i Y. Tadi beni is Ph.D. Student in the Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran (e-mail: yaghob_beni@mech.sharif.edu ii M. R. Movahhedy is Associate professor in the Department of Mechanical... more
i Y. Tadi beni is Ph.D. Student in the Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran (e-mail: yaghob_beni@mech.sharif.edu ii M. R. Movahhedy is Associate professor in the Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran (e-mail: movahhed@sharif.edu) iii G.H. Farrahi is Professor in the Department of Mechanical Engineering, Sharif University of Technology, Tehran, Iran (e-mail: farrahi@sharif.edu) ABSTRACT
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لماک یشهوژپ هلاقم تفایرد : 15 يد 1397 شریذپ : 28 نیدرورف 1398 تیاس رد هئارا : نابآ 1398 سیدنت حوطس اب تاعطق يراکزرف دنیارف رد هب حطس ياهانحنا ،راو یگژیو نیرتزراب زا یکی ناونع یم نآ یسدنه ياه دناوت ياهورین رب طق يداعبا تقد رب هجیتن رد و... more
لماک یشهوژپ هلاقم تفایرد : 15 يد 1397 شریذپ : 28 نیدرورف 1398 تیاس رد هئارا : نابآ 1398 سیدنت حوطس اب تاعطق يراکزرف دنیارف رد هب حطس ياهانحنا ،راو یگژیو نیرتزراب زا یکی ناونع یم نآ یسدنه ياه دناوت ياهورین رب طق يداعبا تقد رب هجیتن رد و يراکزرف دشاب راذگریثأت ییاهن هع . نیا رد قیقحت یلدم هئارا اب یلیلحت رازبا يریگرد هیحان جارختسا يارب سیدنت حطس و يورکرس یتشگنا زرف هب ،راو هنوگ ياهورین رب اهانحنا رثا هعلاطم هب ،دشاب هتشاد رب رد ار حطس ياهانحنا حیرص مرف هک يا یم هتخادرپ يراکزرف دوش . با ،روظنم نیا هب هب اب و کیتسیناکم لدم زا هدافتسا اب يراکزرف ياهورین ادت تلاح زا لیدبت شور يریگراک لدم یشرب بیارض هبساحم يارب لیام هب دماعتم یم يزاس دنوش . هب ربتعم عجارم رد دوجوم جیاتن اب لدم زا لصاح جیاتن هسیاقم اب ،سپس هحص یم هتخادرپ نآ يراذگ دوش . علاطم ماجنا اب همادا رد یسررب يراکزرف ياهورین رب يریگرد قمع و حطس ياهانحنا رثا ،کیرتماراپ تا یم دوش . هب جیاتن تسد یم ناشن هدمآ ینیز یحاون رد ،ریثأت نیرتشیب رعقم یحاون رد حطس ياهانحنا ،تباث يریگرد قمع رد هک دهد لکش دنراد اهورین رب ار ریثأت نیرتمک بدحم یحاون ر...
FEM simulation of a new type of fixture for ultrasonic-assisted grinding was performed. This ixture could produce 2D vibration by one piezo-actuator. A special fixture was designed for conducting this research that was able to convert 1D... more
FEM simulation of a new type of fixture for ultrasonic-assisted grinding was performed. This ixture could produce 2D vibration by one piezo-actuator. A special fixture was designed for conducting this research that was able to convert 1D vibration to 2D. The designed ixture can produce elliptical vibration by using one piezo-actuator because of special format with appropriate mode-shapes and suitable phase angle in suitable frequency. The designed fixture was analyzed in different processes for gathering the best results and being sure for accuracy of the results. The ability of fixture to undergo machining forces was studied by static analyzing. Finally, different natural frequency and mode shapes of fixture were examined in modal analyzing and the maximum movement and phase angel in fixture were studied by harmonic analysis.
