Research Publications (Engineering and Built Environment)
Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/215
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Item A methodology to design fibre reinforced laminated composite structures for maximum strength(Elsevier, 2003) Walker, Mark; Smith, Ryan E.A procedure to select the optimal fibre orientations and determine the maximum load carrying capacity of symmetrically laminated fibre reinforced composite structures is described. Cylindrical shells subject to combinations of torque and in-plane forces are used to illustrate the methodology and are optimally designed for maximum strength. Torque tubes are generally used as control mechanisms, for example, in the tail fins of aircraft. The finite element method, based on Mindlin plate and shell theory, is used in this application in conjunction with an optimisation routine in order to obtain the optimal designs. The methodology consists of two stages; the objective of the first is to maximise the strength of the cylindrical shells by determining the fibre orientations optimally while the objective of the second stage is to maximise the in-plane compression loading subject to a failure criterion. The effect of different shell aspect ratios, wall thickness, layer numbers and boundary conditions on the results is investigated.Item A computational methodology to select the best material combinations and optimally design composite sandwich panels for minimum cost(Elsevier, 2002) Walker, Mark; Smith, Ryan E.A procedure to select the best material combination and optimally design sandwich laminates with fibre reinforced skins and low density cores for minimum cost is described. Sandwich constructions generally provide improved stiffness/mass ratios and provide more tailoring opportunities than monolithics, and thus greater chance of satisfying design constraints. The objective of the optimisation is to minimise the laminate cost by selecting the skin and core material combination, layer thicknesses and skin fibre angles optimally, subject to load and mass 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 methodology and its benefits are demonstrated using graphite, glass or kevlar/epoxy facings, and balsa or PVC cores.Item A procedure to select the best material combinations and optimally design composite sandwich cylindrical shells for minimum mass(Elsevier, 2006) Walker, Mark; Smith, Ryan E.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. The objective of the 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, Glass or Kevlar/Epoxy facings, and Balsa or PVC cores.Item A technique for the multiobjective optimisation of laminated composite structures using genetic algorithms and finite element analysis(Elsevier, 2003) Walker, Mark; Smith, Ryan E.A methodology for using genetic algorithms with the finite element method to minimise a weighted sum of the mass and deflection of fibre reinforced structures with several design variables is described. The design constraint implemented is based on the Tsai–Wu failure criterion. Symmetrically laminated composite rectangular plates with eight layers are used to demonstrate the technique. Thus, the four fibre orientations and laminae thicknesses are to be determined optimally by defining a design index comprising a weighted average of the objective functions and determining the minimum. In addition, the fibre orientations and layer thicknesses must be selected from a set of discrete values. Results are presented for different load distributions, and various combinations of clamped, simply supported and free boundary conditions. The effect of aspect ratio on the results is also investigated.