https://repositorio.unifei.edu.br/jspui/handle/123456789/88 Sat, 02 May 2026 09:28:35 GMT 2026-05-02T09:28:35Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4394 Título: Estudo Foto- e Solvatocrômico de Complexos de Lantanídeos com Espiropirano Abstract: In this study, coordination complexes comprising the entire series of trivalent lanthanide ions (La³⁺ to Lu³⁺, except Pm³⁺) were synthesized and characterized, employing a derivative of the spiropyran molecule named: 3-(3',3'-dimethyl-6-nitrospiro[chromene-2,2'-indolin]-1'-yl)propanoic acid(SPCOOH), as the ligand. Structural characterization was conducted using vibrational spectroscopy in the infrared (FTIR) and Raman spectroscopy, with the results providing evidence that metal coordination occurs through the oxygen atoms of the carbonyl group and the phenolate moiety of the merocyanine isomer, as indicated by bathochromic shifts. UV-Vis spectroscopic analyses revealed hypsochromic shifts in the absorption bands of the complexes relative to the free ligand, supporting the formation of the complexes and corroborating the vibrational spectroscopy findings. Mass spectrometry analyses indicated the formation of complexes containing two or three ligand molecules per metal center, in addition to water molecules and nitrate ions within the coordination sphere. Stability kinetics studies performed in acetonitrile demonstrated that the complexes exhibit good stability, with no evidence of complete dissociation over the analysis period. Solvatochromism experiments carried out in linear chain alcohols (methanol, ethanol, 1-propanol, 1-butanol, and 1-octanol) revealed a trend of decreasing maximum absorption wavelength with increasing atomic number of the lanthanides, although no direct correlation with solvent polarity was observed. Finally, all complexes exhibited fluorescence, with similar emission profiles attributed to the influence of the SPCOOH ligand. This work provides unprecedented insights into the structural and electronic properties of lanthanide complexes with spiropyran derivatives, thereby expanding the current understanding of the coordination chemistry of these elements and highlighting their potential applications in optical materials and molecular sensors. Tipo: Tese Wed, 27 Aug 2025 00:00:00 GMT https://repositorio.unifei.edu.br/jspui/handle/123456789/4394 2025-08-27T00:00:00Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4393 Título: Vibration-based damage localization in composites structures: integrating CNNs, mode shapes, and digital image correlation Abstract: Composite sandwich structures offer high stiffness-to-weight ratios but are highly susceptible to complex internal damage mechanisms that are often difficult to detect using conventional inspection techniques. This work proposes a vibration-based Structural Health Monitoring (SHM) framework that integrates mode shape analysis, image processing techniques, Digital Image Correlation (DIC), and Convolutional Neural Networks (CNNs) for automated damage detection, localization, and sizing in composite sandwich structures. The investigated damage consists of a controlled stiffness-reduction region introduced by inserting a lower-stiffness material within the laminate, simulating internal debonding or delamination-type defects. A simulation-driven methodology is first established, in which mode shapes obtained from finite element models are transformed into image-based representations. These representations are used to train CNN models, demonstrating that image-based modal features outperform traditional approaches relying solely on global modal parameters, achieving detection accuracies above 90% under numerical conditions. The framework is further enhanced through physically informed image transformations, including residual-based representations, curvature enhancement, and multi-modal strategies that combine information from multiple vibration modes, as well as attention mechanisms embedded within the CNN architecture. These improvements lead to consistent performance gains, with accuracy increases of up to 10–15% and reductions of up to 20–30% in damage localization error compared to baseline image representations. Finally, the proposed framework is validated experimentally using mode shapes extracted from DIC measurements. Despite measurement noise, experimental uncertainty, and discrepancies between numerical and experimental domains, the models maintain robust performance, achieving damage detection accuracies above 85%, average localization errors below 10 mm, and reliable estimation of damage size under real testing conditions. The main contribution of this thesis is to demonstrate that vibration mode shapes, interpreted as spatial information, combined with advanced image representations and deep learning architectures, enable accurate localization and sizing of internal stiffness-reduction damage in real composite sandwich structures. These findings highlight the practical feasibility of the proposed methodology for real-world SHM applications. Tipo: Tese Thu, 19 Feb 2026 00:00:00 GMT