997.In the process of use many parts are subjected to the impact action of abrasive particles contained in a flow (jet) of gas or liquid and ones present on the contacting surfaces in the form of an abrasive layer. Despite the large number of publications devoted to problems of wear of parts, no universal criterion has been developed for evaluating the wear resistance of materials operating under various wear conditions. The present work concerns hydraulic and impact abrasion of various steels and alloys of nonferrous metals. In establishing the dependence of the wear resistance of the studied materials on their proper'des the authors take into account for the first time the rigidity of the stress state of the worn surfaces, which allows them to explain the special features of the behavior of the materials when subjected to various kinds of abrasion wear.In choosing the material for a part used under conditions of wear it is very important to determine what structure and properties are optimum for providing their maximum endurance [1,2]. The problem of optimizing the structure and properties to obtain a combination of high wear resistance and the requisite structural strength for the part, i.e., an optimum ratio of the surface and bulk strength of the part under specific operating conditions, is no less important. This paper presents results of a study of wear in various materials with the aim of developing a universal criterion of wear resistance.Tests of cylindrical specimens for hydraulic abrasion wear were conducted in a trough installation [2,3] with movement of the specimens at a linear sped v = 3.1 m/sec in a working medium consisting of water and quartz sand with particles 0.3 -1.6 turn in size in a 3-to-7 proportion (volume fractions).In tests for impact abrasion wear cylindrical specimens 10 mm in diameter collided periodically, by impact of their end faces, with an anvil covered with a 14A32NM abrasive cloth. At the moment of collision the abrasive cloth was immobile, i.e., the impact was direct. The impact energy in the tests was 0.5 J.The mechanical properties and the relative wear resistance (K, w )HA and (K~x u )la of the materials tested for hydraulic (HA) and impact (IA) abrasion wear are presented in Table I. In both series of tests the standard specimens were made of carbon steel 25L in a cast state.St. Petersburg State University of Water Communications, St. Petersburg, Russia.The dependence of (K6u)m,, of the materials on their hardness HI'is presented in Fig. la. The points in Fig. 12 can be grouped around four cu~'es corresponding to a power dependence (K,~I.)H A = const I HV",where cons h is a constant and t7 is an exponent varying from 3 to 1.5. In the lower part of Fig. l a we present dependences of the coefficient of rigidity of the stress state P of the studied materials on their hardness for angles of collision ct between the abrasive particles and the worn surface equal to 90 ~ , 45 ~ , and _~ 0 ~ At c~ z 0 ~ the collision betv,,een the particles and the surface of the specimen occur...

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The friction of polyamide-6 against tin bronze BrO5Tz5S5 is investigated. The experiments on a friction machine MI-1 according to the scheme of «a stationary ring against a rotating roller» arranged by both direct and reverse friction pair are carried out. The reverse pair is tested under both water lubrication and dry condition, whereas the direct pair is tested just under water lubrication. The lubrication is implemented by partially immersing the roller into the tray filled with fresh water. At first every friction pair underwent breakingin with the load equal to that taking place on the surface of real stern-tube bearings during their breaking-in. Then the friction moment is recorded at different loads. When dealing with dry friction, the breaking-in, however, is implemented under water lubrication condition mentioned above, then the roller and the ring are dried thoroughly with paper napkins and fixed again exactly on the previous position. It turned out that friction in polyamide-tin bronze pair under boundary lubrication with water does not depend on the initial roughness of both polyamide and bronze element. And the friction does not depend on the friction scheme (direct or reverse pair) either. Even at comparatively high pressure, characteristic for the real stern-tube bearings breaking-in, the water comes in between the rubbing surfaces. The friction under lubrication condition is caused completely by adhesion, which, in its turn, results from dispersion interaction between adsorbed water films (under water lubrication) or immediately rubbing surfaces (under dry condition). Application of water reduces the friction by 25 % compared to the dry friction.

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.