Design of geomembrane specimen for biaxial tensile testing

A numerical–experimental framework is developed to optimise the design of geomembrane specimens for biaxial tensile testing. Specifically, the geometry and adhesive bonding method of specimens are optimised to maximise strain in the central measuring region while reducing premature failure caused by stress concentrations outside this region. Numerical simulations are used to generate stress distribution datasets, and an objective function integrating two metrics—stress concentration and load transfer efficiency—was used to evaluate specimen geometries. Four key geometric parameters are optimised using a derivative-free subdivision method. Specimens are reinforced by adhesive bonding outside the central region, with bonding methods optimised through uniaxial tensile tests to minimise the effect on inherent material properties. Biaxial tensile tests are conducted to validate and compare three promising geometries obtained from numerical optimisation. The final optimal specimen design achieves a peak central strain of 160.2%, significantly exceeding the previous results. This optimised specimen design provides a valuable basis for future studies on geomembrane biaxial tensile testing.