نشریه مهندسی مکانیک مدرس
سال بیستم شماره 9 (شهریور 1399)

In the present study, Cu/Zn/Al multi-layered composite was processed by accumulative roll bonding (ARB) through nine passes. Afterwards, heat treatment processes at various temperatures (750-950℃) and times (10-25min) were done on the prepared composites to fabricate CuZnAl shape memory alloys. The microstructure (composites and alloy) were investigated using scanning electron microscopy and X-ray diffraction. Tensile properties and shape memory effect of the composites and alloys were also investigated by tensile test. The microstructure investigations show that plastic instability and shear bands occurred in different layers in the composite. In addition, a composite with a uniform distribution of Zn and Al reinforcing layers was produced after nine passes. The tensile strength of the composite increased from the first cycle to the third ARB cycle and then decreased from the fifth to the ninth ARB cycle. Finally, the best UTS (about 330MPa) and elongation (about 31.52%) values were obtained on the third and first pass, respectively. The results showed that CuZnAl shape memory alloy was successfully fabricated by the accumulative roll bonding process and next heat treatment. It was also found that the alloys treated at 900°C and cooled in ice water consist of martensitic phase. Additionally, the alloy annealed at 900°C for 15 minutes exhibited a good shape memory effect and strength (about 503MPa).

In impact mechanics, layered targets are important due to their high resistance to projectiles penetration. This paper deals with the analytical and numerical analysis of the penetration of tantalum projectiles on semi-infinite ceramic-metal layered targets. In the analytical study, a new modified analytical model based on the analytical model of Fellows is presented. The modifications made to the Fellows analytical model include the changes of velocity of the projectile and ceramic, the angle and timing of the formation of the ceramic cone, the erosion of ceramic, projectile and backing. Each of these modifications alone reduces or increases the depth of penetration, and all of these modifications together improve the depth of penetration. Numerical analysis is done using Abaqus software. The behavior of projectile, ceramic, and aluminum is modeled on the actual behavior of the materials and the deformation. The projectile and backing behavior is modeled with the Johnson-Cook equations and the ceramic behavior with the Drucker-Prager plasticity equation and the state equation of Mie-Gruneisen. The results of the new correction analytical model and numerical simulation are compared with the results of other authors and experimental data. The results show very good agreement. The new modified analytical model, by removing the Fellows model defects, provides a more accurate prediction of the depth of projectile penetration in the ceramic-metal layered targets. So, the weakness of this model, which is related to the unpredictability of penetration depth at low speeds, has been remedied.

In the current study, shear compaction processing was used for the recycling of aluminum machining chips and direct converting of them to bulk parts. In this processing, machining chips are first loaded in a cylindrical chamber, then a rotating tool with a defined rotational speed and aligned axis with the chamber is placed on the chips, in the following, the temperature inside the chamber increases due to the friction. Then, the process continues until all chips are transformed into a bulk part. After producing the samples, properties such as density, porosity, microstructure, hardness, and wear of the recycled parts were examined. The results showed that there is a possibility of transforming aluminum chips into a completely bulk part without porosity, with a density of about 2.67g/cm3 and hardness of more than half of the base metal via shear compaction process. The amount of heat during the process leads to the consolidation of the chips and nucleation of new grains with dynamic recrystallization. Finally, a review of the total results and properties of the recycled samples showed that they could be used as a industrial part directly or after a secondary process.

The study of micro-scale fluid behavior is known as microfluidics, which has received much attention in many scientific fields. In the current research, the droplet generation in the micro channel has been studied numerically and experimentally. Two micro channels were fabricated by soft lithography method and the results of generated droplets were compared. The process of droplet formation was investigated using two fluids including water (dispersed fluid phase), and oil (continuous fluid phase) at different flow ratios. The images of the droplet formation and crossing steps in the micro channels were analyzed using image processing. The results showed that by increasing the ratio of dispersed to continuous flow, the size of droplets was increased, the droplet formation distance (the distance of the produced droplets) was increased, and the frequency of droplets generation was decreased. Also, the proposed new geometry leads to the production of smaller droplets with higher production frequencies. In the basic geometry, the droplet diameter was observed to be between 117 and 700 micrometers while in the proposed geometry, the diameter of droplets is between 46 and 466 micrometers. In the proposed geometry, the size of the produced droplets decreases, and the production frequency increases.

