حبیب دانش منش

The application of ultrafine-grained or nanostructured aluminum is very interesting owing to its high strength to weight ratio. Welding of these materials is one of the main challenges. Regarding the potential of the solid-state friction stir welding in joining of nanostructured materials, in the current research different equipment and techniques like optical and scanning and transmitted electron microscopes, Vickers microhardness, and uniaxial tensile tests were employed to study the effect of major welding parameters on the bonding quality of friction stir welded ultrafine-grained Al 1050 alloy produced via accumulative roll-bonding (ARB) method. The studied parameters were rotation and traveling speeds, pin geometry as well as welding atmosphere temperature. The results show the microhardness enhancement of the weld zone by decreasing the rotation speed or increment of traveling speed due to lower heat generation within the stir zone. Investigation of the pin geometry depicts an insignificant impact of this variable on the weld tensile properties. Only in the case of a threaded pin, a slight enhancement in the tensile properties was achieved. Submerge or underwater welding could improve joint strength. However, the application of extremely cold water with respect to 25° C water shows a reverse effect and leads to severe weld quality degradation owing to defects formation (like internal channels and surface discontinuity).

Thermoplastic polyurethane elastomer (TPUs) were synthesized by poly (oxytetramethylene) glycol (PTMG), hexamethylenediisocyanate (HDI) and 1, 4- Butanediol (BD) at three different molar ratios (1:4.2:3, 1:2.1:1, 3:4.2:1).The effect of stoichiometric balance on the acoustic and damping properties was evaluated. Fourier Transformed Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), X-ray Diffractometry (WAXS), Scanning Electron Microscope (SEM), specific gravity, Dynamic Mechanical Thermal Analysis (DMTA) and specific gravity were used to investigate the structures. PUUEs chemical structures were characterized by FTIR. The data on the scattering of the wide-angle X-ray is ascribed to the TPU matrix hard parts phase segregation.The results of DSC and XRD backed up the amorphous and crystalline type of PUEs with 12 and 33 wt % of hard segment (HS), respectively. Changing in molecular structure cases changing in hard segment and specific gravity. This was enhanced in HS, leading to changing in storage modules and damping factor. Damping factor decrease 75% and velocity and acoustic absorption coefficient, in room temperature and 1Hz frequency, changes 200%.

In this study, the effect of overlapping percentage on microstructure and mechanical properties of a single-pass coating by Inconel 625 powder laser has been investigated for quench-tempered ASTM A592 steel. In order to have a structural analysis, the inter dendritic distance was evaluated. For this purpose, scanning electron microscopy (FESEM) and Digimizer software were adopted. In order to investigate mechanical properties, elastic modulus, toughness, and micro hardness were evaluated. For the evaluation of elastic modulus, Noop indentation method was used, and for toughness studies, Evans method was applied. After the investigation, it was found that in the overlapping of single-pass 50% coatings, the heat input value is lower than overlapping in single-pass 75% coatings. It also contains a finer structure with much higher mechanical properties. This is in such a way that the inter dendritic distance in single-pass 50% coatings is about 0.91 µm. The average diameter of the dendritic columns is about 0.32 µm, hardness value is about 10%, Knoop hardness is about 9 units, elastic modulus is about 37 GPa, and toughness is about 9 MPa m1/2 higher in comparison with the 75% overlapping case.

The purpose of this work is to develop a new type of calcium silicate nanocomposite, with low setting time, good workability and high strength. This new nanocomposite is prepared by mixing Nano Fast Cement, Nano Hydroxyapatite, polyvinyl alcohol and colloidal nano silica. The effect of three additives (hydroxyapatite nanoparticles, colloidal nano silica and polyvinyl alcohol solution) on its physical and mechanical properties was investigated. Using Taguchi design method, the effect of different levels of additives and optimum percentages of each additive on having nano composite with high compressive strength, low setting time and good workability were determined. According to the results, the most effective factor on the mechanical properties of nanocomposite (compressive strength, flexural strength and flexibility) is polyvinyl alcohol, that level of three (6%) has the highest signal to noise ratio, indicating that the optimal level for this factor is level three. Also, factor A, which represents the hydroxyapatite nanoparticles, is the signal-to-noise value of all surfaces almost close to each other, indicating that this factor does not have much effect on the mechanical properties. And according to the test results, the most effective factor on the setting time is percentage of hydroxyapatite nanoparticles. The optimal level for this factor is level one (zero for hydroxyapatite). Thus, the optimum percentages for nanocomposite production with the highest strength and the lowest setting time and good workability are 6% polyvinyl alcohol, 0% hydroxyapatite and 0.5% nanosilica.

