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Role of Flaw Statistics in Contact Fracture of Brittle Coatings



P Miranda, Antonia Pajares, F Guiberteau, F Cumbrera, Brian R. Lawn


A flaw statistics analysis is here developed to account for systematic differences between experimentally observed and theoretically predicted critical loads for the initiation of contact-induced radial cracks in brittle coatings on compliant substrates. Specific attention is drawn to deviations in critical load (PR) data from ideal quadratic dependence on coating thickness (d), i.e., PR d2, especially at low d values. It is postulated that these deviations are attributable to the existence of distributions in flaw size and location, in relation to the bell-shaped tensile stress fields responsible for initiation of the radial cracks at the coating lower surface. A statistics-based expression is derived for the mean values of PR in terms of flaw density and size distribution. Data from model bilayers consisting of glass plates of different thicknesses d bonded to polycarbonate substrates are used as an illustrative case study. Controlled pre-abrasion flaws are introduced into the lower glass surfaces before joining into the bilayer configuration, to enable a priori characterization of distribution parameters by image analysis. Finite element modelling is used to determine the tensile stress distribution at the coating lower surface. The predicted statistics-based PR(d) function is shown to fit the data within uncertainty bounds. Implications concerning the continued usefulness of the ideal, PR d2 relation for designing ceramic coatings for failure resistance are considered.
Acta Materialia
No. 18


bilayers, brittle coatings, contact loading, flaw statistics, radial cracks, strength


Miranda, P. , Pajares, A. , Guiberteau, F. , Cumbrera, F. and Lawn, B. (2001), Role of Flaw Statistics in Contact Fracture of Brittle Coatings, Acta Materialia (Accessed March 3, 2024)
Created September 30, 2001, Updated October 12, 2021