Dry sliding metals process modelling: dynamical system paradigm

Abstract

The progressive damage and material loss occurring on a component surface as a result of its movement relative to the adjacent working parts has profound economic consequences (substitution costs, inactivity of machines, loss of production, etc.). Several authors have reported that friction losses in internal combustion engines represent approximately 20% of total energy consumption; in the railroad industry, it reaches nearly 50%, and it is as high as 80% in the textile industry. Studies show that about one third of the total world energy consumption is lost in the friction between solids. Friction can be considered as one of the most relevant industrial problems associated with mechanical elements. To solve this problem, equations and friction and wear models have been developed; these are used to predict the parts life cycle and the machine failure occurrence. However, the best models and equations have a very limited usefulness. In addition, it can be observed that much knowledge about friction and wear is dispersed or fragmented mainly due to the fact that each modeling approach identifies its own study variables related to the dominant wear mechanism occurring in the mechanical pair studied, excluding the other wear mechanisms. The existing influence between the different wear mechanisms has been demonstrated in multiple works; as well as the macromechanisms dependence on wear micromechanisms. Therefore, the fact of discarding the pre-existing correlational domain between the possible responses of a mechanic pair to external inputs is to continue studying the problem from a single approach. Likewise, this is evidenced by the poor role played by the dynamic studies in modeling process of sliding between solids. A high percentage of the models developed in this field are static despite the fact that wear, the heat by friction and material loss represent some of the factors governed by a machine’s dynamic performance. At the same time, a large part of the tribological tests are carried out in a stationary state in which, the tribometer’s exogenous inputs are not manipulated during the test; that is, the emergent dynamics caused by changes in the exogenous entries to the system are excluded. Therefore, a dynamic model that includes the most important aspects of a dry sliding process between metals has not been found in literature, a model not only describes the variables involved in it but also classifies and hierarchizes them. This research gap has already been identified by Ashby (1992), Rymuza (1996), Viafara and Sinatora (2010) among others. For this purpose, it is necessary to use a sufficiently robust theoretical framework such as the Theory of Dynamic Systems, which is able to identify, classify, quantify the relevant variables, describe and predict the behavior of the predominant phenomena taking place within the sliding process between dry metallic solids through the development of a dynamic model represented under the State Space Theory