Sharif Digital Repository

Herein, the NH2-UiO-66 metal organic framework (MOF) has been green synthesized with the assistance of high gravity to provide a suitable and safe platform for drug loading. The NH2-UiO-66 MOF was characterized using a field-emission scanning electron microscope, transmission electron microscope (TEM), X-ray diffraction, and zeta potential analysis. Doxorubicin was then encapsulated physically on the porosity of the green MOF. Two different stimulus polymers, p(HEMA) and p(NIPAM), were used as the coating agents of the MOFs. Doxorubicin was loaded onto the polymer-coated MOFs as well, and a drug payload of more than 51% was obtained, which is a record by itself. In the next step, pCRISPR was... 

In this study, for the first time, the influence of the nanoporous Zr-based NH2-UiO-66 metal-organic frameworks (MOFs) on the tensile strength and fracture toughness of the epoxy coating was investigated. In addition, the impacts of the UiO particles' functionality (i.e., NH2 or GMA) on the MOFs/epoxy interfacial bonding and nanoparticles dispersion quality in the epoxy resin were examined by the tensile test, dynamic mechanical thermal analysis (DMTA) and field emission-scanning electron microscope (FE-SEM). The NH2-UiO-66 and GMA-UiO-66 MOFs chemical structures were investigated by FT-IR, BET, and FE-SEM approaches. The FE-SEM investigation of the fracture morphology (at the cross-section... 

For the first time, the UIO-66, NH2-UIO, and NH2-UIO particles covalently functionalized by Glycidyl Methacrylate (GMA@NH2-UIO), were utilized as the novel functional anti-corrosive fillers. The functionality, high surface area, phase composition, excellent thermal properties as well as chemical stability of the Zr-MOFs were proved by FT-IR, BET, XRD, TGA, and water stability tests, respectively. The smart pH-sensitive controlled-release activity of the corrosion inhibitors (i.e., Zr ions and organic compounds) from the prepared Zr-MOFs was proved by the water stability test of the Zr-MOFs particles in the acidic (pH = 2), neutral (pH = 7.5), and alkaline (pH = 12) solutions containing 3.5... 

This study aims at understanding the metallurgical and mechanical response of Hastelloy X nickel-based superalloy to the thermal cycle of gas tungsten arc welding (GTAW), post welding solution treatment (ST), and aging. In the as-weld condition, the weldment was characterized by the formation of the M6C carbide, sigma phase, and micro-solidification cracks in the interdendritic zones of the weld metal, and constitutional liquation of M6C carbide in the heat-affected zone. It is demonstrated that neither the weld metal nor the heat-affected zone could adversely affect mechanical properties of the welded joint in as-weld condition. However, to alleviate the microstructural heterogeneity,... 

This research explored the influences of shielding gases on the appearance of weld beads and the microstructures and mechanical properties of thin-wall samples using conventional gas metal arc welding as the heat source by using 5356 aluminium alloy welding wire as the raw materials and nitrogen (N2) and argon (Ar) as the shielding gases. The results showed that under the same parameters and after mono-layer single-bead welding was performed using N2 as the shielding gas, the bead height was higher, the bead width was narrower, and the penetration depth was shallower. The grain size of the thin-wall sample protected by N2 was 43.5–47.8 % smaller than that obtained under Ar protection.... 

For the first time, the UIO-66, NH2-UIO, and NH2-UIO particles covalently functionalized by Glycidyl Methacrylate (GMA@NH2-UIO), were utilized as the novel functional anti-corrosive fillers. The functionality, high surface area, phase composition, excellent thermal properties as well as chemical stability of the Zr-MOFs were proved by FT-IR, BET, XRD, TGA, and water stability tests, respectively. The smart pH-sensitive controlled-release activity of the corrosion inhibitors (i.e., Zr ions and organic compounds) from the prepared Zr-MOFs was proved by the water stability test of the Zr-MOFs particles in the acidic (pH = 2), neutral (pH = 7.5), and alkaline (pH = 12) solutions containing 3.5... 

The effect of welding current and polarity, i.e. AC and DCEN, on imposed thermal cycles, mechanical properties, microstructural events and residual stresses was investigated in GTA welding of AA5052. A three-dimensional thermo-mechanical model was utilized to evaluate thermal responses and residual stresses distribution in the weldments. Tensile testing and hardness measurements were also conducted to study the effect of welding polarity on the mechanical properties of components. Microstructural observations utilizing optical microscopy were carried out to assess the microstructural evolutions. The results show that wide varieties of microstructures are produced in DCEN sample from cells at... 

Al-1050 clad St-12 sheets were first produced by cold roll bonding process with clad layer thickness of 350 and 1000 μm. Then, Al-5052 aluminum alloy and Al-1050/St-12 sheets were lap joined using gas tungsten arc welding with Al–Si filler metal. The effects of the clad layer thickness and welding current were studied on the joint properties. Macro/microstructural observations were done using optical and scanning electron microscopes (SEM) equipped with energy dispersive spectroscopy (EDS). Shear-tensile and microhardness tests were used for evaluation of the mechanical behavior of the joint. The results indicated that presence of the aluminum clad layer reduced the Al–Fe intermetallic... 

Efficient control of a gas metal arc welding (GMAW) process enables one to obtain high quality products as a consequence of achieving a high quality weld. Although control of the droplet detachment frequency in the welding process would play a great role in improving the welding quality, measuring this variable is difficult and expensive. In this paper, we attempt to control the frequency of droplet detachments without directly measuring it. To this end, we utilize the hybrid property of the GMAW process to indirectly control the frequency. Specifically, a mixed logical dynamical (MLD) model is obtained by considering the hybrid act of the process during droplet detachment. Then, a nonlinear... 

