http://jafari3000.persiangig.com/document/Article(11-20)/1-s2.0-S0263822310001947-main.pdf

Optimum stacking sequence design of composite materials Part II: Variable stiffness design

Tailoring of laminated composite structures by changing ply angle and thickness locally provides a unique opportunity to take full advantage of anisotropic properties of composite materials Variable stiffness design has become more attractive with the development of industrial fibre placement machines Strength design is one of the areas where fibre steering is advantageous Design methods that consist of directly optimising fibre angles or fibre path coefficients can lead to local optima and/or non-continuous solutions These problems can be alleviated by using lamination parameters as design variables, which provide a compact definition of laminate stiffness Additionally these parameters are continuous and the design space has shown to be convex Dependency of strength failure criteria on ply angles may preclude using lamination parameters as design variables Here, a recently developed method which incorporates the strength failure criteria in the lamination parameter space by using a conservative failure envelope for all ply angles is utilised A hybrid approximation for the failure index is developed and is guaranteed to be convex using a convexifying approach As an example strength maximisation of a panel with a central hole under uniaxial tension is investigated Numerical results show improvements in strength with respect to the quasi-isotropic design Although there is a common belief that design for stiffness can be served as a surrogate for strength design, it is shown that considering the strength as a design criteria especially for structures with large stress gradients is very important

Design of variable stiffness panels for maximum strength using lamination parameters

3D printing of optimized composites with variable fiber volume fraction and stiffness using continuous fiber

The use of curvilinear fibre paths to develop variable stiffness laminates is now recognised as a promising technique offering great potential for performance improvements over conventional ‘straight fibre’ laminates. Its manufacture is feasible by fibre placement technologies, such as automated fibre placement. However, these technologies present a set of limitations that need to be included in the design to guarantee the manufacturability and quality of the composite laminates. Although this approach experiences an increasing interest from the specialised literature, most of the works completed overlook the manufacturing reality and, as a result, variable stiffness laminates are not used in industry. This work aims to provide a review of the State-of-the-Art on design for manufacture of variable stiffness in order to highlight the current gaps and research needs. As a conclusion, tools for analysis of the effect of manufacturing defects, manufacturing optimisation of gaps/overlaps or cycle time and the ...

http://journals.sagepub.com/doi/pdf/10.1177/0954405415600012

A review on design for manufacture of variable stiffness composite laminates

Recent advancements of additive manufacturing technology have enabled the fabrication of complex geometries and fiber placement along customized paths. The proposed approach introduces a novel framework for the optimized topology and the fiber paths in order to create variable stiffness designs. The optimized distribution of the material is achieved by two different methods: a density-based method and a level-set method for orthotropic materials. The fiber orientation of each element or the fiber path is considered as the design variable. The optimized orientation is obtained using an energy-based method and a level-set based method. In addition to a fiber angle filtering scheme, three new approaches for the design of fiber infill pattern are introduced to enforce the fiber path continuity across the domain, ensure manufacturability, and achieve reduced compliance. The effects of fiber infill pattern techniques on the compliance is demonstrated in three benchmark case studies.

Stiffness-based optimization framework for the topology and fiber paths of continuous fiber composites

Trajectorial fibre steering of composite tows within composite laminates has been investigated as a means of producing composite structures with increased strength. Strategies to design the fibre trajectories in laminates have included aligning the fibres with principal stress vectors and a newly developed concept of load paths. In the laminate, the steered plies were inter-mingled with unidirectional or fabric plies. A manufacturing technique for the steered plies has been proposed. Applications include a specimen containing an open hole and a specimen with a pin-loaded hole. Specific strength increases of 62 and 85%, respectively, were achieved.

M.W. Tosh

Papers

On the design, manufacture and testing of trajectorial fibre steering for carbon fibre composite laminates