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Modeling of friction pad in disc brakes as a distributed parameter system (mass-inherent damping-elasticity) is made in order to show the conditions of stable vibrations, The interface characteristics of the pad/disc assembly beside the negatively sloped friction-velocity relationship are taken into account. The interface characteristics are represented by the effective contact stiffness as well as the friction damping of both pad and disc surfaces. It is shown that continuous modification of the equivalent contact stiffness by wear mechanism or by any other mechanism, is the mean cause of squeal triggering. The analysis has shown that stability can be attained at all possible squeal frequencies of the friction pad by the good selection of its geometrical configuration (thick, wide and short brake pad) and its material loss factor within certain limits. Moreover, it is necessary to choose the appropriate way of pad fixation inside the caliper to give higher modes of vibrations.

The stability of vibratory motions of the drum/shoe assembly in drum brakes, is studied. The behavior of this assembly is explained in terms of the vibration modal numbers of the drum and the shoe. The equations of motion of the distributed parameters system are obtained where both motions of drum and shoe are considered to be coupled by the tangential distributed friction force. This force is generated by frictional sliding between the rotating drum and a pinned-pinned shoe and it depends on the relative velocity of sliding. The domains of stability at different vibrational modes of both drum and shoe are shown. Geometric induced instability is likely to occur at the first mode of the drum for all extension modes of the shoe. In case of flexural modes of the shoe, instability is found to be dependent upon the drum radius and the angle subtended by the shoe.