P91 steel is widely used in the construction of power plant components and the wider use of this steel is in the future planning of power plants in Iran. The preheating, the temperature control between the welding passes and the post-welding heat treatment, are required to obtain optimum toughness and creep resistance. Preheating, and most importantly post-heating are essential to prevent hydrogen remaining and the cracking problem. In this study, the effect of post-welding heat treatment (PWHT) and electrode drying on microstructure and mechanical properties of SMAW multi-pass weldment of P91 steel plate was studied by changing post-heating and baking processes. The optical microscope and FESEM microstructural studies, as well as ambient tensile tests, were done on a variety of different conditions from wet electrodes to post heated specimens that were used in order to evaluate the welding characteristics of SMAW process on the mentioned material. It was seen that utilizing wet electrodes with no immediate subsequent post-heating caused a noticeable decrease in tensile, and yield strength. On the other hand, post-heating treatment increases the number of precipitates in the weld metal and HAZ and the size of the primary austenite grains in the weld metal and HAZ becomes more homogeneous.

The subcooled flow boiling happens when the bulk flow temperature and the interface temperature are lower and higher, respectively than the saturated temperature corresponding to the flow pressure. One way to increase the heat transfer mechanism is to use high porosity metal foams in the ducts, which have a high surface area to volume ratio that increases the heat transfer surface area and the heat transfer coefficient of the duct. In the current study, an experimental apparatus was constructed, and subcooled flow boiling in an annulus tube was investigated. The annulus tube is in the vertical direction, and the internal and external diameters are 50.7 and 70.6mm, respectively. The operating pressure was 1atm, and the working fluid was water. The metal foam used is nickel with 10ppi and a porosity of 95%. In this investigation, heat flux and mass flow rate effectiveness on the heat transfer coefficient are considered. The experiments were performed in the mass flow rate range of 0.012kg/s to 0.0286kg/s in which the flow consists of both forced convection and flow boiling. The mass flow reduction causes the heat transfer coefficient increment to 30% in subcooled boiling regions. The use of porous media also increases the subcooled flow boiling heat transfer coefficient up to 30%.

Spot welding process due to its ability to create a qualitative connection between metal plates and the absence of restrictions on old welding methods such as the impossibility of welding metals by many differences in their melting point is considered as one of the fastest and most economical methods. In this method, an atomic bonding is created on the surface of plates due to high-velocity impact and metal plates are welded together. In the present study, a gas mixture detonation set up was used to perform the impact spot welding tests. Also, the steel plate with a thickness of 4mm was considered as a base plate and steel plates with 1, 2, and 3mm thickness were used as front layers. They were under direct contact with flat- and spherical-nosed metallic projectiles with a mass of 650 and 1300g, respectively. The diameter of the projectiles was 25mm and the average velocity was 600 meters per second. To study the morphology of the weld interface in impact spot welding, the interface of the welds was studied using scanning electron microscope (SEM). Also, the effect of flyer plate thickness and stand-off distance on the spot welding of plates due to projectile impact was studied. The results showed that by increasing the thickness of the flyer plate, the formation of a damaged central area will be decreased. The results also confirmed that when higher stand-off distance was utilized, the velocity of impact was not sufficient to create continuous weld.

Using vortex flowmeter is affordable, in addition, simple installation, high reliability, and high accuracy are some advantages of the vortex flowmeter. Vortex flowmeter works based on the vortex shedding principle, hence, the presence of particles in gas-solid flows may results in modulation in the turbulence intensity of the carrier phase and manipulate vortex shedding generated by a bluff body. In this study, the performance of the vortex flowmeter in the presence of particles with different sizes, density, solid volume fraction, and solid mass loading was studied with CFD simulation. The results indicated that the volume fraction and particles diameter are two significant parameters that affect vortex frequency. The vortex frequency is proportional to the velocity of gas flow and volume flow rate is calculated by Q= VA where V is average velocity in a pipe section with the area of A. Notwithstanding the neutral effect of microparticles on vortex frequency, moderate particles lessen the vortex frequency approximately by 20%. To coincide with the increase of solid volume fraction, the vortex frequency will descend, and in the high level of solid volume fraction, the vortex pattern goes to reach the instability. Since the size and volume fraction of the particles affects the frequency and consequently velocity, the gas flow rate measured by the vortex flowmeter is influenced by the presence of the particles. The numerical results have been validated with experimental data. The maximum relative error between the numerical simulation and the corresponding experimental data is 0.46% and 6.72 % for single-phase and gas-solid two-phase flows, respectively.