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Introduction - This study aimed to compare the amount and pattern of stress and strain distributed around periodontally compromised splinted teeth and the two-implant abutments supported six-unit fixed partial denture (FPD) using finite... more
Introduction - This study aimed to compare the amount and pattern of stress and strain distributed around periodontally compromised splinted teeth and the two-implant abutments supported six-unit fixed partial denture (FPD) using finite element analysis (FEA). Methods and Materials - Six mandibular anterior teeth of a dental model were scanned and the scans were transferred to 3D CAD design and finite element software. Jaw bone was also designed and the teeth were splinted by fiber-reinforced composite (FRC) band. In another model, two implants were placed at the site of canine teeth and a six-unit FPD was designed over them. Models were transferred to finite element software and after meshing and fixing, they were subjected to 100- and 200-N loads under 0 and 30° angles. Results - Apical areas and crestal bone showed the highest accumulation of stress and strain in periodontally compromised splinted teeth. Crestal bone and bone between crestal microthread and the first thread of implant body had the highest accumulation of stress and strain in the implant supported six-unit FPD. Conclusion - The results showed significantly higher shear stress, von Mises stress and von Mises strain in peri-implant bone compared with bone around periodontally compromised teeth. Increase in applied load magnified this difference. Also, a greater difference was noted in stress and strain in bone around teeth and implants when oblique load was applied.
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Finite element analysis of huge and/or complicated structures often requires long times and large computational expenses. Superelements are huge elements that exploit the deformation theory of a specific problem to provide the capability... more
Finite element analysis of huge and/or complicated structures often requires long times and large computational expenses. Superelements are huge elements that exploit the deformation theory of a specific problem to provide the capability of discretizing the problem with minimum number of elements. They are employed to reduce the computational cost while retaining the accuracy of results in FEM analysis of engineering problems. In this research, a new shell superelement is presented to study linear/nonlinear static and free vibration analysis of spherical structures with partial or full spherical geometries that exist in many industrial applications. Furthermore, this study investigates the effects of changing the superelement size and its number of nodes on solution accuracy. The governing equations of composite spherical shells are derived based on the first-order shear deformation theory and considering large deformations. For solving the nonlinear governing equations, the tangent stiffness matrix has been extracted and the Newton–Raphson method is employed. The capability of the presented shell superelement is investigated in several problems under linear/nonlinear static and free vibration analysis. The results acquired by the presented shell superelements are compared with available results in the literature and conventional shell elements in a commercial software. Results comparisons reveal high accuracy at a reduced computational cost in the superelement model.
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This paper presents the influence of the severe shot peening process on the fatigue life of the laser-cladded Inconel 718 specimens which can be employed during refurbishment of components enduring high mechanical cyclic loads such as gas... more
This paper presents the influence of the severe shot peening process on the fatigue life of the laser-cladded Inconel 718 specimens which can be employed during refurbishment of components enduring high mechanical cyclic loads such as gas turbine components. In order to quantitatively evaluate the destructive effect of laser cladding on the fatigue endurance, fatigue tests are first performed on the as-received and laser-cladded specimens. Then, microstructural analysis by scanning electron microscope (SEM) is carried out to identify the root causes of the drawback of laser cladding. Moreover, by employing a comprehensive laser-cladding FE analysis considering cyclic plastic material modeling, the induced residual stress distribution is determined. To decrease the detrimental effects of laser cladding on the microstructure and residual stresses, the specimens are next subjected to severe shot peening treatment, and then, extra sets of fatigue tests are conducted on the specimens. The conducted experiments show that the laser cladding can cause the deterioration of the fatigue life of the specimens at about 40%, and the damaged fatigue life can be almost restored by the severe shot peening. The experiments also indicate that the clad-toe zone is the weakest area concerning fatigue issues in laser-cladded specimens with or without shot peening post-process. Hence, the clad-toe zone needs some special attention.
