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The techniques for characterization of the shear strength of friction materials were reviewed and a new double-lap-shear test method was developed. Various types of friction materials were tested for shear strength by this new technique. The effects of different material properties and processing factors such as resin type, resin content, resin cure rate, fiber geometry, fiber content, and test environment on the shear strength of the friction materials were also examined. Positive correlations between the shear strength and the mechanical life of wet friction materials were established. Accurate determination of shear strength in wet friction materials is vital in predicting the performance and durability of friction materials for friction plates, transmission bands, and torque converter lockup clutches.

Two important phenomena which govern the performance of wet friction composite materials operating in transmission oils have been examined. Both the elastic deformation behavior, and the liquid permeability of fiber reinforced polymeric wet friction composite materials are important input parameters to any accurate oil flow model which predicts the interface temperature of wet friction clutch facing polymeric materials. Liquid permeability, pore size, and pore size distribution of three different classes of wet friction materials were measured by a recently developed automated pore permeameter. Darcy's Law for laminar flow through homogenous porous media can be used to describe the anisotropic liquid permeability of wet friction materials. The elastic deformation of the three classes of wet friction materials was also determined.