Mechanics of an adhesive tape in a zero degree peel test: effect of large deformation and material nonlinearity.

The common pressure sensitive adhesive (PSA) tape is a composite consisting of a stiff backing layer and a soft adhesive layer. A simple and common way to test how adhesive tapes respond to large shear deformations is the zero degree peel test. Because the backing is very stiff compared to the adhesive layer, the region where the adhesive layer is subjected to large shear can be hundreds of times its thickness. We use a large deformation hyperelastic model to study the stress and deformation fields in the adhesive layer in this test. We present a closed-form solution for the stress field in the adhesive layer and use this solution to determine how load is transferred from the backing layer to the adhesive. Our analytical model is then compared with finite element results, and except for a small region near the peel front, the predicted stress and deformation agree well with the finite element model. Interestingly, we find very different results from the classical linear theory established by Kaelble. In particular for large deformations, our analysis shows that the lateral stresses (parallel to the rigid substrate) are much larger than the shear stress in the adhesive layer. The discrepancy in the stress state and the deformation state with the linear theory is particularly large near the peel front, which we study with a finite element model. These new results will be very useful to interpret experiments and in particular to identify the high stress regions where failure is likely to initiate in zero-degree peel tests also called shear resistance tests in the PSA industry.