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Abstract To achieve higher accuracy in the prediction of cutting forces in finish milling process of sculptured parts, the curvatures of in-process workpiece surface are necessary to be taken into consideration in the calculation of... more
Abstract To achieve higher accuracy in the prediction of cutting forces in finish milling process of sculptured parts, the curvatures of in-process workpiece surface are necessary to be taken into consideration in the calculation of cutter-workpiece engagement boundaries. These curvatures, however, are not readily available in tool path data, as the main existing source of geometrical information of the process. In this paper, first, a new straightforward algorithm is proposed to extract the principal curvatures and principal directions of the in-process workpiece surface from ball-end finish milling tool path data. These quantities, then, are employed to calculate the boundaries of engagement between the tool and workpiece geometries. In the next step, the cutting forces acting on a helical ball-end tool are formulated utilizing mechanistic approach and with the inclusion of radial run-out effect. By minimizing the square error between the predicted and experimentally measured cutting forces, the cutting force coefficients and radial run-out parameters are identified. Finally, the validity of the proposed force model is demonstrated by comparing the simulated forces with experimental measurements. The performed simulations show that the model can well capture the variation of milling forces along curved tool paths resulting from the variation of surface curvatures. Furthermore, it is shown that depending on the machining tolerance used in the tool path generation step, saw-tooth-like fluctuations may appear in the time history of milling forces originating from the approximation of curved paths by single steps (straight lines). All of the geometrical input parameters of the proposed force model are extracted from tool path data and hence it is quite flexible to be integrated into process modeling/optimization systems.
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Chatter vibration is a major obstacle in achieveing increased machining performance. In this research, a finite element model of chip formation in a 2D milling process is used to predict the occurrence of chatter vibrations, and to... more
Chatter vibration is a major obstacle in achieveing increased machining performance. In this research, a finite element model of chip formation in a 2D milling process is used to predict the occurrence of chatter vibrations, and to investigate the effects of various machining parameters on this phenomenon. The dynamic properties of the machine tool at the tool tip are obtained based on experimental modal analysis, and are used in the model as the cutter dynamics. The model allows for the natural development of vibration as the result of the chip-tool engagement, and accounts for various phenomena that occur at the chip-tool interface ultimately leading to stable or unstable cutting. The model was used to demonstrate the effects of the machining parameters, such as the axial depth of cut, radial immersion, and feed rate, on the occurrence of chatter. Additionally, the phenomenon of jumping out of the cut region could be observed in this model and its effect on the chatter process is demonstrated. The numerical model is verified based on comparisons with experimental results.
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This paper presents a new analytical model for calculating the cutter-workpiece engagement (CWE) boundaries in the ball-end finish milling process of curved surfaces. To this end, first, a quadratic mathematical representation considering... more
This paper presents a new analytical model for calculating the cutter-workpiece engagement (CWE) boundaries in the ball-end finish milling process of curved surfaces. To this end, first, a quadratic mathematical representation considering the principal curvatures of the surface is employed to locally describe the workpiece surface around the instantaneous cutting region. This description, then, is utilized to find the intersection curves of the tool rotary and workpiece surfaces in three ball-end milling modes including slotting, first cutting, and following cutting. Through comparison studies, the model predictions are verified by the corresponding results obtained via solid modeling in computer-aided design (CAD) environment. The agreement between the results indicates that the model can accurately calculate the CWE boundaries in the ball-end milling of all inclined, convex, concave, and saddle surfaces. Good performance of the model is also demonstrated by comparing the computation time of the model with that of the z-map method. Finally, parametric studies are performed to reveal the effects of surface curvatures and cutting depth on the CWE region. The results show that the CWE is more affected by the surface curvatures as the cutting depth decreases, especially at the concave and saddle regions of the workpiece surface. The proposed analytical model is capable of calculating the CWE boundaries in both three-axis and five-axis milling processes, and there is no need to neither use any numerical solutions nor update the in-process workpiece geometry during the simulation of the CWE boundaries.
