A novel test rig to study the effect of fretting wear on the forced response dynamics with a friction contact

Lakshminarayana Reddy Tamatam,Daniele Botto,Stefano Zucca

doi:10.1007/s11071-021-06658-y

Lakshminarayana Reddy Tamatam, Daniele Botto + Show 1 more

Open Access

https://doi.org/10.1007/s11071-021-06658-y

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Journal: Nonlinear Dynamics	Publication Date: Jul 1, 2021
Citations: 4	License type: open-access

Affiliation: Polytechnic University of Turin

Abstract

This paper presents a novel test rig to study the effect of fretting wear and of the contact surface evolution on the forced response of systems with dry friction contact. This rig allows simulating contacts similar to the type of contacts present between the shrouds at the blade tip. Several research groups have been studying how fretting wear affects the dynamic response of mechanical systems, developing numerical prediction tools that consider dry friction contact and nonlinearity. The aim of this work is to experimentally study the evolution of contact interfaces and how this evolution affects the system dynamics. Experimental results will aid to validate the numerical predictions. The test rig developed for this activity is made of a cantilever beam fixed at one end and with a friction contact at the free end. The contact couple is made of two replaceable specimens. The contact is loaded via a lifting mechanism through a screw with fine thread. Fretting wear test was performed at a constant frequency and force amplitude, exciting the beam with an electromagnetic shaker. To emphasize the change of the dynamic response, frequency sweeps were performed at various intervals during the wear test. The full range test with ‘changing preload’ due to progressing wear was performed until a full loss of contact. This paper describes the test rig design, intent, set-up, instrumentation, test plan and results. Results include the frequency response curves for unworn contact, wear profiles at multiple intervals and the effect of wear on the frequency response. Though energy dissipation per cycle is quite small, wear leads to material loss at the contact with a sufficiently large number of cumulative cycles and substantially affects the dynamic response. Results collected in this research activity are of particular importance to validate numerical tool that aim to simulate the dynamic behaviour of systems with dry friction contacts that undergo material loss caused by wear.

Highlights

A complex mechanical structure such as a turbomachine is made up of many individual components connected through mechanical joints
This paper presented a novel test rig to study the effect of fretting wear on the forced response dynamics with a friction contact and changing preload
The dynamic response and specimen surface scans were captured at various intervals throughout the test

Summary

Introduction

A complex mechanical structure such as a turbomachine is made up of many individual components connected through mechanical joints. These joints create interfaces between the components. Some of the crucial joints such as blade root, shroud contact, under-platform dampers are designed to undergo relative motion at the interfaces to provide friction damping and reduce the peak vibration levels. The partial or full slip occurring at the interfaces during vibration excitation could lead to fretting wear [1, 2]. Fretting wear leads to loss of material over accumulated millions of cycles and damage the contact interface. Unintended degradation of the interfaces due to wear could hamper the performance and lead to undesirable consequences

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