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Definition of Scratch And Mar

For grained surfaces such as pp/talc in automotive applications we use the Erichson multi-finger scratch and mar tester that generates a pattern of crossed lines on test plate. Thereby, the scratching force as well as the diameter of the scratching head can be adjsuted. The difference in color before and after the scratching is measured (D L) and taken as indicator for the scratch resistance. Secondly, we use the five finger scratcher to evaluate the scratch resistance of grained surfaces. 

 It is a fast method to evaluate the scratch resistance at different forces in one single test.Scratch and mar are types of mechanical surface damage that can occur during normal usage and handling, shipping or assembly procedures.  Defined as "the resistance of a solid body to penetration by an edge or protuberance on a second body that is moving along its surface", scratches are usually associated with a single occurrence in the specimen surface.  Normal scratching includes deformation such as plowing, but might also involve material cracking, peeling and removal.  

 In comparison, marring is the term used to describe relatively fine surface scratches generally characterized by shallow damage, distributed over a relatively large area that typically spoils the appearance of a surface coating.  It may be convenient to consider mar resistance as a surface property, whereas scratch or abrasion resistance involves the body of the material as well.

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