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Abstract Selective Laser Sintering (SLS) is a rapidly growing additive manufacturing process, because it has the capacity to build parts from a variety of materials. However, the dimensional accuracy of the fabricated parts in this... more
Abstract Selective Laser Sintering (SLS) is a rapidly growing additive manufacturing process, because it has the capacity to build parts from a variety of materials. However, the dimensional accuracy of the fabricated parts in this process is dependent on the ability to control phenomena such as warpage and shrinkage. This research presents an optimization algorithm to find the best processing parameters for minimizing warpage. The finite element method was used to simulate the sintering of a layer of polymer powder, and the warpage of the layer was calculated. The numerical model was verified through comparison with experimental results. A back-propagation neural network was used to formulate the mapping between the design variables and the objective function. Results of 40 simulation cases with various input parameters such as scanning pattern and speed, laser power, surrounding temperature, and layer thickness were used to train and test the neutral network. Finally, The Genetic Algorithm was employed to optimize the objective function, and the influence of parameters on warpage was investigated.
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Laser-assisted machining (LAM) is a growing trend in machining of hard to cut materials. In most experimental cases, LAM is carried out in two stages; first, laser and machine parameters are tuned to adjust the temperature at the material... more
Laser-assisted machining (LAM) is a growing trend in machining of hard to cut materials. In most experimental cases, LAM is carried out in two stages; first, laser and machine parameters are tuned to adjust the temperature at the material removal point (Tmr), and second, the cutting tool is engaged to cut the points that have already been heated by the laser. Alternatively, an analytical model for the prediction of temperature filed can replace lengthy experimentation needed for tuning the material removal temperature. This paper presents an analytical solution to the transient temperature field in a rotating cylinder subject to a localized laser heat source based on Green's functions. The analytical solution is validated by comparing the surface point temperatures to thermal experiments on DIN 1.7225 steel, which shows good agreement in trend and values. Furthermore, a finite element model is developed and verified by the results of the same experiments, providing a more detail...
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Modeling of the laser-assisted machining (LAM) process requires an accurate estimate of the surface absorption coefficient. In addition to the laser type and material properties, this parameter is dependent on the state of the process in... more
Modeling of the laser-assisted machining (LAM) process requires an accurate estimate of the surface absorption coefficient. In addition to the laser type and material properties, this parameter is dependent on the state of the process in terms of surface quality, texture, oxidation state, and temperature change during the machining process. In this article, two methods are presented for calculating this coefficient based on the surface temperature obtained from measurement by a pyrometer and an analytical model of the process. In the first method, the pyrometer is fixed on a lathe bed while in the second method, a co-moving pyrometer is used. Temperature measurements in both methods are compared with the results of the analytical model which is developed based on Green’s function approach. Both of the methods are tested for AISI 304 stainless steel samples, and the absorption coefficient is determined for several material and machining conditions. The values determined agree with each other and with values reported in other research works. In addition, the results show that the absorption value is not totally independent of the machining conditions, i.e., for accurate applications, it would be advantageous to determine this coefficient per machining case utilizing the proposed method.
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A molecular dynamics study of bond strength and interface conditions in the <mml:math altimg="si1.gif" overflow="scroll" xmlns:xocs="http://www.elsevier.com/xml/xocs/dtd" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.elsevier.c...more
Abstract High ductility of metals as well as high strength of ceramics has made the metal/ceramic composites an attractive material for many applications requiring high strength to weight ratios. An important issue in using this material... more
Abstract High ductility of metals as well as high strength of ceramics has made the metal/ceramic composites an attractive material for many applications requiring high strength to weight ratios. An important issue in using this material is the behavior of the material and its ceramic–metal interface under various loading, especially at high strain rate. To provide a better understanding of the interface conditions, in this work, a molecular dynamics study of the interface behavior in Al / α _ Al 2 O 3 composite as the result of tensile and shear loadings is presented. For this purpose, the reactive force field (ReaxFF) potential function is utilized. The effects of crystallographic orientations and atomic layers in the interface region on the deformation and fracture strength of the interface are examined. The radial distribution function, atomic planar density and mean bond length parameters as well as stress–strain curves are employed to identify the strength of the interface structures. The results show the highest tensile and shear strengths in the interface with O-termination of alumina, which can be explained by the formation of strong ionic bonds in the Al / Al 2 O 1 interface. Moreover, the higher atomic planar density in (1 1 1) planes of aluminum and its similarity with that of alumina leads to a higher tensile and shear strength in the interface. Furthermore, the deformation mechanism in shear mode is shown to be controlled by planner sliding and local amorphization at the interface zone.
