جستجوی مقالات مرتبط با کلیدواژه « finite element modeling » در نشریات گروه « مکانیک »

In this paper, the effect of including SiC nanoparticles in the weld zone on the maximum shear strength of friction stir lap welded 7075 aluminum alloy is investigated, both experimentally and numerically. This objective is carried out by studying the effects of rotational and transverse speeds, tilt angle, the shape of the tool and the penetration depth. The numerical investigation is based on developing an FE model by means of Deform and ABAQUS to simulate the welding procedure, which results are verified by the experimental findings. Experimental procedure is designed based on Taguchi method. The verification of the developed FE model shows that the simulation results are in proper agreement with the experimental findings. In general, including SiC nanoparticles in the weld zone can increase the maximum shear strength up to 24%, compared to the case of where the specimens are welded without SiC. Furthermore, applying the threaded tapered tool leads to higher shear strength in comparison with the squared shape tool, i.e., the strength of the specimens welded by threaded tapered tool are 4 to 5% higher without SiC inclusion and 4 to 7.5% higher with SiC, compared to the same case welded by squared tool. In addition, while the rotational speed has the highest influence on the findings, the tilt angle does not affect the results that much.

Auxetic materials with negative Poisson’s ratio, as a group of metamaterials, attracted significant attentions among researchers due to their interesting and remarkable mechanical properties. Rigid rotating structures are a subcategory of auxetic materials which can show the same behavior in various directions by tuning their parameters, but due to using rigid rotating blocks their relative density is high. As the rotating blocks are connected by weak joints, stiffness and strength of these structures are low and considering high relative density of these structures specific mechanical properties are even in worse condition. In this research, novel lattice structures based on rigid rotating structures but with remarkably lower relative density were presented. To reduce relative density of these structures, bar elements were used instead of rigid blocks. 3D printing method was used to manufacture samples with these structures and then tensile test was performed on the samples. Poisson’s ratios of the samples were measured by recording image of the structures before and during deformation. The behavior of the structures was predicted by finite element method and compared with experimental measurements. Both of the methods showed auxetic behavior of the structures. Then deformation mechanism of the structures and the effect of the structures shape on the auxeticity were investigated.

In this paper, the combination of digital image correlation and hole drilling methods has been used to investigate and measure the residual stress of polymer components. The bending stress was created by a three-point bending system and measured by the provided equipment. These stresses are considered in theory to be equivalent to the residual stresses within the component. Digital image correlation method utilized as a novel method to measuring released strain. In this regard, Plexiglas polymer materials in various thicknesses were analyzed under the different values of 3-point bending test. Finally, the obtained results from the introduced method in this paper, with the results of Finite element analysis and simulation have been compared and validated. Unlike the samples that have an unknown amount of residual stresses, the residual stresses in these specimens have a certain amount that can be compared and verified with the simulation and analytical results. Polymer materials have a higher released strain range than metals and it is possible to investigate the strain released by digital image correlation. The results show that the combination of digital image correlation and hole drilling techniques as innovations presented in this paper are capable of measuring residual stresses with a high accuracy less than 10% and also because of their major advantages. The method of using strain gauge would be a suitable alternative to the hole drilling whit strain gauge method for measuring residual stress in polymer samples.

Todays, hydrogels have attracted many researchers due to their unique properties in responding to exterior stimuli and swelling-induced by water absorption. According to their reversible swelling, it is important to predict their mechanical response. The functionally-graded temperature-sensitive hydrogel is one of the most applicable materials in industry. Thus, to study the mechanical behavior of these materials, an energy density function is introduced which includes network stretch energy and mixing part. Then, considering functionally-graded properties along the thickness, bending of FG temperature-sensitive hydrogels is solved analytically under plane-strain assumption. Verifying the presented analytical procedure, the results are compared with outcomes of finite-element-method. To solve diverse problems by finite-element-method, UHYPER subroutine has been written and verified in free-swelling problem. Next, the radius, radial stress and tangential stresses are studied by both methods for FG temperature-sensitive hydrogels. Finally, according to the importance of factors such as semi-angle and bending curvature in the industrial designs, these factors are investigated by changing the temperature in range of 320 to 288. Results demonstrate the capability of these material to be implemented in sensors and actuators. In addition, the continuity of stresses field is the other reason of utilizing FG hydrogels, while the multi-layer hydrogels do not have continuous stress fields.

