Structural and functional regularities of the damage accumulation and failure in metals under dynamic loading and wear

Abstract

The effect of damage caused by friction and wear on the accumulation of fatigue damage in the near-surface layers of the material used in technical systems operating under dynamic loading is studied. A comparative study of the samples of carbonized Cr – Mn – Si steel under ultrasonic loading in the range up to 109 cycles and the samples of steel 45 loaded at a permanent frequency of 100 Hz to simulate conditions of tribological tests for frictional fatigue revealed the same types of damage occurring in the characteristic frequency ranges of loading. To assess the effect of friction fatigue on damage accumulation and the probability of operational failures the authors have supposed that the processes of structural damage accumulation in cyclic and frictional fatigue are similar. The analysis of experimental data on the behavior of the friction coefficients and the magnitudes of broadening X-ray lines which characterize changes in the dislocation structure of the metallic structural materials (steels and titanium alloys) upon friction and the friction fatigue curves confirmed that the process of friction fatigue failure occurs via the mechanisms of low and high cycle fatigue that proves the validity of the proposed approach. The calculation results for the probability of the compressor failure are presented as an example. The calculations are based on the friction fatigue curves in a wide range of loading cycles obtained upon testing the crankshaft neck. The use of friction fatigue curves thus obtained provided assessment of the effects of combined action of the dynamic loading and friction, resulting in increased gaps and the dynamic loads (due to the wear of contacting parts) on the fatigue damage accumulation, durability and the reliability of the mechanical systems during operation.