Evaluation of Valid Thickness in ASTM Standard Tensile Specimen Considering Stress Triaxiality and Strain Path

This study investigates the valid thickness range for ASTM E8 tensile specimens under plane-stress uniaxial tension conditions. Finite element simulations were performed on specimens with varying thicknesses, and stress triaxiality and strain path were analyzed as the primary evaluation criteria. An ideal uniaxial tension state was defined by a stress triaxiality of approximately 0.333 and strain path of -0.5. The results indicate that specimens with a thickness of up to 8.0 mm satisfy both these conditions. Outside this range, notable differences in stress triaxiality and strain path between the surface and mid-thickness were observed, indicating a departure from the intended uniaxial tension state. Thus, this study provides a guideline for determining the appropriate specimen thickness to ensure accurate tensile testing under plane-stress uniaxial tension conditions. The proposed methodology may also be applied to evaluate the validity of tensile specimens in other mechanical testing conditions.