فهرست مطالب mohammad reza shabgard

Usually, payloads are carried on long routes with different road surface conditions and road obstacles by commercial vehicles from factory to destination. These road conditions cause truck and its cargo exposed to shock and vibration of different amplitudes and frequencies that may impose catastrophic damages to delicate sensitive payloads. The aim of this paper is to present 3-D model of a secondary suspension system, including double-ended magnetorheological dampers in cargo vehicles to protect sensitive cargo against induced excitations due to various road surface roughness. First, a double-ended magnetorheological damper was modeled, fabricated, and dynamically tested. Harmonic tests at different frequencies were performed using a UTM test machine and applying different electric currents to the damper. Considering these tests results, the parameters of modified Bouc-Wen model for the damper are identified. Using the updated model for the damper, 3-D model of secondary suspension system with four magnetorheological dampers in the four corners of the cargo holder pallet is provided. The impact of the secondary suspension against the loads imposed by three types of road surface profiles, namely harmonic long wave, the bumpy surface, and surface with random roughness, is investigated. Furthermore, the effect of various uneven cargo mass arrangements on the magnitude of the dynamic loads of the payload are investigated. The results show that with increasing electric current at different road profiles, the vertical displacement amplitude has an average decrease of 40% in peak and 30% decrease in RMS and at the same time the isolation region has acceptable characteristics.

One of the important parameters in electrical discharge machining is the presence of micro cracks on the workpiece surface (recast layer). Therefore, the aim of this study was to investigate the possibility of increasing the mechanical properties of aluminum surface by alloying elements (copper and nickel) diffusion to the recast layer and thus removing surface micro cracks. For this purpose, pulse on time and pulse current in with and without ultrasonic vibration have been considered as input parameters and the presence of surface micro cracks has been investigated using microscopic images. Also, the yield stress of the surface layer was calculated using the surface micro hardness. Based on the obtain results, surface without micro cracks has been created on the aluminum surface due to the diffusion of copper and nickel into the workpiece surface which increased aluminum surface yield strength from 90MPa to 280MPa without ultrasonic vibrations and to 310MPa while applying ultrasonic vibrations. In other words, ultrasonic vibrations cause an average of 20% increase in surface layer yield strength. In addition, according to the wear test, in the case of using ultrasonic vibration, improving the mechanical properties of the surface has caused thinner grooves on the aluminum surface.

In this study, the electrochemical machining (ECM) of the 304 stainless steel with the response surface methodology (RSM) approach for designing, analyzing and mathematical modeling was used. The electrolyte type, concentration and current parameters were considered as the machining parameters. The mathematical model for the responses was presented and based on the type of electrolyte including NaCl, NaNO3 and KCl. The results showed that the current has the highest effect on Surface Roughness (SR) and Material Removal Rates (MRR) and respectively it improves them to 0.465μm and 0.425gr/min. The electrolyte concentration has the highest effect on Over Cut (OC) and causes to increase its values. Under the conditions of NaCl electrolyte, 1 molarity concentration and 55 A current, the optimum condition 0.4006 gr/min MRR, 0.75 mm OC and 0.465mm SR was achieved.

In this investigation, the material removal rate, tool wear rate and surface integrity obtained by EDM, ultrasonic vibrations assisted EDM and magnetic field assisted EDM were studied and compared with together to show the quality of the effects of applying each of ultrasonic vibrations to tool and magnetic field around gap distance of EDM process on material removal rate, tool wear rate, and surface integrity. According to the results, applying ultrasonic vibrations to tool electrode leads to an increase of 71% in material removal rate of EDM process while applying magnetic fields around gap distance of EDM process leads to an increase of 41% in material removal rate (of course in the best conditions). Also, applying magnetic fields around gap distance of EDM process leads to a decrease of 35% in surface roughness obtained by EDM process while the surface roughness of ultrasonic vibrations assisted EDM is higher than EDM process. Also, the created surface damages in the case of ultrasonic vibrations assisted EDM is the lowest and in the case of EDM process is the highest.

