Office of Technology Transfer – University of Michigan


Technology #1867


Multi-disc brakes and clutches sometimes exhibit thermoelastic instability – thermal distortions generated as a result of an unstable interaction between frictional heating, thermoelastic distortion and elastic contact. These “hot-spots” are high thermal gradients on the rubbing surface and count among the most dangerous phenomena in frictional brakes and clutches leading to damage and early failure. It has been shown that hot-spots may induce a cycling of tensile and compressive stresses with plastic strain variations. Consequently, thermal fatigue may occur and with potential relation with the developments of cracks on the disc surface. These high local temperatures may also lead to poor braking performances such as brake fade or undesirable low frequency vibrations called “hot judder”. Experimental observations of hot-spots have been reported in many practical applications, particularly in railway and aircraft brakes.


HotSpotter is a software tool for evaluating the susceptibility of axisymmetric multi-disk brakes and clutches to thermoelastic instability. It predicts the critical rotational speed at which a clutch or a multi-disk brake will exhibit hot spots. It also predicts the form of the resulting non-uniformity in temperature – for example, the number and location of the hot-spots generated. The method has been implemented in a convenient interactive windows-based software package available for PC or UNIX operating system.

Applications and Advantages


  • HotSpotter can be used as an aid in the design of transmission clutches and disk brakes against thermoelastic instability


  • No other methods are currently known that allow prediction of hot-spot occurrence and distribution