Comparative Behavior under Tensile and Three-Point Bending Tests for a Composite with Quadriaxial Fabrics and Epoxy Resin

This paper continues recent research of the authors, comparing the experimental results for two test types (tensile and three-point bending), obtained for the same composite. The composite was obtained from 8 layers of quadriaxial glass fiber fabric (with 1200 g/m² and (supplied by Castro Composites Spain) and a bicomponent epoxy resin SikaBiresin® CR82 (supplied by Sika Group Austria). Specimens measured 9 mm × 29 mm × 280 mm, with a bending span of 100 mm and a tensile gauge length of 150 mm. Tests were conducted at rates of 10 mm/min, 200 mm/min, 500 mm/min, and 1000 mm/min. Tests were carried out on Instron 2736-004 universal testing machine. Results show that flexural strength exceeded tensile strength by ~20–26% across all test rates, consistent with the Weibull effect. However, the absorbed energy in tension was more than six times higher than in bending, particularly at higher test rates. Stress–strain curves revealed three characteristic zones: (i) linear elastic, (ii) nonlinear up to maximum stress, and (iii) post-peak failure. Overall, the results demonstrate that mechanical characterization of composites requires both tensile and bending tests. Using only one test type may lead to incomplete or misleading evaluations of structural behavior. For engineering applications, the choice of test should reflect the dominant loading scenario in service. The study confirms that tensile tests capture the composite’s capacity for deformation and energy absorption, while bending highlights outer-layer fragility. Both test types are therefore required for reliable structural characterization and design.