Optimization and experimental validation of uniaxial and biaxial tensile test specimen design for polymers

The uniaxial tensile test specimen geometries for polymers, along with the testing procedure, are defined by the ISO or ASTM norms. Despite this, both experimental observations and numerical results show that fracture typically occurs outside the gauge zone. This can lead to significant inaccuracies during material characterization. Moreover, there are currently no established standards that define cruciform specimen geometry for biaxial tensile testing. In this study, improved uniaxial and biaxial tensile specimens were designed employing optimization schemes in Simulia Abaqus software in combination with trial-and-error approach, with the goal to ensure that the maximum stress. Finite element simulations confirmed that stress and strain are homogeneous and maximal in the gauge zone for all these specimens for various material models: linearly elastic, isotropic and anisotropic hyperelastic, and elasto-plastic. The thickness of the improved specimen for uniaxial testing can be arbitrarily changed within a certain range, whereas the cruciform specimen should only be scaled uniformly to preserve the optimal load transfer. Furthermore, experimental testing was performed on specimens additively manufactured using various technologies and types of materials, showing failure locations for both uniaxial and biaxial cases in gauge zones. Compared to standards and literature, novel specimens showed improvement and increased characterization accuracy.