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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 75
Edited by: B.H.V. Topping and Z. Bittnar
Paper 130

A Methodology to Select the Best Material Combinations and Optimally Design Composite Sandwich Cylindrical Shells for Least Mass

M. Walker and R.E. Smith

Centre for Advanced Materials, Design & Manufacture Research, Durban Institute of Technology, South Africa

Full Bibliographic Reference for this paper
M. Walker, R.E. Smith, "A Methodology to Select the Best Material Combinations and Optimally Design Composite Sandwich Cylindrical Shells for Least Mass", in B.H.V. Topping, Z. Bittnar, (Editors), "Proceedings of the Sixth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 130, 2002. doi:10.4203/ccp.75.130
Keywords: composite sandwich cylinders, optimal design, computational methodology.

A methodology to select the best material combination and optimally design composite sandwich cylinders having fibre reinforced skins and low density cores for minimum mass is described. Sandwich constructions generally provide improved stiffness/mass ratios and more tailoring opportunities than monolithics, and thus greater chance of satisfying design constraints. For example, the stiffness [1] or buckling load capacity [2,3] of laminated structures can be enhanced via sandwich construction. The tailoring is mostly achieved by maximising the mechanical properties as a result of selecting the fibre angles of the skins optimally, and thus realising the full potential of fibre-reinforced sandwiches.

The objective of this optimisation is to minimise the laminate mass by selecting the skin and core material combination, layer thicknesses and skin fibre angles optimally, subject to load and cost constraints. As the optimisation problem contains a number of continuous (ply angles and thicknesses) and discrete (material combinations) design variables, a sequential solution procedure is devised in which the optimal variables are computed in different stages. The procedure and its benefits are demonstrated using Graphite (C), Glass (G) or Kevlar/Epoxy (K) facings, and Balsa (B) or PVC (PVC) cores. Six candidates result from these material combinations (viz. C/B, C/PVC, G/B, G/PVC, K/B and K/PVC).

For a particular buckling load capacity and cost requirement, together with a choice of skin and core material combinations that results in candidates, the design optimisation procedure consists of two steps:

Step 1. For each candidate, determine the skin fibre angle optimally by determining the value of for which the resulting skin and core thicknesses lead to a minimum candidate mass, viz.

subject to

and ,

where is the buckling load capacity required, and the maximum cost allowable.

Step 2. Select the candidate with least mass.

When the six candidates are compared for a particular choice of geometry, boundary conditions and cost constraint, the effect of the skin fibre angle on the resulting mass was found to be important, and thus selecting this optimally is beneficial. In addition, it is shown that the best candidate can be several magnitudes lighter than the heaviest rival.

The effect of the cylinder radius, length and cost constraint was also investigated, and it was found that generally the best candidate was either C/PVC or K/PVC, due to the fact that PVC core material is very light, whilst Graphite /Epoxy and Kevlar/Epoxy have similar density values, although the former is 30% costlier.

S. Adali, E.B. Summers, V.E. Verijenko, "Minimum weight and deflection design of thick sandwich laminates via symbolic computation", Composite Structures, 29, 145-160, 1994. doi:10.1016/0263-8223(94)90096-5
A. Muc, "Buckling and failure analysis of FRP faced sandwich plates", Composite Structures, 48, 145-150, 2000. doi:10.1016/S0263-8223(99)00087-2
B. Hao, "Buckling and Postbuckling of soft-core sandwich plates with composite facesheets", Computational Mechanics, 25, 421, 2000. doi:10.1007/s004660050489

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