In this paper, effect of input parameters (pulse on time, pulse current, voltage and duty cycle) of electric discharge deposition process on surface quality parameters including surface hardness, surface deposited layer thickness and roughness of AISI H13 tool steel using Ti-Cr-Cu alloys as electrode was studied. SEM was used to investigate the thickness of the surface layer, and the hardness of surface deposited layer was measured by microhardness test. Also, XRD method was used to identify the compounds on the surface and deposited surface roughness was controlled using Ra parameter. Based on the obtained results, TiC, Cr7C3 and Fe2C are formed at the deposited layer due to surface alloying and increasing surface hardness. Also, by increasing the pulse current and the pulse on time, the surface hardness and depth of the deposited layer were increased. Furthermore, with increase in input voltage, the thickness of the surface layer is increased and the workpiece surface roughness is reduced. Also, by increasing the duty cycle due to the increase in the number of sparks in time, the depth of the surface deposited layer is increased.

In this paper, considering the importance of surface integrity, effect of ultrasonic vibration of the Monel 400 electrode with a frequency of 20 kHz on the output parameters of the aluminum surface properties (surface hardness and wear resistance, thickness of the surface layer, the depth of copper and nickel diffusion to the aluminum surface and surface roughness) by the method of electrical discharge surface alloying has been studied. Based on the results of the SEM images, the surface layer thickness in the combination of ultrasonic vibration with the electrical discharge alloying process is more than the non-vibration mode. Therefore, increasing the thickness of this layer increases the surface wear resistance. Also, the microhardness test results show that surface hardness of the aluminum has increased to 450 vickers after the combination of ultrasonic vibration with the alloying process. According to the results of EDX analysis, the diffusion depth of alloying elements (copper and nickel) is higher in ultrasonic electrical discharge alloying, So that the surface layer thickness is up to 50 microns. Also, based on the results of surface roughness measuring, ultrasonic vibrations reduce the aluminum surface roughness after surface alloying.

Although the electrical discharge process is a material removal process, it is attempted to be used for surface operations as well, so considering the new method, it is important to analyze the mechanism of the electrical discharge surface alloying process. Nickel base alloys are widely used due to their high resistance to corrosive environments, especially at high temperatures, especially in environments where stainless steels and duplexes lose their performance. This paper first discusses the mechanism of surface alloying by electric discharge method and then, as an experimental work, examines the surface alloying of aluminum with nickel-copper alloy (Monel 400) to improve its surface properties. Therefore, the parameters of pulse on time and pulse current are considered as input parameters and the depth of hardened layer as output variable. The results of this study show that using Monel 400 electrode with negative polarity as an alloying electrode is a successful method to improve the surface properties of aluminum by eliminating harmful layers resulting from electrical discharge machining.

The creation of modified layer on metal surfaces using new methods is one of the procedures in surface engineering which can improve the surface mechanical properties. The electrical discharge process is a new method that can form a modified layer on the metal surfaces. This study aims to improve of pure aluminum surface properties through Electrical Discharge process with Monel 400 electrode. In order to design the experiments, the pulse on time and the pulse current were considered as input parameters. The SEM images indicated that the increase in the pulse on time and the pulse current can increase the thickness of the modified layer. Based on the obtained results, the thickness of improved layer varied between 35 to 75 microns. The results of the EDX analysis showed the diffusion of the copper and nickel to the aluminum surface. Moreover, the results of microhardness testing of the surface layer showed that after Electrical discharge process, the surface hardness has increased and the surface hardness as 35 Vickers has reached more than 400 Vickers.

Cartilage shows neither repairs nor regenerative properties after trauma or gradual wear and causes severe pain due to bones rubbing. Bioprinting of tissue-engineered artificial cartilage is one of the most fast-growing sciences in this area that can help millions of people against this disease. Bioprinting of proper bioscaffolds for cartilage repair was the main goal of this study. The bioprinting process was achieved by a novel composition consisting of alginate (AL), Halloysite nanotube (HNT), and methylcellulose (MC) prepared in bio-ink. Also, the effect of Russian olive (RO) in chondrocytes growth on bioscaffolds was also investigated in this work. Compressive, hardness and viscosity tests, Energy-Dispersive X-Ray Spectroscopy (EDX), Fourier-Transform Infrared Spectroscopy (FT-IR), Differential Scanning Calorimetry (DSC), water-soluble Tetrazolium (WST) assay, and also transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were carried out. The results show that in constant concentrations of AL, MC, and RO (20 mg/ml AL, 20 mg/ml MC, and 10 mg/ml RO) when concentration of HNT increased from 10 mg/ml (T-7) to 20 mg/ml (T-8) compressive stiffness increased from 241±45 kPa to 500.66±19.50 kPa. Also, 20 mg/ml of AL in composition saved proper water content for chondrocyte growth and produced good viscosity properties for a higher printing resolution. RO increased chondrocytes living cell efficiency by 11% on bioprinted scaffolds in comparison with the control group without RO. Results obtained through in-vivo studies were similar to those of in-vitro studies. According to the results, T-7 bio-ink has good potential in bioprinting of scaffolds in cartilage repairs.

