Coupled thermoelastic crack problems.
Item
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Title
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Coupled thermoelastic crack problems.
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Identifier
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AAI8820887
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identifier
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8820887
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Creator
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Phurkhao, Pichaya.
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Contributor
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Adviser: Mumtaz K. Kassir
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Date
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1988
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Civil
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Abstract
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In this research, coupled thermoelastic problems of stationary cracks are discussed. It is assumed that the crack is disturbed by thermal and/or elastic waves generated by external thermal and/or mechanical excitations. Two classes of problems of particular interest are investigated in detail. These are the scattering of plane harmonic thermoelastic waves and the sudden application of thermal and/or mechanical loadings to the crack surfaces (transient problems). Integral transform techniques are employed to formulate the problems and reduce them to Fredholm integral equations of the second kind and/or to a system of simultaneous algebraic equations. The resulting equations are then solved numerically and the singular stress field near the crack tip, which is of paramount importance in determining crack propagation, is determined in explicit form. Also, the magnitude of this stress field, which is conveniently described by a parameter k{dollar}\sb1{dollar} (stress-intensity factor), is calculated.;The effect of the frequency of the input thermal and/or elastic waves as well as the influence of coupling upon the dynamic stress-intensity factor for few materials are determined and displayed graphically. In the transient problems, a numerical Laplace inversion technique is used to convert the values of k{dollar}\sb1{dollar} in the Laplace plane to the regular time domain, and the results are compared to the corresponding steady-state values to reveal the influence of inertia and coupling on the dynamic stress-intensity factor.;For both problems, the important results are; (1) the stresses are singular of order r{dollar}\sbsp{lcub}1{rcub}{lcub}-{lcub}1\over2{rcub}{rcub}{dollar} as r{dollar}\sb1\to{dollar} 0 at the crack tip, (2) the inertia effect upon the variation of k{dollar}\sbsp{lcub}1{rcub}{lcub}\prime{rcub}{dollar} with frequency and time is found to be significant while the coupling effect is negligibly small, and (3) k{dollar}\sbsp{lcub}1{rcub}{lcub}\prime{rcub}{dollar} is proportional to material constants and crack size. It is also observed that there is a peak in k{dollar}\sbsp{lcub}1{rcub}{lcub}\prime{rcub}{dollar} in both problems. The corresponding values of time and frequency vary depending upon material properties and crack size. In applying the methodology of Linear Elastic Fracture Mechanics (LEFM), the information gained is essential to determine the conditions of crack propagation under thermal loading.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
