Marco Antônio Luersen

Optimization of hybrid laminated composites using a genetic algorithm

This work aims at developing a genetic algorithm (GA) to pursue the optimization of hybrid laminated composite structures. Fiber orientation (predefined ply angles), material (glass-epoxy or carbon-epoxy layer) and total number of plies are considered as design variables. The GA is chosen as an optimization tool because of its ability to deal with non-convex, multimodal and discrete optimization problems, of which the design of laminated composites is an example. First, the developed algorithm is detailed explained and validated by comparing its results to other obtained from the literature. The results of this study show that the developed algorithm converges faster. Then, the maximum stress, Tsai-Wu and Puck (PFC) failure criteria are used as constraint in the optimization process and the results yielded by them are compared and discussed. It was found that each failure criterion yielded a different optimal design.

Curved fiber paths optimization of a composite cylindrical shell via Kriging-based approach

While conventional design and manufacturing techniques of fiber-reinforced laminates keep the fiber orientation angle constant within a layer, automated tow-placement technology allows fabricating laminates with curved fibers. This offers more flexibility to tailor the mechanical properties and improve the performance of laminated structures. Exploiting this flexibility requires an efficient method for finding optimal or near-optimal fiber configurations. In this paper, laminated cylindrical shells are studied. Curvilinear variations for the fiber orientations are adopted in the circumferential and longitudinal directions. The computational burden, typical in numerical optimization of complex structures, is reduced using a Kriging model, which substitutes for direct finite element simulation. A sequential quadratic programming algorithm is employed as local optimizer, coupled with a restart strategy to search for the global optimum in the entire design space. Some numerical cases are presented: the maximization of the fundamental frequency of the shell considering different boundary conditions and the minimization of the maximum displacement with a constraint on the buckling load.

Optimal curved fibre orientations of a composite panel with cutout for improved buckling load using the Efficient Global Optimization algorithm

ABSTRACT Composite structures with cutouts (like panels with holes) are a challenge to design because discontinuities of this kind provoke stress concentrations and become critical regions. With curved fibres, the effect of these discontinuities can be decreased by choosing the fibre paths properly. In this article, fibre-path optimization to improve the buckling load of laminated composite panels with cutouts is studied. Two fibre path parameterizations are tested: the usual curvilinear Cartesian and the radial one, proposed in this article, in which the fibre orientations vary linearly with the Euclidean distance from the centre of the panel. To reduce the simulation costs associated with the optimization, the Efficient Global Optimization (EGO) algorithm is used. EGO is a technique based on a stochastic process approach (Kriging) that approximates expensive-to-evaluate functions and sequentially maximizes the expected improvement to update the surrogate at each iteration. A stiffened panel with a cutout subjected to compression and in-plane shearing loads is analysed. The results show that the buckling load when curved fibres are used is substantially higher than the buckling load for straight-fibre laminates. In addition, the optimization framework indicates a low final computational burden.

Fiber Bragg grating tuning with notch-type spring device

This paper presents a notch-type spring mechanism based on the traction principle for tuning fiber Bragg gratings, which magnifies the displacement of piezoelectric actuators. Practical tuning ranges up to 8 nm and tuning times below 20 ms are demonstrated. Oscillations that affect the device due to the rapid voltage change applied to the actuator are mitigated using either an electronic filter or a viscoelastic neutralizer technique.

ANÁLISE DE UMA MOLA ORTODÔNTICA DO TIPO DELTA E SUA INFLUÊNCIA NA MOVIMENTAÇÃO DENTÁRIA: UM ESTUDO NUMÉRICO EXPERIMENTAL

Em odontologia sao frequentemente utilizados dispositivos conhecidos por alcas ortodonticas para a movimentacao dentaria em um tratamento clinico. As alcas ortodonticas sao elementos fabricados em fio metalico, cujas forcas e momentos gerados sao diretamente relacionados com os tipos de movimentos de translacao, rotacao controlada e nao controlada dos dentes para fins especificos. Este artigo alia analises de elementos finitos tridimensionais, amplamente utilizados em engenharia, com metodos experimentais para o desenvolvimento de uma alca ortodontica tipo delta. Foram avaliadas as tensoes atuantes, as forcas, os momentos e a relacao momento forca, a fim de prever alguns tipos de movimentos dentarios com o uso da alca proposta. Verificou-se forca de extrusao dentaria nula e ativacao maxima de ate 8,0 mm (tensao maxima de von Mises igual a 1.226,8 MPa), bem como a possibilidade da inducao dos movimentos dentarios de inclinacao nao controlada – controlada de raiz e inclinacao controlada de coroa com o uso desta alca. Palavras-chave: Alcas ortodonticas, metodo dos elementos finitos, analise experimental. ABSTRACT Devices known as orthodontic springs are frequently used in dentistry to provide dental movement in a clinical treatment. Orthodontic springs are, basically, elements manufactured in metallic wire which forces and moments are directly related to the types of translation movement, controlled tilt and no controlled tilt of the teeth. This article allies three dimensional finite element analysis, largely applied in engineering, with experimental methods for the development of an orthodontic delta spring, evaluating the stresses, forces, moments and the ratio moment force, in order to foresee some types of dental movements with the use of the proposed spring. It was verified null dental extrusion forces and maximum activation of up to 8.0 mm (maximum von Mises stress equal to 1,226.8 MPa) as well as the possibility of the induction of dental movements like no controlled – controlled tilt of root and controlled tilt of crown with the use of this spring. Keywords: Orthodontic springs, finite element method, experimental analysis.

Optimisation of a Laminated Composite Cylindrical Shell With Curvilinear Fibre Paths Using a Surrogate-Based Approach

Conventional design and manufacturing techniques of fibre-reinforced laminated materials keep the fibre orientation angle constant within each ply. However, with the development of advanced tow-placement technology it is now feasible to produce composites with curved fibres. This offers more flexibility to tailor the mechanical properties and improve the performance of laminated structures. In this paper, fibre path optimisation of a laminated cylindrical shell is studied. Curvilinear variations for the fibre orientations are adopted in the circumferential and longitudinal directions of the shell. In order to reduce the computational cost a surrogate-based optimisation strategy is proposed to pursue the optimum design. The laminated shell is subjected to bending and torsion loads and the maximum displacement magnitude is minimised while a constraint on the buckling load is imposed. Numerical studies are presented for two cases. First, only circumferential variation in the fibre orientations is considered. Then, circumferential and longitudinal variations are assumed.Copyright