Date of Award

1993

Degree Name

M.S. in Mechanical Engineering

Abstract

Prestressing materials in order to improve structural characteristics is a common engineering practice. Probably the most evident case is the use of prestressed concrete. This class of material is utilized in situations where the structure is loaded in tension. The prestress is obtained by using steel wires which are loaded in tension prior to the curing of the concrete. When the load is released, the brittle concrete is compressed, allowing for the superposition of externally applied tension. An analog to prestressed concrete has been developed by the author for use with advanced composite materials. However, the goals of this new method of composite fabrication are different than with concrete. The difference in thermal expansion coefficients of the matrix and fibers as well as a large change in temperature following cure result in three dimensional residual stresses. Applying an external load to the fibers during the cure cycle is seen as a means of both mitigating these stresses as well as prescribing a greater degree of fiber linearity within the composite. The effect of applying stresses to the fibers prior to consolidation is determined through both mathematical and experimental techniques. A boundary value problem is posed utilizing an elasticity method based on a concentric cylinder model. This model allows for the prediction of the stress/strain state at any point away from the ends of the laminate. The results obtained from the boundary value problem are used with classical laminated plate theory in order to determine the ply stresses as a function o f fiber prestress lev e ls. The experimental procedure includes both the fabrication and mechanical testing o f prestressed laminates as w ell as comparison to data obtained from conventionally processed composites

Keywords

Composite materials Fatigue, Composite materials Fracture

Rights Statement

Copyright © 1993, author

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