Sharif Digital Repository

Mode I and II stress intensity factors are derived for an inclined crack breaking the surface of a half-plane which is subjected to an un-symmetrical singular contact loading due to the contact of a tilted wedge with the half-plane. The method used is that of replacing the crack by a continuous distribution of edge dislocations and assume the crack to be traction-free over its entire length. A traction free crack is achieved by cancelling the tractions along the crack site that would be present if the half-plane was un-cracked. The stress distribution for an elastic uncracked half-plane subject to a tilted wedge shaped indenter is derived analytically using the Muskhelishvili’s potential... 

The first project ,paid to review and analysis types of crack and agents Also, was referred methods to control them in rail industry .
The wheel of Alestom train and UIC60 rail were simulated and stress analysis by software FEM (ANSYS and ABAQUS) , and effect of various parameters such as applied forces , train wheel diameter , contact position and rail inclination on stress values was studied . For comparision of results has been used analytic Hertz theory .
By using experimental data on the subsurface crack , those cracks were created in the wheel . For load on the modeling wheel and rail, ,assuming contact on the wheel rolling point , were used vertical load of wagon weight ( with... 

In this study, Interfacial crack is modeled by the extended finite element method (XFRM) in order to evaluate the stress intensity factors for interface crack problems. These problems have crack edge discontinuity, material interfaces and singularity at the crack tip, which is inappropriate to finite element (FEM) mesh. Furthermore, around crack tips and interface edge, extremely fine discretization is required to achieve reasonable accuracy. All these factors increase the time and cost of the FEM solution. Recently the extended finite element method is developed and applied to interface fracture problems. In the XFEM, special enrichment functions are added to the finite element displacement... 

First stage blades tempreture in the turbine rotor section for the advanced turbines has increased up to 1100oc. The blades should be under mentioned condition for the long times up to 70000 hours and accordingly creep happens. Fatigue–creep interaction is the main reason for the failures of many engineering components under high temperature and cyclic loading. In this thesis, a model for the life prediction of fatigue–creep interaction which was developed by other investigators has been modified to predict fatigue–creep interaction on the nickel-based superalloys. In this model, the law of energy conservation and the momentum conservation principle are used to describe the process of... 

The problem of fretting fatigue due to the inherent complexity and high probability of its occurrence in many engineering systems, is very important for engineering design. Fretting Fatigue is a significant failure mode in many contacting mechanical components, in which two contact surfaces experience low amplitude oscillatory movement due to cyclic loading. There are many significant contact fatigue problems in structural design which fretting fatigue at lap joints in aging aircraft and fretting fatigue of dovetail joints in gas turbine engine are the most important of them. Numerical simulations provide an appropriate and powerful tool for parametric study of fretting fatigue behavior of... 

Modeling of contact is a important problem in word science, so a lot of method presented by researchers .
In practical industry, if members of contact have complex shape or large deformation, analytical method can not solve the problem and use numerical method.
This method by using ansys , first analyze one-area contact and compare between numerical result and analitical result, then analyze two-area contact between two body with vertical force, and compare result with considering effect of slip and target surface.
Finaly to analyze a practical multiple contact problem, use modeling of tyre and road surface partial slip, and compare between ansys result with experimental result ,... 

Surface roughness has an enormous influence on many important physical phenomena such as contact mechanics, sealing, adhesion and friction. Contact mechanics was studied as an important topic for long years in order to realize the friction phenomena, contact fatigue and fluid leaking between rough surfaces. Therefore, the contact of rough surfaces has been widely invistageted by engineers for different purposes like rejouvination, prevention of environmental pollution and stress analysis. Failure modes have been studied in this research for a specific type of injector by experimental methods. After that, injector's rough surfaces were modeled. Firstly the proper point cloud was modeled by... 

In this study composite is built based on epoxy which is reinforced with 3D graphen foam using the RTM (resin transfer molding) method in which the molding is done by hand, through injecting epoxy to graphen foam.Good scattering and neat meshing of 3d graphen planes in composite have resulted in its improved mechanical quilities.The subject of the present study is the synthesis of graphen foam from graphen oxide and making graphen foam/epoxy composite in order to improve its mechanical properties. In order to do that, firstly graphen foam is forged from graphen oxide in a 3d mesh, in a way that single graphen planes in polymer matrixes are eliminated.Having very little density, very high... 

Purpose of these investigations is modeling and prediction of foam graphene like linear elastic modules and density of that material. In this modeling with two numerical method molecular dynamics and finite element method is used in that with multiscale method various numerical method match together. At the beginning of the modeling various image of foam graphene in Nano abd meso scale in the case of size and scale survaied till with this checking, scale of the work and varios of modeling was created and with this modeling linear elastic modules and density were estimation  

In this thesis contact problem between wheel and rail has been studied. Also rolling contact fatige (RCF) has been studied in detail. Unlike previous studies that have focused on FEM solution, in this study the problem has been formulated based on analytical methods. Evaluating the loads in wheel-rail contact zone is necessary to find the defects. This thesis presents the evaluation of the stress field inside elastic rolling bodies with an elliptic area of contact. This kind of model can be applied to wheel-rail contact mechanics. The problem has been solved for two main models: with friction and without friction. The results have shown that shear stress reaches the maximum magnitude... 

