Test Rig for Wear and Contact Parameters Extraction for Flat-on-Flat Contact Surfaces

In aircraft engine the blade resonant vibration amplitude is reduced by increasing the structural damping by using, for example, tip shrouds. These devices dissipate the energy generated at the contact surfaces between the relative motion and the friction force. Contact parameters as friction coefficient and contact stiffness are required to characterize the dynamics of the shrouded blade systems. Moreover if at the contact surfaces severe wear occurs a loss of interference takes place, the shroud is not longer able to dissipate energy and a catastrophic blade failure could take place. A test rig for contact parameters measurement and micro wear characterization of flat-on-flat contact surfaces has been developed. One of the specimens is attached to the rig frame, basically an inertial mass and four springs, excited by an electromagnetic shaker. The second specimen is allowed to approach the first specimen and to rotate in such a way the geometric contact between the two surfaces occurs on three points. In this way a real “flat-to-flat” contact has been obtained. The tangential contact force and the relative displacements between specimens are measured and the friction coefficient and contact stiffness, are determined. The expected results are the contact parameters and the wear behaviour of real flat-on-flat contact surfaces. The aim of this work is to describe the design principle of the test rig and show the first measurements.