Analysis of blister tests by using hypersingular integral equations

It is essential to determine the fracture characteristics of adhesive bonds. The blister test is commonly used to measure the adhesion strength and to evaluate the performance of adhesive bonding. The test procedure involves a thin film bonded to a substrate except for a circular disbond where either a uniform pressure or a point load is applied. The applied loading is increased gradually until its critical value at which adhesive failure occurs. The concept of energy release rate can be applied to predict adhesive failure. However, the calculation of energy release rate requires accurate prediction of singular stresses or stress intensity factors at the crack (disbond) front based on the theory of elasticity. The previous solutions based on the theory of elasticity permit only the determination of energy release rate which is not directly suitable for comparison with experimental measurements. These solutions employ the derivative of the crack surface opening displacements as the primary unknowns, thus leading to singular integral equations with Cauchy-type singularity. The present study employs the crack opening and sliding as primary unknowns rather than their derivatives, thus leading to hypersingular integral equations. Solution to these singular integral equations permits the determination of not only the complex stress intensity factors but also the crack opening displacements. The analysis predictions are compared with both the finite element simulations and previous benchmark solutions.