In this research, the surface contact and lateral stress distribution due to the contact between a rigid flat punch and a FG coating is investigated through macro and micro mechanical modeling due to FEM. The effects of important parameters in modeling of contact mechanics, both macro mechanically and micromechanically investigated. Study of such parameters is important, especially in fracture mechanics point of view, since stress distribution of mechanical contacts can cause the crack nucleation and evolution and finally catastrophic failure. Investigating the effective parameters in FEM models and analyzing the result admittedly help to improve manufacturing methods in order to smooth the... 

In this research, the surface stress distribution function due to the contact between a rigid rounded apex wedge and a FG coating is investigated. This study is important, especially in the fracture mechanics point of view, because stresses due to the contact can be considered as a fine crack source which grows gradually and finally leads to the failure of the structure. The structure includes two components. The first is the FG coating and then, the homogeneous substrate which is connected to the FG coating. Usually, it is considered that the homogeneous substrate is a metal, and properties at the connection are metallic, then properties change gradually through the thickness of the FG... 

In recent years, one of the important and challenging issues that has drawn many engineers’ attention is the system reliability. Generally, the possibility of the system’s satisfactory performance under specified operating conditions, for a given period of time, is defined as the System Reliability. Analytical and Simulation methods are two main reliability techniques. In the Analytical technique, mathematical models with some simplification are applied, whereas the Simulation technique utilizes significant number of experiments which are extremely costly and time-consuming. In spite of carrying out analytical methods for proving results, simulation is carried out in different analyses... 

The present research proposes a new method to establish a practical framework for extension of gas turbine life time. This method is based on an nine-step operational algorithm which is capable for different types of gas turbine. The essential inputs for this algorithm includes documents of inspection and knowledge of repair and maitenance experts. In this algorithm is used the Bayesian network probabilistic method. Therefore, based on the observations and the knowledge of experts, gas turbine Bayesian network is produced. According to this Bayesian network consequenses are created. Furthermore, making the steps of the algorithem more explicit, FTA and FMEA methods are used to creat the... 

In many industrial devices and machines, variable loading is applied to the parts, which will lead to fatigue in these parts. Most of these components are in contact with other components, and when the device is operating, low-amplitude movements occur at the contact point. Variable loading conditions and low-amplitude movements at the point of contact can cause failure on parts called FRETTING FATIGUE. This type of failure occurs in many aerospace components, such as where the compressor blade roots connect to the disc. In recent years, many failures due to fretting fatigue has been reported, which has made the need to take solution to prevent this type of failure more and more obvious. One... 

This research explored the corrosion effect of NaCl solution on the surface quality of AZ31 magnesium alloy. Cubic-shaped specimens were immersed in standard 3.5% NaCl solution for 1, 2, 3, and 4 hours. The size of corrosion pits, fatigue crack propagation area, and surface topology were characterized. Fatigue tests were carried out on pre-corroded AZ31 specimens under different stress amplitudes. The correlation between the corrosion time and the virtual crack size was obtained. The virtual crack size is a new parameter that can relate the corrosion to the fatigue life. A new model was proposed to map the surface topology on the virtual crack size of pre-corroded AZ31 magnesium alloy. The... 

In contacts, the presence of both variable loading and low-amplitude movements causes a kind of fatigue in these components called FRETTING FATIGUE. fretting fatigue has reduced the life of parts. Due to the high cost of replacing some parts in case of failure, it is necessary to take effective measures to delay this exhaustion. One of the effective solutions that can be applied is the use of coating and surface treatments in the contact areas. In this research, first, the fretting fatigue maps of Ti-6Al-4V alloy have been calculated and drawn according to the recommendations of the ASTM standard by using finite element methods. In the next step, by using experimental experiments, the damage... 

Different reasons, all structures have inside crack or surface crack when crack growth is more at the frequancy load and it is one of the main factor in the diagnosis of structural life that this sensitivity is much greater aerial parts industry. The aim of this project, designing a new structure for the auxiliary engine compartment of the aircraft with the damage tolerance theory for cargo aircraft within the country are making. In the first stage after reviewing activitation past, the evaluation design rules between each company design its obligations, standards in design and then conceptual plan to make. Then reload force plan to make. At this stage with regard to maneuver the airplane... 

In this thesis, bayesian network has been used in analyzing the failure of a structural component. The design life of a structural component of a system can be limited or unlimited depending on the working conditions considered by the designers. However, usually during the operation of an industrial system or device, a structural component of it fails prematurely, in other words, its actual life is less than the design life. In this case, the failure must be analyzed to find the causes and factors. The method of work is such that first, according to the problem and the type of failure, the required analyzes and studies are considered. Then, a number of samples of the components, whose... 

A Cylinder Liner is one of the most important functional parts that gives a wear protective surface of cylinder block for piston and piston rings. Liners are used in automotive, ships, power aircrafts, and power generation units and the most load carrying part in internal combustion engine. Liners are subjected to various stresses during the engine working status. The stresses which act on cylinder liner are stress due to action of gas pressure and heat. Result of that stresses, wear developed inside of liner and internal or external cracking of cylinder liner takes place. In this paper, complete thermo-mechanical analysis of cylinder liner and failure mechanisms detected in alloyed cast...