Date of Award

Spring 1991

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Engineering Mechanics

Committee Director

Chuh Mei

Committee Member

Gene Hou

Committee Member

Stephen Rizzi

Call Number for Print

Special Collections; LD4331.E57G73

Abstract

The development of supersonic and hypersonic flight vehicles such as the High Speed Civil Transport and the National Aero-Space Plane has created an increased need for analysis of structures at very high temperatures. Bisplinghoff and Pian, Yang and Han, and Dokmeci and Boley have conducted experimental and analytical studies to determine the effect of elevated temperatures on the vibration characteristics of isotropic plates, Chen and Chen, and Meyers and Hyer have clone studies on thermal buckling and post-buckling of composite plates, respectively.

The thermal loads which will be imposed on the new high speed aircraft will be too great for aluminum and possibly other metallic panels to endure. Therefore, emphasis must be placed on the analysis of high strength composite materials, such as carbon-carbon, for the design and manufacture of these aircraft. These materials must be able to withstand very high temperatures and still retain their structural integrity and strength. As with isotropic plates, thermal buckling will occur with composite plates, and large increases in temperature will create thermal deflections which are large in the von Karman sense. This thermal post-buckling and its effect on vibration response must be understood for analysis and design of these flight vehicles.

The high thermal loads will have several effects on the behavior of a laminated plate. First, the loads will create thermal stresses within each composite layer, as shown by Eq.(2.19). The load creates a [KN AT] matrix which will influence the lin­ear stiffness matrix, [K]. The material properties of the plate will also change with increasing temperature, thus affecting the laminate stiffness ABD matrix, Eq.(2.27).

This thesis research will develop and present a finite element formulation for the thermal post-buckling and free vibration of thin, rectangular composite plates sub­ jected to large temperature variations over the plate ll.T( :e, y). The effect of moder­ ately large initial, stress-free imperfections on the thermal deflection and vibration characteristics of these panels will also be studied. The temperature dependence of the material properties of the plate will be considered as well. The von Karman nonlinear strain-displacement relations are used to account for the large thermal deflections and initial imperfections, and the equations of motion are derived from the principle of virtual work. The system equation is solved by splitting it into its static and dynamic deflection terms, creating two equations. Newton-Raphson iteration is used to solve the incremental static equation for the thermal post-buckling with a given temperature distribution. The final static thermal deflection is then used in the time dependent equation to solve the eigenvalue problem for the natural frequencies and vibration modes of the thermally buckled plate.

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DOI

10.25777/9k8v-dv68

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