Sharif Digital Repository

Effects of cold rolling on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti-Cr maraging steels were studied. To investigate the microstructure and mechanical properties, optical microscopy, scanning electron microscopy, X-ray diffraction, tensile test, and hardness test were used. The results show that the solution-annealing treatment in the cold-rolled steel redounds to the formation of submicrocrystalline Fe2 (Mo, Ti) Laves phase particles, which are stable at high temperatures. These secondary Laves phase particles prevent from recrystallization at high temperatures and correspond to semi-brittle fracture in the subsequent aging treatment  

Two different types of welds, Metal Inert Gas (MIG) and Friction Stir Welding (FSW), have been used to weld aluminum alloy 5083. The microstructure of the welds, including the nugget zone and heat affected zone, has been compared in these two methods using optical microscopy. The mechanical properties of the weld have been also investigated using the hardness and tensile tests. The results show that both the methods could successfully be used to weld such alloy. The strength of the joints is comparable to the strength of the base metal in both cases. However, FSWed samples have shown higher strength in comparison to the MIG samples. The results also show that the extension of the heat... 

In this study, static strain aging behaviour of cold rolled steel strips was considered with emphasis on the distribution of residual hydrostatic stress developed during temper rolling. In order to assess residual stress distribution produced by the temper rolling, a three-dimensional model was first employed. Then, samples were rolled at a reduction of 4% under single and double pass rolling programmes and the kinetics of static strain aging phenomenon as well as the required activation energies were then evaluated using hardness and tensile tests on the deformed samples. Considering the predicted residual hydrostatic stress distribution, it was found that tensile hydrostatic stresses... 

Hot tensile properties of as cast NiTi and NiTiCu shape memory alloys were investigated by hot tensile test at temperature range of 700-1100°C using the strain rate of 0.1s-1. The NiTi alloy exhibited a maximum hot ductility at temperature range of 750-1000°C, while the NiTiCu alloy showed it at temperature range of 800-1000°C. It was found that at temperatures less than 750°C, diffusion-assisted deformation mechanism was inactive leading to semi-brittle type of failure and limited ductility in both alloys. Also it was found that at temperature range of 800-1000°C, dynamic recrystallization is dominant leading to high ductility. Likewise, the fracture surface of the specimens presenting the... 

In this study, the plastic instabilities associated with the Portevin-Le Chatelier (PLC) and their effects on the mechanical properties and the fracture surfaces have been investigated for AA 5083. Tensile tests were performed at various temperatures and strain rates in order to do so. Then, serrated and smooth yielding domains were determined in Ln ε̇-1/T diagram. The stress-strain curves related to the serrated domain show the values of flow stress decreases by increasing the strain rate at a constant temperature. In addition, the plot of critical strain versus imposed strain rate indicates an inverse manner at very low strain rates. It is confirmed that the type of PLC bands alters the... 

Microstructure and mechanical properties development of X80 weld metal by addition of different amounts of alloying elements such as Nickel and Manganese to the covering of electrodes were investigated. For this reason samples were welded with electrodes that Ni value changed between 0.8%- 3.5% in tow critical amounts of Mn: 0.7 and 1.6. Tensile test and microhardness results indicated the suitable ranges of Ni and Mn for acceptable mechanical properties. In addition, optical microscopy and scanning electron microscopy were applied to link the microstructure with mechanical properties. The hardness of weld metals were found to increase linearly with Mn and Ni, which was attributed mainly to... 

