A finite element analysis of a 'S' cam brake
thesisposted on 20.10.2010, 10:59 authored by C. Watson
An analysis of a commercial vehicle drum brake fitted with a typical asbestos free friction material has been investigated by the finite element method. The "GAPFRIC" concept has been extended to model in three dimensions the frictional interface between brake linings and drum. This approach incorporates an accurate representation of the brake itself to include such features as the brake drum stiffener and mounting flange. The brake shoe representations include the actual web and platform thus eliminating the need for shoe stiffness approximations to a curved beam of uniform section as used in previous two dimensional work. The mechanical "GAPFRIC" analysis is combined with a thermal analysis of the brake to form a brake analysis package. The package is fully automatic; the output from each stage of the analysis is post processed and the results used to modify the original data file. Variations in physical properties exist between new and used friction material and these are incorporated in a five phase idealisation of the friction pair. Modifications to allow for the change of coefficient of friction with temperature were made by means of tables within the coding. In addition friction material wear was included in the analyses using an empirically derived wear criteria. Analyses were completed to investigate the effect of combined axial and circumferential distortions on temperatures at the friction interface, interfacial pressure distributions and subsequent brake performance. Predicted results show that high temperatures are reached at certain regions on the rubbing path and the temperatures may fluctuate during a brake application. Pressure variations are seen to exist both around and across the surface of the linings. The coupling of pressure and temperature variations combined with frictional changes over the lining produce changes that result in the frictional drag per unit area tending to be reasonably constant over the interface between drum and lining. The predicted values of brake torque and brake factor f rom the three dimensional analyses have been compared with results derived f rom the earlier two dimensional brake analysis and validated by comparison with measured results from a brake mounted on a dynamometer. Similarly predicted brake drum and lining temperatures were compared with measured values and some reasonable trends established. The work itself presents a better physical description of the behaviour at the friction surface during braking to improve the determination of brake drum performance.
- Aeronautical, Automotive, Chemical and Materials Engineering
- Aeronautical and Automotive Engineering