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ABSTRACT Angular contact ball bearings are the most commonly used types of bearings. Although simple in appearance, these bearings have a complicated and nonlinear behavior, and have significant effect on the dynamics of a rotating... more
ABSTRACT Angular contact ball bearings are the most commonly used types of bearings. Although simple in appearance, these bearings have a complicated and nonlinear behavior, and have significant effect on the dynamics of a rotating system. Accounting for high speed effects adds to the complexity of their behavior. The governing equations of the bearing amount to the solution of a set of nonlinear equations for each rolling element at each iteration, which represents a tedious and expensive solution. In this work, a simplified model for angular contact ball bearings under the action of arbitrary loading including high speed effects and preload is presented. The model considers five degrees of freedom for relative displacement of rings and a mean contact angle for inner and outer raceway contacts are introduced which renders the solution for all rolling elements to that for a single one. The use of the simplified model at high speeds is justified by presenting the analysis of a complete spindle-bearing system using the simplified model and comparing the results with those of the full model.
ABSTRACT Tolerance analysis is an analytical tool for the estimation of accumulating effects of the individual part tolerances on the functional requirements of a mechanical assembly. This article presents a comprehensive feature-based... more
ABSTRACT Tolerance analysis is an analytical tool for the estimation of accumulating effects of the individual part tolerances on the functional requirements of a mechanical assembly. This article presents a comprehensive feature-based method for tolerance analysis of mechanical assemblies with both dimensional and geometric tolerances. In this method, dimensional and geometric tolerance zones are described by the combination of fuzzy modelling and small degrees of freedom (SDOF) concept. In this model, the uncertainty in dimensions and geometric form of features is mathematically described using fuzzy modelling, and the kinematic effects of tolerances in assemblies are expressed by SDOF concept. In the proposed method, complicated GD&amp;T concepts such as various material modifiers (maximum material condition, least material condition and regardless of feature size), envelope requirement, bonus tolerances and Rule No. 1 (Taylor principle) in several conditions are accurately modelled. Compatible with the proposed model, a procedure for modified worst case and statistical tolerance accumulation analysis is introduced. An algorithm is laid out that describes the steps and the procedure of tolerance analysis. The application of this method is demonstrated through an example, and the results are compared with experimental results.
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ABSTRACT Functional quality in the mechanical products is governed mainly by the degree of satisfaction of the design requirements, which itself depends on the variations in the effective variables. The functional parameters cannot be... more
ABSTRACT Functional quality in the mechanical products is governed mainly by the degree of satisfaction of the design requirements, which itself depends on the variations in the effective variables. The functional parameters cannot be easily measured in mass production, and thus, are not usually considered as a direct inspection objective. Process capability indices are useful tools for evaluating the ability of a process to produce the dependent variables of a product that meet certain specifications. In this paper, the conventional process capability concept is extended to develop a computational tool for analysis of the functional quality of a mechanical product. Through defining new proper indices called functional process capability indices (FPCp, FPCpk, FPCpm, and FPCpmk), a statistics-based process capability analysis method is used to estimate the ability of a manufacturing process for meeting the functional requirements of a mechanical system. Using this approach for statistical design of a mechanical product, the effects of variations in manufacturer’s dimensions on the functional requirements of a product can be evaluated. A parameter is introduced which quantifies the contribution of variables that reduce the functional process capability. The applications of the proposed method are demonstrated through implementing it on two case studies and the results are discussed.
