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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.
- 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.
- 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.
- Characterisation and evaluation of the mechanical behaviour of endodontic-grade NiTi wiresPublication . Pereira, Samuel; Carvalho, André; Reis, Luis; Freitas, Manuel; Montalvao, DiogoWith the introduction of new materials and advances in medical science, the endodontic files have changed since the early days of root canal treatments. In the late days, we have seen an increasing use of Nickel-Titanium (NiTi) alloys. At body temperature, NiTi alloys present a superelastic behaviour, which allows to be more effective in the removal of the tooth pulp tissue, and in the protection of the tooth structure. Anyhow, these NiTi instruments will eventually fracture, usually without any visual signal of degradation. Thus, there is a need of studying these alloys, as they present a high hysteresis cycle and non-linearities in the Elastic domain. Currently, there is no international standard to test NiTi endodontic files, so various authors have attempted to design systems that can test them under fatigue loads, usually based on empirical setups. Following a systematic approach, this work presents the results of rotary fatigue tests for two Alfa Aesar (R) Nitinol wires with different diameters (0.58mm and 0.25mm).The formulation is presented, where the material strength reduction can be quantified from the determination of the strain and the number of cycles until failure, as well numerical FEM simulation to verify the analytical model predictions.
- Effect of surface treatment on adhesively bonded aluminium-aluminium joints regarding aeronautical structuresPublication . Correia, Sérgio; Anes, Vitor; Reis, LuisThe structural integrity of several structures could be determined by their joints strength. Over the years, adhesively bonded joints have been often chosen to achieve a compromise between mass reduction and higher mechanical strength. Among others, the reduction in stress concentrations, the ability of producing smooth surfaces with no discontinuities and the reduced weight penalties are some of the factors that make this type of joints so attractive. Normally, to increase the bond strength, the materials to be bonded must be subjected to a kind of surface treatment. For metals, and more specifically, for aluminium alloys, phosphoric acid anodizing and chromic acid anodizing have been the most used treatments worldwide. However, recent investigations show that these kinds of anodizing are detrimental to health due to the release of carcinogenic substances. With this in mind, it is of the utmost importance to find alternative surface treatments that can ensure an effective bond. In this paper, a vast experimental study was performed based in the single lap joint ASTM D 1002 standard method, with the objective of determining the best alternative surface treatment (Sulfuric Acid Anodizing and Boric-Sulfuric Acid Anodizing), for aluminium-to-aluminium joints, using two types of adhesives, namely the AF 163 and the EA 9658 AERO. Results show that the optimum surface treatment is different for each type of adhesive and this fact has a huge influence on mechanical behavior of this type of aeronautical adhesive joints.
- A new risk prioritization model for failure mode and effects analysisPublication . Anes, Vitor; Henriques, Elsa; de Freitas, M.; Reis, LuisFailure modes and effects analysis is a framework that has been widely used to improve reliability by prioritizing failures modes using the so‐called risk priority number. However, the risk priority number has some problems frequently pointed out in literature, namely its non‐injectivity, non‐surjectivity, and the impossibility to give weights to risk variables. Despite these disadvantages, the risk priority number continues to be widely used due to its higher simplicity when compared with other alternatives found in literature. In this paper, we propose a novel risk prioritization model to overcome the major drawbacks of the risk priority number. The model contains 2 functions, the risk isosurface function that prioritizes 3 risk variables considering their order of importance in a given risk scenario, and the risk prioritization index function which prioritizes 3 risk variables considering their weights. The novelty of the proposed model is its injectivity, surjectivity, and ease of use in failure modes prioritization. The performance of the proposed model was analyzed using some examples typically used to discuss the conventional risk priority number shortcomings. The model was applied to a case study and its performance correlated with other risk prioritization models. Results show that the failure modes prioritization reached with the proposed model agrees with the expectations made for the risk scenario.
- Damage evaluation under complex fatigue loading conditionsPublication . Reis, Luis; Caxias, J.; Soares, Henrique; Rodrigues da Costa, Pedro; Anes, Vitor; Freitas, M.Fatigue damage and life assessment of multiaxial loadings is still an issue yet to resolve. Many methods have been proposed with promising agreements with the experimental results. However, the performance of such methods is, more than often, purely based on fatigue tests with simple loading conditions. In this work the stress scale factor (SSF) criterion and the virtual cycle counting (vcc) method are used to estimate fatigue life and damage accumulation with two damage accumulation rules. Fatigue tests were carried out with three different variable amplitude random loadings, applied to several specimens made from a 42CrMo4 high-strength steel. Fatigue crack plane measurements were compared with predictions from several critical plane models. The applied methods provided very acceptable results making the SSF package (SSF equivalent stress and virtual cycle counting method) a good method to estimate fatigue life and assessment of the damage accumulation in random fatigue loadings.