Ti-6Al-4V alloy due to excellent mechanical properties mainly is used in the aerospace, automobile and biomedical industries. Electrical discharge machining (EDM) are used extensively for machining of this alloy. Due to the thermoelectric nature of this process, unwanted changes happen on machined surface such as development of residual stresses and the change in the corrosion resistance. The aim of this study is the experimental investigation of the effect of input parameters (discharge current and pulse on time) on the amount and distribution of residual stresses and corrosion resistance changes of the machined surface in EDM process of Ti-6Al-4V alloy. For this purpose, samples of Ti-6Al-4V alloy were machined by EDM process and residual stresses induced successive sparks in different setting (different discharge currents and pulses on time) were measured by nanoindentation method and SEM images of machined surface used to better assess of samples surface integrity. TOFL measurement method used to determine the corrosion resistance of the samples. Results indicate that at this process tensile stresses is formed on surface and mentioned stresses increase with depth initially and after reaching a maximum dropping out and eventually leads to pressure stress. By increasing pulse on time and discharge current, maximum tension residual stress only slightly increases and is near ultimate tensile strength of work piece material. Comparison of corrosion results indicated that the corrosion resistance of EDMed samples, was less than the not machined specimens.

In this study electrical discharge process was used to increase surface wear resistance of pure aluminum. Pulse-on-time and pulse current were considered as input parameters of the electrical discharge process. Experimental results reveal that the electrical discharge process is a successful method for improving the surface wear resistance of aluminum, so that this method has greatly increased the surface wear resistance of aluminum parts. Results indicate that with increase input parameters (pulse-on-time and pulse current) weight loss of the aluminum specimens is reduced and the wear resistance increases. The XRD analysis demonstrated that Al3Ni2 and AlCu intermetallic compound and Al4C3 were formed on alloyed surface. The presence of these compounds and hard particles at the surface increases the wear resistance. Also, friction coefficient measurements show that, after electrical discharge process and improving surface wear resistance, the friction coefficient slightly increased due to the presence of hard particles on the alloyed surface.

Electric discharge machining is one of the most widely used non-traditional machining techniques which use thermal energy for machining in small dimensions, machining complex shapes and machining hard materials with high strength such as ceramics and heat-treated steels. In this study the ultrasonic vibrations and magnetic field assisted EDM process as a new hybrid process was introduced and used for machining of AISI H13 too steel, to solve the EDM process limitations such as low material removal rate. In this investigation, several experiments were designed and performed based on full factorial method by selecting pulse current and pulse duration as most effective parameters of EDM process in order to study the effects of applying ultrasonic vibrations to tool electrode and external magnetic field around gap distance of EDM process, simultaneously, on material removal rate and tool wear rate. According the results, applying ultrasonic vibrations to tool electrode and external magnetic field around gap distance of EDM process, simultaneously, despite the increases of tool wear rate, increases the material removal rate as compared with EDM (60%), ultrasonic vibrations assisted EDM (40%) and magnetic field assisted EDM processes (55%) in all pulse durations and pulse currents except in pulse current of 32 A. In pulse current of 32 A, because of the interference of the influences of applying ultrasonic vibrations to tool electrode and external magnetic field around gap distance, the material removal rate and tool wear ratio are decreased.