In this study investigated the effects of momentum variations on fracture energy in Charpy impact testing of API X65 steel by experimental and numerical methods. Experimental analysis was conducted in the various speed of impact about 3.50 to 5.72 m/s and impact energy varied about 450 to 1200 J. The experimental results showed that increase of about 63% in impact speed increased the fracture energy about 15%, because of material properties dependence on loading rate. Numeral studies were performed in two categories with ABAQUS software. First mass variation in constant velocity assumed standard quantity about 5.5 m/s in which impact energy varied about 300 to 1200 J and the second, velocity variation with constant mass assumed 50 kg that impact energy varied about 625 to 1600 J. The simulation results showed the variations in mass had not any effect in fracture energy and in all analyses, it was about 265 J. However, increasing the velocity variations with constant mass, caused a slight reduction of about 5% in the fracture energy. The reason for the difference between experimental and numerical results is the lack of consideration of the effect of strain rate on mechanical properties of tested steel in numerical analysis.

Wind turbines are one of the most important renewable energy production devices and improving their efficiency leads to more effective exploitation of clean energies. Flow separation on wind turbine blade is one of the major reasons of performance loss in wind turbines. The present paper investigates the effect of single dielectric barrier discharge plasma actuator (SDBD) placement on a critical section of wind-electric wind turbine blade (660kW)) designed inside country. An experimental investigation for assuring the validity of the numerical simulations has been performed. Then, two dimensional simulations were extended to evaluate the effect of plasma actuator performance on flow characteristics. Numerical simulations are based on the latest enhanced electrostatic plasma actuator models. The fluid flow is incompressible and the free stream velocity is about 20m/s. The results clearly indicate that frequency and voltage increase can significantly correct the flow pattern in post stall condition. A linear pattern has been achieved between the frequency and aerodynamic coefficients variations. The best improvement for the range under investigation is more than 800% for aerodynamic performance and approximately 50% for separation point delay.

Thermal image analysis can be used to identify and detect patch defects in the interface between multilayer sheets. Specimens made for testing were carbon fiber and glass fiber patches on aluminum sheets that were embedded in composite patch layers, for interlayer separation, in different metal-patch joints. The defect pattern was designed so that the bugs at the edge and center of the patch were tested simultaneously. In this study, the effects of depth and dimension of separation faults with pulsed heat treatment were identified and investigated. Then, the factors affecting the accuracy of the identified defect size were investigated. In the thermal images obtained, almost all the defects can be identified by pulsed thermography and with increasing the size of the defect the thermal difference with the sound areas increases. It was found that the defects in the carbon fiber field were up to an average of 1°C, there was a greater thermal difference than that of glass fiber field. However, the results showed that the accuracy of the measurement of defects in glass fiber was 2 times higher than that of carbon fiber.

In this paper, the large inelastic deformation and failure mechanism of single and multi-layered circular plates under repeated uniform impulsive loading were studied. The ballistic pendulum was used to conduct a series of experiments (67 experiments) on aluminum alloy plates with different structural configurations. Three different layering configurations including single, double, and triple-layered plates made of the same material were considered and tested for the range of charge masses from 1.5g to 12.5g up to five times for repeated loading. The experimental results indicated large plastic global deformation with thinning happening at the clamped boundary and also tearing for some experiments. The results also represented that the maximum permanent deflections of plates were increased by the increase of the charge mass and the number of blast loads. On the other hand, the progressive deflection of the plates at the center was decreased exponentially with increasing the number of blasts. Furthermore, in the numerical modeling section, the Group Method of Data Handling (GMDH) neural network was used to present a mathematical model based on dimensionless numbers to predict the maximum permanent deflection of single and multi-layered circular plates under repeated impulsive loading. In order to increase the prediction capability of the proposed neural network for this process, the experimental data were divided into two training and prediction sets. Good agreement between the proposed model and the corresponding experimental results is obtained and all and 77% of data points are within the <10% error range for single and multi-layered plates, respectively.

