Sharif Digital Repository

Fatigue is one of the most common failure modes that reduce the structural integrity of asphalt pavements. Dynamic tests are used as fatigue performance indicators for asphalt mixture. However, these tests are expensive and require special equipment and set up. At this research, the main goal is to develop a fuzzy model which is more efficient than the existing regression model for prediction of the fatigue life. A database from the available data from various research was compiled. For each model, a comparison between Fuzzy and regression output by actual outputs was done and it was seen that the fuzzy modeling can predict fatigue life very closely. Finally, the required software for this... 

The ever increasing usage of modified binders in road construction requires that the effect of different modifiers on the performance characteristics of the asphalt binder be determined through laboratory testing. The current Superpave protocol for performance grading asphalt binders has proven to be insufficient to properly characterize modified binders, thus researchers have searched for other testing methods to complement or possibly replace some of the Superpave tests. Most notable are the time sweep test for fatigue resistance, the multiple stress creep and recovery test (MSCR) for rutting resistance and the direct tension test (DTT) for low temperature cracking characteristics. In the... 

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... 

The goal of this research is design and manufacturing of a device for fatigue test and 3D crack propagation in spur gear roots. Clearly it should be able to test gear in oscillated bending load and control the amplitude and period of loading. Designed setup in this project using a electro hydraulic actuator can do it up to 50 KN and 10 Hz in amplitude and frequency and a PLC controls it during the test time. System can load gears symmetric or anti symmetric and simulate the effect of shaft misalignments, bearing damage and gear production tolerances on the gear loading. System completely designed, built and tested during this project and using experimental data, its performance was... 

Many airlines operate different fleets under different service conditions. These aircraft fleets need to be maintained in service. Safety, reliability and economic reasons motivate manufacturers, airlines and airworthiness authorities to investigate about different approaches to aircraft maintenance. At first, corrective maintenance which was developed for other industries was used by the aircraft industry but due to increasing complexity of aircrafts and their systems the industry started using time based maintenance. After years of operation and fleet experience, this industry started developing a program of its own i.e., MSG-1, MSG-2 and MSG-3. These maintenance programs have been evolved... 

Hydrated lime has been used as an anti-stripping agent with acceptable performance. Numorous studies have been conducted to evaluate hydrated lime as an anti-stripping agent, however effect of hydrated lime on performance properties of asphalt mixture has not been fully addressed. In the present study, the effect of hydrated lime was investigated. In this study, three methods of adding hydrated lime were evaluated. These methods consist of a) adding dry hydrated lime to dry aggregates, b) adding hydrated lime to the binder to form mastic, and c) adding slurry lime to dry aggregates.
More uniform distribution of hydrated lime on aggregate surface in the slurry method improved performance... 

The introduction of multi phase steels in recent years resulted in a considerable increase in development of some industries such as automobiles. By inducing soft and hard phases together, these steels could bring better mechanical properties than classical ones. Recent studies on 4340 ferritic- bainitic and ferritic- martensitic dual phase steels, indicate that 34 volume percent ferrite with hard phase, has the best combination of strength, toughness and fatigue properties. In present research, by proper heat treatment on a 4340 steel, it is tried to prepare specimens ferritic- bainitic- martensitic triple phase steels with 34 volume percent of ferrite and different percents of martensite.... 

Recently, mechanical properties of advanced materials such as nanostructured and ultra-fine materials and especially nanocomposites were studied by lots of researcher. In this study, fatigue behavior of Al-SiC nanocomposites is observed. Ultra-fine grains Al matrix nanocomposites reinforced with 50 nm diameter SiC nanoparticles were produced by milling and hot extrusion. For this purpose, pure aluminum powder was mixed with 2, 4 and 6 Vol. % of SiC nanoparticles and then milled by planetary mill. The milled powder then were degased in an Argon atmosphere furnace, cold pressed and then hot extruded. Closed die-hot forging was used with about 18.8% reduction in cross section in order to... 

Transient liquid phase (TLP) bonding of Al2024-T6 alloy, using gallium interlayer, has been investigated. Bonding experiments were carried out using two basic methods; Conventional and Temperature gradient TLP bonding. Optimum values of isothermal solidification temperature and time, pressure, surface roughness, heating rate and homogenizing conditions were determined in conventional TLP bonding experiments. Aluminum oxide layer was not removed before TLP bonding to prevent gallium attack.this layer is crashed during bonding. Al2O3 particles are not soluble in the liquid and are pushed into liquid by solidification front progression. These particles are accumulated in grain boundaries and in... 

Welded joints are the most used joints in industrial applications. Fatigue analysis of welded joints is of great importance. Residual stresses produced during welding process play an important role in fatigue failure of welded joints. Residual stresses’ effect on fatigue life of the structures is similar to mean stresses and can be accounted for like mean stress effect. However residual stresses are not constant and do change in service. In this thesis, welding process has been modeled using FE software ABAQUS in order to predict residual stress distribution due to welding. The predictions show good agreement with measurements especially for longitudinal residual stresses. Then cyclic load... 

