Fractured surfaces of epoxy adhesives and fractals under mode I loading (2nd Report, Fatigue crack growth properties and fractal dimensions)

The effects of rubber modification and adhesive thickness on the fatigue-fractured surfaces of epoxy adhesives under mode I cyclic loading were examined using fractals. When the energy release rate range, ΔG_I is higher than 100 J/m² the fractal dimension of fractured surfaces becomes high due to rubber modification under the same ΔG_I. The fractal dimension decreases with increasing fatigue crack growth rate, da/dN. A relationship is given by the following equation between the parameter, S (= da/dN×ΔG_I) and the fractal dimension, D for unmodified and rubber-modified adhesives. log S = log(da/dN·ΔG_I) = α₄·D+β₄ where α₄ and β₄ are experimental constants. Whether the adhesives contain rubber particles or not, the fractal dimension as well as the da/dN-ΔG_I relation is little affected by adhesive thickness.