The development of scratch test methodology and characterization of surface damage of polypropylene

摘要

A new scratch test methodology is proposed. The new test methodology isdeveloped based on the principles of materials science and solid mechanics, whichinclude the consideration of material parameters, use of microscopy for imageanalysis and the finite element method (FEM). The consistency and reproducibility oftest results are shown using a new scratch test device on two sets of neat and talcfilledpolypropylene (PP) systems. Three different test conditions, i.e., linear loadincrease under constant rate, constant load under constant rate, and linear rate increaseunder constant load, have been conducted to determine the most effective, informativetest conditions for evaluation of scratch resistance of polymers. Experimentalobservations and FEM results show a good qualitative correlation. The uniqueadvantages of the new scratch test method for evaluating scratch resistance ofpolymers are discussed. A systematic study of surface damage effected by aprogressive scratching load is performed on model polypropylene (PP) systems. Mar-scratchand stress -whitening transitions can be readily observed, and thecorresponding critical loads determined. Distinctive scratch hardnesses and surface damage features arefound for different material systems. Visibility of scratched surface is quantifiedusing gray level analysis via a flatbed scanner and a commercial image analysis tool.It is found that the onset of scratch visibility can be determined accurately andreproducibly using the custom -built scratcher under progressive loading condition.Talc particles are found to be responsible for the increased light scattering, leading togreatly increased visibility. The observed scratch visibility is also found to be relatedto the measured frictional force profiles. Approaches for producing scratchresistant PP are discussed.