In situ analysis of the fragmentation of polystyrene films within sliding contacts

Fracture processes of thin (10–100 μm) polystyrene films on PMMA substrates have been investigated within macroscopic single-asperity sliding contacts with rigid spheres. Using the resources of in situ contact visualization, the development of cracks has been analyzed under both elastic and plastic conditions for various values of the ratio of the contact radius to the film thickness. Under elastic contact conditions, damage mechanisms were dominated by the formation of a network of regularly spaced cracks at the leading edge of the contact. These processes were analyzed in the light of a fragmentation model based on contact mechanics simulations of the stress field induced within the cracked films. It emerged from this contact mechanics analysis that the mean spacing between adjacent cracks can be correlated to the strength of the polymer coating.