Carrasco, Alvaro G. ; Baghshetsyan, Armen ; Pott, P. P. ; Schlaak, Helmut F. (2014)
Test stand for anisotropic friction coefficients of a friction layer of 2D-carbon fiber arrays used in piezo motors.
Actuator 2014, International Conference and Exhibition on new Actuators and Drive Systems. Bremen (23. - 25. Juni 2014)
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Kurzbeschreibung (Abstract)

with an inclination of 45° and fiber length of 1,5 mm were assessed. The fiber arrays with about 12000 fibers (2,3 x 0,3 mm²) are dynamically and perpendicularly pressed against a contact surface with frequencies up to 200 Hz and 100 μm stroke. A 3D piezoelectric force sensor at the base of the fibers is used to measure the load applied. The contact surface is a metallic beam supported horizontally by membrane springs fixed at both ends. Hereby, the normal force applied to the fibers is split by the contact in two force components at the beam surface: normal and tangential. The membrane springs provide a large stiffness in normal direction and very low stiffness in tangential direction at this configuration. Due to the resulting friction and the bending of the fibers, a displacement of the beam is achieved in the tangential direction. As the mass of the beam is well known, the tangential force transferred to the beam is mathematically deduced from the measurement of the velocity of the beam’s motion. This is performed by a laser vibrometer. Thanks to the 3D force sensor statements regarding the friction coefficient during the bending of the fibers can be determined. The measurements deliver a friction coefficient of about 0,6. This has a direct dependency with the stiffness of the membrane springs. They were oversized for a resonance frequency greater than 200 Hz, as a linear deflection of the springs was targeted. Due to this new test stand it is now possible to measure the reaction forces out of the interaction between a 2D carbon fiber array and a contact surface. In order to minimize the influence of non-linear behaviour of the membrane springs to the measurement, they were intentionally oversized. This requires greater forces and respectively more fibers. Nevertheless, the bending behaviour of the fibers can now be characterised by the presented measurement method. Further studies will determine the optimal fiber length, or the optimal deflection range of the fibers. This can now be accomplished by models validated on the described test stand. Also further investigations are required to enhance the coupling of the fibers to the contact surface.

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