Indentation stress-based models to predict fracture properties of brittle thin film on a ductile substrate

Abstract

Abstract In the present work, nano-indentation experiments were performed on the surface of alumina film and diamond-like carbon (DLC) film on PEEK substrates using an axisymmetric indenter. After indentation, ring cracks were noticed in the film by scanning electron microscope. Stress analysis results indicated that radial tensile stress on the surface of the film outside the contact region of the indenter caused the ring crack. Then, two stress-based models were proposed to predict fracture stress and fracture toughness of brittle thin film on a ductile substrate based on the crack channeling criterion. The models were expressed regarding critical indentation load, ring crack radius, plastic zone radius, and film thickness. The stresses in film predicted by the present models were validated using axisymmetric finite element analysis. Finally, the models were utilized to evaluate fracture toughness of the alumina film and DLC film in experiments.