Search for: fatigue-life
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    , M.Sc. Thesis Sharif University of Technology Fatemi, Reza (Author) ; Abedian, Ali (Advisor)
    Retrofitting of old mechanical structures by composite materials is one of the most important issues of the world.High reproducing and replacement cost of structures leads to, researchers try to retrofitting old structures and increase their capabilities and so increase their service age. Their research results leads to decreasing cost in one hand and introduce new application of composites in aviation industry in the other hand.Retrofitting mechanical structures show us the important of elements with more stress than the others. The probability of failure is more in these element than the other that we call critical element.These elements in fact are critical parts of an aerial structures... 

    Fatigue analysis of antiroll bar for periodic and random inputs using various theories and introducing a new method

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings, 13 November 2009 through 19 November 2009, Lake Buena Vista, FL ; Volume 13 , 2010 , Pages 71-76 ; 9780791843864 (ISBN) Azadi, M ; Zahedi, F ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2010
    In the present paper, fatigue analysis of an antiroll bar is investigated and compared for several criterions by using the finite element method (FEM) and also the experimental results. The validity of some of commonly used criterions in estimating fatigue life including Mcdiarmid and Von Misses theories is examined in which the inputs are considered as periodic data. For random inputs, some other methods are proposed including new suggestions and also a new criterion are established for estimation of fatigue life based on Mcdiarmid and Von Misses criterions. Prediction capability of mentioned new criterion which is evaluated for the antiroll bar, shows better results than other methods... 

    Effect of Grinding and Shot Peening on Fatigue Life of Welded Joints

    , M.Sc. Thesis Sharif University of Technology Hassani Gangaraj, Mostafa (Author) ; Farrahi, Gholamhossein (Advisor)
    Metallurgical initial defects, stress concentration due to change in geometry and induced tensile residual stress during welding create an extraordinary high possibility of fatigue cracks nucleation and propagation in the weld toe region. Despite this, the ever increasing use of welding in offshore, aerospace and automotive industries, as the most applied mechanical joint, has occasioned a very extensive attempt to achieve an in-depth understanding of failure mechanisms and fatigue life improvement techniques of welded joints. Generally, these techniques could be classified into two broad categories. The first consists of methods that modify the geometry and the other is related to the... 

    Rolling Contact Fatigue under Influence of Residual Stresses

    , M.Sc. Thesis Sharif University of Technology Masoudi Nejad, Reza (Author) ; Farahi, Gholamhossin (Advisor)
    Rolling contact fatigue (RCF) phenomena is important in reducing the fatigue life and increasing the cost of maintenance. Accurate prediction of crack growth on wheels and the influence of residual stresses by FEM modeling can affect the maintenance planning. Therefore, investigation of rolling contact fatigue and its effect on rolling members life seem necessary. The first step to solve a rolling contact fatigue problem is the residual stress determination. In this research, wheel/rail contact is assumed. A bandage wheel with accurate geometry using finite element method is studied. For this purpose, a 3D elastic-plastic finite element model in ANSYS is conducted using model. The... 

    Analysis of Fatigue Cracks in Frame 360 Section 41 of B747

    , M.Sc. Thesis Sharif University of Technology Mashayekhi, Rouhollah (Author) ; Adibnazari, Saeid (Advisor)
    In this project, the structure of an aircraft and its sensitive areas has been studied for fatigue damages and then the design philosophies have been analyzed. Subsequently, relevant analysis and calculations have been conducted on a critically important part of the airframe (due to its location), which has suffered fatigue due to the age of the aircraft. This part belongs to the airframe of a Boeing 747, known as frame 360 in section 41 of the body of the aircraft, in which the numerous flight cycles have led to the creation and propagation of fatigue crack.
    In the first stage of this project, the remaining life time of the frame has been estimated using theoretical relationships. In... 

    Determination of Fatigue Behavior of Nanostructure of Severe Shot-Peened A356.0

    , M.Sc. Thesis Sharif University of Technology Rahmani, Edris (Author) ; Farrahi, Gholamhossein (Advisor)
    In this study a layer with compressive residual stress was created by severe shot peening and hence surface grains was changed to nanostructure. Fatigue life will be increased as a result of compressive residual stress. Surface roughness increase, is one of the disadvantages of severe shot-peening process. Re-shot-peening with the smaller shots and lower intensity is proposed for reducing surface roughness. Numerical simulation as a powerful method, used to investigate the effects of shot-peening parameters on the residual stress distribution, surface roughness and grain size. Obtained results indicate that more energy in process can improve residual stress distribution and grain size unlike... 

    Experimental Investigation of the Effect of Almen Intensity and Coverage on Microstructure and Fatigue Behavior of High Carbon Steel Subjected to Severe Shot Peening

    , M.Sc. Thesis Sharif University of Technology Maleki, Erfan (Author) ; Farrahi, Gholamhossein (Advisor)
    In most cases, material failures occur on their surfaces, such as fatigue fracture, wear and friction, fretting fatigue and corrosion, so surface modification is one of the most effective techniques to improve the strength of materials. Correction of near surface grain size to nanoscale is one of the effective ways to improve the strength, fatigue life, toughness and etc. With increasing evidences of novel properties in nanostructured materials, it is reasonable to propose to achieve surface modification by the generation of nanostructured surface layer so that the overall properties and behaviors of the material are significantly improved.By means of surface severe plastic deformation, the... 

