Scholarly Communications Project

Analysis of Tow-Placed, Variable-Stiffness Laminates


Chris Waldhart

Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of

Master of Science in Engineering Mechanics


Zafer Gurdal, Chair
Calvin Ribbens
Robert M. Jones

June 5, 1996
Blacksburg, Virginia


It is possible to create laminae that have spatially varying fiber orientation with a tow placement machine. A laminate which is composed of such plies will have stiffness properties which vary as a function of position. Previous work had modelled such variable-stiffness laminae by taking a reference fiber path and creating subsequent paths by shifting the reference path. This thesis introduces a method where subsequent paths are truly parallel to the reference fiber path. The primary manufacturing constraint considered in the analysis of variable-stiffness laminates was limits on fiber curvature which proved to be more restrictive for parallel fiber laminae than for shifted fiber. The in-plane responses of shifted and parallel fiber variable-stiffness laminates to either an applied uniform end shortening or in-plane shear were determined. Both shifted and parallel fiber variable-stiffness laminates can redistribute the applied load thereby increasing critical buckling loads compared to traditional straight fiber laminates. The primary differences between the two methods is that parallel fiber laminates are not able to redistribute the loading to the degree of the shifted fiber. This significantly reduces the increase in critical buckling load for parallel fiber variable-stiffness laminates over straight fiber laminates.

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