In the research transient liquid phase bonding of AL6061-SiC composite was performed using copper as interlayer. The joining praocess was performed in various tetemperatures (560c and 580c and 600c) And times (6 and 8 hours). Optimum Joining condition was determined by using optical and of the joint, micro hardness test was performed from the bonding zone to the bulk of the base composite. The fatigue endurance limit of Al6061-SiC composite was determined by several fatigue tests and TLP bonded samples were loaded under achieved endurance limit stress. Finally fatigue fracture surface of both base composite and TLP bonded samples were studied by using of scanning electronic microscope  

In order to reduce stress concentration, crankshaft is designed with a fillet radius in the corner of pin to web contact. Fatigue fracture under bending load initiated in fillet region is known as the main failure mechanism of crankshaft, so fillet rolling process is used to increase the bending fatigue resistance of the crankshaft. This process induces compressive residual stress under fillet surface in order to retard the fatigue initiation and to slow fatigue crack propagation. At first, influence of fillet rolling process on bending fatigue resistance of a ductile cast iron crankshaft is investigated. The residual stress distribution under the crankshaft fillet induced by this process... 

Concrete as a heterogeneous, quasibrittle and practical material has always been a challenging material for modeling. Although numerous models have been proposed since now, many of them have some deficits. Microplane is a multiscale model which introduces some micro-planes as interaction planes between concete and aggregates. To generate concrete behavior, stress-strain relations are established on these micro-planes. In the present study, two prominent microplane models, M2 and M4, has been used in 2D and 3D Finite element framework. M2 model has been applied and developed to produce FRC behavior for uniaxial tension and compression under static and cyclic loading. To better optimize M2... 

A large number of bridges in Iran are deteriorating under long and heavy traffic loadings, while getting closer to the end of their design life time. Therefore, many of them have been exhibiting various problems such as excessive vibration or large deflection under the normal service loadings. So, mitigating traffic-induced bridge vibration and damages is necessary to extend their efficient period of serviceability. On the other hand, application of active and passive control devices in structural retrofitting have absorbed the attention of many engineers and researchers. In this work, the performance of an active control system made of piezoelectric actuators is investigated in reducing the... 

By increasing growth of the composite materials and achieving nano-materials and understanding the unique and specific properties, using materials for production with ideal specifications widely spread. So far nano-materials were used for strengthening materials and producing composite and then nano composites were produced.
Regarding to widespread use of polymer matrix composites, nano particles for reinforcement polymers were used. Thus desirable and unexpected properties were observed in polymer matrix nano composites.
In this project, due to the unique properties of carbon nano tubes such as high strength and modulus, low density, and high ratio of length to diameter. They are... 

The purpose of the present study was to investigate the effects of friction stir welding parameters on the fatigue life of friction stir welded sheets of Aluminum 7075 alloy. The welding process was carried out under three different rotational speeds and three different welding speeds and specimens were extracted transversely to be used for rotating-bending fatigue tests. Optical microscope and SEM images were used respectively for studying the microstructure of the weld zone and fractography. It was the indicated that an increase in the welding speed or a decrease in the rotational speed will result in an increase in the fatigue life  

In this thesis failure analysis of a critical part in a landing gear of a commercial aircraft was conducted.Fatigue phenomenon was determined as the reason for the failure and fracture of the mentionedcomponent. Fractography investigation of the fracture surface and charasteristicswas conducted.Scanning Electron Microscope was utilized for the study of the fracture surface. In the fracture surface, fatigue striations were observed. An experimental model of the crack growth is presented by using the fracture surface characteristics. By counting the fatigue striations and measuring their distance betwwn them on the fracture surface, the rate of the crack growth and crack growth life were... 

Production of nanocrystalline (under 100nm) or submicron materials (100-1000nm), has been created to one of the most important problems in engineering. A well-known method to create Ultra-Fined Grains (UFG) is imposing high strains to metals in order to break the structure. Among lots of ways forproducing UFG metals, Equal Channel Angular Pressing (ECAP) is one of the most famous and common ways. On the other hand, Shot Peening has been being used for a long time to improve mechanical properties of metals by introducing nanocrystalline layer at the surface of specimen. The aim of the work, is investigation of the effect of combination of ECAP and Shot Peening on High Cycle Fatigue of 6082... 

All over the world availability of electrical power is an important matter. Electrical power is a basic requirement in each country so with increasing the demand, supply system should be adjusted.Compressed Air Energy System (CAES) stores the excessive produced energy as compressed air and will inject it to gas turbine to produce energy in peak load hours.This project aim is modeling and analyzing of CAES considering reliability. In this project some of failure mechanisms have been identified and modeled and then the performance effect on system failure have been surveyed. This project innovation is incorporating operational models with reliability to determine the best performance for... 

Today, everyone is looking for ways to achieve comfort and safety in the workplace and, in so doing, appeals to various sciences. One of these sciences is "ergonomics", which examines the human relationship with the work. One of the areas that could be of great interest is the driving ergonomics. After all nowadays, many people use personal vehicles. The increasing use of personal vehicles has increased the number of accidents and deaths. In recent decades, many researches have been done in the field of driver fatigue detection. To avoid road accidents, researchers have focused on monitoring driver and vehicle behavior and tried to analyse status of the driver. Using computer vision, we can...