Analysis of tow placed, parallel fiber, variable stiffness laminates

Abstract

It is possible to create laminates, composed of plies with spatially varying fiber orientation, which have stiffness properties that vary as a function of position. Previous work had modeled such variable stiffness laminae by taking a reference fiber path and creating subsequent paths by shifting the reference path. We introduce 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 laminae. The in-plane responses of shifted-and parallel-fiber variable-stiffness laminates to applied uniform end shortening 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 difference 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. (Author) Abstract Using advanced manufacturing techniques it is possible to create laminates, composed of plies' with spatially varying fiber orientation, which have stiffness properties that vary as a function of position. Previous work had modeled such variable stiffness laminae by taking a reference fiber path and creating subsequent paths by shifting the reference path. This paper 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 applied uniform end shortening 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.

Flutter Analysis of Composite Laminates With Curvilinear Fibres

“…The angle of the reference fibre path, ✓, is a linear function of the x-coordinate and, in order to define the other fibre paths, this reference fibre path is shifted in y-direction [2].…”

“…These two techniques alter the final shape of the design by occupying more space and increasing the weight. The variable stiffness concept using curvilinear fibres [1,2,3] can propose a panel with different, and under-controlled stiffness. This concept suggests to rotate fibre orientation in a region with high stress.…”

Optimization of course locations in fiber-placed panels for general fiber angle distributions

“…Traditionally the choice of these lay-ups was motivated by manufacturability, while nowadays lay-ups with changing or even non-conventional fiber angles are avoided because of the lack of allowables. However, research on composites with a varying in-plane fiber orientation has shown that variable stiffness can be beneficial for structural performance [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17], because variable-stiffness laminates are able to redistribute the loading more efficiently than constant-stiffness laminates. In most cases curvilinear fiber paths manufactured by tow placement are used to construct the variable-stiffness laminates [4, 5, 9-11, 15, 18-20].…”

Design of Composite Layers With Curvilinear Fiber Paths Using Cellular Automata

“…In-depth study of rectangular panels with curvilinear fiber paths, termed variable stiffness panels, was performed in a series of publications by Gürdal et al [16][17][18] . These panels are manufactured by either shifting or parallel fiber path generation starting from a linearly varying orientation base curve.…”