Influence of gas tungsten arc welding on the thermal responses, residual stress distribution and final mechanical properties of the naturally age-hardened (T4) and artificially age-hardened (T6) AA2024 plates was studied. The results showed that age hardening and over-aging occurred in various sections of the heat-affected zone (HAZ) of T4 sample, depending on their locations, while in the HAZ of T6 sample, over-aging is the governing phenomenon. Also, subsequent natural aging occurred in HAZ, weld metal (WM) and partially melted material (PMM) of both weldments. This recent phenomenon is more obvious in the T4 sample in comparison with the T6 one. In both microstructures, weld metal is the... 

In this paper gas tungsten arc welding (GTAW) was applied to dissimilar lap joining of Al6061 and Zn-coated galvanized low carbon steels using Al-5 wt% Si filler metal. The joining mechanism was based on a hybrid brazing/welding mechanism. Three factors contributed to the joint strength including (i) low heat input rate of GTAW process which reduce the intermetallic compound layer growth during joining, (ii) the special role of Si in the filler metal which was able to change the nature of reaction layer from predominantly η-Al5Fe2 phase to predominately less brittle Al-Fe-Si phase and (iii) the flux-like action of Zn-coating which ensures complete wetting of steel surface by Al melt. It was... 

Al-Mg aluminum alloy was lap joined to aluminum clad steel sheet using pulsed gas tungsten arc welding process and Al-Si filler metal. The effects of the welding heat-input were investigated on the joint microstructure and mechanical properties. Weld metal microstructure, formation of intermetallic compounds (IMCs) at the joint interface and the fracture locations were studied using stereo, optical and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). The joint strength of the welds was evaluated by shear-tensile test. The results showed that presence of a thin aluminum clad layer with 350 μm thickness drastically decreased the Al-Fe intermetallic... 

An adaptive extended Kalman filter is designed to estimate the arc length in a gas metal arc welding system. The simulation results show that the estimated variables track the true variables of the non-linear model with negligible error and are robust against parameters uncertainties. The proposed estimator also operates adequately in a highly noisy welding environment. Because of the low computational requirements and little lag produced in the process dynamic, use of the proposed estimator would be valuable in the design of a controller for the gas metal arc welding system  

It is proposed to employ melting rate, heat input, and detaching droplet diameter as controlled variables to control heat and mass transfer to work piece in a gas metal arc welding process. A two-layer architecture with cascade configuration of PI and MPC controllers is implemented to incorporate existing constraints on the process variables, improve transient behavior of the closed-loop responses and reduce interaction level. Computer simulation results are presented to indicate usefulness of the proposed controlled variables selection and applying two-layer control architecture to control heat and mass transfer to work piece  

This study concentrates on the effects of weld sequence and welding fixtures on distribution and magnitude of induced arc welding residual stresses built up in butt-joint of Gas Tungsten Arc Welding (GTAW) AA5251 plates. Aluminum plates have been welded under different welding conditions and then, longitudinal and transverse residual stresses were measured in different points of the welded plates employing hole-drilling technique. The results indicate that welding sequence significantly alters the distributions of both longitudinal and transverse residual stresses while the changing in the weld sequence leads to 44% decrease in longitudinal residual stress. Besides, both the geometry of weld... 

In this paper, we present a method to dynamically observe two important variables of a Gas Metal Arc Welding (GMAW) process, i.e. arc voltage and arc length. To do this, we use Kalman filter to estimate these two variables in a high level noisy environment of GMAW process both in open and closed loop modes  

In this work, thermo-mechanical behavior of an aluminum alloy during gas tungsten arc welding (GTAW) is studied using a three-dimensional mathematical model. The model can be employed to determine residual stresses and their distribution after the welding operation. The effects of the strain hardening and the temperature dependency of material properties have also been considered in the calculations. Model validation has been performed using experimental measurements of residual stress by means of hole-drilling technique. The measurements have been carried out at the heat affected zone (HAZ) and base metal next to the welding line. In addition, microstructural observations have been made to... 

In this work, temperature field and weld pool geometry during gas tungsten arc welding of 304 stainless steel are predicted by solving the governing equations of heat transfer and fluid flow under quasi-steady state conditions. The model is based on numerical solution of the equations of conservation of mass, momentum, and energy in the weld pool. Weld pool geometry, weld thermal cycles, and various solidification parameters are then calculated by means of the model predictions. The model considers the effects of various process parameters including welding speed and heat input. It is found that the weld pool geometry, predicted by the proposed model, is in reasonable agreement with the... 

In the present study, the temperature and the velocity fields during gas tungsten arc welding of commercial pure aluminum were simulated using the solution of the equations of conversation of mass, energy and momentum in three dimensions and under steady-state heat transfer and fluid flow conditions. Then, by means of the prediction of temperature and velocity distributions, the weld pool geometry, weld thermal cycles and various solidification parameters were calculated. To verify the modeling results, welding experiments were conducted on two samples with different thicknesses and the geometry of the weld pool was measured. It is found that there is a good agreement between the predicted... 

Since the mechanical properties and the integrity of the weld metal depend on the solidification behaviour and the resulting microstructural characteristics, understanding weld pool solidification is of importance to engineers and scientists. Thermal and fluid flow conditions affect the weld pool geometry and solidification parameters. During solidification of the weld pool, a columnar grain structure develops in the weld metal. Prediction of the formation of the microstructure during welding may be an important and supporting factor for technology optimization. Nowadays, increasing computing power allows direct simulations of the dendritic and cell morphology of columnar grains in the...