The aim of the current research was to investigate the effect of pressure gradient in the gap on morphological and geometrical characteristics of the powder synthesized by electrical discharge method and optimizing it. Electrical discharge is a modern and high performance approach towards yielding ultrafine powder. The pressure gradient was inducted by pulsed flushing using various current flows of deionized water and ethanol and, two rods of graphite and tungsten were used to yield tungsten carbide powder. Scanning Electron Microscope (SEM) images show that the powder contains both electrode's material and is within nano range. Furthermore, the SEM images demonstrate that with increasing pressure gradient there is a decline in powder agglomeration. Particle Size Analysis (PSA) results reveal that the mean particle size of the powder produced in deionized water and ethanol is approximately 100nm and the particles produced in ethanol are smaller. Moreover, the size of the crystals of the synthesized particle are within 30-44 nm range. X-ray diffraction showed that the dominant phases of the powder in ethanol and deionized water are WC1-x and W2C respectively. Overall, the results prove that causing steep gradient in the gap, it is possible to synthesize geometrically uniform powder with decent production rate.

Electrical discharge machining is one of the usual and widely used machining processes for machining hard metals and alloys which has low machinability by traditional machining methods. Due to the thermoelectric nature of this process, changes in metallurgical and mechanical properties of machined surface and development of residual stresses in components are inevitable. In this research machining of Ti-6Al-4V titanium alloy is conducted by ultrasonic assisted electrical discharge machining process and the effects of ultrasonic vibration of tool on the machining efficiency, surface integrity such as surface micro-cracks, residual stress and surface hardness has been evaluated. Machined surface were imaged by scanning electron microscopy imaging to study the size and distribution of surface micro-cracks. Residual stresses along the depth of the machined surface, evaluated using Nano indentation technique and hardness of discharged surface is measured using a micro hardness measuring instrument. The results show that applying ultrasonic vibration increases electrical discharge machining process efficiency (about 90%), reduces the amount and size of surface micro-cracks, changes residual stress distribution and decreases the amount of it (average 17%); Increases of surface hardness caused by ultrasonic assisted electrical discharge machining process is 13% more than the traditional electrical discharge machining process.

Abrasive flow machining (AFM) is a relatively new process with low material removal ratio for deburring, removing recast layers and finishing industrial components with complex shapes among non-conventional machining processes. In this process, the finishing is handled by flowing of the composition of viscoelastic and abrasive particles on workpiece surface, under the pressure of piston. In this research, the abrasive flow machining process of H13 tool steel with applied an external magnetic field around the workpiece for improve the material removal ratio and surface roughness has been investigated and the effect of magnetic field intensity, abrasive particles mesh and the hardness of workpiece as the input parameters on the process outputs including surface roughness and material removal ratio was studied. Also the regression model of MRR and surface roughness was developed and variance analysis was performed. Results of experiments indicated that increase in abrasive-particles mesh leads to decrease surface roughness and material remove ratio and increase in magnetic field intensity causes to increase material removal ratio and decrease surface roughness. Also the material removal ratio is decreased with increasing of workpiece hardness and on the same condition; better surface finish was achieved in the case of harder workpiece.

In order to achieve better mechanical properties of the nanocomposites containing carbon nanotubes, the carbon nanotubes should be oriented in a specific direction in the polymer matrix. This produces nanocomposites with anisotropic properties. Experimental study on the effect of injection direction and carbon nanotubes orientation on the mechanical properties of a multi-walled carbon nanotube (MWCNT)/polymethyl methacrylate (PMMA) anisotropic nanocomposite is the main aim of this article. Therefore, variable input factors including MWCNT concentration (0, 0.5, 1 and 1.5 wt%) and its in-flow and perpendicular directions were studied. First, nanocomposites were produced by co-rotating twin-screw extrusion. After that the nanocomposite sheets were fabricated by injection molding and test samples were cut into standard dimensions by laser cutting. The parameters including elastic module, yield strength, elongation, impact strength and hardness were studied. In addition, the effect of MWCNT on the melt flow index and optical properties was studied. Morphology of nanocomposites was carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Increasing the elastic modulus by about 51%, tensile strength by 19% and elongation by 27% with addition of 1.5 %wt MWCNTs were also found. The results also illustrated that the elastic modulus improved by 10% and tensile strength by 13 % in the direction perpendicular to the flow direction. Yet more elongation was observed in in-flow direction. A little drop in hardness, a slight increase in impact strength and a decrease in luster and transparency by increases in MWCNTs loading were other noticeable results. A reduction in melt flow impact from 11 to 6.3 g/10min was another remarkable finding.

