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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.

Oil Paintings and Mechanics : How To Save Art Treasures Using Knowledge from Dynamics

Kracht K., Wagner U. v.

Machine Dynamics Research

2011

Vol. 35, No. 4

49-61

Oil paintings of the old masters are valuable not only for education and social life but also from an economical point of view. These artworks undergo vibrations due to multiple reasons. During exposition there is excitation by public or external traffic load. Higher excitation levels are reached during transports. Consequences may be the emergence of cracks or loss of paint slabs. For protecting an oil painting from damage it is essential to be aware of its condition.Conventional techniques applied by conservators are based on visual detection. In contrastto this, our work is based on knowledge from dynamics applied to this new field. Test objects were prepared by a docent of old painting techniques of Berlin Universityof Arts. They were aged at different levels by a research institution for paint and varnish atMagdeburg. After aging the dummies are investigated for their dynamical behavior usingdifferent excitations (harmonic, broad-band) and measuring dynamic responses. Speciallaser equipment and the experimental set up were developed for measurements on thesurface of painted canvas. Strong influences of the alteration of the dummies andcharacteristic nonlinearities could be observed during these measurements. Cracks wereinitiated during dynamic fatigue tests and correlated with dynamic responses. Acorresponding modeling is based on a Kirchhoff plate with non-constant pre-stress. The presented work should finally lead to condition monitoring of oil paintings and techniques for the prevention of artworks from vibrations.