Fracture mechanics characterization of mixed-mode toughness of thermoplast/glass interfaces (brittle/ductile interfacial mixed-mode fracture)

Interfacial toughness is enhanced when the mode-mixity of the biaxial near-tip stress state approaches mode II. Conversely, when the near-tip mode-mixity is close to pure mode I, the interfacial toughness curve exhibits a minimum. This toughness minimum is believed to represent the so-called intrinsic adhesion, Within linear elasticity, the biaxial, singular near-tip solution for an open interface crack may be employed for characterizing the local stress state as long as non-linearities due to crack-wall contact and plastic flow are contained within a length scale small enough compared to the extension of the near-tip opening-dominated fields. In the present work, the interfacial mixed-mode fracture toughness curve was determined for a polyethylene/ glass compound. Subsequent to the reduction of experimental data based on the linear-elastic crack model, the applicability of linear-elastic fracture mechanics is verified by comparing the estimated extension of the plastic zones to the extension of the K-dominance zone, It is found that within the mixed-mode range accessible to linear-elastic fracture mechanics the apparent interfacial fracture toughness varies by about an order of magnitude.