This paper experimentally investigated the effects of electrical discharge machining processes parameters on fatigue resistance of 16MnCr5 alloy steel. 16MnCr5 alloy steels have good wear resistance. For this purpose, pulse current and pulse time have been considered as variables in the process. The selected EDM parameters were pulsed current (8, 16 and 32A) and pulse time (25, 100 and 400µs). Tests were conducted in full factorial mode and the R. R. Moore fatigue test machine was used to determine the fatigue life of components. The results show that by increasing the spark current and pulse duration 16MnCr5 alloy steel fatigue life is reduced. Respectively, the greatest resistance to fatigue achieved at current of 8A and pulse time of 25 microseconds and lowest resistance to fatigue achieved at pulse current of 32A and pulse time of 400 microseconds. Resistance to fatigue crack depends on cracks density on the surface of the workpiece and heat-affected zone, where the density of cracks increase resistance to fatigue will be reduced. Also in the specimens that have low resistance to fatigue, fatigue cracks are initiated from multiple points of the cross-section. It seems the reason for this phenomenon is the high surface roughness in the samples. EDM machining with high energy sparks can decrease the fatigue strength of 16MnCr5 by as much as factors of 3-5.

Electrolyte type, due to the nature of its constituent ions, affects the reaction rate, the uniformity of the electric field and formation of the external layer on the workpiece surface in the machining area during the electrochemical machining process, as well as it causes to create different dissolution behaviors of the workpiece. Therefore in this study the effect of sodium chloride, sodium nitrate, potassium chloride and hydrochloric acid electrolytes with different currents on the electrochemical machining characteristics of stainless steel 304, including material removal rate, side gap and surface roughness, has been investigated. The results showed that the formation of passive layer during the machining with sodium nitrate electrolyte reduces the material removal rate and side gap compared with sodium chloride and potassium chloride electrolytes. According to the experimental results the surface roughness in the sodium chloride and potassium chloride electrolytes is decreased by increasing the machining current, but increases in the sodium nitrate electrolyte. Also the material removal rate slight increase and side gap increase at sodium chloride, sodium nitrate and potassium chloride when combined with hydrochloric acid. On the other hand, the surface roughness reduces in the combined sodium chloride and potassium chloride electrolytes, but increases in the combined sodium nitrate electrolyte.

Titanium alloy Ti-6Al-4V is one of the most used industrial alloys that is used often in important and risky applications. One of the requirements for machining such parts is to achieve the appropriate surface integrity. Powder mixed electrical discharge machining is a process which has different mechanism compared with traditional electrical discharge machining process; and it often used in order to obtain good surface finish. In this study two different kind of Nano powders SiO2 and Al2O3 added in dielectric for machining of Ti-6Al-4V titanium alloy; so that the effect of adding them on the output characteristics of the electric discharge process, including removal rate, tool wear ratio, surface roughness and integrity is investigated and compared. In order to investigate surface micro cracks and heat altered layer, surface and cross section of it were studied by scanning electron microscopy imaging. The results show addition of Nano powders into dielectric, especially SiO2, increases material removal rate, the effect of Nano powders on tool wear ratio depends on machining condition and setting. SiO2 Nano powder decreases surface roughness more than Al2O3 Nano powder. Surface integrity of machined sample in terms of micro-cracks and depth of the heat altered layer is improved with the addition of nanoparticles.

In the present study, in order to investigate the effect of impact angle and sand jet pressure on the erosion rate and residual stress in sand molding operation, the experiments are performed using gray cast iron, pearlitic ductile iron (PDI) and austempered ductile iron (ADI) as workpiece materials. To fulfill this objective, experimental tests are conducted in full factorial design with workpiece material, impact angle and jet pressure as input and erosive wear rate and residual stress as output parameters.According to the results, variation of impact angle of erosive particles intensively affects the erosion rate of materials in a way that, among the experiments which are carried out in lower impact angles (15 to 30°), ADI cast iron shows the maximum erosive strength however as the impact angle shifts to higher values (75 to 90°), PDI cast iron becomes more resistance against erosion. It can also be noted from the SEM images that in sand shooting process, the presence of flake graphite in gray cast iron causes more formed and grown cracks which significantly intensifies its erosion rate relative to ADI and PDI cast irons. Additionally, comparative analysis of results revealed that formation of surface micro cracks in gray cast iron material causes less induced compression residual stresses relative to ADI cast iron whose great stiffness leads to higher magnitudes of compression residual stress in sand molding operation.

