S. Filippi

Measurement of Tangential Contact Hysteresis During Microslip

This paper describes a measurement system designed to determine the hysteresis that develops between two surfaces as a result of small-amplitude tangential relative motion. Hysteresis is determined by measuring the tangential force and relative displacement of the contacting surfaces as they oscillate. These measurements also produce values of contact parameters such as friction coefficient and tangential contact stiffness. Although these parameters depend on the tribological properties, most of them also exhibit strong sensitivity to measurement errors. The measurement system described here avoids or at least reduces many of the measurement artifacts. This paper validates the measurement system by analyzing and estimating potential errors and describes corrections to systematic errors where possible.

Experimental Characterization of Contact Hysteresis at High Temperatures

The current paper presents a measurement system for the experimental determination of contact hysteresis cycles at temperatures up to 800° C. A test rig was designed to conduct experiments in a wide range of temperatures, with different combinations of normal and tangential load, frequencies and contacting materials. An induction system supplies the heat for measurements of hysteresis cycles at the required temperatures. Measurements show the dependence of the friction coefficient on temperature.Copyright

Friction damping of interlocked vane segments: experimental results

Experimental methods and results of the stator bladed segment of an aircraft engine are presented. Investigation concerns the energy dissipation due to friction between contact surfaces of adjacent segments. The influence of the force normal to the contact surface (due to interference between adjacent segments) on friction damping is shown. Moreover, the experiments show the nature of friction at contact surfaces. The parameters of a contact model to be used in a numerical analysis have been identified from the experiments.

Friction damping of interlocked vane segments: validation of friction model and dynamic response

Aim of the present work is the validation against experimental results of the dynamic calculation of a vane segment with two friction contacts. The segment is in contact with two adjacent supports as in the experimental setup [1]. An empirical friction model derived from the experiments is introduced. The calculation has been performed for different interlocking values (different values of force normal to the contact surfaces). An analysis about the dependence of the parameters of the adopted empirical contact model on the hysteresis cycle shapes has been performed.Copyright

A Test Rig for Frictionally Damped Bladed Segments

The paper describes the development of an instrumented test rig suitable to carry out vibration testing of the bladed segments of a turbine (belonging to a stator low pressure stage) in which the friction occurring at the contact of neighboring segments is used in service to damp the vibrations. The system is able to assign the desired preload to the segment and to measure the forces exerted in the contact and the relative displacements due to slipping. The main results that can be obtained concern the type of motion that takes place (stick/slip) and the effect of the interlocking on it, the friction coefficients, the contact tangential stiffness, and, more generally the frequency response.

An Experimental Method for the Measurement of Blade-Root Damping

Stresses produced by vibrations reduce the life of turbo engine blades. The design of disk assemblies requires the capability to predict their dynamic behavior. In order to achieve this objective, knowledge of damping associated with the contact between blade and disk is fundamental. This paper proposes a technique to measure the influence of blade-disk attachment on the dynamics of turbo engine blades. Moreover, experimental values of damping and resonance frequencies are presented as a function of the amplitudes of vibration and of centrifugal load at the attachment.Copyright

Forced Response of Interlocked Vane Segments: Numerical Predictions and Experimental Results

Resonant vibrations affect fatigue life of vane segments. Friction damping is employed to reduce vibration amplitude. When vane segments are assembled, they are twisted so that lower platforms are in contact. The sum of displacements of the two ends of the lower platform after twisting is defined ‘interlocking’. Different ‘interlocking’ values correspond to different values of normal contact force. When interlocked vanes vibrate under external force excitation, energy is dissipated by friction forces at lower platform contacts providing damping to the system. The aim of this paper is the experimental validation of a numerical code for forced response calculation of interlocked vane segments. Since friction forces depend on relative displacements of bodies in contact, the system is nonlinear. System force response is computed by means of Harmonic Balance Method (HBM). Contact model implemented in the code is characterised by tangential and normal stiffness to take into account local compliance of the contact area. Gross slip occurs when the instantaneous ratio of tangential force to normal force is equal to the friction coefficient. Also effect of microslip is taken in account. The experimental set-up used to validate the code is made of a vane segment fixed at the outer radius to an aluminium frame and in contact with two supports at the inner radius. Comparison between the numerical predictions and experimental results is performed for different values of interlocking (i.e. force normal to the contact).© 2006 ASME

Friction Damping of Interlocked Vane Segments: Experimental Results

Experimental methods and results of the stator bladed segment of an aircraft engine are presented. Investigation concern the energy dissipation due to friction between contact surfaces of adjacent segments. The influence of the force normal to the contact surface (due to interference between adjacent segments) on friction damping is shown. Moreover the experiments show the nature of friction at contact surfaces. The parameters of a contact model to be used in a numerical analysis have been identified from the experiments.Copyright