#### Date of Award

3-2004

#### Document Type

Thesis

#### Degree Name

Master of Science

#### Department

Department of Aeronautics and Astronautics

#### First Advisor

Anthony N. Palazotto, PhD

#### Abstract

An automated test system was developed by the USAF Turbine Engine Fatigue Facility (TEFF). This system was initially designed to reduce the time and manpower required to characterize damping treatments. It is based on a digitally controlled environmental chamber with automated data acquisition and processing. Several outputs are available including identification of natural frequencies, modal damping ratios from the acquired frequency responses, and changes in damping with response amplitude; however, the TEFF additionally desires the capability to study fatigue under a free boundary condition. The system consists of a test specimen suspended by a pendulum to closely simulate free boundary conditions and to minimize the dissipation of vibrational energy. Two rare earth magnets are attached to a specimen. The magnetized end is inserted into an orthogonal magnetic field produced by an electromagnet. Alternating the current oscillates the direction of the magnetic field by 180 degrees. The effect of the electromagnet's magnetic field on the specimen's magnets is the application of a torque; as this torque alternates directions, it excites vibration in the beam. This torque, while useful, was not fully understood. The purpose of this thesis is threefold: 1. Develop an equation to predict the magnetic field produced by an electromagnetic coil; 2. Develop an equation for predicting the torque exerted on the beam; and 3. Experimentally validate the accuracy of these equationsAn automated test system was developed by the USAF Turbine Engine Fatigue Facility (TEFF). This system was initially designed to reduce the time and manpower required to characterize damping treatments. It is based on a digitally controlled environmental chamber with automated data acquisition and processing. Several outputs are available including identification of natural frequencies, modal damping ratios from the acquiries frequency responses, and changes in damping with response amplitude; however, the TEFF additionally desires the capability to study fatigue under a free boundary condition. The system consists of a test specimen suspended by a pendulum to closely simulate free boundary conditions and to minimize the dissipation of vibrational energy. Two rare earth magnets are attached to a specimen. The magnetized end is inserted into an orthogonal magnetic field produced by an electromagnet. Alternating the current oscillates the direction of the magnetic field by 180 degrees. The effect of the electromagnet's magnetic field on the specimen's magnets is the application of a torque; as this torque alternates directions, it excites vibration in the beam. This torque, while useful, was not fully understood. The purpose of this thesis is threefold: 1. Develop an equation to predict the magnetic field produced by an electromagnetic coil; 2. Develop an equation for predicting the torque exerted on the beam; and 3. Experimentally validate the accuracy of these equations.

#### AFIT Designator

AFIT-GSS-ENY-04-M04

#### DTIC Accession Number

ADA426593

#### Recommended Citation

Hoover, Todd M., "An Electromagnetic Tool for Damping and Fatigue Analysis" (2004). *Theses and Dissertations*. 4123.

https://scholar.afit.edu/etd/4123