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- Multi-objective optimization of pultruded composite sandwich panels for building floor rehabilitationPublication . Garrido, Mário; Madeira, JFA; Proença, M.; Correia, J. R.Composite sandwich panels are being increasingly considered for civil engineering structural applications, offering high versatility in constituent materials and their geometrical arrangement. This translates to a high number of design variables, in addition to a potentially large number of design requirements and objectives related to the panels' functions. This paper presents an optimization study of a composite sandwich panel system for building floor rehabilitation, using the Direct MultiSearch (DMS) method. Pultruded multicellular panels with a polyurethane (PUR) foam core and carbon- or glass-fibre reinforced polymer (C/GFRPF) faces and ribs/webs are considered. The panel architecture was defined using 3 geometrical variables and 14 material related variables. In addition, 8 competing objective functions were studied, related to aspects such as structural serviceability and resistance, thermal insulation, acoustic performance, cost minimization, and environmental performance. The results are presented in the form of Pareto optimal sets, from which several conclusions are drawn regarding common design-related options. The influence of core material density, of the number of ribs/webs, or of the type of fibre reinforcement and its respective layup on the different objective functions are addressed. Optimal solutions for meeting different design purposes are presented, providing useful insights for structural designers and sandwich panel manufacturers.
- Characterization and optimization of hybrid carbon-glass epoxy composites under combined loadingPublication . Infante, Virginia; Madeira, JFA; Rui B. Ruben; Moleiro, Filipa; Teixeira De Freitas, SofiaThis work is intended to characterize the mechanical behavior of hybrid carbon-glass composite plates under combined loading of bending and torsion, and to determine the optimal ply fiber orientations to minimize the maximum out-of-plane displacement under such loading conditions. Hybrid composite plates were manufactured with 10 plies each and different stacking sequences using hand lay-up, with carbon fiber and glass fiber reinforcements in an epoxy matrix. Two experimental setups (involving two distinct boundary conditions) are here considered to test the composite plates, both simulating combined loading of bending and torsion. Numerical simulations of the experimental tests were performed in ABAQUS (R) and validated with the experimental data. Using the ply fiber orientations as design variables, the hybrid composite plates were then optimized using global and local optimization using direct search (GLODS). The objective function of minimization of the maximum out-of-plane displacement is carried out through an interactive cycle between GLODS and ABAQUS (R). Specimens of three optimized laminates were also manufactured for experimental validation. The optimization process contributed to improve the performance of the hybrid composite plates in more than 30% when compared to some non-optimized plates.
- Optimal cruciform specimen design using the direct multi-search method and design variable influence studyPublication . Miguel Gomes Simões Baptista, Ricardo; Cláudio, R. A.; Reis, L.; Madeira, JFA; Freitas, M.Nowadays the development of new testing machines and the optimization of new specimen geometries are two very demanding activities. In order to study complex material stress and strain distributions, as in-plane biaxial loading, one must develop new technical solutions. A new type of testing machine has been developed by the present authors, for the fatigue testing of cruciform specimens, but the low capacity of the testing machine requires the optimization of the specimen in order to achieve higher but uniform stress and strain distributions on the specimen center. In this paper, the authors describe the procedure to optimize one possible geometry for cruciform specimens, able to determine the fatigue initiation life of material subjected to out of phase in-plane biaxial fatigue loadings. The high number of design variables were optimized using the direct multi-search method, considering two objective functions, the stress level on the specimen center and the uniformity of the strain distribution on a 1.0 mm radius of the specimen center. Several Pareto Fronts were obtained for different material thickness, considering the commercially available sheet metal thickness. With the optimal solution, the influence of every design variable was studied in order to provide others with a powerful tool that allows selecting the optimal geometry for the desired application. The results are presented in the form of design equations considering that the main design variable, the material thickness, was chosen from a Renard series of preferred numbers. The end user is then able to configure the optimal specimen for the required fatigue test.
- GA topology optimization using random keys for tree encoding of structuresPublication . Madeira, JFA; Pina, H. L.; Rodrigues, H. C.Topology optimization consists in finding the spatial distribution of a given total volume of material for the resulting structure to have some optimal property, for instance, maximization of structural stiffness or maximization of the fundamental eigenfrequency. In this paper a Genetic Algorithm (GA) employing a representation method based on trees is developed to generate initial feasible individuals that remain feasible upon crossover and mutation and as such do not require any repairing operator to ensure feasibility. Several application examples are studied involving the topology optimization of structures where the objective functions is the maximization of the stiffness and the maximization of the first and the second eigenfrequencies of a plate, all cases having a prescribed material volume constraint.
- Optimization of a composite impact attenuator for a formula student carPublication . Castro, J. M. P. B. C.; Fontana, M.; Araújo, Aurélio L.; Madeira, JFAThe current impact attenuator used by the Formula Student team of University of Lisbon is an out-of-shelf solution consisting in an aluminum honeycomb. The competition regulations defined for the impact attenuator’s design allow room for innovation, which can be used to build more efficient structures and explore new materials. The main objective of this work is to design and optimize a composite impact attenuator lighter than the solution currently used by the team. Experimental results and numerical models presented in previous works are considered in the development of a new approach. Several design parameters are studied and their influence on the behavior of the impact attenuators are taken into account. Direct Multisearch (DMS) algorithm directly coupled to Abaqus software is used to perform the optimizations. The lighter solutions’ mass is compared to the baseline aluminum structure’s and detailed descriptions are presented for chosen optimal designs, which constitute an improvement regarding the baseline’s mass.