Testing methods scratch behavior

To assess the scratch behavior of polsmiers, scratch tests are performed. A compendium of the use of various instruments and methods applied is given in Reference (20). Although different setups have been used for scratch studies, the basic principle relies on the use of a stylus to scratch a surface (2,3,21 3). The stylus can be made of materials ranging from diamond and sapphire, to tool steel, and silicon nitrite for the case of AFM tips. It also comes with a variety of geometries including conical tips with different included angles, spherical tips of different radii, and Berkovich tip. In addition, the observation length scale and controlled experimental parameters are instrument specific. 

Individual scratch is often done with a constant loading rate (which includes constant load) and constant scratch rate. The scale of damage of interest varies from macroscopic features to those of nanometer scale. This renders comparisons between studies difficult. The recent concerted industry-university effort (6,7,44) has led to the development of a scratch test method and universal scratch testing equipment to facilitate good scratch test practices and fimdamental study of scratch behavior of polymers. Figure 4 presents the scratch tester that was developed. It aims to provide reasonable capability to vary experimental conditions for capturing the essential scratch characteristic of the materials with reliable and reproducible results. One unique feature of the tester is its ability to alter scratch load and velocity at a linear rate. This feature is foimd to be useful in understanding scratch behavior of polymers, to be presented in later sections. 

For hardness determination, different methods are possible scratching the surface, penetration of an indenter with static or dynamic loads, or rebound as a result of elastic material behavior. The methods with a penetrating indenter are the most important ones. The applied methods are distinguished, e.g., by the shape of the indenter. Brinell hardness is determined by a ball-shaped indenter, while Vickers hardness applies a pyramid-shaped one. After the indenting test with a certain load, the surface area of the indentation is measured which delivers a value for material hardness. Determination of Rockwell hardness uses the depth of the indentation instead of the surface area (Bargel and Schulze 1988). Independent of the method, the so-called surface hardness... 

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