1,720,992 research outputs found
Non-Newtonian cfd modelling of a valve for mud pumps
Full text linkMud pumps, like those used in the field of oil well drilling, are typically of the reciprocating type and are designed to circulate drilling fluid under high pressure down the drill string and back up the annulus. automatic valves must be applied to the fluid end in order to grant the desired pumping effect. from the engineering point of view, the design of the valve geometry must ensure that the phenomenon of cavitation does not occur and that, during the pumping action, the stiffness of the reaction coil spring is able to avoid reaching the condition of end stroke of the valve. Cavitation consists in the development of vapour cavities in the liquid phase. Inside the cavities, the pressure is relatively low. When subjected to higher pressure, the voids implode and generate an intense shock waves that promote the wear for the components (i.e. valve, valve seat, etc.). a deep understanding of the fluid behaviour is crucial for an effective design. Transient CfD simulations of the valve opening have been performed using a non-Newtonian fluid model able to describe the drilling muds. after a deep literature review, the Herschel-Bulkley model was selected as the most suitable for emulating the drilling mud. With the abovementioned approach, the reaction spring and design the valve seat to avoid premature wear phenomena were properly designed. The simulations have been also done considering a Newtonian fluid behaviour, in order to better understand the importance of considering the non-Newton behaviour for an effective design
Dynamic modeling of gears: An innovative hybrid FEM-analytical approach
Full text linkGearboxes are widely used in several applications ranging from the automotive to the industrial and robotic sectors. A planetary gearbox is a special kinematic gear arrangement that, taking advantage of a planet carrier, ensures high reduction ratios together with a very small design. Therefore, they are widely employed for transmissions which require a high power density. There are several fields of applications including, but not limited to, mechatronic, automation and wind power generation. To improve the design of new solutions, for performing monitoring activities on actual gearboxes and for the definition of maintenance schedules, the availability of physical models able to accurately describe the behavior of the system, both in healthy and damaged conditions, would represent a great support. Experimental and numerical studies of the behavior of gearboxes are already available in the literature. Nevertheless, while the experimental approaches are valid only for the specific configuration tested, the numerical techniques show limitations related to the computational effort required. This paper presents an innovative approach for the characterization of the behavior of two different geared transmissions. It is based on a hybrid approach that combines finite elements (FE) with analytical formulations. In detail, the solver computes separately the macro deformation of the bodies (numerical solution based on a coarse grid) and the contacts (solved analytically avoiding the need of mesh refinements). The computational effort is reduced significantly without affecting the accuracy of the results significantly. This approach was used to investigate and understand the vibro-dynamical behavior of a back-to-back test rig (typically used for the characterization of the surface fatigue strength of gears) and of an industrial planetary gearbox. The results obtained for the healthy - not damaged - gearboxes were compared with experimental measurements for both configurations in order to validate the hybrid approach. Once the models were validated, the same methodology was eventually used to study the effects of typical gear failures and in specifically surface fatigue (pitting), on the vibrational response. The capability to reproduce the effect of damages with the model of a gearbox represents the first indispensable step of a Structural Health Monitoring strategy. State-of-art and challenges are analyzed and discussed in the paper
DESIGN FOR ADDITIVE MANUFACTURING – MATERIAL CHARACTERIZATION AND GEOMETRICAL OPTIMIZATION
No full textAdditive manufacturing (AM) is a more and more appreciated manufacturing technology. This growing interest is related to the high flexibility of this approach and its capability to produce any geometry, opening new possibilities. An example is the improvement of the system performances exploiting lattice and reticular in substitution to the traditional solid design. Despite this premise, in real applications, part of the benefits is lost due to the inferior performances of the AM steels and the higher costs of additive manufacturing. In this scenario, the mechanical properties of a 17-4 PH SS produced via additive technology were characterized with experimental tests. The results were compared with data concerning the cast material. In this way, it was possible to execute a quantitative evaluation of the performance reduction. Three components, such as a hip prosthesis, a blow plastic bottle die, and an automotive gear, were chosen as representative examples. These three mechanical components are typically produced in quite different batch sizes. The hip prosthesis, the blow plastic bottle die, and the automotive gear were redesigned (design for AM) via a finite element (FE) approach. The new designs fulfill the original requirements in terms of strength showing however improved inertial properties. The original and new designs were exploited to quantify the benefits of introducing AM in different applications
