Hydrostatic bulging of adhesive-bonded laminates

Abstract

Laminates consisting of two or more adherends bonded together using structural adhesives are gaining much attention, particularly in the aircraft and automobile industry. These laminates are frequently formed into panels and shells for use as containers, pressure chambers and rupture discs. The forming techniques include the hydrostatic bulging of a blank to the desired polar height or shape. When used as a pressure chamber or a rupture disc, the shell is subjected to uniform pressure, similar to the forming conditions during hydrostatic bulging. In this investigation, various types of adhesive-bonded laminates were formed into axisymmetrical shells by hydrostatic pressure at room temperature until failure occurred. It was found that the laminated shells are nearly spherical in shape and that the evolution of shape with polar height is similar to that for shells formed from a single sheet material. Theoretical values of strain and forming pressure computed from a recently developed model are found to compare well with the measured values. Furthermore, the stress-strain relationships of laminates can be predicted from those of the adherends using the rule of mixtures based on the "equal-strain" (in the two adherends) hypothesis. Thus, in using the model, only the tensile stress-strain relationships of the adherends are required. © 1989.