On the useful life of tribo-pairs experiencing variable loading and sliding speed

Abstract

Tribo-pairs experiencing fluctuating operating conditions are expected to have lower useful life compared to those that operate in a steady state condition. The objective of the present study is to gain insight into the wear characteristics of such tribo-pairs operating in dry conditions and to develop a general procedure to reliably predict their useful life. Results are presented based on a series of experiments performed using a ball-on-disk tribometer. The disk is made of brass coated with a black paint to clearly detect the onset of failure defined as the time when the steel ball contacts the brass disk and friction force rapidly fluctuates and becomes erratic. First, experiments are performed at various loads (1 N, 2 N and 3 N) at a constant sliding speed (0.1 m/s), and different sliding speeds (0.05 m/s, 0.1 m/s and 0.2 m/s) at a constant load of 2 N) for establishing the useful life. Following these experiments, fluctuating operating conditions are imposed by varying (i) loading sequence, (ii) sliding speed sequence and (iii) both load and sliding speed in an arbitrary manner. For all these experiments the remaining useful life for the last sequence are determined by considering Miner's constant C = 1 and cumulative power to failure of 103 W. The results revealed that the maximum error between the power generation method and experimental results vary from 2% to 10.3%, while using Miner's constant, the error was substantially higher. Further, the applicability of power generation method is validated for an extreme operating condition for an Al-steel tribo-pair. Finally, a detailed mathematical explanation is provided to illustrate the reason for the advantage of power generation method over Miner's rule.