In this research the abrasive flow finishing process (AFF) of AISI H13 hot work steel was studied and the effects of various process parameters such as flow pressure (extrusion pressure), abrasive particles densities, abrasive particles sizes and the first quality of surfaces on variations of surface roughness and material removal have been investigated. The results showed that increasing the density of abrasive particles leads to increase in variations of surface roughness and material removal. Increase of extrusion pressure from 4 to 6 MPa causes the increase in variations of surface roughness and material removal and from 6 to 8 Mpa leads to decrease in the two latter. Electron microscopic results showed that increase of finishing process time over 4 hours causes a detrimental effect on the surface of the specimens, as a result of penetration and stabilization of abrasive particles in the form of broken particles. Also according the results of this paper, increasing the size of abrasive particles leads to higher variations of surface roughness and material removal, and this process is more effective in finishing of rougher surfaces.

The erosion of core boxes caused due to sand shooting in core molding process is one of major concerns of foundry industry. This paper study the effect of impact angle, blasting pressure of sand particles and the type of heat treatment on erosion of AISI H13 tool steel that is widely used in producing core dies. The workpiece material used in this study was AISI H13 tool steel. The tests were performed on a sand shooting machine which simulated the core molding process experimentally. The results show that the erosion of samples is a function of impact angle, shooting pressure and heat treatment as the erosion increases with the increase in shooting pressure. Among the heat treated samples the highest level of erosion has been observed for quench tempered, martempered, carburized and nitrated samples respectively. The Scanning Electron Microscopy (SEM) of surface of templates show that by changing the impact angle from 20 to 90 degrees, the material removal type changes from cutting mechanism to fracture. Further analyses revealed that with increase in shooting pressure from a threshold value abrasive particles trap on the surface of the samples that makes the Mechanically Mixed Layer (MML) and so that decreases the erosion rate. Results express that silica sand causes more erosion than chromite sand; also the erosion increases with increase in size of sand particles.

Thermite welding is a chemically reaction welding process. The weld joint is produced by pouring of superheated molten metal around the joint to be welded، applying with or without of pressure. the importance of mechanical properties and microstructure of thermite welded components، this paper studies the effects of Mn (it is one of the available choices to improve mechanical properties of steels microstructure) on mechanicaland metallurgical properties (hardness، impact resistance، tensile strength، elongation and wear resistance) of St49 steel in thermite welding process. The results show that with the increases of Mn in welded metal، tensile strength and impact resistance are increased but when the Mn content exceeds a certain level (% 2. 5)، the characteristic values ​​of the welded metal is reduced. Also، results show that with the increases of Mn wear resistance and the hardness of the welded metal were increased and the highest hardness in the railhead is 700 (Bhn) and in of rail web is 600 (Bhn).

This paper studies the effects of soluble cutting fluid-based CuO Nanofluid on machining force and surface roughness in turning of hardened AISI 4340 tool steel. These influences, Moreover, are compared with the outputs of similar tests through dry and soluble cutting fluid. The obtained results showed 1% volume fraction of CuO Nanoparticles added to soluble oil as cutting fluid was considerably reduced machining force and surface roughness in comparison to soluble cutting oil and dry. The investigations indicated that CuO Nanofluid reduced surface roughness and machining force by 49% and 24% respectively. Moreover, the results illustrated that the lowest surface roughness obtained in cutting speed 250 m/min, feed rate 0.1 mm/rev and cutting nanofluid.

In this paper the effect of input parameters of the EDM process (pulse on-time، duty cycle and tool polarity)، on the surface integrity (surface roughness، density of surface crack، and white layer thickness) in the machining AISI H13 tool steel has been studied. The result of this research shows that in the positive tool polarity the white layer thickness and density of surface cracks in the low pulse on-time are higher than that of the tool polarity chosen to be negative. However in the negative polarity in the high pulse on-time، density of surface cracks and the thickness of the white layer are higher on the machined surface. Moreover، according to the obtained results، density of surface cracks and the average of the white layer thickness is reduced when the duty cycle increases in the two conditions of tool polarity. By the increase in the pulse on time، the amount of surface roughness is increased.