Relationship between wear rate and mechanical fatigue in sliding TPU–metal contacts

The present paper reports the process for obtaining a law of wear by friction that reproduces the behaviour of a contact pair between a guide shoe insert, made of TPU, and the corresponding guide, made of steel, in a lift guide shoe application. After an initial identification of the TPU wear type as fatigue wear, the wear law is fitted from tests carried out in a tribometer, obtaining a relationship between the TPU worn volume and two fundamental variables: the travelled distance and the applied load. Archard's law, a relationship commonly used by many authors in the literature, is taken as a starting point, analysing its validity in this case and proposing an improved fitting by means of a potential law.Additionally, in order to analyse in depth the physical phenomena that guide the wear process present in the contact pair under study, and corroborating what was stated by the law fitted previously, the wear process is studied by means of observations by SEM and confocal microscopy by finite element simulations at micro-level, analysing the interaction between material and countermaterial. The results from these analyses are compared with conclusions stated by several authors in the literature in similar studies of other polymers. Finally, this study is completed with an analysis of the analogy between wear and mechanical fatigue, relating both phenomena, in order to confirm the assertion stated in previous studies: the wear process in TPU occurs as a result of repeated crack propagation in the subsurface layer of the material at small scale.