The most recent studies have shown, due to high specific strength, and modulus, low density, low fabrication cost, and easy production processes, the raw material used is polymer. Thermosets are the most studied polymers during recent researches, they generally have higher chemical and thermal resistance than thermoplastics. Despite theseimportantadvantages, there are also some disadvantages, the most important imperfection of thermosetting polymers is their brittleness. In this study Epoxy/(up to 1.5 wt%)silica nanocomposites fabricated by casting method and then mechanical and thermal properties of nanocomposites are evaluated and Fourier Transform Infrared Spectroscopy (FT-IR) was implemented to study molecular bonding . Mechanical tests results showed 43%, 12% and, 40 % increase in strength, flexural strength and, toughness, respectively. Thermal gravimetric analysis results showed 22% decrease in Reduction of mass and Dynamic mechanical analysis results illustrated an increase in Glass transition temperature of Epoxy/0.3 wt% nanosilica from 74.5 ◦C to 75.4 ◦C, and an increase in storage modulus from 1.8Gpa to 2.3Gpa at 30◦C.

flexible polyurethane foam (PU) and monolithic polyurethane sandwich panel samples reinforced with different weight percent of TiO2 nanoparticles (0.25, 0.5, 0.75, 1, 1.5 and 2) have been successfully prepared. The effects of TiO2 nanoparticles on the physical and thermal properties of mentioned samples were examined. In order to observe morphological structure of polyurethane (PU) samples, scanning electron microscopy (SEM) were used. Research results showed that by increasing TiO2 nanoparticles to 2 wt.%, the density of foam and sandwich panel increased to 32.2% and 62.6%, respectively in comparison with pure sample and amount of water absorption decreased to 45% and 58.8%, respectively. The results of UV analysis showed that the maximum amount of UV rays absorption in PU foam reinforced with 2 wt.% of TiO2 nanoparticles equals to 3.21 at wavelength of 450 nm. Investigation results of TGA analysis showed that the presence of TiO2 nanoparticles caused improvement thermal stability of PU nanocomposites. By increasing TiO2 nanoparticles to 1 and 2 wt.%, the degradation temperature at weight loss equals to 10 wt.% of PU increased 14.5 ºC in comparison with pure sample. Also the degradation temperature of weight loss equals to 50 wt.% of samples reinforced with 1 and 2 wt.% of TiO2 nanoparticles increased 1 and 3 ºC, respectively.

In the present research, the finite element analysis of the surface transformation hardening in the vicinity of workpiece discontinuity was performed both thermally and metallurgically using ABAQUS finite element software. In order to predict the volume fraction of the obtained phases and the hardness profile during continuous cooling stage, the appropriate user-defined subroutine based on the Kirkaldy kinetic model was employed in the data flow of the software. Besides the effects of different controlling strategies and the application of a quenching medium at the discontinuity surface was investigated. Based on the obtained results, these strategies which are based on controlling the input power and travelling speed of the heat source as a function of the maximum temperature at the surface, allows for gaining a more uniform thermal history at the surface. However, as these strategies could not control the cooling rate in the vicinity of discontinuities, applying a quenching medium with an optimum cooling power is essential in order to achieve a uniform hardened layer at the workpiece depth.

