Scratch tests were used to evaluate the durability of duplex elastomeric co
atings under single pass, continuous loading, low speed sliding contact. Th
e coatings consisted of a softer elastomer top layer (effective modulus = 3
MPa) on a stiffer elastomer bond layer (effective modulus = 23 MPa) on epo
xy-coated steel. Duplex coating thicknesses ranged from 0.1 to 1 mm. Two di
fferent scratch styli were used: a 1.6 mm radius steel ball and a conical p
in with a 0.8 mm radius diamond tip. The tangential force increased monoton
ically with normal force, then dropped suddenly; the onset of this drop is
defined as the critical tangential force, T-c. T-c increased linearly with
increases in both bond and top coat thicknesses, but the thickness dependen
ce of the bond coat was 2 to 3 times more than that of the top coat. Optica
l and Raman microscopy of scratch tracks associated the damage at T-c with
either tearing of the top coat behind the slider or debonding of the bond c
oat ahead of the slider or a combination of both. The thickness dependence
of T-c is discussed qualitatively in terms of both stress and fracture mech
anics models that account for damage to elastomer-coated substrates.