Blow-off pressures for adhering layers

Abstract

An analysis is given of the critical internal pressure P at which a circular debond (“blister”) will grow in size, in terms of the tensile modulus E and thickness t of an adhering layer, and the strength Ga of its adhesion to a rigid substrate. Measurements of blow-off pressure are reported for adhering layers of pressure-sensitive tapes having widely different effective modulus and thickness, and with blisters having a range of diameters. Satisfactory agreement is obtained with the theoretical predictions, suggesting that the theory is basically correct in assuming that relatively thin layers behave like elastic membranes. Attention is drawn to the unusual form of the dependence of the debonding pressure P upon the resistance Et of the layer to stretching and upon the detachment energy Ga: P4 ∝ EtG. Even though the adhering layer is assumed to be linearly elastic, the markedly nonlinear (cubic) relation between pressure P and volume V of the blister, or maximum height y, leads to this unusual result. The detachment energy is given by a particularly simple function of the pressure P and maximum deflection y of the blister: Ga = 0.65Py, independent of the stiffness of the adhering layer and diameter of the blister.