ABSTRACT
Two types of measurements are relevant to adhesion [1-4]: (i) the stress at which the interface separates, a c, and (ii) the energy dissipated per unit area upon extend ing a crack along the interface, r, (in J/m2). The latter has the same role as the fracture toughness in homogeneous materials [5-7]. The former includes effects of defects and of stress concentrations (especially at free edges) [3] and is thus test specific and inherently stochastic. While both are important, here, the energy den sity is emphasized, since it is amenable to quantitative comparison with mecha nisms and models [2,8-10] and moreover, in principle, the measurements can be used explicitly in design codes and durability models for multi-layer systems. That is, a methodology similar to fracture mechanics-based design of structural compo nents [5-7] could be used subject to the construct of the appropriate numerical code [11]. This prospect can only be realized if the test methods yield quantitative meas ures of r , . Accordingly, the emphasis of this brief overview is on a pathway toward a quantitative design strategy applicable to multi-layer systems.
