Experimental tests with a high-pressure flow visualization cell clearly reveal that the shear deformation in a lubricant film at elevated pressures can localize by a mechanism vastly different from previously reported mechanically-induced shear bands. Verification by numerical solution of the energy equation shows that for a stress-controlled experiment, provided that the Brinkman number is sufficiently large, the local temperature experiences a rapid rise. The rapid rise of temperature along with the local rate of shear favors an unstable temperature profile. The research provides valuable insight into the behavior of lubricants under extreme conditions since this phenomenon may be operating in the thermally dominated regime of EHD traction. Furthermore, the fact that the hot shear band is isolated from the metal boundaries by a cooler liquid, may confound recent attempts to infer the shear stress distribution in a concentrated contact from IR temperature measurement of the metal temperature distribution.

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