Sharif Digital Repository

Isothermal solidification is a key feature of transient liquid phase bonding which prevents the formation of deleterious intermetallic phases in the joint centerline and results in bonds with improved mechanical performance. This paper discusses the metallurgical characteristics and mechanical properties of an as-cast IN718 superalloy bonded by diffusion-induced isothermal solidification of Ni-7Cr-4.5Si-3.2B-3Fe (wt%) filler metal. After transient liquid phase bonding of as-cast IN718 at 1000 C for 60 min, a bond exhibiting a solid solution microstructure with joint efficiency of 72% in terms of shear strength was obtained. The joining process was effectively able to prevent the formation of... 

The microstructural evolutions and mechanical properties of vanadium microalloyed steel (30MSV6) during precipitation hardening were studied. The effects of aging temperature and cooling rate on mechanical strength (yield strength and ultimate tensile strength) were similar. Increasing aging temperature or cooling rate firstly increased the mechanical strength of specimens up to their maximum values, which then decreased with further increase in aging temperature or cooling rate. Microstructural evolutions revealed that cooling rate had significant effects on the pearlite interlamellar spacing and size of pre-eutectoid ferrite. Unlike the effect of austenitizing temperature, the pearlite... 

Activities conducted in this study can be divided into two general sections: synthesis and analysis and identifies the properties. A geopolymeric cement production process includes two steps of thermal activation and alkaline activation. Geopolymers are cementitious materials synthesized by a polycondensation reaction between an aluminate and silicate. The geopolymeric structures of the products were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). XRD results showed that there are no significant differences between the XRD patterns of geopolymers and metakaolin. The structure of the geopolymer is typically... 

Let G be a graph. A minimal coloring of G is a coloring which has the smallest possible sum among all proper colorings of G, using natural numbers. The vertex-strength of G, denoted by s(G), is the minimum number of colors which is necessary to obtain a minimal coloring. In this note we study these concepts, and define a new concept called the edge-strength of G, denoted by s′(G). We prove the celebrated Brooks' theorem for χ(G) replaced by s(G) and we also prove the following upper bound for s(G): s(G) ≤ ⌈col(G) + Δ(G)/2⌉, where col(G) is an invariant based on linear orderings of the vertices. Also, it is proved that s′(G) lies between Δ(G) and Δ(G) + 1, as for χ′(G), but it may be not... 

This paper presents results of an experimental study to evaluate a new retrofit technique for strengthening shear deficient short concrete beams and columns. In this technique a mortar jacket reinforced with expanded steel meshes is used for retrofitting. Twelve short reinforced concrete specimens, including eight retrofitted ones, were tested. Six specimens were tested under a constant compressive axial force of 15% of column axial load capacity based on original concrete gross section, Ag, and the concrete compressive strength, fc′. Main variables were the spacing of ties in original specimens and the volume fraction of expanded metal in jackets. Original specimens failed before reaching... 

The main purpose of this paper is to assess the impact of the geometry and size of the aggregate, as well as the drying temperature on the compressive strength of the ordinary concrete. To this end, two aggregates with sharp and round corners were prepared in three different aggregate sizes. After preparing concrete samples, the drying operations were carried out in the vicinity of room temperature, cold wind, and hot wind. Next, the linear relationship between the concrete strength and the studied parameters was estimated using Multiple Linear Regression (MLR) method. Finally, the Taguchi Sensitivity Analysis (TSA) and Decision Tree Analysis (DTA) were applied in order to determine the... 

This paper focuses on the performance evaluation of several concrete models in reinforced concrete (RC) structures subjected to seismic loading. Despite many studies conducted on implementing different characteristics of concrete in constitutive models, there is an essential need for investigating the ability of these models in predicting the behavior of structures in seismic applications. In this paper, several developed plasticity-based constitutive models with the combination of fracture and continuum damage models are investigated for application in seismic loading conditions. Damage-based isotropic and anisotropic models and smeared cracking approach have been applied as complementary... 

In this work, the production and properties of Al 6061/SiC composites, made using a squeeze casting method, were investigated. SiC preforms were manufactured by mixing SiC powder, having a 16 and 22 pm particle size, with colloidal silica as a binder. 6061 Al melt was squeeze cast into the pores of the SiC preform to manufacture a DRA composite containing 30v/o reinforcement. The aging behavior, tensile properties and fracture mechanism of the cast material were studied. The results show that higher hardness, yield strength, tensile strength and Young's modulus can be obtained by the addition of SiC particles to 6061 Al alloy, whereas tensile elongation decreases. This is mainly caused by a... 

Development and construction of hydraulic structures like dams, the concrete durability in these kinds of structures has gained special attention. One of the crucial factor in concrete technology is it durability in hydraulic structures. Concrete has to resist against abrasion due to the crash of particles carried by water. To enhance the abrasion resistance of concrete different methods have been offered. In the present stud, the role of water-cement ratio in compressive and abrasion strength of nano silica concrete was investigated. The constructed concrete samples with 3% nano silica and water-cement ratios of 0.33, 0.36, 0.40, 0.44 and 0.50 were experimented. Other design features... 

The economic growth or asset of country basically depends on the amount of goods which can be produced by the combination of land, capital, manpower and natural resources. Therefore, changing natural resources into production is the new process of economical development, and technology is the brain of this type of transformational activities. This tool not only makes the changing operation possible but also, in the world economy makes the survival and growth foundation of business enterprises. The Development of today's technology has caused some change in the productivity and costs, and because of this, the global and national structure in the areas of production, business and employment... 

