https://repositorio.ufu.br/handle/123456789/5467 Mon, 22 Jun 2026 22:39:41 GMT 2026-06-22T22:39:41Z https://repositorio.ufu.br/handle/123456789/48757 Title: Avaliação da suscetibilidade à fragilização por hidrogênio em aços avançados de alta resistência aplicados na indústria automotiva Abstract: Hydrogen embrittlement has become a major challenge in the application of advanced high-strength steels (AHSS) in the automotive industry. Hydrogen uptake may occur throughout the material lifecycle, particularly during pickling, annealing, galvanizing, welding, and phosphating processes. The issue becomes more critical under mechanical shearing conditions, since the high dislocation density and microvoids generated at sheared edges promote localized hydrogen accumulation and abrupt fracture. Therefore, evaluating hydrogen effects under sheared-edge conditions is essential to assess the susceptibility of AHSS to hydrogen embrittlement. In this study, the hydrogen embrittlement behavior of DP1200 and TRIP1000 steels was investigated considering different edge-cutting conditions obtained by varying the punching clearance. A new methodology was proposed to enable ex-situ hydrogen charging at controlled levels, followed by constant load (CLT) and slow strain rate (SSRT) mechanical testing. Increased cutting clearance, associated with greater local deformation and the presence of microvoids, resulted in higher susceptibility to hydrogen embrittlement in both steels. Under favorable cutting conditions (12% clearance), the critical hydrogen contents were 0.27 ppm for DP1200 and 0.61 ppm for TRIP1000. However, when the clearance was increased to 25%, corresponding to reduced edge‑stretching capability, the critical hydrogen thresholds dropped significantly, reaching levels below 0.27 ppm for DP1200 and 0.24 ppm for TRIP1000. These findings highlight the importance of strict edge‑quality control, particularly for electro‑galvanized products. In this context, especially for DP1200, which showed greater sensitivity to this failure mode, post‑processing strategies, such as thermal desorption treatments, may be required to reduce hydrogen content and mitigate edge‑cracking risk during the service. The hydrogen effect on fatigue and weldability was also assessed. Stress‑controlled fatigue tests revealed hydrogen‑assisted embrittlement in both steels, although fatigue‑life reductions were more consistent for DP1200. Early crack nucleation was linked to the enhanced interaction between hydrogen and inclusions, which functioned as preferential initiation sites. In resistance spot welds (RSW), hydrogen promoted more brittle fracture modes without significantly affecting joint strength. Overall, these findings contribute to advancing the understanding of hydrogen embrittlement mechanisms in AHSS designed for automotive applications. Fri, 06 Mar 2026 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/48757 2026-03-06T00:00:00Z https://repositorio.ufu.br/handle/123456789/48661 Title: Desenvolvimento de uma metodologia de instrumentação e avaliação da integridade de estruturas de concreto armado em operação contínua via técnica da impedância eletromecânica e o auto codificador variacional. Abstract: The monitoring of civil structures that are in full operation has been gaining more and more space in Brazil and worldwide, due to large structures such as bridges, viaducts, and dams that are reaching the end of their useful lives and need periodic and increasingly frequent maintenance. The advancement in the studies of Structural Integrity Monitoring (SHM) and Artificial Intelligence (AI) has opened a wide range of applications in monitoring structures and making possible increasingly accurate and robust diagnoses, especially in the construction sector. In this context, this paper presents a methodology for instrumentation and evaluation of a reinforced concrete structure that is in continuous operation, using the techniques of ISHM (Structural Integrity Monitoring based on Electromechanical Impedance Technique), ultrasound and AI. For this, the proposed methodology was applied in detail to a reinforced concrete beam that supports a mezzanine at the Laboratório de Mecânica de Estruturas Prof. José Eduardo Tannús Reis (LMEst-UFU). The results showed how important the methodology was to identify and separate situations in which alarms from structure monitoring systems could present FalseNegatives and make correct decisions about the possible measurement limits for a given structure. Thus, the objective was satisfactorily achieved and several suggestions for future work were presented. Thu, 28 Jul 2022 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/48661 2022-07-28T00:00:00Z https://repositorio.ufu.br/handle/123456789/48591 Title: Dispositivo de resistência vibratório para treinamento muscular de membros inferiores Abstract: The practice of sports and physical exercise in general has a major influence on people’s fitness and quality of life. In this context, it is of fundamental importance to develop low-cost muscle training/rehabilitation equipment that is efficient and accessible. The aim of this study was to design, build and test a extension/flexion machine with a cam-spring resistance system and a device for applying mechanical vibration in the direction of muscle shortening. Two identical conventional extension chairs were purchased, one of which had its resistance system replaced by a cam-spring system with mechanical vibration and the other was kept completely original to be used in the tests as a basis for comparison, with identical postural parameters. The new equipment is simple, compact, low inertia and allows mechanical vibrations to be applied in the direction of muscle shortening with adjustable frequency and amplitude. Due to its low inertia design, the equipment also allows milimetric load variation and exercises to be performed at higher speeds and with less risk of injury. The comparative tests evaluated the activation amplitude of the electromyographic signal in the right and left rectus femoris muscles of trained individuals during bilateral extension/flexion movements on the conventional chair and the new equipment. The sample consisted of 7 trained male volunteers aged between 18 and 40. The protocol consisted of 4 types of exercise: conventional machine with controlled speed (CEC), new machine with controlled speed (CAME), new machine with controlled speed and addition of mechanical vibration (VIBRA) and new machine with maximum speed (POT). A significant increase in the amplitude of the electromyographic signal was observed in the POT compared to the other exercises, both in the concentric and eccentric phases. Overall, the equipment proved to be effective, safe and with great innovative potential for improving training gains. Thu, 29 Feb 2024 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/48591 2024-02-29T00:00:00Z https://repositorio.ufu.br/handle/123456789/48457 Title: Modelagem computacional de escoamentos turbulentos utilizando a metodologia da fronteira imersa dos volumes fantasmas Abstract: The capability to digitally simulate the physical world has transformed the manner in which science and engineering interact with nature. As one of the most challenging fields of this transformation, Computational Fluid Dynamics (CFD) has established itself as a fundamental pillar, enabling the high- fidelity representation of complex flows. However, within the scope of immersed boundary methods, the faithful representation of intricate interfaces and their efficient geometric processing remain critical challenges for the robustness and viability of current numerical tools. This thesis presents the development, extension, and improvement of the Ghost-Cell Immersed Boundary Method (IB-GCM) integrated into the MFSim computational platform. The work focuses on the solution and validation of flows involving dynamic and thermal effects, as well as fluid-structure interaction (FSI). The methodology was validated through classical cases, such as Poiseuille flow with thermal effects and flow in coaxial ducts, demonstrating sealing capabilities when using zero-thickness boundaries. Flow around a sphere was simulated in both laminar and turbulent regimes, applying Large Eddy Simulation (LES) closure models and utilizing Adaptive Mesh Refinement (AMR) to efficiently capture high gradients in the vicinity and wake of the sphere. In the context of FSI, the vibration of a submerged plate was validated, and the dynamic response of a clamped-clamped beam subjected to cross-flow was analyzed. Finally, a preliminary analysis of an injector applied to industrial-scale projects was performed. The results consolidated in this thesis ratify the IB-GCM method as a robust, accurate, and versatile tool, capable of addressing the complexity of coupled transport phenomena in complex geometries, bridging the gap between high-rigor academic research and the technological demands of modern industry. Fri, 20 Feb 2026 00:00:00 GMT https://repositorio.ufu.br/handle/123456789/48457 2026-02-20T00:00:00Z