Interference fit joints are widely used in the industry to produce tight joints. These type of connections have produced more beautiful and smaller joints by eliminating other joints such as keys which are defected with stress concentration. Interference fit joints could be applied under dynamics and statics design loads, successfully. Interference fit joints are always imperfect, such as other industrial products and also affected by some parameters which directly affect the operation of these joints. For instance, contact surface of every manufactured joint parts are not a perfect cylinder and always there are some form defects. The variation of these parameters could affect the performance and strength of interference joints, so these parameters should be considered. Some effective parameters on the strength of interference fit joints are friction coefficient, roughness, materials properties, dimensions and geometric irregularities of contact surfaces. In this study the effect of diameter of shaft and interference value variation on the friction coefficient in contact surface and strength of joints are investigated. Finite element results are interacted with experimental ones to estimate friction coefficients. Also, factorial method, which is a statistical method for design of experiments, are used to analysis the effects of pressure, which is vary by variation of interference, and radius of contact surface curvature on friction coefficient and strength of joints. Results indicate that the friction coefficient changes with diameter of interference surface, inversely and increase of interference and consequently, pressure leads to growth of friction coefficient.

Due to developments in additive manufacturing (AM) techniques, design and producing cellular structures with complex topologies accompanied with appropriate mechanical properties and lightweight have become possible and the application of cellular porous materials has been increasing in various areas. In the current study, a novel cellular structure with adjustable radially graded relative density and properties inspired by bone tissue structure is designed and introduced. The cellular structure has five layers and is achieved by repeating a regular four-sided unit-cell in radial, peripheral, and axial directions by a specific pattern. Next, using analytical relations, the mechanical properties of the structure are derived. The obtained theoretical solution is validated by numerical modeling and experimental test of a polymeric specimen manufactured by SLA method. Comparison of the results shows good precision of the theoretical solution. Furthermore, the effect of design parameters including the height of representative volume element, the number of the sides of start shape, and radius of the struts on mechanical properties and their distribution is studied. Using genetic algorithms single-objective and multi-objective optimization is performed on elastic properties of the structure. The single-objective optimization results for structure with 70, 75, and 80% porosities led to 32.9, 35.92, and 35.68% improvement of elastic modulus to mass, respectively and 116.35, 96.48, and 73.62% increase of yield strength to mass at similar porosities compared to base models with same porosities. The results show proper ability of the structure in creating distribution of mechanical properties and porosity and its potential capability for use in bone replacement applications.

In this paper, finite element method is employed to study the buckling behavior and mechanical properties of double-walled carbon nanocones. In this regard, double-walled nanocones with different geometries, including lengths and angles, and boundary conditions are investigated. Based on the similarity between the nanostructures and space frames, structural mechanics approach is employed to study the mechanical behavior of the nanocones. In this approach, the carbon nanocones are considered as space frame and beam and mass elements are utilized to model the atoms and bonds. The results show that the elastic modulus of the carbon nanocones decreases by increasing the apex angle and length. Besides, it is shown that the influence of the apex angle on the critical buckling force of the carbon nanocones is more significant than the length effect. Increasing apex angle and length of the carbon nanocones lead to increasing and decreasing of the critical buckling force, respectively.

According to their time and rate dependent response to the exterior loads, there was too much complexity to predict mechanical responses. Thus, a thermodynamically consistent viscoelastic-viscoplastic-viscodamage model is considered to predict their mechanical responses. Along this purpose, the explicit time-discrete form of the constitutive model is used in the finite element software ABAQUS by VUMAT subroutine. This method is valuable since its accuracy, low running time and no need of Jacobian matrix calculations. After validating ABAQUS user subroutine with experimental data obtained from creep, creep-recovery and repeated creep-recovery tests on the polymer, constitutive model sensitivity to the material parameters such as viscoelastic, viscoplastic and damage properties has been investigated. Along this purpose, it can be observed that increasing viscoplastic and damage parameters could cause rising in viscoplastic strain and damage variable. Then, the direct effects of loading time and stress level and the indirect effects of unloading time on polymer strain and damage variable were investigated in the two repeated creep-recovery tests with constant and increasing amplitudes. For instance, doubling increasing amplitude cycle number from 50 to 100 could rise service life and decrease about 75 percent of damage level.

