Sharif Digital Repository

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... 

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... 

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... 

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... 

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... 

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... 

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  

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... 

In recent years, investigation of mechanical properties of micro- and nano-structure materials, and peculiarly nanocomposites have been attracted a wide variety of researches. In this regard, friction-stir-processed (FSPed) metal matrix nanocomposites have been considered an important case with appropriate mechanical properties especially for fabrication of ultra-fine grained Al alloys and Al-matrix nanocomposites. In this research, Al matrix hybrid nanocomposites were fabricated via multi passes-friction stir processing (FSP) of Al-Mg alloy (AA5052) with different amounts (~2 and 3 vol%) of pre-placed TiO2 (30 nm) particles nanoparticles. It was revealed that employing of cumulative FSP up... 

Aging Aircraft with life extension, Conversion or replacing them with new aircrafts are of the decisions in front of airliners after their retirement. Decision making for repairing aircraft to increase its life is depended upon various parameters like its cost and reliability. The thesis evaluated the reliability of the structure of an aircraft before and after life extension. For this purpose, using the statistical data, the predominant failure modes are studied and based on these failure modes the border between fracture and health of the structure which is called limit state function is defined. After this using first order reliability method (FORM), the probability of the failures is... 

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... 

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... 

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... 

In presence of epistemic and aleatoric uncertainties of the structural systems, it is better to investigate the events in probabilistic manner. Bayesian inference is an approach that can update the current knowledge of probabilities with new evidence. The main objective of this study was evaluating the advanteges of using Bayesian approach in two main area of structural health monitoring, model calibration and decision making. In each of these two areas, one case study was conducted. First case study was prediction of crack growth life in a pre-cracked aluminum plate and the results showed that using Bayesian approach in calibration of crack growth model and measurement model of health... 

After World War II, steel bearings containing copper element have been developed by the Navy of the United States of America with the HSLA-100 brand. Since 1890 and in order to manufacture tanks and tools for the body of navy equipment, the steel HY 80 was used instead of HSLA-100. Because of the high carbon content, the welding properties of the HY 80 are low. Furthermore, increasing of hardness and decreasing of toughness in the heat-affected zone generated during the welding process lead to susceptibility of this alloy to hydrogen cracking and brittle fracture. Therefore, in order to minimize the cost of welding, low-alloy high strength steel (HSLA) is used which contain copper. Reducing... 

Recycling of asphalt pavements has received much attention in recent years for its environmental and economical benefits. Because of increase in costs of raw materials and energy carriers, reuse of a high portion of reclaimed asphalt pavements (RAP) eliminates an enormous amount of waste and reduces the cost of hot-mix asphalt (HMA) mixtures. There are some problems in high-RAP mixtures such as high content of fine aggregate and filler, low temperature cracking potential because of higher stiffness of RAP binder, and low mixture workability. In this research, RAP fractionation was used to sort out and eliminate fine aggregate and filler. An organic-based softening agent was used to improve... 

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  

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...