Percorrer por autor "Mota, A. F."
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- Image driven analysis of plates coated by cold spray coating process using a layerwise approachPublication . Mota, A. F.; Loja, Amélia; Singh, Harminder; Kalsi, S. B. S.; Barbosa, JoaquimFunctionally graded materials are characterized by its continuous spatial properties' variation which provides them a better behaviour concerning strain and stress transition, hence avoiding the abrupt changes typical of composite fibre reinforced laminates. Although manufacturing systems and techniques used in the production of such materials has evolved significantly, porosities may arise as non-desirable characteristic. Other situations exist where pores are desirable as they may contribute to a specific better performance. Regardless the specific application, it is expected that mechanical properties of graded material will be affected by the existence of porosities. This work presents a study on the static and free vibrations behaviour of plates constituted by a substrate coated by the cold spray coating process. This coating presents inherent porosities which distribution matters to characterize in order to assess its influence on the plate behaviour. To this purpose, a layerwise approach considering the first order shear deformation theory was used, in order to be able to carry out a more representative study of the system substrate-coating. The results obtained show that for a small relation between the coating thickness and the plate's total thickness, the relative deviations obtained, considering the porosity-free coating plate as reference, denotes no evidence of significant influence of the number of terms on the volume fraction approximation, for the static and free vibrations results.
- Mechanical behavior of a sandwich plate with aluminum foam core, using an image-based layerwise modelPublication . Mota, A. F.; Loja, Amélia; Barbosa, J.I.; Vinyas, M.Functionally graded materials are an advanced type of composite materials whose properties’ spatial evolution can be designed through the definition of the spatial distribution of the constituent phases’ mixture. This feature is particularly important if specific non-homogeneous properties’ requirements are required without introducing abrupt phases’ transitions, as happens in laminated materials. Porosities’ distributions within these materials, may constitute a design requisite for some applications, such as medical implants, but can also be highly undesirable in other cases such as for aeronautical applications. Regardless the specific situation, its characterization is of high importance to the prediction of the resulting materials’ behavior. This work is focused on the static and free vibrations’ analysis of a sandwich plate with a porous aluminum foam core and outer aluminum skins. The porosities’ distribution is modeled by different fitting functions, based on data obtained from a preliminary image processing stage of X-ray CT image of the sandwich plate’ cross-section. A layerwise approach is considered for subsequent numerical simulations’ purpose, where the sandwich skins’ kinematics are modeled using the first order shear deformation theory, while the core is modeled by a higher order shear deformation theory. Fitting functions’ influence on the plate’ behavior is also assessed.
- Mechanical behavior of porous functionally graded nanocomposite materialsPublication . Mota, A. F.; Loja, AméliaMaterials used in biomedical applications need to cope with a wide set of requisites, one of them being their structural adequacy to a specific application. Thus, it is important to understand their behavior under specified standard cases, namely concerning their structural performance. This objective constituted the focus of the present study, where nanocomposite functionally graded materials integrating di_erent porosity distributions were analyzed. To this purpose a set of numerical simulations based on the finite element method, reproducing American Society for Testing and Materials (ASTM) tensile and bending tests were considered. The results obtained show a good performance of the models implemented through their preliminary verification. It is also possible to conclude that carbon nanotubes and porosity distributions provide di_erent and opposite e_ects in the context of the nanocomposite materials analyzed.
- Variable stiffness composites: optimal design studiesPublication . Marques, Filipe Eduardo Correia; Mota, A. F.; Loja, M.A.R.This research work has two main objectives, being the first related to the characterization of variable stiffness composite plates’ behavior by carrying out a comprehensive set of analyses. The second objective aims at obtaining the optimal fiber paths, hence the characteristic angles associated to its definition, that yield maximum fundamental frequencies, maximum critical buckling loads, or minimum transverse deflections, both for a single ply and for a three-ply variable stiffness composite. To these purposes one considered the use of the first order shear deformation theory in connection to an adaptive single objective method. From the optimization studies performed it was possible to conclude that significant behavior improvements may be achieved by using variable stiffness composites. Hence, for simply supported three-ply laminates which were the cases where a major impact can be observed, it was possible to obtain a maximum transverse deflection decrease of 11.26%, a fundamental frequency increase of 5.61%, and a buckling load increase of 51.13% and 58.01% for the uniaxial and biaxial load respectively.