Browsing by Author "Madeira, J. F. A."
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- Deformation prediction of composite specimens subjected to three-point bending testsPublication . Monte, Sara M. C.; Infante, Vírginia; Moleiro, F.; Madeira, J. F. A.A computational and experimental study was carried out in order to determine the deformations of specimens made in laminated composite material when subjected to three - point bending test. The specimens were produced using unidirectional carbon fiber prepreg with different aspect ratios and different lamination schemes. The experimental deformations of the bending tests were obtained using an innovative method called digital image correlation. At the computational level, two models were compared: the first developed in ANSYS and the second, not available in any commercial program, developed by MOLEIRO, 2010.The latter presents a mixed Layerwise formulation that assumes displacements and transverse stresses as independent variables, and therefore is able to a priori fulfill the interlaminar continuity C^0 of tranverse stresses and displacements. ANSYS model uses a solid element, in the laminated structural version, and assumes a displacement formulation. It was concluded that the ANSYS model results are more similar to the experimental results of longer specimens and the Layerwise mixed model results are more similar to the experimental results of shorter specimens.
- Design optimization of cruciform specimens for biaxial fatigue loadingPublication . Baptista, Ricardo; Cláudio, Ricardo; Reis, L.; Guelho, I.; Freitas, M.; Madeira, J. F. A.In order to correctly assess the biaxial fatigue material properties one must experimentally test different load conditions and stress levels. With the rise of new in-plane biaxial fatigue testing machines, using smaller and more efficient electrical motors, instead of the conventional hydraulic machines, it is necessary to reduce the specimen size and to ensure that the specimen geometry is appropriated for the load capacity installed. At the present time there are no standard specimen’s geometries and the indications on literature how to design an efficient test specimen are insufficient. The main goal of this paper is to present the methodology on how to obtain an optimal cruciform specimen geometry, with thickness reduction in the gauge area, appropriated for fatigue crack initiation, as a function of the base material sheet thickness used to build the specimen. The geometry is optimized for maximum stress using several parameters, ensuring that in the gauge area the stress is uniform and maximum with two limit phase shift loading conditions. Therefore the fatigue damage will always initiate on the center of the specimen, avoiding failure outside this region. Using the Renard Series of preferred numbers for the base material sheet thickness as a reference, the reaming geometry parameters are optimized using a derivative-free methodology, called direct multi search (DMS) method. The final optimal geometry as a function of the base material sheet thickness is proposed, as a guide line for cruciform specimens design, and as a possible contribution for a future standard on in-plane biaxial fatigue tests.
- Optimization of fibers orientation in a composite specimenPublication . Monte, S. M. C.; Infante, V.; Madeira, J. F. A.; Moleiro, F.This article is devoted to the study of the optimal design of fibers orientation in a composite specimen with the objective to minimize the displacement. The composite specimen considered is within the scope of aerospace and mechanical applications. The objective function associated with the composite design is computed based on a static analysis of a finite element solid model, which allows one to define (or control) the fibers orientation. The recent global and local optimization using direct search methods (GLODS) is used for the optimization process. To validate and compare the numerical and optimized results, the specimens were manufactured and tested experimentally. The orientation of the layers that minimize the maximum displacement is achieved through the computational interaction of the optimization program, GLODS, in loop with the finite element program, ANSYS. It is shown that the optimized lamination schemes found by GLODS minimized about 60% of the displacement compared to the nonoptimized specimens.
- Optimization of fibers orientation in a composite specimenPublication . Monte, Sara M. C.; Infante, Vírginia; Moleiro, Filipa; Madeira, J. F. A.The main purpose of this study was to optimize the fibers orientation in a composite specimen with the objective to minimize the displacement. This composite specimen can be used in aerospace or mechanical structures. The objective function was performed with static analysis by altering the fibers orientation in a finite element solid model, computed using the ANSYS program. A recent method for global optimization GLODS (Global and local optimization using direct search) was used for the optimization process. In the sequence, specimens were manufactured and experimental tested, in o order to validate the numerical results obtained.