Sharif Digital Repository

Over the past few decades considerable experimental and numerical studies have been conducted on the Reinforced Concrete columns to Steel beams (RCS) connections. Most of those researches have focused on studying the joint failure modes and ultimate joint strength of specimens utilizing strong beams and columns with weak joints. In this paper, two interior RCS connections were designed based on the Strong Column-Weak Beam (SCWB) criterion. Both specimens were tested under quasi-static reversed cyclic loading. The tested specimens were modeled by a finite element method, which verified with experimental results. Several models with different joint details were investigated using the verified... 

The main purpose of the present work is multi-objective shape optimization of a projectile tip for impacting and normal penetrating. Velocity drop, weight and inner volume of projectile have been considered as three conflicting objective functions. For this purpose, at the first step, finite element modeling was done using ABAQUS/Explicit and projectile penetration was examined in different geometric dimensions. Hammersley sequence sampling was employed for designing computer experiments. In the next step, results of the FEM were employed as raw data for MLF-type neural network training to achieve a mathematical model which is able to describe velocity drop behavior. Projectile weight and... 

Switched reluctance machines (SRMs) suffer from ultra-low-frequency torque ripple in single pulse mode. This ripple is the result of an imbalance in phase currents, when multiphase excitation occurs. This paper investigates the origin of this imbalance and identifies the imbalanced phase. Excitation shifting strategy, which delays excitation of the imbalanced phase, is then proposed. The delay angle adjusts current amplitude in the imbalanced phase to attain a perfect balance between all phases. The excitation shifting strategy is a general solution, which is applicable to both three-phase and four-phase machines. In addition, the proposed method can be implemented by a much simpler drive... 

The theoretical need to recognize the link between the basic microstructure of nonlinear porous materials and their macroscopic mechanical behavior is continuously rising owing to the existing engineering applications. In this regard, a semi-analytical homogenization model is proposed to establish an overall, continuum-level constitutive law for nonlinear elastic materials containing prolate/oblate spheroidal voids undergoing finite axisymmetric deformations. The microgeometry of the porous materials is taken to be voided spheroid assemblage consisting of confocally voided spheroids of all sizes having the same orientation. Following a kinematically admissible deformation field for a... 

The objective of this paper is to introduce and demonstrate an algorithm for stress-constrained topology optimization. The algorithm relies on tracking a level-set defined via the topological derivative. The primary advantages of the proposed method are: (1) the stresses are well-defined at all points within the evolving topology, (2) the finite-element stiffness matrices are well-conditioned, making the analysis robust and efficient, (3) the level-set is tracked through a simple iterative process, and (4) the stress constraint is precisely satisfied at termination. The proposed algorithm is illustrated through numerical experiments in 2D and 3D  

The creep deformation behavior of short fiber composites has been studied by an approximate analytical model. A perfect fiber/matrix interfacial bond is assumed and a power law function is considered for describing the steady state creep behavior of the matrix material. The results obtained from the proposed analytical solution satisfy the equilibrium and constitutive creep equations. Also, a parametric study was undertaken to define the effects of geometric parameters on the steady state creep strain rate of short fiber composites. The present model is then validated using the results of finite element method. The predicted strain rate and stress components by the proposed analytical... 

The objective of this study is to develop a general finite element formulation associated with an incremental adaptive procedure which established for thermoviscoelastic stress analysis of orthotropic cylinders made of polymers. This paper concerned with development of a numerical algorithm for the solution of the quasistatic initial/boundary value problems involving the linear viscoelastic media with thermal and mechanical deformations. The viscoelastic constitutive equations, represented in an integral form and involving relaxation functions, are transformed into an incremental algebraic relation. An incremental relaxation is then developed for the finite element formulation to deal with... 

Thermo-mechanical responses, developed microstructure, and mechanical properties in friction stir welding (FSW) of artificially aged AA2017 plates were investigated. A finite element analysis was first employed to evaluate hot deformation behavior of the alloy during welding. Also, hardness, yield strength, and microstructure of the welded alloy were examined using the results of the model and experimental testing. It was found that strain and temperature fields during welding are asymmetrically distributed and the maximum temperature locates in advancing side. Furthermore, considerable grain refinement is observed in the stir zone where recrystallized grains in the range of 3 to 8 m are... 

This paper presents the results of parametric analyses of the yielding moment (My) of Bolted Flush Endplate Beam (BFEB) splice connections using Finite Element Modeling (FEM) tools. The connection components were modeled using three-dimensional brick elements, while contact between the endplates was modeled using Coulomb friction. Materials for beam, endplate and bolts were considered to behave non-linearly. Finite element results with three experimental and numerical studies were compared, and all indicated good agreement, which is also briefly reviewed in this paper. Using verified FEM, fairly large parametric studies, based on the practical configuration of BFEB connections, were carried... 

