Sharif Digital Repository

In the presented research, vibrational, and amplitude behaviors of a sandwich spinning disk made of two laminated layers and graphene nanoplatelets reinforced composite (GPLRC) core has been reported. The Coriolis and centrifugal impacts have been taken into account due to its rotational feature. The stresses and strains have been obtained through the high-order shear deformable theory (HSDT). The structure’s boundary conditions (BCs) are determined using laminated rotating disk’s governing equations employing energy methods and ultimately have been solved via a computational approach called generalized differential quadrature method (GDQM). The rotational disk’s vibrations with different... 

Recent experiments on metals have shown that all of the stress invariants should be involved in the constitutive description of the material in plasticity. In this paper, a plasticity model for metals is defined for isotropic materials, which is a function of the first stress invariant in addition to the second and the third invariants of the deviatoric stress tensor. For this purpose, the Drucker-Prager yield criterion is extended by addition of a new term containing the second and the third deviatoric stress invariants. Furthermore for estimating the cyclic behavior, new terms are incorporated into the Chaboche's hardening evolution equation. These modifications are applied by adding new... 

Recent research studies on ductile fracture of metals have shown that the ductile fracture initiation is significantly affected by the stress state. In this study, the effects of the stress invariants as well as the effect of the reverse loading on ductile fracture are considered. To estimate the reduction of load carrying capacity and ductile fracture initiation, a scalar damage expression is proposed. This scalar damage is a function of the accumulated plastic strain, the first stress invariant and the Lode angle. To incorporate the effect of the reverse loading, the accumulated plastic strain is divided into the tension and compression components and each component has a different weight... 

In this paper, design and prototyping of two-speed capacitor-run single-phase axial-flux induction motor (AFIM) for direct-drive applications is presented. The proposed structure has single stator-single rotor configuration with high magnetic pull between the stator and rotor, which may compel rotor to lock. Although the most efficient method to overcome this problem is using a second rotor or stator in the mirror with the first one, it is not applicable in low-cost applications. So, in this paper, two new and fast construction techniques are proposed to fabricate an AFIM with extra low air-gap length and minimum cost. Beside design and optimization process, a thermal equivalent circuit... 

Crack detection by Piezoelectric Wafer Active Sensors (PWAS) is one of the emerging methods of Non-destructive Evaluation (NDE). These sensors can assess the health state of the structure in far filed through the analyzing the high frequency Lamb wave propagation. As PWAS is the essential part of this method, simulation and modeling of these sensors and their interaction with the host structure, strongly affect the accuracy of results. In this study, unlike the previous works, in which some certain areas of the host structure were considered as a sensor and actuator, the direct simulation of electro-mechanical interaction of the PWAS and the host structure is modeled among modeling the PWAS... 

When properties of the displacing fluid are considered, the rising profile of the penetrating fluid in a capillary tube deviates from its classical Lucas-Washburn profile. Also, shape of capillary tube can affect the rising profile in different aspects. In this article, effect of capillary tube's shape on the vertical capillary motion in presence of gravity is investigated by considering the properties of the displacing fluid. According to the fact that the differential equation of the capillary rising for a non-simple wall type is very difficult to solve analytically, a finite element simulation model is used for this study. After validation of the simulation model with an experiment that... 

In this paper, design, simulation and optimization of a novel electrothermally-activated polymeric microactuator capable of generating combination of bidirectional lateral and rotational motions are presented. The composite structure of this actuator is consisted of a symmetric meandered shape silicon skeleton, a SU8 thermal expandable polymer and a thin film chrome layer heater. This actuator is controlled by applying appropriate voltages on its four terminals. With the purpose of dimension optimization, a numerical parametric study is executed. The modeled actuator which is 1560 ?m long, 156 ?m wide and 30 ?m thick, demonstrates a remarkable lateral displacement of 23 ?m at power... 

Residual stresses resulted from localized non-uniform heating and subsequent cooling during welding processes enact an important role in the formation of cracks and welding distortions and have severe effect on performance of welded joints. The present research performs a three dimensional transient thermo Elasto-plastic analysis using finite element technique to simulate welding process. Welding simulation procedure is developed using the parametric design language of commercial code ANSYS for single pass T and butt welded joints. The procedure verified with predicted residual stress field found in literature to confirm the accuracy of the method. The material of the weld metal, HAZ and the... 

To determine the curvature of the exit profile in the extrusion process of non-symmetrical flat dies, the dead metal zone profile was predicted using the energy minimization method. The dead zone is a natural non-linear die for the process and it is pragmatic to use this non-linear die to estimate the value of the exit profile curvature and the required bearing length for reducing this deviation. The velocity field is calculated based on Hermite cubic spline and some additional assumptions. In non-symmetrical dies the entrance section of the deformation region is not flat. Considering this fact, axial velocity decreases with increasing the distance to die center line which is in agreement... 

Failure in sheet metal forming can occur by necking, fracture or wrinkling. By using a forming limit diagram (FLD) as a powerful tool to prevent sheets metal failures in the forming process, provides parameters controlling throughout forming. There are different developed methods for predicting FLDs, which estimate sheet metal forming strains limits. Assessment of FLD estimation reveals that there is a dependency between the effect of several factors containing normal stress, shear stress, sheet thickness, mechanical properties, metallurgical properties, yield function, strain path, and bending with formability. In this research, the effects of bending via two finite element models are... 

