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On the Identification of Dynamic Friction Material Properties under Brake Squeal Relevant Loading Conditions

Hornig S. A., Wagner U. v.

Machine Dynamics Research

2012

Vol. 36, No. 3

29-44

Brake squeal is a disruptive high frequency noise generated by friction-induced self excited vibrations of the brake system. Great effort is spent on the improvement of brake squeal prediction reliability, using mathematical-mechanical simulation models. In this context friction material properties are one of the decisive factors for the successful brake squeal simulation. Because of the nonlinear and load dependent friction material behavior, it is mandatory to identify friction material properties under squeal typical loading conditions. For this reason a measurement method reproducing squeal typical operating conditions is under development by the authors’ research group. The present paper shows the actual development stage of this measuremet method, presenting the dynamic compression test rig, estimated friction material characteristics, and emphasizing important influence factors on the dynamic compression measurement results. In this context a particular focus is set on the derivation of correction factors when converting the measured stiffness of specimens with restriced dimensions and boundary conditions into material stiffness.

Bifurcation Behavior and Attractors in Vehicle Dynamics

Hochlenert D., Von Wagner U., Hornig S.

Machine Dynamics Problems

2009

Vol. 33, No. 2

57-73

Nonlinear self-excited systems in vehicle dynamics are discussed using the examples of squealing automotive disk brakes and the stability behavior of a railway wheelset. Both systems show self-excited vibrations for specific operation states. The self-excited vibrations are due to friction forces between pad and disk in the case of the automotive disk and due to contact forces in the case of the railway wheelset respectively. The analysis of the nonlinear equations of motion shows that the trivial solution looses stability either through a sub- or through a supercritical Hopf bifurcation depending on the system's parameters. In the case of a subcritical Hopf bifurcation two stable solutions coexist and the initial conditions determine which solution emerges. The properties of the nonlinear systems such as critical velocities, limit cycle amplitudes and attractors of coexisting solutions are calculated using center manifold reduction and normal form theory.