Mass Optimisation of Variable Angle Tow, Variable Thickness Panels with Static Failure and Buckling Constraints

Abstract

By taking advantage of curved fiber paths, Variable Angle Tow (VAT) laminates increase the design space for tailoring the structural behavior of thin-walled aerospace structures. In recent years, advancements in Automated Fiber Placement (AFP) and Continuous Tow Shearing (CTS) have facilitated the manufacture of these laminates. The CTS technique holds the advantage of reducing many of the manufacturing defects characteristic of the AFP process such as fiber wrinkling, tow gaps and tow overlaps, while also allowing for tighter steering radii. On the other hand, the CTS process features added complexity due to the coupling of fiber steering angle with tow thickness. In this study, a minimummass design of a typical aircraft wing panel under end-compression subject to pre-defined manufacturing, static failure and buckling load constraints is sought. The geometric effects of the asymmetric thickness distribution of the CTS panel on the critical buckling loads, postbuckling paths and static failure behavior are captured for the first time. A hybrid optimization scheme that couples a genetic algorithm with a pattern-search algorithm is used to define a VAT laminate that reduces the mass of both square and rectangular aircraft panels by 31% compared to a baseline straight fiber design. The optimization of the fiber paths is driven by two distinct requirements, namely local and global stiffness tailoring that influence the buckling performance and static strength, respectively. Finally, the initial postbuckling behavior of the optimized designs is investigated using Koiter's perturbation approach, which reveals that postbuckling stability should be considered when optimising VAT panels manufactured by the CTS technique.

Optimal design, manufacturing and testing of non-conventional laminates

“…Continuous tow shearing is a new manufacturing method, leading to varying fiber angles without any gaps or overlaps, but with a thickness variation that is coupled with the change in fiber angle [32,16]. By using a genetic algorithm, coupled with a pattern-search algorithm, or using the infinite strip method, large improvements in structural performance have been shown [33,34]. A more comprehensive review of optimization strategies can be found in Ghiasi et al [35] To exploit the possibilities of VSL fully, a three-step approach has been developed at Delft University of Technology.…”

Effect of steering limit constraints on the performance of variable stiffness laminates

“…Continuous tow shearing is a new manufacturing method, leading to varying fibre angles without any gaps or overlaps, but with a thickness variation that is coupled with the change in fibre angle [22,23]. Using a genetic algorithm, coupled with a pattern-search algorithm, or using the infinite strip method large improvements in structural performance have been shown to be possible [24,25]. A more comprehensive review of optimisation strategies can be found in Ghiasi et al [26] The lamination parameters are optimised in step one of the three-step optimisation approach, which has the disadvantage that a fibre angle retrieval step is needed.…”

Mixed shell element for static and buckling analysis of variable angle tow composite plates

“…Higherorder finite elements have also been used to study the bending [36] and vibrational response [37,38] of VAT plates. At the same time, the pseudo-spectral Differential Quadrature Method (DQM) has been shown to be a fast, accurate and computationally efficient technique for solving the variable-coefficient higherorder differential equations for bending [39], buckling [26,40] and postbuckling [27,41] of VAT plates and cylindrical shells [42,43]. For a recent review on the differential quadrature method the interested reader is directed to [44].…”

“…For a recent review on the differential quadrature method the interested reader is directed to [44]. The work by White et al [42], Raju et al [45] and Groh & Weaver [43] has shown the efficiency and effectiveness of using Koiter's asymptotic analysis within a DQM framework to study the critical and post-critical behavior of VAT plates and shells. Furthermore, a strong-form finite element method based on DQM has been used to study the static [46] and vibrational response [47] of doubly-curved VAT laminates.…”