The present study has been pursued for two purposes, to clear experimentally the method of measuring the scratch hardness of plastics by using Martens hardness tester on one hand, and on the other to find theoretically and also experimentally the relation between scratch hardness and Vickers hardness for plastics.
The results obtained are as follows;
1) The sectional form of the scratched groove on plastics has wider variety than that on metals.
2) The width of the scratched groove slightly decreases with the increase of scratching speed.
3) The time to measure the width of the groove has to be limited within about 5 minutes after scratching, because the width of the groove decreases with time according to the retarded elasticity.
4) The ratio of the vertical load P on the scratcher to square of the groove width b2 is almost constant at any vertical load for each plastics, so the scratch hardness Hc has been represented by the following formula;
Hc=P/b2
5) The relation between the scratch hardness Hc and Vickers hardness Hv is shown by the following equation;
Hv=4/π·α2·β·sinθ0/2·Hc
where α and β are the constants which are nearly the same in every plastics, that is, 0.815 and 2 respectively, and θ0 is the vertical angle of conical scratcher.