STRESS-ANALYSIS OF ELASTIC-PLASTIC CONTACT DAMAGE IN CERAMIC COATINGSON METAL SUBSTRATES

An elastic-plastic analysis of damage in ceramic coatings on metal sub strates from contacts with spherical indenters is made using finite el ement modeling, Computations are carried out specifically for plasma-s prayed alumina:titania on a soft steel, The algorithm assumes an elast ic sphere with frictionless contact on a flat elastic-plastic layered specimen, and incrementally evaluates the expanding contact field as a function of applied load, Two key aspects of the contact field are ex amined: (i) the indentation stress-strain curve; (ii) the damage zone geometry, Composite coating/substrate indentation stress-strain curves are computed for two coating thicknesses, using input material parame ters from iterative fits to data from control tests on free-standing c oating and substrate materials. Contours of principal shear stresses, most notably those contours corresponding to yield zone boundaries in both the softer substrate and the harder coating, are mapped out in th e fully plastic region, Corresponding distributions of tensile stresse s are also mapped out, and are shown to correlate with the locations o f transverse fractures in the coating, General implications concerning material and geometrical design of ceramic-based layer structures are discussed.