Molecular simulations of deformation and failure in bonds formed by glassy polymer adhesives

The mechanical behavior of glassy polymer bonds is examined with molecular dynamics simulations. We show that the interfacial strength of the bond in mode I (tensile) and mode II (shear) fracture is strongly influenced by the coupling between the adhesive and adherends as well as by the roughness of the substrate surface. Failure occurs at the substrate (interfacial failure) when the interaction is weak, and in the bulk (cohesive failure) when the interaction is strong. The transition from interfacial to cohesive failure under mode I loading is nearly unaffected by roughness, while roughness leads to a dramatic increase in interfacial strength under mode II loading. Stress mixity is another crucial parameter that determines whether the polymer fails through shear deformation or through cavitation and crazing. By varying the geometry of the adhesive bond, we illustrate different limiting behaviors of a rupturing film.