Dual-phase (DP) steels with different martensite contents were produced by subjecting a low carbon steel to various heat treatment cycles. In order to investigate the effect of dynamic strain aging (DSA) on mechanical properties, tensile specimens were deformed 3% at 300 °C. Room temperature tensile tests of specimens which deformed at 300 °C showed that both yield and ultimate tensile strengths increased, while total elongation decreased. The fatigue limit increased after pre-strain in the DSA temperature range. The effects of martensite volume fraction on mechanical properties were discussed  

Alumina flakes were prepared by solution combustion method and milled to provide powder. XRD and SEM data exhibited microsized flakes with 100 nm thickness and nanosized grains. Then the powders were dispersed in polystyrene (PS) and poly methyl methacrylate (PMMA) matrixes and thin sheets of composites were produced by solution method. Mechanical properties of the composites were characterized using tensile test and their fracture surfaces, elemental composition and hydrophobic property were tested by SEM, EDX and contact angle techniques, respectively. The results exhibited better mechanical properties compared to pure polymer samples i.e. the elastic modulus in PMMA and PS composites,... 

In this study both the quench aging and static strain aging kinetics of a 6082 Al alloy were investigated at a temperature range of 130-200°C using the Vickers hardness and tensile test. The activation energy and dislocation density were determined at different stages of the aging phenomenon. The former was used to analyse the kinetics of aging and the latter to interpret the competition of strengthening and recovery mechanisms during aging. It is shown that different activation energies are achieved depending on the aging time and temperature relating to formation of appropriate precipitates at different stages of aging. Moreover, it is revealed that prestrain reduces the activation energy.... 

A mathematical model based on Kocks-Mecking-Bergstrom model, has been proposed to predict the flow behavior of age hardenable aluminum alloys, under different conditions of solution heat treatment and hot deformation. Considering the published literature, most researchers have taken into account the precipitation and solution strengthening contribution to the flow stress by a constant and some others have ignored these effects. So these available descriptions cannot be applicable directly to different conditions of solution heat treatment. In order to enable these constitutive descriptions to take into account the effects of soaking time and temperature, we introduce in this research a... 

Dual phase (DP) steels with network and fibrous martensite were produced by intercritical annealing heat treatment cycles. Some of these steels were deformed at dynamic strain aging temperatures. Room temperature tensile tests of specimens deformed at 300 °C showed that both yield and ultimate tensile strengths for both morphologies increased, while total elongation decreased. Fatigue test results before and after high temperature deformation showed that dynamic strain aging has a stronger effect on fatigue properties of dual phase steels with fibrous martensite. Cracks in DP steels with fibrous martensite propagate in a tortuous path in soft ferrite phase, while they pass of both hard and... 

In this paper, mode I fracture toughness of rock was determined by direct and indirect methods using Particle Flow Code simulation. Direct methods are compaction tension (CT) test and hollow centre cracked quadratic sample (HCCQS). Indirect methods are notched Brazilian disk (NBD) specimen, the semi-circular bend (SCB) specimen, hollow centre cracked disc (HCCD), the single edge-notched round bar in bending (SENRBB) specimen and edge notched disk (END). It was determined that which one of indirect fracture toughness values is close to direct one. For this purpose, initially calibration of PFC was undertaken with respect to data obtained from Brazilian laboratory tests to ensure the... 

In this work, microstructural evolutions and mechanical properties of AISI 304L stainless steel were studied after rolling operations at elevated temperatures. Rolling experiments were conducted under warm and hot rolling conditions in the range of 600-1000 °C employing different reductions. Then, the developed microstructures and the mechanical properties of the steel were evaluated by means of uniaxial tensile testing, metallographic observations, and x-ray diffraction method. Besides, two-dimensional finite element analysis coupled with artificial neural network modeling was developed to assess thermo-mechanical behavior of the steel during and after rolling. The results show that... 

In recent years, pozzolana are being increasingly used in different types of concretes and mortars. This investigation aims to evaluate the effect of replacing 7, 14, 21, and 28% cement (by weight) with silica fume (SF), granulated blast furnace slag (GBFS), zeolite, and fly ash (FA) under elevated temperatures. Forty mix designs were built with various water-to-cement ratios and plasticizers. Three hundred and six specimens were prepared, and the flexural, uniaxial compression and tensile tests were performed on specimens after exposure to elevated temperatures between 25°C and 900°C. The X-ray diffraction (XRD) test was then performed on the two series of specimens. Accordingly, the...