https://repositorio.unifei.edu.br/jspui/handle/123456789/4393 2026-02-19T00:00:00Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4355 Título: Desenvolvimento e caracterização de ligas multicomponentes refratárias à base de AlCrNiNbMoW obtidas por metalurgia do pó Abstract: High-entropy alloys have emerged as a promising alternative for producing materials with exceptional properties. Among these alloys, refractory alloys, comprising refractory elements, stand out for their significant innovation in the development of materials for high-temperature applications. These applications require thermal stability, wear resistance, and oxidation resistance in extreme environments. Composed of five or more principal elements in equiatomic or near-equiatomic proportions, these alloys exhibit high configurational entropy, facilitating the formation of stable solid solutions, in contrast to conventional alloys. Traditionally, these alloys are produced via fusion, a method plagued by economic, environmental, and production drawbacks, as well as heterogeneous structures and elemental segregation. To overcome these challenges, this study proposes the use of powder metallurgy, which fosters the formation of homogeneous alloys with enhanced solubility in the solid state. This approach offers advantages such as minimal waste, rapid production, sustainability, and innovation compared to conventional methods. This investigation examines the influence of varying atomic proportions of Al and Cr on phase formation and oxidation resistance in the refractory alloy AlCrNiNbMoW produced via powder metallurgy. The variation was implemented at 25% increments from the equiatomic proportion to the total replacement of Al by Cr. The results revealed that all alloys achieved densification of up to 95% relative to the theoretical value and exhibited similar microstructures, comprising solid solutions with body-centered cubic (BCC) crystalline structure and Laves phases. Oxidation tests revealed the formation of aluminum, niobium, chromium, and tungsten oxides. The alloy Al4,2Cr29,2Ni16,7Nb16,7Mo16,7W16,7 demonstrated the smallest mass gain (0.037 g/cm²). It was observed that reducing the Al content favors an increase in the fractions of Ni, Mo, and W, and stabilizes Nb in the matrix. The increase in the Cr content had little influence on the oxidation resistance. This study highlights the potential of high-entropy effects in developing novel refractory alloys via powder metallurgy, featuring homogeneous microstructures and optimized properties for high-temperature applications. Tipo: Tese Fri, 12 Dec 2025 00:00:00 GMT https://repositorio.unifei.edu.br/jspui/handle/123456789/4355 2025-12-12T00:00:00Z https://repositorio.unifei.edu.br/jspui/handle/123456789/4354 Título: Avaliação de métodos de união de materiais compósitos termoplásticos Abstract: This study presents the results of the fabrication of laminated plates of carbon fiber and Elium®150 resin and glass fiber using the Vacuum Assisted Resin Transfer Molding (VARTM) method. It describes the use of material joining techniques, such as bonding and infrared light welding, using this resin for joining composite materials. Elium® resin was thermally characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and thermomechanical analysis (TMA). The DSC analysis of the pure resin resulted in a peak curing temperature of 82.92ºC, glass transition temperature (Tg) of 94.16ºC, and curing enthalpy of 216.63 J/g. The DMA results showed a Tg of 50.82ºC for the pure resin, 71.9ºC for the carbon fiber, and 98.47ºC for the glass fiber. TMA results showed a Tg of 91ºC for the carbon fiber and 93ºC for the glass fiber. TGA indicated the onset degradation temperature of 300ºC for both the pure resin and the composites. Ultrasound tests did not detect defects or voids in the glass or carbon laminates. Processing parameters were established using 150, 175, and 200ºC with pressures of 0.4 to 0.5 MPa after the heating phase in the welding process. Shear tests demonstrated higher shear stress values of 14.6 MPa for glass fiber composite samples processed at 150ºC and 0.4 MPa pressure. The glass fiber samples showed better anchorage between the fiber and the matrix due to more effective chemical compatibility. The carbon fiber samples exhibited significant adhesive failures, with the resin detaching from the fiber, indicating insufficient adhesion. This behavior is consistent with the loss of matrix rigidity observed through DMA, particularly at higher welding temperatures. All bonded laminate samples exhibited higher shear strength, with values of 14.68 MPa (carbon fiber) and 16.73 MPa (glass fiber) compared to infrared light-welded samples, which showed maximum values of 14.16 MPa (glass fiber) and 9.91 MPa (carbon fiber). These results support the fact that the bonded samples were processed below the glass transition temperature determined by the DMA technique, thus maintaining their rigidity. Tipo: Tese Thu, 05 Dec 2024 00:00:00 GMT https://repositorio.unifei.edu.br/jspui/handle/123456789/4354 2024-12-05T00:00:00Z