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- Load characterization on the joints of the A320 engine inlet cowl acoustic panelPublication . Conceição, Bruno; Anes, Vitor; Reis, LuisAircraft operate in environments in which the components are subject to large temperature and pressure variations. In aircraft structures such as the engine nacelles, composed by several components and different materials, the presence of wear and corrosion becomes noticeable due to their operation in such environments. Corrective actions must be employed to the components which present this kind of problems. The acoustic panels of the inlet cowl of the Airbus A320/A321, present corrosion problems on the aluminium doublers of the joints. In order to develop a corrective action to the joint of the acoustic panels, the analysis of the mechanical behaviour and forces acting on the joint must be carried out. In this work, a methodology involving Computational Fluid Dynamics, Finite Element Method and Computer Aided Design tools is developed in order to evaluate the mechanical behaviour of the acoustic panels joint. The assessment of the aerodynamic loads acting on the inlet cowl was performed using STAR CCM+ software. The structural analysis of the joint members of the acoustic panels was made with the use of FEM tools in ANSYS Workbench software. The critical steps involved in the analysis are explained. Obtained results are discussed and conclusions are presented.
- Bonded joints of dissimilar adherends at very low temperatures - An adhesive selection approachPublication . Anes, Vitor; Pedro, R.; Henriques, E.; Freitas, M.; Reis, L.Maintenance, repair and overhaul companies have been reporting corrosion failure events in the Airbus A320 CFM56-5b intakes. These intakes are attached to the power plant frame by a dissimilar material bonded joint, where liquid shim adhesive is used to avoid the dielectric formation between dissimilar materials. In previous works, the authors reported that the A320 intakes corrosion is a result of the adhesive inability to avoid the dielectric formation, which is a result of micro-cracks formation within the adhesive layer. The main reason that lead to these cracks is the adhesive aging and thermal cycling at very low temperatures, which quite often reach values lower than -50ºC. This paper studies the effect of negative thermal loading on dissimilar materials bonded joints. Two epoxy adhesives are studied and compared, namely the Hysol EA-934, which is the adhesive currently used in the A320 Airbus intakes, and the Hysol EA-9394, a second generation adhesive candidate to replace the actual adhesive. A numerical study was performed in order to simulate the adhesive joint using a finite element analysis commercial package, where several hypotheses were explored. These hypotheses where focused on the effects of several factors on the adhesive layer stress distribution. Factors such as temperature range, boundary conditions, variation of the coefficient of thermal expansion with temperature, and interfacial cracks between the adhesive layer and dissimilar adherend materials were analyzed. Results show that very low temperatures have a negative impact on the adhesives strength and micro-cracks formation may result from thermal loads below zero degrees Celsius, even for adhesives without any aging. Moreover, low temperatures in dissimilar materials bonded joints may create stress states that surpass the adhesive lap shear strength. Some conclusions are drawn regarding adhesive selection for dissimilar materials bonded joints in order to overcome these issues.
- Failure mode analysis of a 1.9 turbo diesel engine crankshaftPublication . Mateus, J.; Anes, Vitor; Galvão, Ivan; Reis, LuisThis paper reports a failure mode analysis of a 1900 cm(3) turbo diesel engine of a well-known commercial brand. The engine is a supercharged diesel engine with turbocharger, producing a maximum power of 81 kW; it was produced in 1999 and collapsed at 120,000 km without warning. A fracture occurred at the crankpin n degrees 1 of the crankshaft in the region of web-fillet. Crankshafts are mechanical power transmission components with complex geometries and experience multiaxial stress states in main journals and crankpins. The objective of this work is to determine the root cause that led to the crankshaft collapse. A fractographic, metallographic, and numeric analysis were performed to understand the crankshaft failure mode and its mechanical mechanisms. Results show that the crankshaft failure resulted from a fatigue process governed by normal stresses raised by two possible processes, namely, a notch in the crack initiation spot, or the crankshaft misalignment.
