Fracture of metal/polymer/metal assemblies: Viscoelastic effects

The purpose of this work is to link the polymer viscoelastic properties (especially its relaxation time) and the adhesive behaviour of steel/polymer/steel assemblies. A wedge test device developed in the laboratory allows one to introduce the wedge into the assembly at a controlled speed and to follow the crack propagation with a camera-equipped microscope. The adherence energy (calculated from the equilibrium crack length) and the crack propagation rate are measured for different wedge introduction rates. Polymer equivalent relaxation time is determined for each introduction rate according to the time-temperature superposition principle. Relations between adherence energy, crack propagation rate, and calculated equivalent relaxation time values are proposed. These quantitative relations confirm the major influence of polymer viscoelastic properties on the rate sensitivity of adhesive behaviour.