Experimental observation and finite element method modeling on scratch-induced delamination of multilayer polymeric structures

Scratches that result in delamination are common in multilayer polymeric laminates and coatings. In this study, the adhesive failure among a set of model double-layer epoxy coatings was experimentally investigated and numerically analyzed using the finite element method modeling based on the maximum principal stress criterion. The adhesive failure on the model epoxy coatings was generated using an ASTM-standard linearly increasing normal load scratch test. The parametric study reveals that delamination may initiate at locations underneath both scratch shoulder and behind scratch tip during scratching. It is also found that the magnitude and direction of peak tensile maximum principal stress developed at the interface are affected by both the laminate thickness and the material parameters of each layer. The parametric analysis shows that the onset of delamination can be delayed by possessing a softer base layer, a top or base layer with a higher yield stress, a base layer with a lower strain-hardening slope, and a lower surface coefficient of friction. The Mode I delamination at the interface will become dominant in a multilayer system when the base layer has a higher modulus and a lower strain hardening slope. The usefulness of the present study for determining the delamination resistance of multilayer polymeric laminates and coatings is discussed.