- On the determination of J-resistance curve of metallic materials using the unloading compliance technique and normalization methodPublication . Leite, A.; Balhana, A.; Anes, Vitor; Reis, L.In the present work, a study is made about the experimental determination of the fracture resistance curve (R curve) of metallic materials, using the methods: resistance curve and normalization, guided by the ASTM E 1820 standard. The resistance curve method, used here, consists in obtaining the “R curve” (expressed in integral J) through a single specimen. Within this method, the elastic compliance technique was used to obtain crack extension values. The normalization method consists in obtaining the resistance curve (expressed in integral J) directly from the force vs displacement diagram and the initial and final crack lengths, measured at the fracture surface. wo sets of specimens of two metallic materials were tested. Two specimens from each set were submitted to the normalization method, while the remaining were studied with the resistance curve method, implemented in the Instron Wavematrix software, based on the procedure of ASTM E 1820. It was not possible to obtain the value of Fracture Toughness in plain strain, JIC, since ductile crack sizes did not comply with all mandatory items of the standard ASTM E 1820, namely a crack tunnelling effect was observed, being the crack front much deeper than its value near the free surface Within each material, the respective resistance curves were compared using both methods.
- Stress-Based Model for Calculating the Opening Angle of Notch Cracks in a Magnesium Alloy under Multiaxial FatiguePublication . Videira, Henrique; Anes, Vitor; Reis, LuísThis paper presents a model to calculate the opening angle of crack initiation in notched fractures subjected to multiaxial loading. To validate the proposed model, a study was performed on polished AZ31B-F magnesium alloy specimens under multiaxial high-cycle fatigue loading. The specimens exhibited a notch in the smaller cross-sectional area, which was created with a special drilling jig to promote the formation of fatigue cracks in this localized area of the specimen. The load paths used in the experiments and numerical analyses were proportional and non-proportional, resulting in different stress states in the crack front opening, which were determined by finite element analysis to validate the proposed model. To obtain more accurate numerical results for these estimates, these finite element analyses were performed using the nonlinear Chaboche plasticity model of ABAQUS (R) 2021 software. A sensitivity analysis was also performed to determine which load component-axial or torsional-has a greater influence on the fatigue strength and contributes significantly to the crack opening process. The results show that the type of load path and the stress level of each load component-axial and torsional-has a strong influence on the opening angle of the notch crack and the fatigue lifetime of the specimen. This result is confirmed not only by the experimentally determined fatigue strength, but also by a fractographic analysis performed on the surface of the specimens for both load paths. Moreover, the results show an acceptable correlation between the experimental results and the estimates obtained with the proposed model and the stresses obtained with the finite element analysis.
- Evaluation of a phenomenological elastic‐plastic approach for magnesium alloys under multiaxial loading conditionsPublication . Anes, Vitor; Reis, Luis; Freitas, M. DeMagnesium alloys are greatly app reciated due to their high strength to weight ratio, stiffness, and low density; however, they can exhibit complex types of cyclic plasticity like twinning, de‐twinning, or Bauschinger effect. Recent studies indicate that these types of cyclic plastic deformations cannot be fully characterized using the typical tools used in cyclic characterization of steels and aluminium alloys; thus, it is required new approaches to fully capture their cyclic deformation and plasticity. This study aims to propose and evaluate a phenomenological cyclic elastic‐plastic approach designed to capture the cyclic deformation of magnesium alloys under multiaxial loading conditions. Series of experimental tests were performed to characterize the cyclic mechanical behaviour of the magnesium alloy AZ31BF considering proportional loadings with different strain amplitude ratios and a nonproportional loading with a 45° phase shift. The experi mental results were modulated using polynomial functions in order to implement a cyclic plasticity model for the AZ311BF based on the phenomenological approach proposed. Results show good correlations between experiments and estimates.
- Fatigue life of a railway wheel under uniaxial and multiaxial loadingsPublication . Soares, Henrique; Anes, Vitor; de Freitas, M.; Reis, LuisIn this paper, a railway wheel material is under evaluation using multiaxial fatigue testing. The experiments were conducted using a servo-hydraulic machine with standardized specimens. All samples were machined from a single worn-out railway wheel. The damage scale between normal and shear stresses was evaluated in the normal stress space for proportional and non-promotional loadings. Moreover, the uniaxial SN curves were obtained. A critical plane analysis was performed using theoretical criteria and experimental results. Results show a strong influence of heat treatments on the material fatigue behavior.
