Comparative analysis of specimen geometries in material extrusion 3D printing: Implications for mechanical property evaluation

This study investigated the influence of specimen geometry on the mechanical properties of 3D-printed parts by material extrusion (MEX). Four widely used technical standards were evaluated (ASTM D638, ASTM D3039/D3039M-14, ISO 527/2, and ISO 37), and all possible geometries were tested. The specimens were subjected to uniaxial tensile loading using a universal testing machine to obtain the mechanical properties of ultimate tensile strength, yield strength, and Young modulus. Mean, SD, and CV values, as well as NS10 (number of specimens tested to reach at least 10 valid data) are geometry-dependent. A critical analysis of these data allowed proposing the standard evaluation index (I-SE) of the specimen geometry (standard) based on data variance and test efficiency to achieve valid data. The results indicate that ASTM D638 performed better than any other standard. For investigations involving the mechanical properties of tensile strength Types I and II (ASTM D638) are the most recommended specimens geometry (standard) for 3D MEX printing because it combines the lowest CV with the minimum NS10. By following it, researchers and material suppliers can ensure accurate and reliable assessments of the mechanical properties of 3D-printed parts, contributing to increased safety, reliability, and quality in additive manufacturing. Notes: MEX - Material Extrusion, ASTM - American Society for Testing and Materials, ISO - International Organization for Standardization, SD - Standard Deviation, CV - Coefficient of Variation, NS10 - Number of specimens tested to reach at least 10 valid data, I-SE - Standard Evaluation Index.