A new technique for measuring axial damping and its application to metal-matrix composites /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1990.
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| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| Abstract: | A majority of the current experimental techniques for measuring damping employ either flexural or torsional vibrations. In either case the strain field is non-homogeneous. If the material damping is linear, that is strain independent, then the measured quantity is a true representation of the intrinsic material damping. If, on the other hand, the material damping is non-linear, that is strain dependent, then, in addition to the intrinsic material damping, the measured quantity is also a reflection of the non-homogeneity of the strain field. 4 This dissertation presents a new technique for measuring the intrinsic material damping by employing a homogeneous strain field. Specimens were subjected to a time-harmonic uniform uniaxial tension using an MTS apparatus at frequencies between 0.5 Hz and 10 Hz. Using the elementary theory of Fourier transforms, the phase difference between the stress and the strain was resolved in the frequency domain (rather than in the time domain) to an accuracy of 9.587x10^-5 radians (5.49x10^-3 degrees). A flexural apparatus was also developed to measure damping in a non-homogeneous strain field. In this case, damping was determined using the well-known logarithmic decrement technique. Both apparatuses incorporated digital data acquisition and were fully automated. The application of both techniques was illustrated by measuring the damping of a [±θ]s metal-matrix composite as a function of ply-angle, θ . Unidirectional Pitch 55 graphite fibers in a matrix of 6061 aluminum were tested for the following values of θ: 0°, 15°, 30°, 45°, 60°, 75° and 90°. In addition, the damping of two [0g] graphite/magnesium composites was measured in flexure. Following a recent calculation by Ni and Adams, expressions for axial damping were derived based on the damping properties of a lamina. In addition, the expressions derived by Ni and Adams were extended to include stress and strain terms which had been previously neglected. For both the flexural and axial damping of the metal-matrix composites tested, satisfactory agreement between the theory and experiment was observed. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Aerospace engineering." |
| Physical Description: | xxv, 227 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |