5.1 Scratch tests are performed on specimens:

(1) to evaluate the scratch resistance of a particular material,

(2) to rank the relative scratch resistance of different materials, or

(3) to determine the scratch coefficient of friction of materials.

5.2 Since polymers exhibit mechanical properties that are strongly dependent on temperature, the test standard prescribed herein is designed to yield reproducible results when users perform tests under the similar testing environment and on specimens of the same material and surface texture that are subjected to the same conditioning procedures.

5.3 Certain polymers are self-healing (recoverable) when subjected to scratches and other physical deformations because of their viscoelastic and relaxation properties. It is important to note the difference between the instantaneous (if readily measurable) and residual scratch damage and compare results appropriately to ensure reproducibility. It is recommended that 24 hours be allowed for viscoelastic recovery when considering residual scratch depth.

5.4 "Whitening" of the scratched surface is a key damage mechanism that has prompted much concern in automotive and other applications where surface aesthetics is important. This type of damage is undesirable because it is evident to the human eye. The critical normal load at which this phenomenon appears serves as a benchmark in ranking material performance, especially from an aesthetic point of view.