, and final part properties. Key to these issues is having reliable test methods to measure properties of interest. This work used an AON-M2 industrial printer to investigate material extrusion manufacturing. Past research has frequently shown interlayer weld strength (i.e., Z-direction strength) is the weakest property in material extrusion parts and has also shown this property is difficult to measure, with significant data scatter and poor failure modes common for tensile specimens printed vertically. Using acrylonitrile butadiene styrene, the current work investigated in-plane shear testing to interrogate interlayer weld strength based on ASTM D3846, Standard Test Method for In-Plane Shear Strength of Reinforced Plastics, which uses a notched coupon loaded in compression. Further, a modified version of ASTM D3846 was investigated using smaller unnotched “minishear coupons.” Both test methods were found to provide very consistent results, with coefficients of variation of 5% or less; however, the ASTM D3846 notched coupons showed evidence of excessive gage section rotation and interference with the test fixture. The minishear test method did not have this problem and also allowed direct measurement of strain, thereby providing shear modulus. The authors note that in assessing the effect of process on properties, choice of the basis of comparison is important. While many researchers use injection molded properties, the authors believe this is misleading because the injection molding process itself affects properties. Instead, the authors investigated measurement of the polymer filament directly. New methods for filament shear and tension testing were developed that provided good coefficients of variation and allowed direct comparison between three-dimensional printed coupon properties and filament properties in shear.
Presented by Richard G. Cole (National Research Council Canada), in collaboration with Kazem Fayazbakhsh (Ryerson University), Abraham Avalos (AON3D), and Nicholas Nadeau (AON3D), as part of the
Polymers and Polymer Matrix Composites in Additive Manufacturing session at the ASTM International Conference on Additive Manufacturing (ASTM ICAM 2020).