Failure of Glass Layers on Polymeric Substrates From Vickers Indentation
Herzl Chai, Brian R. Lawn
A study is made of median crack evolution in brittle coatings subjected to sharp contacts. A model bilayer system consisting of a glass plate bonded to a polycarbonate base, with a Vickers pyramid as indenter, is used to demonstrate the evolution in situ. Newly initiated median cracks have the geometry of subsurface pennies containing the indentation axis and an indenter diagonal. The median cracks undergo a phase of stable downward growth with increasing load. Beyond the coating mid-plane, flexural stresses (coupled with the local contact field) elongate and accelerate the median cracks downward through the lower half of the brittle plate, causing unstable failure. Critical loads corresponding to this failure state diminish with decreasing layer thickness until, at small thicknesses ( 300 m in our bilayer system), failure occurs spontaneously at initiation, i.e. without any stable growth phase. The highly deleterious nature of the median failure mode in a broad spectrum of brittle coatings and films is emphasized.
and Lawn, B.
Failure of Glass Layers on Polymeric Substrates From Vickers Indentation, Scripta Materialia, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=850138
(Accessed December 7, 2023)