Impact of the lacks of fusion induced by additive manufacturing on the lubrication of a gear flank
Full text linkAdditive Manufacturing (AM) is becoming a more and more widespread technology. Its capability to produce complex geometries opens new design possibilities. Despite the big efforts made by the scientific community for improving the AM processes, this technology still has some limitations, mainly related to the achievable surface quality. It is known that AM technologies pro-mote the formation of LACKS of fusion inside the material. In some cases, the external surfaces are finished with traditional machining. This is the case of AM‐produced gears. While the grinding operation aims to reduce the surface roughness, the presence of porosities just below the surface of the wrought component, could lead, after grinding, to the exposure of those porosities leading to a pitted surface. This phenomenon is surely not beneficial in terms of structural resistance, but can help the lubrication promoting the clinging of the lubricant to the surface. The aim of this paper is to study this effect. Micro‐Computer‐Tomography (μ‐CT) analyses were performed on a 17‐4 PH Stainless Steel (SS) produced via Selective Laser Melting (SLM). The real geometry of the pores was reproduced virtually and analyzed by means of multiphase CFD analyses in the presence of centrif-ugal effects
Structural modelling of multilayer skis with an open source FEM software
Full text linkThe design process of a ski is characterized by a short time of development due to continuous advancements in the material science and in the manufacturing processes as well as in customer’s requirements. Nowadays, the development process is very often still based on several physical prototypes and trials and Finite Elements Analysis (FEA) is a significant method to reduce times needed. The aim of this work is to develop a reliable numerical simulation of an existing mountaineering ski, able to predict the performance of the real element. For this purpose, an initial mechanical characterization of all the constituents used in the ski manufacturing was performed. Tensile tests in two directions were performed on flat bone-shaped samples laser cut from sheets. Combining the results of the tensile tests with Digital Image Correlation (DIC) data it was possible to approximate the four in-plane (XY) elastic properties, namely, the two elastic modules, the shear module and the Poisson ratio (Ex, Ey, Gxy, νxy). The DIC free software used is GOM Correlate. Results of the combined “tensile tests – DIC” approach were after verified with FEM simulations reproducing the testing configuration. The digital model of the ski was created starting from the nominal geometry. The whole procedure of modelling, meshing and FE analysis was performed in the open source software Code_Aster/Salome-Meca. Using this kind of software, which code is free to use and modify, permits to reduce costs due to its free license. The real component was tested in a three-point bending and torsion test. This kind of experiments were replicated on the FEM model and results were compared. The comparison highlighted discrepancies of 2.5%–10% with respect to the real component
DESIGN for ADDITIVE MANUFACTURING: IS IT AN EFFECTIVE ALTERNATIVE? PART 1 - MATERIAL CHARACTERIZATION and GEOMETRICAL OPTIMIZATION
No full textAdditive manufacturing (AM) is becoming a more and more widespread (and trendy) approach. Its flexibility and capability to manufacture any topology has opened new possibilities: AM could lead to significant performance improvements thanks to the exploitation of lattice or reticular structures as partial replacement of the traditional solid design. The potential of this technology knows no bounds. However, in the real world, the lower performances of the materials and the high manufacturing costs significantly restrict the fields of application for which the adoption of AM results effective. In this context, the mechanical static and fatigue properties of a 17-4 PH stainless steel produced via AM were experimentally measured and compared with those of the wrought material to quantify the performance reduction. Based on these data, three components, namely a hip prosthesis, a blow plastic bottle die, and an automotive gear were selected as representative examples to show the pros and contra of AM. The three components were chosen because they belong to three quite dissimilar fields and are produced in different batch sizes. The three original designs were specifically optimized for AM by means of finite element (FE) simulations. The new solutions fulfil the strength requirements of the original parts showing at the same time reduced weights and inertias. The traditional and new designs were compared in terms of production times and costs to quantify the real benefits of AM for different applications
DESIGN for ADDITIVE MANUFACTURING: IS IT AN EFFECTIVE ALTERNATIVE? PART 2 - COST EVALUATION
No full textAdditive Manufacturing (AM) is becoming a more and more widespread (and trendy) approach. Its flexibility and capability to manufacture any topology has opened new possibilities: AM could lead to significant performance improvements thanks to the exploitation of lattice or reticular structures as partial replacement of the traditional solid design. The potential of this technology knows no bounds. However, in the real world, the lower performances of the materials and the high manufacturing costs significantly restrict the fields of application for which the adoption of AM results effective. In this context, the mechanical static and fatigue properties of a 17-4 PH Stainless Steel produced via AM were experimentally measured and compared with those of the wrought material to quantify the performance reduction. Based on these data, three components, namely a hip prosthesis, a blow plastic bottle die, and an automotive gear were selected as representative examples to show the pros and contra of AM. The three components were chosen because they belong to three quite dissimilar fields and are produced in different batch sizes. The three original designs were specifically optimized for AM by means of Finite Element (FE) Simulations. The new solutions fulfil the strength requirements of the original parts showing at the same time reduced weights and inertias. The traditional and new designs were compared in terms of production times and costs to quantify the real benefits of AM for different applications
Trasmissioni CVT ibride una possibilità per ottimizzare l'efficienza dei motori a combustione interna
No full textLa massimizzazione dell’efficienza globale delle macchine è un tema di sempre maggiore centralità che interessa in particolare la progettazione dei propulsori e la domanda di sistemi ad elevata efficienza è in costante aumento in ogni settore. Inoltre, gli standard EURO/TIER per la riduzione delle emissioni inquinanti dei veicoli stradali/agricoli rispettivamente, impongono un miglioramento dell’efficienza sia dei motori, sia delle trasmissioni. per questo motivo, le risorse dedicate alla ricerca in tale ambito sono in continuo aumento
How characterizing the efficiency of agricultural machines
No full textWhen speaking of quantification of the efficiency of a system, we mean the calculation of its thermodynamic efficiency, defined as the mathematical ratio between the input energy, i.e. the energy entering the considered system (in any of its forms: electric, chemical, thermal ...), and the output energy (once more, in any of its forms), expressed with a pure number (between 0 and 1) or as percentage. The quantification of the efficiency is not a simple operation because it implies a very precise control of the energy flows that cross the boundary of the analysed system, but it is always useful as it is associated to the goodness of the energy transformations that occur inside that system.
The operation of calculation of a system’s efficiency has another very interesting implication, which concerns the quantification of the portion of input energy that is dissipated inside the system as heat, and, hence, which is cause of structural expansions and possible overheating affecting also adjacent systems
Ductile damage assessment of Ti6Al4V, 17-4PH and AlSi10Mg for additive manufacturing
No full textA great research effort has been spent during the latest years in the characterization of additive manufacturing (AM) alloys, mostly focused on the analysis of microstructure and on the assessment of mechanical strength, especially under high cycle fatigue loads. Post-process treatments have been also investigated, as methods to further improve the AM materials performance. On the contrary, still fewer data are available on AM materials ultimate static strength. The present paper is intended to present a comprehensive experimental and numerical static characterization of Ti6Al4V, 17-4PH, and AlSi10Mg alloys processed via selective laser melting. A dedicated set of specimen geometries was devised to induce desired multiaxial stress state, and experiments were carried out both on as built and machined AM samples. The results were employed to identify the constitutive behavior of the materials and to calibrate four different ductile damage models. The failure prediction capabilities of the tuned models were thoroughly analyzed and discussed. The overall mechanical properties and the ductility of the investigated alloys were estimated based on the experimental results and on the information provided by the tuned models. Additionally, a comparison with data collected on the corresponding wrought materials, performing the same experiments, was carried out. The results showed a limited reduction of yield and failure strength and a significant reduction in the ductility of AM materials with respect to their wrought counterparts. Moreover, for the less ductile alloys, a weaker dependence of the strain to fracture from the stress state was observed
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