The effect of time-related parameters such as loading velocity, load application time, and gauge reading time on Rockwell hardness measurement was investigated for polymers such as polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC) and acrylic plate. It was found that keeping the specific requirements of the test procedure, especially for the time parameter related one, is very important to obtain reliable and repeatable data in polymer hardness measurement. These characteristics of plastic hardness measurement are because of the good elastic properties of polymers and showed continuous deformation even at the time of data reading. The optimum condition for hardness measurement appeared to be 4s for load application time, 15s for test load application net time, and 15 s for gauge reading time after unloading. After this preliminary test for establishing protocol, a round robin test was carried out for six laboratories and it appeared that the testing machine should be one in which time-related variables are controllable. In other words, hardness tester with a function of plastic mode test showed much better repeatability in measurement data because of the automatic reading of data at a specific time. Verification of hardness tester using brass reference block was not enough to guarantee the reliability test results or reduced data scattering for polymer.
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