Scratch testing: a means of characterising the in-service performance of automotive polymers

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Scratch testing: a means of characterising the in-service performance of automotive polymers

Pickles, M.J. / Hutchings, I.M.

A wide variety of polymers is currently used in automotive applications where accidental or deliberate surface damage may detract from their appearance or impair their function: for example in instrument panel trim, light fittings or bumpers. This paper presents an experimental study of the scratch testing technique for characterising the resistance of polymers to scratching and damage. This technique involves traversing an indenter of well-characterised geometry across a specimen surface, under constant normal load and velocity. The scratch hardness may then be deduced from the geometry of the indenter, the normal load and the resulting scratch width. The scratch test has been applied to four different TPO (Thermoplastic Olefin) materials. The effects of ambient temperature are investigated in detail and the scratch hardness values are correlated with conventional tensile test data. The deformation modes associated with both blunt (spherical) and sharp (conical) indenter geometries have been studied. The effects on scratching and surface damage of painting the upper surface of the polymer have also been investigated.