- A new approach for agile teams' allocation in open innovation projectsPublication . Anes, Vitor; Abreu, António; Dias, Ana; Calado, João Manuel FerreiraDue to constant change in the marketplace, it can be difficult for companies to secure the material, human, and technological resources necessary for competitive innovation activities. In this sense, and to overcome these constraints, the open innovation model is a quite successful approach, where the sharing of resources among companies allows the formation of an innovation ecosystem. However, the execution time of these projects can be negatively affected if the performance of each work team is not taken into account. In this work, the application of the agile approach in open innovation projects is proposed as a way to reduce the uncertainty both in the execution time of the projects and in the respective implementation costs. In this sense, a methodology for optimal team assignment for agile teams in open innovation projects according to their performance on each project task is developed to determine the optimal team assignment that leads to the shortest project execution time. This methodology will support decision making in the project management of open innovation projects, especially in the selection of the internal and external work teams that will participate in a given innovation project. The application of the proposed methodology is illustrated with an example describing and analyzing the different steps of its application. The results show that with the proposed methodology it is possible to take into account the performance of each team when calculating the project execution time and that the project execution time varies depending on the assignment of the agile teams to the project tasks. It is also shown that it is possible to determine the optimal assignment with the shortest project execution time.
- Evaluation and numerical modeling of phenomenological approach for AZ31B-F magnesium alloy under multiaxial fatiguePublication . Moreira, R.; Anes, Vitor; Freitas, M. De; Reis, L.Magnesium alloys have been attractive to use in structural components due to their high strength to weight ratio, low density and high damping capacity. However, magnesium alloys show peculiar plastic deformation mechanisms under cyclic loads (twinning and de-twinning) that causes the asymmetric material behaviour and limits their use in structural components. Recent researches indicate that this type of plastic deformation mechanism cannot be fully characterized using the typical tools used in steels. Therefore, the phenomenological Hypo-strain (HYPS) model has been developed to capture the asymmetric behaviour of magnesium alloys under uniaxial and multiaxial loadings. This study aims to evaluate the phenomenological Hypo-strain approach for AZ31B-F magnesium alloy and to implement the HYPS model on an external subroutine (UMAT) to run on Abaqus. The goal is to reach a numerical tool that can be used to accurately describe the cyclic elastic-plastic behaviour of magnesium alloys in synergy with finite element packages. In order to characterize the cyclic behaviour of AZ31B-F magnesium alloy, experimental tests were performed considering proportional and non-proportional loadings. To evaluate the implemented model in UMAT, these results were correlated with the experiments and with the analytical HYPS approach. Moreover, the estimates were also correlated with the Armstrong-Frederick model available on Abaqus/Standard 6.14 library. The results have shown that the HYPS model was successful implemented on the UMAT subroutine with a good correlation between experimental tests and the HYPS model. Some remarks between the HYPS and Armstrong-Frederick models are drawn.
- Fatigue damage assessment under random and variable amplitude multiaxial loading conditions in structural steelsPublication . Anes, Vitor; Caxias, J.; Freitas, M.; Reis, L.Fatigue damage assessment of multiaxial random loadings is a complex issue and a subject of actual interest in mechanical design. In this work, the performance of the stress scale factor (SSF) criterion is evaluated under variable amplitude loading conditions, and damage accumulation approaches. This evaluation is performed by taking into account two types of loading spectra, namely the loading block spectra (where the loading pattern is well identified and repeated until rupture), and the random loading spectra (where the stochastic behaviour of the axial and shear loading components do not allow a direct identification of the loading pattern). Moreover, the validity of the hypothesis in which the SSF damage map remains valid for any high strength steel under variable amplitude loading conditions is also inspected by analysing fatigue life correlation of the 1050 QT steel and the 304L stainless steel under a multiaxial loading block.
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