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In this paper asymmetric plane strain rolling is analyzed by using an elastic-plastic ALE finite element method. Results of the ALE finite element investigation of curvature development due to inequality in work rolls/plate surface finish... more
In this paper asymmetric plane strain rolling is analyzed by using an elastic-plastic ALE finite element method. Results of the ALE finite element investigation of curvature development due to inequality in work rolls/plate surface finish (interface friction) and speed mismatch are presented. Reasonable agreements were found between the numerical method and experimental results. The ALE technique is found to be a convenient method for simulation of processes such as asymmetrical rolling where the material is deformed in an unexpected shape.
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ABSTRACT In mechanical assemblies, the performance, quality, cost and assemblability of the product are significantly affected by the geometric errors of the parts. This paper develops the statistical error analysis approach for... more
ABSTRACT In mechanical assemblies, the performance, quality, cost and assemblability of the product are significantly affected by the geometric errors of the parts. This paper develops the statistical error analysis approach for dimensional control in automotive body multi-station assembly process. In this method, the homogeneous transformation matrices are used to describe the location and orientation of part and assembly features and the small homogeneous transformation matrices are used to model the errors. In this approach, the effective errors in automotive body assembly process are classified in three categories: manufacturing errors (dimensional and geometric tolerances), locating errors (fixture errors) and process errors (joining errors). In a mechanical assembly, small variations due the errors propagate according to a complex mechanism that in this approach it formulated in error analysis procedure. The propagation chain of geometric errors is described based on CAD models. The estimation of the error accumulation and the percent contributions of individual errors are based on the statistical model (root-sum-square method). The application of the proposed method is illustrated through presenting an example problem.
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ABSTRACT Receptance coupling substructure analysis (RCSA) is extensively used to determine the dynamic response of milling tool at its tip for the purpose of prediction of machining stability. A major challenge in using this approach is... more
ABSTRACT Receptance coupling substructure analysis (RCSA) is extensively used to determine the dynamic response of milling tool at its tip for the purpose of prediction of machining stability. A major challenge in using this approach is the proper modelling of the joint between the substructures and determination of its parameters. In this paper, an inverse RCSA is developed for experimental extraction of tool-holder frequency response function (FRF) including joint parameters. The accuracy and efficiency of this method is evaluated through an analytical investigation. It is shown that the extracted holder FRF can provide a highly accurate prediction of the tool tip FRF. The developed method is used in prediction of tool tip FRF with different values of the tool overhang. The proposed approach is validated through experimental validation.
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ABSTRACT Special superelements are often used to improve the computational efficiency and improve accuracy of finite element modeling. Structures with tapered and spherical geometry exist in many engineering problems. In this work,... more
ABSTRACT Special superelements are often used to improve the computational efficiency and improve accuracy of finite element modeling. Structures with tapered and spherical geometry exist in many engineering problems. In this work, special tapered and spherical superelements are presented that can be used for modeling of tapered and spherical bodies in thermo mechanical analyses with computational efficiency. The performance of these superelements under thermal and structural loads is demonstrated by presenting several examples and comparing the results with those from conventional 3D brick elements, which shows high accuracy at reduced computational cost.
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ABSTRACT Prediction of the thermo-mechanical behavior of machine-tool spindles is essential in the reliable operation of high speed machine tools. In particular, the performance of these high speed spindles is dependent on their thermal... more
ABSTRACT Prediction of the thermo-mechanical behavior of machine-tool spindles is essential in the reliable operation of high speed machine tools. In particular, the performance of these high speed spindles is dependent on their thermal behavior. The main source of heat generation in the spindle is the friction torque in angular contact ball bearings. This paper presents an effort to develop a comprehensive model of high speed spindles that includes viable models for the mechanical and thermal behavior of its major components, i.e., bearings, shaft and housing. Spindle housing and shaft are treated as six-degree-of-freedom Timoshenko beam elements. Bearings are modeled as two-node elements with five displacements and a thermal load component at each node. Mutual interaction between the thermal and structural behavior of both spindle shaft/housing and bearings is characterized through thermal expansion and the rate of heat generation/transfer. Components are combined to form a finite element model for the thermo-mechanical analysis of spindle-bearing systems.The results of simulation for a typical spindle system are presented.