Increasing the lifetime and improving the performance of structures through redesign and optimization are important, especially in marine structures. In general, there are two main groups of marine structures: onshore and offshore structures. Most marine structures are offshore, and these are divided into two categories: floating or sunken. One of the important parameters in the design of sunken structures is the critical load resulting from the buckling of walls, which can cause damage to the structure. In the present paper, three rectangular aluminum and steel compartments of different conditions and sizes were modeled using design analysis methods. Then, different finite element analyses... 

Finite element analysis is an effective tool to evaluate the material properties of living tissue. For an interactive optimization procedure, the finite element analysis usually needs many simulations to reach a reasonable solution. The metamodel analysis of finite element simulation can be used to reduce the computation of a structure with complex geometry or a material with composite constitutive equations. The intervertebral disc is a complex, heterogeneous, and hydrated porous structure. A poroelastic finite element model can be used to observe the fluid transferring, pressure deviation, and other properties within the disc. Defining reasonable poroelastic material properties of the... 

Gold and copper thin films are widely used in microelectromechanical system (MEMS) and nanoelectromechanical system (NEMS) devices. Nanoindentation has been developed in mechanical characterization of thin films in recent years. Several researchers have examined the effect of surface roughness on nanoindentation results. It is proved that the surface roughness has great importance in nanoindentation of thin films. In this paper, the surface topography of thin films is simulated using the extracted data from the atomic force microscopy (AFM) images. Nanoindentation on a rough surface is simulated using a three-dimensional finite-element model. The results are compared with the results of... 

Nanoscratch testing is a highly reliable method used to extract a variety of film properties. It is proven that many of the experimental factors can influence the obtained results, such as the probe tilt, the scratch depth, etc. On the other hand, the surface roughness of the samples is an important parameter in nanoscratch and other similar tests, including the nanoindentation test. Thus, the effect of surface roughness on both the nanoscratch experiments and finite element simulations has been investigated. By performing scratch tests on gold and copper films and carrying out the finite element (FE) simulations on the rough and smooth surfaces, the importance of surface morphology was... 

In this paper, a mathematical modeling of a microcantilever gyroscope is presented considering the nonlinearities of the system due to electrostatic forces, fringing field, geometry and the inertial terms. The microgyroscope is actuated and detected by electrostatic methods and subjected to coupled bending oscillations. First a system of two nonlinear integro-differential equations is derived which describes flexural-flexural motion of electrostatically actuated and detected microbeam gyroscopes. Afterward, static deflection and pull-in instability of the microgyroscopes acted upon by DC voltages in both (driving and sensing) directions are studied for different parameters. The model's... 

In switching power supplies, the transformer leakage inductance (TLI) is of considerable practical significance. Ordered winding is the certain assumption in previously reported works for the calculation of the TLI value. However, disordered windings are usually unavoidable in practice and their effect on the value of the TLI is considerable. The problem becomes more complex when the number of winding turns increases. In this paper, the effect of winding disorder on the TLI value is investigated. In disordered wrapping, the winding turns arrangement (WTA) of each produced transformer is different from the others. Thus, each produced transformer has an exclusive TLI value in a disordered... 

Characteristics of connections in steel moment-resisting frames are of utmost importance in determining the seismic performance of these structural systems. The results of several previous experimental studies have indicated that Partially Restrained (PR) connections possess excellent properties, which make them a reliable substitution for Fully Restrained (FR) connections. These properties include needing less base shear, being more economic, and, in many cases, being able to absorb more energy. In this study, the behavior of two proposed PR connections with torsional plate is studied through finite element simulations. The results of the numerical studies regarding initial stiffness and... 

In this article, the static behavior of micromirrors under the effect of capillary force is studied. The dimensionless equations governing the static behavior and the pull-in state of the micromirror under capillary force are obtained, and the effects of different geometrical parameters on the pull-in angle of micromirrors are investigated. The static behavior of micromirrors is studied both numerically and analytically using the homotopy perturbation method. It is observed that with increasing the instability number defined in this article, the rotation angle of the micromirror is increased and suddenly the pull-in occurs. The results of the presented model are then verified by comparing... 

In the selective laser sintering (SLS) method, layers of powder are scanned by a laser beam and sintered. The thermal gradients created by laser heating and the subsequent cooling of the sintered sections results in thermal stresses and part warping in the final part. Thermal gradients are dependent on the scanning algorithm, in particular, the scan vector length. In this work, an efficient scanning algorithm for the SLS process is presented with the aim to minimise the part warping in the final part due to thermally induced residual stresses, while maintaining the production time at a minimum. The proposed algorithm is implemented in a finite element simulation and scanning parameters... 

Models for chatter prediction in machining often use a mechanistic force model that calculate the force as the product of a material dependent cutting constant and chip area. However, in reality, the forces are the result of complex interaction between the tool and the chip, and are affected by many factors. The effects of these complex, and often nonlinear, factors on the machining dynamics may only be included in chatter prediction if the chip formation process is simulated concurrently with simulation of the machining dynamics. In this paper, finite element simulation of the chip formation process is combined with simulation of chatter dynamics and the inter-relationship between the chip...