High ratio of strength to weight in fiber reinforced polymer composites causes to their applications in many of the structures and components. In this study an experimental and numerical investigation on four composite cylinders’ response to low-velocity impact is carried out. The studied cylinders were considered to be carbon-only, kevlar-only, kevlar-outside/carbon-inside, and carbon-outside/kevlar-inside. The experimental impact test was applied on the samples using a drop-weight impact apparatus without initial velocity with a spherical steel impactor. In the numerical part, a finite element (FE) modeling technique has been used in ABAQUS software to investigate the impact behavior. In this paper, various types of modeling methods, meshing process and types of elements such as conventional shell, continuum shell and solid elements were discussed in the software. The issues of concern were the contact force, contact duration, and deflection of the specimens. It was found that kevlar fiber has more ability to absorb energy compared to carbon fiber and that the carbon-only specimen has the greatest contact force and the lowest deflection compared with the other samples. To validate the experimental data, they were compared with the results obtained from FE analysis and a strong concurrence was found between them.

Rutting is one of the most critical distresses influenced the asphalt pavement performance and its service life. Due to the complexity of the mechanical asphalt pavement responses, to study the mechanical behavior of this material under applying loads, a thermodynamically consistent visco- elastic visco- plastic visco- damage constitutive model has been presented in the implicit time discrete form to predict their mechanical responses within the framework pf the finite element method in software ABAQUS- Standard. It is worthy to mention that employing an implicit time discretization technique reduces the computational cost and a more stable solution is found. In this work, rutting phenomenon and prediction of the asphalt pavement service life has been investigated under three types of moving loading regimes, which forty percent of rutting difference has been obtained by comparing the pulse and equivalent loadings under moving load that would cause erroneous predictions in asphalt pavement service life.

The destruction of asphalt pavements is one of the biggest problems in road construction in the world, which incurs a huge amount of annual rebuilding. The healing process to recover damage is one of the effective methods to extend the life of these pavements, which has been presented by researchers in recent years. Self-healing polymers are a class of smart materials that, without the need for external stimulation, can repair part of the damage generated as microcracks and microvoids in their microstructures. Along with the purpose of the study, i.e., investigating the effect of healing in the lifetime of asphalt pavements, the explicit time-discrete form of the thermodynamically consistent model is presented in order to be utilized in a finite element ABAQUS software by VUMAT subroutine. The discretization method mentioned here has benefits such as low calculation costs and high reliability in response. Then, three-dimensional modeling of general vehicles' tire has been done using hyperelastic and viscoelastic materials in order to have the desired deformation on the pavement after applying the load. In the following, to evaluate permanent deformations (common failures in the asphalt pavement) and the effect of the healing process on its dilation, it is necessary to simulate its behavior in high-cycle loadings. In order to reduce the cost and time of computation, an alternative method has been used. In this method, in order to speed up the growth of damage and, also, healing effect, tire moving velocity has decreased. This may increase the time of loading on asphalt; therefore, rate of damage increase. In this simulations, the life of the asphalt pavement is compared with the effect of healing and without the effect. The results obtained from the simulations show that, by applying the effect of healing, the growth rate of damage and destructions caused by the permanent deformation of the pavement decreases, and the pavement lifetime can be increased up to more than 70%.

In this paper, the atomistic finite element model is used to study the compressive behavior and mechanical properties of singlewalled carbon nanotubes-graphene nanosheets junctions with different boundary conditions. Considering nanotubes as space frame structure, classical structural mechanics approaches can be used to study their mechanical behaviors. The beam and mass elements are used to model the bonds and atoms, respectively. In order to determine the properties of the beam elements, the energy tems in molecular mechanics are equated to those in the structural mechanics. The present analysis provides useful data about the applicability of finite element model to predict the elastic modulus and critical compressive forces of carbon nanotube-graphene junctions. The results show that in a constant aspect ratio (the ratio of the length to the radius of nanotubes), increasing length of the nanotube leads to decreasing the critical compressive force. While the elastic modulusis constant. Moreover, increasing aspect ratio results in decreasing the critical compressive force negligible increasing in elastic modulus. The amount of critical compressive force of the nanotubes under clamped-clamped boundary condition is more than the other boundary conditions. Finally, the first ten mode shapes of the armchair and zigzag nanotubes are drawn for one-side and two-sided junctions, and it is shown that the mode shapes of the armchair and zigzag nanotubes are almost similar.

