Evaluation of the incubation period of polymers in cavitation wear by the method of profilometry

The possibility of using profilometry for determining the duration of the incubation period of polymeric materials upon their testing for cavitation wear is considered. Six polymeric materials were tested for cavitation wear: plexiglass, fluoroplastic, low-pressure polyethylene, caprolon, Thordon SXL polymer, and epoxy compound. All the polymers were tested in fresh water kept at 20 ± 3°C, using an ultrasonic magnetostrictive vibrator, the vibration frequency and amplitude of the device horn butt were 22 kHz and 28 μm, respectively. The distance between horn butt and the butt-end surface of the cylindrical polymer sample was set at 0.50 mm. The samples were periodically weighed during testing, the roughness of their worn surface was evaluated, and sample mass loss and arithmetical mean deviation of the assessed profile of its surface were plotted as a function of the test duration. Like the cavitation wear of metals, the cavitation wear of polymers is also characterized by the presence of an incubation period, during which the separation of the wear particles from the sample surface does not take place yet. It is shown, that determination of the incubation period from the dependence of the mass loss vs test duration distinguishes is rather laborious, and, moreover, is accompanied by large errors due to water absorption. The use of profilometry was proposed to shorten the time and increase the accuracy of the determination of the incubation period of the cavitation wear of polymers. The arithmetical mean deviation of the profile of the surface under study is measures periodically during testing for cavitation wear. The duration of the incubation period is determined using the dependence of the arithmetic mean deviation of the wear surface profile on the duration of the cavitation impact by the abscissa of the point, in which the monotony and(or) smoothness of the dependence (plot) is violated.