Roughening of Fracture Surfaces: The Role of Plastic Deformation

Post mortem analysis of fracture surfaces of ductile and brittle materials on the μm-mm and the nm scales, respectively, reveal self-affine cracks with anomalous scaling exponent ζ≈0.8 in three dimensions and ζ≈0.65 in two dimensions. Attempts to use elasticity theory to explain this result failed, yielding exponent ζ≈0.5 up to logarithms. We show that when the cracks propagate via plastic void formations in front of the tip, followed by void coalescence, the void positions are positively correlated to yield exponents higher than 0.5.