Evaluation of Stress and Strain Measurement Accuracy in Hydraulic Bulge Test with the Aid of Finite-element Analysis

Numerical simulations of the hydraulic bulge test are carried out by the implicit static finite-element method. The sheet specimen is characterized as a rate-independent elastoplastic material with a power-law hardening rule. The stress and strain relationship of the specimen is evaluated from the internal pressure and nodal coordinates obtained in the finite-element simulation of the hydraulic bulge test. Varying the gauge lengths of the spherometer and extensometer and the ratio of the initial thickness to the diameter of the specimen, their influences on the estimated stress and strain are investigated. By comparing the estimated stress-strain relationship with that of exact input data, the stress and strain measurement accuracy is assessed. Furthermore, the stress state at the apex is examined for orthotropic specimens and is found to deviate by 1-5% from the equi-biaxial stress state.