Significance and Use
Scratch tests are performed on specimens:
(1) to evaluate the scratch or mar resistance of a particular material,
(2) to rank the relative scratch resistance of different materials, or
(3) to determine the scratching coefficient of friction of materials.
Since polymers exhibit mechanical properties that are strongly dependent on temperature, the test method 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.
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 the post-scratch damages and appropriately compare results to ensure reproducibility.
“Whitening” of the scratched surface is a key damage mechanism that has prompted much concern in automotive and other applications where surface aestheticism is important. This type of damage is undesirable because it is evident to human eyes. The critical normal load at which this phenomenon appears serves as a benchmark in ranking material performance.
For polymers that do not exhibit whitening, a scratch groove from severe ploughing is still highly noticeable. In such cases, the normal load required to achieve a certain scratch width shall be reported to characterize scratch visibility and scratch resistance. The critical scratch width shall be decided by users in accordance with the specific material and remains the same throughout a set of tests for a consistent comparison. The variation of the scratch width as a function of the applied load shall also be plotted for comparison purposes.
1.1 This test method describes a laboratory procedure using an instrumented scratch machine to produce and quantify surface damage under controlled conditions. This test method is able to characterize the mar and scratch resistance of polymers by measuring many significant material parameters. The scratch-inducing and data acquisition process is automated to avoid user-influenced effects that may affect the results.
1.2 The values stated in SI units are to be regarded as standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Note 1—FLTM BN 108-13, ISO 1518 and ISO 12137-2 are related to this test method; the contents are significantly different from this method.