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Dynamic vibration absorbers are used to reduce the undesirable vibrations in many applications such as electrical transmission lines, helicopters, gas turbines, engines, bridges and etc. One type of these absorbers is tunable vibration... more
Dynamic vibration absorbers are used to reduce the undesirable vibrations in many applications such as electrical transmission lines, helicopters, gas turbines, engines, bridges and etc. One type of these absorbers is tunable vibration absorber (TVA) which can act as a semi-active controller. In this paper, by applying a (TVA), chatter vibration is suppressed during boring process in which boring bar is modeled as a cantilever Euler-Bernoulli beam. The optimum specifications of absorber such as spring stiffness, absorber mass and its position can be determined by developing an algorithm based upon mode summation method. Finally, using the SIMULINK Toolbox of MATLAB, the analog simulated block diagram of the problem is developed. The advantage of this simulation is that, one can analyze the effect of other types of excitations such as step, ramp, etc on the absorbed system.
Research Interests: Design and Manufacturing
ABSTRACT In this paper, forced vibration analysis of an extended dynamic model of the milling process is investigated, in the presence of internal resonance. Regenerative chatter, structural nonlinearity, tool wear and process damping... more
ABSTRACT In this paper, forced vibration analysis of an extended dynamic model of the milling process is investigated, in the presence of internal resonance. Regenerative chatter, structural nonlinearity, tool wear and process damping effects are included in the proposed model. Taking into account the average and first order expansion of Fourier series for cutting force components; their closed form expressions are derived. Moreover, in the presence of large vibration amplitudes, the loss of contact effect is included in this model. Analytical approximate response of the nonlinear system is constructed through the multiple-scales approach. Dynamics of the system is studied for two cases of primary and super-harmonic resonance, associated with the internal resonance. Under steady state motion, the effects of structural nonlinearity, cutting force coefficients, tool wear length and process damping are investigated on the frequency response functions of the system. In addition, existence of multiple solutions, jump phenomenon and energy transfer between vibration modes are presented and compared for tow cases of primary and super-harmonic resonances.
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ABSTRACT In this article, the effects of volute cross section shape and centroid profile of a centrifugal compressor volute were investigated. The performance characteristics of a turbocharger compressor were obtained experimentally by... more
ABSTRACT In this article, the effects of volute cross section shape and centroid profile of a centrifugal compressor volute were investigated. The performance characteristics of a turbocharger compressor were obtained experimentally by measuring rotor speed and flow parameters at the inlet and outlet of the centrifugal compressor. The three dimensional flow field model of the compressor was obtained numerically solving Navier-Stokes equations with SST turbulence model. The compressor characteristic curves were plotted. For model verification, the results were compared with experimental data, showing good agreement.Modification of a volute was performed by introducing a shape factor for volute cross section geometry. By varying this parameter, new volutes were generated and modeled. The effect of volute cross section shape on compressor pressure ratio and efficiency at design rotational speed were investigated. Also pressure non-uniformity around compressor impeller for new cases was calculated and reported.The results showed how the cross section shape of the volute can influence the compressor characteristics and the non-uniformity of circumferential static pressure as well.
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ABSTRACT In this research, design methods of radial flow compressor volutes are reviewed; the main criteria in volute primary designs are recognized and the most effective ones are selected. The effective parameters, i.e., spiral... more
ABSTRACT In this research, design methods of radial flow compressor volutes are reviewed; the main criteria in volute primary designs are recognized and the most effective ones are selected. The effective parameters, i.e., spiral cross-section area, circumferential area distribution, exit cone, and tongue area of the compressor volute are parametrically studied to identify the optimum values. A numerical model has been prepared and verified through experimental data which are obtained from the designed turbocharger test rig. Different volutes are modeled and numerically evaluated using the same impeller and vane-less diffuser. For each model, the volute total pressure ratio, static pressure recovery and total pressure loss coefficients and the radial force on the impeller are calculated for different mass flow rates at design point and off-design conditions. The volute which shows better performance and causes lower the net radial force on the impeller at desired mass flow rates is selected as an optimal one. The results show the volute design approach differences at the design point and off-design conditions. Improving the pressure ratio and reducing total pressure loss at design point may result in the worse conditions at off-design conditions as well as increasing radial force on the impeller.
