Elastothermodynamic damping in composite and cracked media /
When a composite material is subjected to a stress field, different regions undergo different temperature fluctuations due to the well-known thermoelastic effect. As a result irreversible heat conduction occurs, and entropy is produced which is manifested as a conversion of mechanical energy into h...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1995.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=742818561&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | When a composite material is subjected to a stress field, different regions undergo different temperature fluctuations due to the well-known thermoelastic effect. As a result irreversible heat conduction occurs, and entropy is produced which is manifested as a conversion of mechanical energy into heat. Moreover, the changes in temperature produce a thermal strain that is out of phase with the stress, thus converting mechanical energy into heat, i.e. work is lost. We define this process as elastothermodynamic damping. Herein, using the linear one-way coupled theory of elastothermodynamic relaxation, the elastothermodynamic damping of composite and cracked media is examined. Two equivalent descriptions of elastothermodynamic damping are first established: (1) the mechanical description and (2) the entropic description. An integral-transform technique is then developed to solve for the temperature field of a general composite medium with arbitrary heat generation. With this solution, a general expression for the damping of the composite material is derived. This general solution for the elastothermodynamic damping is then specialized to a solution for a composite material consisting of N-isotropic layers in a rectangular, cylindrical, and spherical coordinate system (i.e. an N-layer slab, cylinder, and sphere, respectively), subjected to any stress field so long as the resulting heat conduction can be described by a single spatial coordinate orthogonal to the layering. With this specialized result the elastothermodynamic damping is examined in laminated, fiber-reinforced, and particulate composites. Finally, the elastothermodynamic damping of cracked media is examined. Specifically, an approximate analysis is given for the entropy produced and work lost in the neighborhood of a Griffith crack subjected to a time-harmonic loading in Modes I, II, and III. In all three Modes the temperature at the crack tip remains bounded. In Mode I the entropy produced (per unit volume per cycle) is finite at the crack tip, whereas the work lost (per unit volume per cycle) goes to infinity as 1/square root of r. Conversely, in Mode II the entropy produced goes to infinity as l/r as the crack tip is approached, whereas the work lost is finite. In Mode III the thermoelastic effect disappears altogether and, therefore, both the entropy produced and the work lost are zero throughout the plate. |
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| Item Description: | Vita. "Major Subject: Aerospace Engineering". |
| Physical Description: | xv, 149 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |