1,721,288 research outputs found
The role of gut hormones in controlling the food intake: what is their role in emerging diseases?
No full textThe use of FEA in the simulation of a metal cutting operations in the presence of random uncertainty
No full textForces and temperatures in specific orthogonal cutting conditions and calculated by finite element analysis, have been evaluated taking into account the uncertainty of some process conditions. A traditional deterministic approach, in machining simulations, is not able to explain the uncertain physical variations related to material characteristics (yield and tensile strenght, hardness, etc.) and tool/chip/workpiece interface conditions (friction and tool wear). During machining operations many different sources of non-controllable process variations usually display their effect leading to a degree of uncertainty in the final parts quality. Statistical tools and methods are increasingly being used in combination with FE numerical simulation, in order to take into account of the variability of the process. Then, if one of the purposes of process design is to study and model robustness or reliability of a given process in aleatory conditions, a CAE study might become a feasible way to do it. Today, the evaluation of the performances of a metal cutting process is possible using several commercial FEA packages. These software tools automatically allow the preventive evaluation of the robustness of technological decisions. In this work the authors, by means the integration between stochastic simulation tools and machining FE codes, have evaluated the process sensitivity to a random variation of uncontrollable parameters or conditions. Furthermore, a specific experimental and numerical activity has been performed in order to better understand the technical capabilities in terms of process simulation in stochastic conditions
A physically based constitutive model of microstructural evolution of Ti6Al4V hard machining under different lubri-cooling conditions
No full textThe metallurgical phenomena taking place during machining processes affect the thermo-mechanical properties of the severely deformed materials, influencing, consequently, the process behavior. The microstructural modifications are difficult to be evaluated when the material is subjected to high speed deformations that are typical of material removal processes. Therefore, the microstructure-based numerical simulations can represent a useful tool able to properly predict their mechanics. Hard turning experiments were conducted on Ti6Al4V alloy, involving different process parameters and lubri-cooling conditions. The worked samples surfaces were assessed in terms of resulting microstructural changes and microhardness. The obtained results (cutting forces, temperature, and surface metallurgical modifications) were considered to develop and validate a physics-based model able to describe the microstructural phenomena occurring under large deformation processes, taking into account the influence of the physical phenomena that accommodate the material plastic strengthening and their resulting effects on the process variables. The dislocations reciprocal influence and their interaction with the material lattice were considered to understand the material viscoplastic flow. Moreover, also the recrystallization phenomena influencing the grain size related strengthening were considered to formulate the model. Then, the developed material model was implemented via user sub-routine in a commercial finite element (FE) software. The FE model was used to in-depth analyze the inner evolution of the processed material and to predict the variables of industrial interest. A good agreement was shown between the experimentally measured variables and the numerically predicted results. Moreover, the model was employed to investigate additional machining conditions via finite element analysis (FEA), demonstrating a huge capability to improve the manufacturing process performances, leading to a deeper knowledge of microstructural evolution and the material machinability under various process conditions
Tool Wear Characterization in Turning of a Nickel Superalloy Through Customized Pin-On-Disk Tests and Acoustic Emission Signals Analysis
No full textLattice structures integration with conventional topology optimization
No full textAdditive manufacturing (AM) processes enable the production of functional parts with complex geometries, multi-materials as well as individualized mass production. Another significant benefit of AM is the ability to produce optimized geometries with near perfect strength to weight ratios. For several years now, the topology optimization techniques assist the designers in order to develop components that have a good material distribution in order to reduce the weight ensuring the request stiffness. Therefore, the topology optimization generates concepts based on the subtractive approach and usually these geometries require a further post processing in order to obtain a geometry "ready to produce" that represents a compromise between the topologic result and the manufacturing constraints. The advent of the AM opens new scenarios in terms of definition of innovative geometries that are not feasible with the conventional processes (such as lattice structures). In order to exploit the AM capabilities, new topology optimization tools are emerging that allow to define innovative concepts that could reach structural performance greater than the result obtainable with conventional topology optimization. In this paper the Authors have studied a new concept design and the performance improvement, of PIN installation equipment, used for thin-walled aerospace workpiece, in order to solve critical dimensioning issues, due to the overcoming of the allowable range tolerances (strain and displacement). Topology optimization has been applied in order to define a new concept design able to satisfy the functionality requirements. Moreover, it has been conducted a study to evaluate the possible advantages offered by the integration of the lattice structure in the topology design in order to improve the performance in terms of weight and structural characteristics
A numerical procedure for machining distortions simulation on a SAF 2507 casting workpiece
No full textThe workpiece distortion that occurs during machining, can lead to a large increase in the number of the scrap parts. Residual stresses are the main cause of these distortions and they are generally present in both forging and casting products. In order to obtain the desired microstructure and mechanical properties, the workpiece is subjected to heat treatment before being worked. Quenching produces residual stresses that exist throughout a large percentage of the casting or forging part. Distortion occurs as a result of removing stressed material from the workpiece. The component will re-equilibrate and distort as each layer of stressed material is machined away. This paper describes a procedure development for distortions numerical analysis on a SAF2507 casting bulk workpiece. A solubilization heat treatment has been simulated, in order to predict the bulk residual stresses distribution. Different metal cutting processes have been considered to measure the numerical distortions induced in the workpiece
Shape factors and feasibility of sheet metal hydroformed components
No full textThe authors have investigated, in another paper, the problem related to the definition of a "set of shape factors" in order to declare the feasibility of a product through sheet hydroforming. In particular the defined shape factors are three different a-dimensional coefficients by which it is possible to declare the feasibility of a product through the calculation, in different sections, of the three previous shape factors. The robustness of this methodology is related to the correct calculation of the "limit value" of each shape factor. In fact the feasibility is reached if, in any section, the calculated shape factors are higher than their respective limit values. In this paper the authors have performed an extensive numerical and experimental campaign, taking into account a different geometry respect to that of the first paper, in order to: re-calculate the limit value for each shape factor and, then, verify the correctness of the limit values exposed in the previous first paper. The numerical campaign has been used, after the evaluation of the accuracy of the numerical model, in order to study the feasibility of the product without engaging the hydroforming machine. Finite Element Analysis (FEA) has been extensively used in order to investigate and define each shape factor with a proper comparison to the macro feasibility of the chosen component geometry. The limit values that have been calculated by the authors in this paper are slightly different from those calculated in the first paper. From this point of view it is possible that, although the shape factors are a-dimensional coefficients, they are affected by different choices of the users as, for example, the dimensions of the initial blank. Anyway, the small differences in the shape factors limit values do not adversely affect the use of the shape factors in order to predict the feasibility of the product
Advanced finite element model for predicting surface integrity in high-speed turning of AA7075-T6 under dry and cryogenic conditions
No full textGenetic study and surgical correction of euryblepharon.
No full textEuryblepharon is a rare congenital anomaly of the palpebral fissure which consists of an increase in its width. A case has been described in which this characteristic is very marked, and associated with ectropion, lagophthalmos, corneal ulcers; also congenital malformations as twisted feet, hypospadia and inguinal hernia. Apart from a limited increase of the palpebral fissure in the mother, the familiar anamnesis is negative, and likewise examination of the cariogram and research of eventual metabolic modifications. An estimation of the various surgical techniques proposed revealed insufficient strictness regarding the standards generally followed in palpebral plastic surgery. Consequently, a technical variation was set up that will satisfy the needs of correct anatomical-surgical practice
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