A stress-based forming limit diagram for necking prediction which is based on the strain gradient theory of plasticity in conjunction with the M-K model has been represented and used in tube hydroforming. In this study, the finite element model for bulge forming of straight tube has been constructed and verified with published experimental data. The adaptive simulation technique is based on the ability to detect the onset and growth of defects (e.g., wrinkling, and bursting) and to promptly readjust the loading paths. Thus, a suitable load path has been obtained by applying Adaptive Simulation Method in ANSYS Parametric Design Language (APDL)  

Hip dislocation is one of the most frequent complications after total hip arthroplasty. Impingement and dislocation might be caused due to misalignment of the acetabular cup during surgery, or performing dislocation-prone activities afterwards. A finite element model was developed to predict the impingement and dislocation behavior of the prosthetic joint, for different combinations of cup orientation and patient maneuver. Four dislocation-prone activities of daily life and 25 cup orientations were analyzed to determine how close they are to the impingement and subsequent dcislocation events. The angular margin results obtained indicated that the sit-to-stand and standing while bending at... 

The Finite element method was used for evaluation of the effects of material properties on the mechanical performance of the new geometry designed for the Z-shaped open-cell femoral artery self-expanding stent, made of Nitinol wire, by application of crushing force. The behavior of the stents, having two sets of properties, was compared. The stents with higher Af temperature show better clinical behavior due to lower chronic outward force, higher radial resistive strength and more suitable superelastic behavior. Model calculations show that a large change of Af temperature could exert a substantial effect on the practical performance of the stent  

In the area of life assessment, none-destructive methods of inspection and evaluation (NDI/NDE) play important role to ensure if astructure is still healthy enough to get used of. Using ultrasonic stress waves is one of the easiest and cheapest methods of NDI. Accordingly, different modes of lamb wave are mostly of interest..There are various methods for generating lamb waves. One of these methods is using piezoelectric wafer actuator/sensors (PWAS). Accordingly, one of the most important parts of this method is to generate right mode via an appropriate choose of actuating frequency. In this text using a new method for finding tuning frequencies of different lamb wave modes proposed. For... 

Analysis and investigation of the relation between different parts of biological cells such as biomembrane, cytoplasm and nucleus can help to better understand their behaviors and material properties. In this paper, first, the whole elastic properties of mouse oocyte and embryo cells have been computed by inverse finite element and Levenberg-Marquardt optimization algorithm and second, using the derived mechanical properties and the mechanical properties of its bio membrane from the literature, the mechanical properties of its cytoplasm has been characterized. It has been assumed that the cell behavior is as continues, isotropic, nonlinear and homogenous material for modeling. Matching the... 

In order to better understand the mechanical properties of biological cells, characterization and investigation of their material behavior is necessary. In this paper hyperelastic Neo-Hookean material is used to characterize the mechanicalproperties of mouse oocyte cell. It has been assumed that the cell behavior is continues, isotropic, nonlinear and homogenous material. Then, by matching the experimental data with finite element (FE) simulation result and using the LevenbergâMarquardt optimization algorithm, the nonlinear hyperelastic model parameters have been extracted. Experimental data of mouse oocyte captured from literatures. Advantage of the developed model is that it can be used to... 

The deformation behavior of solid solution-treated AA6061 tubes in a novel severe plastic deformation process named Tube Channel Pressing has been assessed. In order to do so, an analysis based on the finite element method and dislocation density model is utilized, and microhardness measurement is carried out to verify the trends of analysis results. By comparing FEM results with experimental data, the optimized geometrical parameters controlling the deformation behavior of the tube in tube channel pressing are determined to obtain the best strain homogeneity and minimum dimensional changes in tube  

A nonlinear inverse finite element method is developed for estimation of initial blank shape and strain distribution in final shape. This method often based on implicit static algorithms, causes sometimes convergence problems because of strong nonlinearities. In order to avoid the converging problems, especially in the quasi vertical walls, an appropriate initial guess is introduced. By using this initial guess, the number of iterations in the nonlinear numerical solution is decreased, solution speed is significantly increased and complicated geometries can be analyzed by this method with good accuracy. Application to a Srail part shows good agreement between commercially available finite... 

An explicit dynamics extended finite element method (X-FEM) is applied to the problems with material interfaces. To this end, the available X-FEM element mass matrix lumping techniques have been identified and assessed. It is shown that all the methods have their own limitations and are not general enough to handle the enrichment functions specifically developed for the elements with material interfaces. Hence, a general element mass matrix lumping technique has been introduced which exactly preserves the kinetic energies of the basic rigid body and enrichment modes. The idea is borrowed from the previously published method for a specific range of enrichment functions and extended to... 

In this paper the dynamics and control of the underactuated flexible needle will be discussed. To evaluate the dynamics of the needle, the study uses Saint Venant-Kirchhoff and finite element method. The model is validated using the experimental data provided in the literature. It is also shown that using iterative decomposition of the dynamics equation the unactuated degree of freedom of the needle tip can be feedback linearized. The effect of the control signal exerted on the tip is projected via iterative decomposition of the dynamics equation. The efficiency of the approach will be next explored through some examples  

In this paper, a polygonal-FEM technique is presented in modeling of arbitrary interfaces in large deformations. The method is used to model the internal interfaces and arbitrary geometries using a uniform non-conformal mesh. The technique is applied to capture discontinuous deformations in the non-conformal elements, which are cut by the interface in a uniform regular mesh. In this approach, a uniform non-conformal mesh is decomposed into sub-elements that conform to the internal interfaces. The geometry of interface is used to produce various triangular, quadrilateral and pentagonal elements at the intersection of interface with regular FE mesh, in which the extra degrees-of-freedom are...