Abstract
Recent research on variable stiffness laminates have shown both numerically and experimentally that further improvement on the buckling performance is possible by incorporating overlaps that result in variable thickness profiles. We present the concept of overlap-stiffened designs that take advantage of the non-linear coupling between the tow steering and the local thickness, allowing embedded regions of higher stiffness into individual plies of a variable-angle tow (VAT) laminate. The proposed method naturally copes with minimum steering radius constraints of different manufacturing processes by connecting transition regions by means of fiber tow arcs, such that the radius of curvature always cope with a desired minimum radius constraint. The present study focuses on two tow-steering processes: automated fiber placement (AFP) and continuous tow shearing (CTS). Each individual ply exploring the overlap-stiffened design is described using 5 design variables, producing a straight stiffener. A first benchmark study compares overlap-stiffened laminates optimized for a maximum volume-normalized buckling performance under bi-axial compression against a reference straight-fiber laminate. In a second benchmark, overlap-stiffened panels were optimized for minimum weight under a design buckling load constraint, and compared against a reference straight-fiber laminate. For both AFP and CTS, is verified that overlap-stiffened VAT panels can achieve at least the double of the volume-normalized buckling performance of an optimized straight-fiber panel. Moreover, the proposed design method can at least achieve the same weight and buckling load carrying capacity of an optimal straight-fiber panel, demonstrating the potential of the proposed design method to include embedded regions of higher thickness.
Highlights
Novel automated manufacturing techniques have the capability to steer the fibers of each layer towards curvilinear paths, producing varying fiber orientation that reflects in variable stiffness, which enables a higher tailoring potential of composite materials
Variable-angle tow overlap-stiffened panels were presented as a new design possibility that explicitly parameterizes variable thickness patterns in order to create embedded stiffened regions
The variable thickness patterns are created by means of tow overlaps in automated fiber placement (AFP), or by the inherent steering-thickness variation in
Summary
Novel automated manufacturing techniques have the capability to steer the fibers of each layer towards curvilinear paths, producing varying fiber orientation that reflects in variable stiffness, which enables a higher tailoring potential of composite materials This opens even more the development and application of advanced lightweight composite structural designs. The linear buckling performance is investigated for panels manufactured by means of AFP and a CTS, and compared with the performance of a well-known optimized straight-fiber laminate plate from Haftka [8] By fulfilling these two goals, the authors can prove the concept for the new overlap-stiffened design method proposed, opening up a new venture of design possibilities
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