In this research friction stir processing (FSP) was used to produce surface composite layer with zirconia reinforcement particles on aluminum AA5086 alloy. The effect of the combination ratio of ZrO2/Graphite powders on microstructure and hardness of surface hybrid composite layer fabricated by friction stir processing on aluminum alloy was investigated. A H13 work steel tool with taper cylindrical pin geometry was used to produce hybrid composite layer. The FSP parameters were 1250 RPM in rotational speed and 50 mm/min in traverse speed of tool. Microstructures of produced samples were evaluated by means of optical microscopy and distribution of particles was evaluated by scanning electron microscopy. The hardness of surface composite layer was characterized using vickers hardness test. The results revealed that FSP caused to grain refinement and by increasing the passes of process to three passes on fabricating surface composite, distribution of zirconia particles on matrix has improved. The maximum of hardness value was achieved by producing surface hybrid composite (15%ZrO2/15%Gr). X-ray diffraction studies were carried out in order to identify the phases present in the stir zone of the specimens. The results showed that no reaction occurred between the aluminum matrix and the reinforcement particles during three FSP passes.

In this research, electromagnetic properties of graphene-epoxy nanocomposite up to wt% graphene, were investigated in X band. Results showed that these nanocomposites do not have significant permeability so that it can be considered equal to 1. However they exhibit high permittivity such that real part of permittivity of 3wt% graphene sample is 8.4 in GHz and 6.8 in 12GHz frequencies, which are respectively 2.9 and 2.3 times that of pure epoxy at the same frequencies. Also imaginary part of permittivity was obtained 5.8 in 8GHz and 4.4 in 12GHz that is respectively 144 and 68 times that of pure epoxy at the same frequency. Also, the average value of loss factor was measured 0.5 and 0.8 for 2 and 3wt% graphene sample respectively. An average effective electrical conductivity of 3S/m for 3wt% graphene sample was attained. Results showed that the epoxy-graphene nanocomposites are very convenient materials for electromagnetic absorption applications.

The Accumulative Roll Bonding process is used as a severe plastic deformation technique to produce aluminum composite sheets with ultra fine structure. In this study the effect of simultaneous use Mg and SiC particles as reinforcements، on the tensile properties of the Al-Mg-SiC hybrid compositeis studied. The Al-Mg-SiC hybrid composites with different amounts of Mg and SiC contents were fabricated by ARB Process. Then Changes in mechanical properties was studied by tensile tests. Results show that a simultaneous increase in both the strength and ductility of produced samples with addition of SiC and Mg particles. Also the Al-Mg- SiC composites have a higher strength and ductility.

Aluminum foam sheets produced by accumulative roll-bonding process via decomposition of a blowing agent، have a great capability for fabricating sandwich structures including aluminum foam cores. A comprehensive design of these structures demands the optimization of foaming parameters، particularly foaming heat treatment. Using preheated furnaces as alternative to infrared image furnaces، which are commonly used for foaming heat treatment، could lead to easier and less expensive foam production. Optimizing the parameters for such heat treatment is the main subject of this study. In order to achieve a preform for foaming heat treatment tests، TiH2 powders were distributed in the aluminum matrix by 7 passes of repeated roll-bonding and cutting. The fabricated preforms were heat treated to convert to the foams in a preheated resistance furnace. Optimized heat treatment parameters for achieving the best combination of porosity and cell morphology were extracted. The best result was aluminum foam with 37. 2 % porosity.

Aluminum and its alloys duo to their low density, good accessibility and ease of converting to foam, become the most used materials in manufacturing of metallic foams. In this study Accumulative Roll-Bonding process has been utilized for distributing TiH2 powders, as foaming agent, in the structure of an aluminum sheet. Then, via a suitable heat treatment the powders were decomposed and the preform was converted to foam. Also, using the uniaxial compression test, compressive strength of the fabricated foam in different loading directions has been investigated and a correlation between compressive strength and porosity and loading direction has been observed. Maximum compressive strength of 21.08 MPa for foam of porosity 30% in the rolling direction (RD) was measured and increasing the porosity, a decrease in compressive strength was observed. The compressive behavior of the fabricated foam was different in three loading directions.