This paper describes the influence of a fractional melting process on the reduction of interdendritic phases, which in turn have an impact on the tensile strength of ZA-27 alloys. The procedure consists of compressing a semi-solid specimen through a porous grinding disc, resulting on coarsening of the dendritic phase, reduction of the microporosity and homogenization of the alloy. © 2002 Elsevier Science B.V. All rights reserved  

In this paper, shear strengthening of RC beams by confining shear critical region is experimentally and theoretically investigated. Confinement is implemented using vertical post-compression force in the shear critical region with steel plate, bolts and angles. The loading tests include (1) loading beams to first major shear crack, then shear strengthening, and reloading to complete failure, (2) strengthening beams from beginning and loading to complete failure, and (3) loading unrepaired beam to complete failure. lnt1uences of concrete strength, shear span length, longitudinal tensile reinforcement, level of post-tensioning, presence of shear reinforcement, use of continuous plates, and... 

Self-compacting concrete (SCC) is a highly-workable concrete that without any vibration or impact and under its own weight fills the formwork, and it also passes easily through small spaces between rebars. In this paper, the effect of steel fibers on rheological properties, compressive strength, splitting tensile strength, flexural strength, and flexural toughness of SCC specimens, using four different steel fiber volume fractions (0.5%, 1%, 1.5%, and 2%), were investigated. Two mix designs with strengths of 40 MPa (medium strength) and 60 MPa (high strength) were considered. Rheological properties were determined through slump flow time and diameter, L-box, and V-funnel flow time tests.... 

This paper investigates the behaviour of C-shaped and L-shaped angle shear connectors embedded in solid concrete slabs. An effective finite element model is proposed to simulate the push out tests of these shear connectors that encompass nonlinear material behaviour, large displacement and damage plasticity. The finite element models are validated against test results. Parametric studies using this nonlinear model are performed to investigate the variations in concrete strength and connector dimensions. The finite element analyses also confirm the test results that increasing the length of shear connector increases their shear strength proportionately. It is observed that the maximum stress... 

This paper presents results of an experimental study to evaluate a retrofit technique for strengthening shear deficient short concrete columns. In this technique a ferrocement jacket reinforced with expanded steel meshes is used for retrofitting. Six short concrete columns, including four strengthened specimens, were tested. Specimens were under a constant compressive axial force of 15% of column axial load capacity based on original concrete gross, A g, and the concrete compressive strength, fc′. Main variables were the spacing of ties in original specimens and the volume fraction of expanded metal in jackets. Original specimens failed before reaching their nominal calculated flexural... 

The aim of this research is bonding of three-layered St/AZ31/St composite by roll-bonding process. The roll-bonding process was performed at three preheating temperatures, 340, 400 and 450°C, with thickness reduction of 30 to 68% and different thicknesses of intermediate layer (AZ31). In order to improve the bonding strength, the as-rolled specimens were annealed at constant temperature of 375°C. For evaluation of bond strength and investigating the formation of a diffusion layer, the results of peel test and microscopic images were studied. Tensile specimens were prepared along the rolling direction to measure the mechanical properties of the composite. The results showed that by increasing... 

Surfaces of cast 1100 aluminum were treated by multi-pass friction stir processing (MP-FSP), which is a solid-state microstructural modification technique using frictional heat and stirring action. An improvement in the mechanical properties was accomplished due to the microstructural modification and reduction of porosities. The yield strengths of the MP-FSPed specimens were significantly increased to about 1.4 times versus that of the base metal. The elongation of MP-FSP sample is about 30% higher than that of the base metal. Also the ultimate tensile strength and hardness of MP-FSPed specimens are improved. Moreover the effect of tool rotation rate and tool travel speed on the mechanical... 

During the past decades, development of reinforcing materials caused a revolution in the structure of high strength and high performance cement-based concrete. Among the most important and exciting reinforcing materials, Steel Fiber (SF) becomes a widely used in the recent years. The main reason for addition of SF is to enhance the toughness and tensile strength and limit development and propagation of cracks and deformation characteristics of the SF blended concrete. Basically this technique of strengthening the concrete structures considerably modifies the physical and mechanical properties of plain cement-based concrete which is brittle in nature with low flexural and tensile strength... 

Mixture of sandy soil and bentonite clay can be used to seal the sanitary landfills and prevent the spread of leachate. Over time, this mixture may be subjected to different landfill contaminants, including acidic pollutants and shear strength variations. The objective of this research was to study the effects of sulphuric acid pollutant with pH values of 7, 3 and 1 on the shear behaviour and strength of clean sand and sand mixed with bentonite clay using common consolidated undrained triaxial tests. The tests results showed that the presence of acid in the soil pore water changes the shear behaviour pattern of the soil. Acid pollutant decreases the clean sand shear strength. In... 

The aim of this study was to evaluate the influence of bonding temperature and holding time on the metallurgical and mechanical properties for weld joints of 5 mm aluminum to copper using Sn interlayer. The bonding temperature varied from 500 to 600 °C whilst the holding time varied from 30 to 120 min under 8 MPa uniaxial load in 1 × 10−4 torr vacuum. The microstructure analysis, phase analysis and distribution of elements in the interface were performed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and element map analysis. It was found that diffusion welding parameters had a significant effect on shear strength. The attained data of tensile strength tests showed...