    Simulation of Trench Effect on Fatigue life of SCR near Touch Down Zone

    , M.Sc. Thesis Sharif University of Technology Askarzadeh, Alireza (Author) ; Raie, Mohammad (Advisor)
    Gas and oil reservoirs on Caspian Sea made Engineers to choose suitable riser for conveying oil and gas. Steel catenary riser is one of the best choices for deep and ultra-deep water. Although these kinds of risers show very good resistance on buckling but cyclic loads made them to fail by fatigue damage. Two sensitive points regarding to fatigue damage are Hang off point and touch down point. Fatigue damage on TDP is related to soil properties. Because of the cyclic movement of the riser a trench would shape on seabed. In this research, based on Finite element analysis, the effect of trench on fatigue life of SCR would be analyzed  

    Fatigue life estimation of spot welds using a crack propagation-based method with consideration of residual stresses effect

    , Article Materials Science and Engineering A ; Volume 527, Issue 23 , 2010 , Pages 6359-6363 ; 09215093 (ISSN) Mirsalehi, S. E ; Kokabi, A. H ; Sharif University of Technology
    In the present paper, a crack propagation-based fatigue life estimation approach has been proposed for resistance spot welds. The presented approach also takes into account the effect of welding residual stresses. It can provide an accurate and systematic prediction of the life of spot weld joints with various dimensions and shapes. Experimental verification tests confirmed the validity of the calculations and good agreement was found between the theoretical predictions and experimental data  

    A Study of Fatigue in Binders Containing Warm Mix Asphalt Additives

    , M.Sc. Thesis Sharif University of Technology Mohajerani, Nicoo Sadat (Author) ; Tabatabaee, Nader (Advisor)
    Modified binders have received a lot of attention in recent years because of their enhanced performance. Modification of binders, however, generally requires higher production temperatures that lead to increased energy consumption and more greenhouse gases. Warm Mix Asphalt additives such as Sasobit are applied to decrease the production temperatures. The objective of this study is to investigate the fatigue characteristics of modified binders utilized in WMA; therefore the influence of Sasobit as well as short term aging on fatigue characteristics of neat and modified binders were studied. The experimental design included one base binder and four modified binders. The base binder is a... 

    New approach for fatigue life prediction of composite plates using micromechanical bridging model

    , Article Journal of Composite Materials ; Volume 49, Issue 3 , February , 2015 , Pages 309-319 ; 00219983 (ISSN) Adibnazari, S ; Farsadi, M ; Koochi, A ; Khorashadizadeh, S. N ; Sharif University of Technology
    SAGE Publications Ltd  2015
    The use of micromechanical models to study composite material's behavior leads to save time and cost. In this paper, bridging micromechanical models have been used in order to observe the behavior of unidirectional laminate composite under fatigue loading. In order to study the fatigue behavior, stiffness degradation has been studied as well as the strength degradation and a driftnet model has been proposed for each of them. The strength degradation has only been studied for the unidirectional fiber, while the stiffness degradation has been studied for the fibers with different fiber angle. The results are compared with macro-mechanical models and other methods in literature  

    A Progressive Multiscale Model to Predict the Fatigue life of Laminated Composite Reinforced with Nanoparticles

    , Ph.D. Dissertation Sharif University of Technology Toozandehjani, Hossein (Author) ; Hoseini Kordkhili, Ali (Advisor)
    The increasing growth of composite materials in various industries and the use of these materials in the production of the main structures, recognized study and simulation of accurate behavior of these materials at different scales. On the other hand, the appearance of Nano-scale materials with amazing physical and mechanical properties and the use of these nanoparticles as reinforcement in the structure of polymer composites, further highlights the importance of simulating the behavior of polymer nanoparticles at different scales. One of the issues that is considered in various industries, especially in the airspace industry, is the phenomenon of fatigue. The complexity of the fatigue... 

    Fatigue life estimation of bolt clamped and interference fitted-bolt clamped double shear lap joints using multiaxial fatigue criteria

    , Article Materials and Design ; Volume 43 , 2013 , Pages 327-336 ; 02641275 (ISSN) Abazadeh, B ; Chakherlou, T. N ; Farrahi, G. H ; Alderliesten, R. C ; Sharif University of Technology
    In this paper seven different multiaxial fatigue criteria based on stress, strain and energy were employed to estimate the fatigue lives of double shear lap joint specimens of aluminum 2024-T3 with bolt clamped and interference fitted-bolt clamped fastener holes. Detailed finite element (FE) simulations were conducted to obtain the stress and strain distributions in the joint to be used to as basic data in estimating the fatigue lives using multiaxial fatigue criteria. The estimated lives were compared with available experimental fatigue test results to investigate the capability of the criteria in predicting the fatigue lives. The results showed that the accuracy of life estimation for any... 

