Measurements from the AK-Master and SAE J2521 show that friction is not a steady state process which depends only on state variables. In the past several years, dynamic friction laws have been developed, in which self-organization processes in the friction interface describe complex tribological effects. These processes can be characterized by the growth and destruction of contact patches, as well as typical wear patterns, on the brake pad (1).
Towards a better comprehension of the friction processes in the boundary layer, measurements under constant reproducible conditions are essential. To this end, the Institute of Dynamics and Vibration employs the Automated Universal Tribotester (AUT) (2). This is based on the pin-on-disk principle and uses down-scaled pad specimens cut out from full brake pads. Between the friction tests, it is important to analyze the surface of the pad specimen to attain information about contact area, roughness and wear, for example.
In order to maintain the highly automated quality of the AUT, the device for measuring the pad´s surface must be compact and mounted within the AUT. Because friction tests often are comprised of many applications, and it is necessary to reduce disc cooling, the measurement device must measure the surface very quickly.
In this paper, a pad specimen topography measurement device will be presented, which operates very quickly within the AUT. A laser triangulation sensor is mounted on a rapidly vibrating linear stage and scans the surface of the pad specimen, which moves perpendicular to the laser. In this way the topography of the full pad specimen can be measured within a few seconds. A single profile can also be measured by deactivating the vibrating linear stage. Such profile information can be used to attain roughness parameters and information regarding the position of the surface within the AUT, for example towards adjusting the focus of the digital camera.
Schramm Tobias, Ostermeyer Georg-Peter, TU Braunschweig, Institute of Dynamics and Vibrations, Germany.