Todays, hydrogels have attracted many researchers due to individual response to exterior stimuli. According to the environmental stimuli, these materials absorb a huge amount of water and swell. Due to the vast application of the functionally graded pH sensitive hydrogels, investigation of their mechanical behavior during changing of pH is very important. In this regard, the energy density is decomposed additively to energy of the network stretching, energy of mixing and energy of dissociation. Considering the variation of properties along thickness, the semi analytical solution is presented under plane strain condition. Verifying the accuracy of presented method, the result of this method is compared with the finite element method including radius, radial and tangential stresses, bending curvature and bending semi angle between pH = 2 to 8. In addition, the continuity of stresses and deformation is one of the benefits of using functionally graded hydrogel instead of multi layer ones.

The laser-assisted additive manufacturing based on the powder is an efficient layer manufacturing process that uses a high-energy laser for the fabrication of polymeric components. The thermal stresses of the laser arise from the thermal gradients generated by the laser and other parameters of the device. Reducing thermal gradients decreases the deformations in the part and increases the fabrication accuracy. The main aim of this paper is to determine the temperature parameters including the preheating temperature or the powder bed temperature, the ambient temperature, scanning power and spot diameter in such a way that the temperature gradient is minimized. The finite element modeling is performed for the selective laser sintering process for polyamide-12 powder. In this paper, thermal gradient by changing temperature parameters based on the temperature model of the finite element and Taguchi experimental design is optimized. In order to reach this aim, the finite element simulation of the selective laser sintering process is first carried out for polyamide-12 powder. In order to verify the simulations, the experimental test is performed by a selective laser sintering device and the obtained results are compared with the finite element model. Then, using the Taguchi method, experiments are designed at the different levels and optimal temperature parameters are obtained. According to obtained results, optimal parameters were obtained to minimize thermal gradients at 451K preheat temperatures, 359K ambient temperature, 10W laser power, and 0.5mm spot diameter.

The magnetic flux leakage technique (MFL) is a widely used method for corrosion detection in the gas pipelines. The inspection of pipelines is typically performed using intelligent PIGs. The MFL intelligent PIG is equipped with an array of magnetizers responsible for inducing a magnetic field in the pipeline wall. The magnetic field leaks out of the pipeline wall at the locations where defects are present. The magnitude of the leakage magnetic field is measured by Hall-effect sensors and used for analysis of defects. In recent studies, the design of the appropriate magnetizer, as a technique to improve the probability of detection of the MFL, has been of great interest to the researchers. In this study, the simulation of the MFL technique was carried out based on Maxwell equations and in 3D using COMSOL software. The specimen under test was a carbon steel plate with a thickness of 10mm, which contained two pitting defects with various depths of 4mm and 6mm. Then, the MFL signals obtained from the defects were analyzed. Following the finite element modeling and obtaining the magnetizer dimensions, MFL system was designed and manufactured. First, the FEM results were experimentally validated. The results of the comparison indicated that there was a good agreement between experiments and FEM. The mean error was below 9%. Finally, MFL experiments were carried out and C-scans from the defects of different depths were obtained. The C-scans can be used for characterization of the defects.

The precise finite element model is an efficient tool for vibrational analysis. It should be mentioned that, in structural dynamic analysis finite element models of system should be able to accurately predict system characteristics such as natural frequencies. Contrary to static analysis, in structural dynamic analysis, it is not possible to overestimate system characteristics or apply safety factor for predicted characteristics; that means that the exact values of system characteristics such as natural frequencies, should be derived in structural dynamic. According to this, constructing a reliable model in the structure dynamic always has great degree of importance in vibrational analysis. In this study, it has been tried to extract a reliable finite element model for a row of a sample turbine of RollsRoyce brand using empirical results. So, the material properties of the disk and the connection between the disk and the blade are corrected and updated using experimental modal analysis results. Also, it has been tried to propose new method to model and update the disk and blade joint. Finally, reliable finite element model could be used for more analysis such as derivation of Campbell diagrams of system.