    The effect of shot peening on fatigue life of welded tubular joint in offshore structure

    , Article Materials and Design ; Volume 36 , 2012 , Pages 250-257 ; 02641275 (ISSN) Habibi, N ; H-Gangaraj, S. M ; Farrahi, G. H ; Majzoobi, G. H ; Mahmoudi, A. H ; Daghigh, M ; Yari, A ; Moridi, A ; Sharif University of Technology
    An offshore structure is exposed to environmental loading and cyclic stress variations throughout its life. This would result in the possibility of fatigue cracking in its members. Cracks in these structures usually initiate around welded areas, then grow progressively from the heat-affected zone to base metal through the thickness of the tubular members. Therefore, fatigue life improvement of offshore structures is of great importance. In this paper, structural analysis of an offshore platform is carried out and the critical joint is specified. The welding process is simulated and the residual stresses due to the welding are determined. Experimental residual stress measurement is carried... 

    Develop Methods of Life Wheel Locomotive Using Finite Element Method

    , M.Sc. Thesis Sharif University of Technology Prhami, Esmat (Author) ; Adib Nazari, Saeed (Advisor)
    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... 

    Application of artificial neural network to estimate the fatigue life of shot peened Ti-6Al-4V ELI alloy

    , Article Fatigue of Materials: Advances and Emergences in Understanding, Held During Materials Science and Technology 2010, MS and T'10, 17 October 2010 through 21 October 2010 ; 2010 , Pages 411-417 ; 9780470943182 (ISBN) Yavari, S. A ; Saeidi, N ; Maddah Hosseini, S. H ; Sharif University of Technology
    An artificial neural network to predict the fatigue life, residual stress and Almen intensity of shot peened alloy Ti6Al4V ELI was developed. To minimize the prediction error, a feed forward model was used and the neural network was trained with back-propagation learning Algorithm. The results of this investigation show that a neural network with one hidden layer and five neurons in this layer will give the best performance. With this structure the network approaches to the desired error in the least time. Furthermore, it was concluded that there is a good agreement between the experimental data, the predicted values and the well-trained neural network. Therefore, the neural network has a... 

    Prediction by Genetic Algorithm and measurement by center hole drilling of residual stresses of MAG weldment

    , Article Advanced Materials Research, 2 November 2008 through 5 November 2008 ; Volume 83-86 , 2010 , Pages 738-745 ; 10226680 (ISSN) ; 0878492976 (ISBN); 9780878492978 (ISBN) Farrahi, G. H ; Majzoobi, G. H ; Fadaee, A ; Sharif University of Technology
    In the present work, specimens were cut out from St-37 plates with 19 mm thickness. The thickness of plates was reduced to 12.5 mm by milling and grinding operations. Then a standard V-shaped fillet was made on one edge of the plates. Two plates were butt-welded by standard metal arc gas (MAG) welding process. Residual stresses induced by welding were measured on 20 specimens by centre hole drilling. Load controlled axial fatigue tests were carried out to determine the fatigue life of specimens. Crack growth rates were obtained from experiment. Fractography of specimens was performed. Genetic Algorithm (GA) was employed for prediction of residual stress value in weldments using the crack... 

    Residual stresses in autofrettaged vessel made of functionally graded material

    , Article Engineering Structures ; Volume 31, Issue 12 , 2009 , Pages 2930-2935 ; 01410296 (ISSN) Haghpanah Jahromi, B ; Farrahi, G. H ; Maleki, M ; Nayeb Hashemi, H ; Vaziri, A ; Sharif University of Technology
    We used an extension of the Variable Material Property method for materials with varying elastic and plastic properties to evaluate the residual stresses in an autofrettaged thick vessel made of functionally graded metal-ceramic composite. It is shown that the reinforcement of the metal vessel by ceramic particles, with an increasing ceramic volume fraction from inner to outer radius, increases the magnitude of compressive residual stresses at the inner section of an autofrettaged vessel and thus, could lead to better fatigue life and load-carrying capacity of the vessel. A parametric study is carried out to highlight the role of ceramic particle strength and spatial distribution, as well as... 

    Experimental investigation and artificial neural network modeling of warm galvanization and hardened chromium coatings thickness effects on fatigue life of AISI 1045 carbon steel

    , Article Journal of Failure Analysis and Prevention ; Volume 17, Issue 6 , 2017 , Pages 1276-1287 ; 15477029 (ISSN) Kashyzadeh, K. R ; Maleki, E ; Sharif University of Technology
    In the present study, the main purpose is investigation of the coatings thickness effect on the fatigue life of AISI 1045 steel. Herein, two different coatings of warm galvanization and hardened chromium have been used on the specimens. Fatigue tests were performed on specimens with different coating thicknesses of 13 and 19 µm. In the high-cycle level, S–N curves are extracted with 13 points for each sample. The results show that the galvanized coating is the most appropriate coating with low thickness, but with significant increasing of coating thickness, the best choice is hardened chromium coating. However, artificial neural network (ANN) has been used as an efficient approach instead of...