Variation in mode II dominated interface fracture of stainless steel-epoxy bonds. Part 1: Mechanical testing

We study variation in measured interface fracture toughness values for three substrate micro-scale surface morphologies taking into account aging. Wedge indentation is used when preparing pre-cracks. The notched coating adhesion test (NCA) is applied to drive the crack along the interface and specimen-wise residual stresses are accounted for. The interfaces suffer short-term aging regardless of the morphology, leading to an even 80% decrease in fracture toughness. Sharp roughness shapes are suggested as the factor for random-like variation for the specimens with nitric acid etched substrates. Electropolishing treatment leads to less variation, but the fracture toughness values are already low after 10–15 days of storage.