Is there delamination wear in polyurethane?

Abstract

Delamination wear is found in the literature of metals, ceramics and composite materials involving layers of different polymers. In the tribological investigations on polymers, the phenomenon of delamination in polyurethane has not generally been cited. This work focuses the damage mechanism of delamination noticed in flat surfaces of thermoplastic polyurethane elastomer (TPU), when sliding against rotating surfaces. A sliding testing rig was conduced using an innovated counterface, based on the taxionomy, proposed by Briscoe for polymer wear mechanisms. It was constituted by a cylindrical metallic axis, manufactured using AISI 1045 steel with seven angular protuberances of different contact angles (15o, 45o, 75o, 105o, 135o, 165o and 180o), instead of conventional sphere. This geometry developed in TPU distinct damage modes during sliding tests. Worn surface examinations were conducted using scanning electron microscope (SEM). The morphologies of the wear sheet detected by SEM suggest that two different processes of damage may have originated the delamination. In one process, associated with a shakedown mechanism as defined by Johnson, every located stress state can be associated with the contact pressure, the traction coefficient and TPU cumulative response of yield surface and elastic sub-surfaces resulting in different lamellae layers. In another process, the creation of wear lamellae occurred by shearing and squeezing a small amount of material following a large number of asperities that have crossed each point on the surface, as suggested originally by Suh. The experiment provided, moreover, wear mechanisms well known as prow formation, ploughing, fatigue (wave formation), melting and tearing.