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Background and aims. The aim of this study was to determine the stress patterns within an implant and the effect of different types of connections on load transfer. Materials and methods. Three different types of implant-abutment... more
Background and aims. The aim of this study was to determine the stress patterns within an implant and the effect of different types of connections on load transfer. Materials and methods. Three different types of implant-abutment connections were selected for this study. Sample A: 1.5-mm deep internal hex corresponding to a lead-in bevel; sample B: a tri-channel internal connection; and sample C: in-ternal Morse taper with 110 degrees of tapering and 6 anti-rotational grooves. Four types of loading conditions were simu-lated in a finite element model, with the maximum von Mises stress set as output variables. Results. The maximum stress concentration at the inner surface of the fixtures was higher than the stress value in bone in all of the samples. Stress values in sample B were the lowest amongst all of the models. Any alterations in the amount and direction of the 100-N axial load resulted in an increase in fixture surfaces stress. Overall, the highest amount of stress (112 MPa) ...
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ABSTRACT In this paper, a tunable vibration absorber (TVA) is designed to suppress regenerative chatter in milling of cantilever plates. In machining industry, the majority of work-piece materials or the interaction of work-piece/cutting... more
ABSTRACT In this paper, a tunable vibration absorber (TVA) is designed to suppress regenerative chatter in milling of cantilever plates. In machining industry, the majority of work-piece materials or the interaction of work-piece/cutting tool causes the cutting forces to demonstrate nonlinear behavior. The application of TVA (as a semi-active controller) is investigated for the process with an extensive nonlinear model of cutting forces. Under regenerative chatter conditions, optimum values of the absorber position and its spring stiffness are found such that the plate vibration is minimized. For this purpose, an optimal algorithm is developed based on mode summation approach. Results are presented and compared for two cases: regenerative chatter under resonance and non-resonance conditions. It is shown that the absorber acts efficiently in chatter suppression of both machining conditions, in a wide range of chatter frequencies. Moreover, using TVA leads to the great improvement in stability limits of the process. Therefore, larger values of depth of cut and consequently more material removal rate can be obtained without moving to the unstable machining conditions.
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Radial forging is an open die forging process used for reducing the diameters of shafts, tubes, stepped shafts and axels, and for creating internal profiles in tubes. In this study, the effect of the workpiece rotation (the... more
Radial forging is an open die forging process used for reducing the diameters of shafts, tubes, stepped shafts and axels, and for creating internal profiles in tubes. In this study, the effect of the workpiece rotation (the circumferential feed) on the strain and residual stress distribution in the inner surface of the tube in the cold radial forging process is investigated using nonlinear three dimensional finite element modeling. To verify the model, the predicted radial forging load is compared with the published experimental data which shows a good agreement. It is shown that for achieving a more favorable residual stress distribution in the workpiece inner surface, the rotation angle associated with each stroke should be reduced. Furthermore, a total rotation angle of 90° seems to be sufficient for finalizing the strain and residual stress distribution in the workpiece inner surface and using additional rotation is just a waste of time and energy in this respect.
ABSTRACT Radial forging is an open die forging process used for reducing the diameters of shafts, tubes, stepped shafts and axels, and for creating internal profiles in tubes. Among parameters affecting process variables, the die geometry... more
ABSTRACT Radial forging is an open die forging process used for reducing the diameters of shafts, tubes, stepped shafts and axels, and for creating internal profiles in tubes. Among parameters affecting process variables, the die geometry is of fundamental importance and greatly influences variables such as forging load, stress distribution on the dies, metal flow during deformation, and surface finish of the forged product. In this paper a generalized slab method analysis of radial forging process is presented which can handle this process with curved shape dies. Results for dies with various curves are presented and it is shown that the analysis reduces to that of Lahoti and Altan [2] when the die has a linear profile.