Determination of non-linear, large, equal biaxial stresses and strains in thin elastomeric sheets by bubble inflation

Abstract

This paper presents a method for investigating the axisymmetric bubble inflation of elastomers by an optical measuring system and determining local stress and strain properties in biaxial deformation. In particular, the local stretch ratios on the bubble shell are evaluated by an element grid [1,2]. Both the pattern and the bubble contour are observed optically on-line during a continuous inflation process. The relations between internal pressure, bubble height and local shell stresses and strains are analysed. Additionally, free and tube-guided inflation using hydraulic and pneumatic pressure systems are compared. As stresses toward the pole of the bubble gradually increase during the inflation process, the experimental method permits an investigation into material properties at high equibiaxial loadings and the determination of constants for different material models. The conclusion of this investigation is that simple assumptions that relate local stress and strain levels to the bubble inflation height cannot be made.