Due to the importance of tumbling mills in processing industries and factories and the lack of an acceptable model for identifying and predicting their performance, it is necessary to optimize these complexes, non-linear, and large systems. This paper aimed to study multi-objective optimization of operating parameters in a tumbling mill. To evaluate the effects of the mill working parameters such as mill speed, ball filling, slurry concentration, and slurry filling on grinding process, power draw, wear of lifters and size distribution of the mill product, it was tried to manufacture a pilot model with a smaller size than the actual mill. For this aim, a mill with 1×0.5m was implemented. The feed of the mill is copper ore with a size smaller than 1 inch. The experiments were done at 65 to 85% of the critical speed. In addition, the combination of the balls was used as grinding media with 10 to 30% of the total volume of the mill. Slurry concentration is 40 to 80% (the weight fraction of solid in slurry) and the slurry filling is between 0.5 and 2.5. In this paper, Adaptive Neuro-Fuzzy Inference System (ANFIS) based multi-objective optimization (NSGA-II) of tumbling mill is done. Level diagrams are used to select the best solution from the Pareto front. The results showed that the best grinding occurs at 70-80% of the critical speed and ball filling of 15-20%. Optimized grinding was observed when the slurry volume is 1-1.5 times of the ball bed voidage volume and the slurry concentration is between 60 and 70%.

The isothermal forging process has the ability to produce complex industrial parts from alloys that do not have high formability, such as aluminum alloys. Eliminating the temperature difference between the part and the die in this method eliminates the problem of cooling the part due to heat transfer to the die. In this study, the hot isothermal forging of AA6061 aluminum alloy in different conditions of process including lubricant type, dimensions and size of primary ingot, temperature and rate of deformation, to produce a complex industrial part numerically and experimentally was investigated. Deform 3D software was used to simulate this process. Comparison of experimental and numerical results showed a good agreement of results. The best dimension of the primary ingot for the studied piece is cylindrical with an initial diameter of 35mm and an initial height of 32mm. Increasing the temperature, reducing the deformation rate and using the appropriate lubricant reduced the amount of required forging force. Reducing the deformation rate from 25-2.5mm/s reduced the required forging force to 1.8 times. Increasing the forging temperature from 380 to 530℃ reduced the amount of forging force about 3.5 times and reducing the hardness of the part about 20%. The results showed that due to the complexity of the forging part, different areas of the part were affected by different strain values, which changes the percentage of secondary phases such as Mg2Si phase in these areas.

Bimetallic parts are widely used in chemical industry, petroleum, heat exchangers, and pressure vessels due to their properties of bimetallic workpieces, especially high weight strength, better mechanical properties, and at the same time reducing cost and weight loss compared to single-layer parts. Among the various processes used to produce these components, extrusion is a good choice for the formation of bimetallic parts due to the compressive stress and the possibility of metallurgical bonding. In the current study, the effect of temperature on the production of bimetallic parts in the case of shell copper and core aluminum alloy by extrusion method has been investigated. In this study, the two-layer connection of metal for a 45% thickness reduction the ratio was performed for three temperatures of 200, 300, and 400°C. Mechanical properties were also examined using a uniaxial tension test and a microstructure by using optical microscopy and scanning electron microscopy. The results showed that at the ratio of 45% thickness reduction at 200°C, there was no acceptable connection between the two layers, and after the process and cutting off the workpiece, the two layers did not separate, but a weak connection was established The microscopy images at the temperature of 300°C showed that this temperature was the threshold for the two-layer connection, and finally, at the 400°C, a more suitable connection was obtained in the bimetal parts.

Due to the increasing costs of energy and reducing fossil fuel, the use of renewable energy is more important. In this study, the possibility of using hybrid energy systems was evaluated to supply electricity to an animal husbandry unit in Mianeh City. For this purpose, three sources including wind turbine, photovoltaics and diesel generator were evaluated in terms of environmental, technical, and economic. This evaluation was performed by Homer Energy Analysis Software, and the results demonstrated that diesel generator is the least expensive solution in compared to other conditions. Then, analysis of the results showed that hybrids of diesel generator-photovoltaic, wind turbine-diesel generator, and diesel generator-photovoltaics-wind turbine systems have low cost, respectively. But environmental results depicted that the use of triple hybrid system in condition of 38% diesel generator, 51% photovoltaic and 11% wind turbine, has lowest emissions, so that carbon dioxide emissions were reduced by 38.4% compared to single diesel. Considering the capital return index, which is a key indicator in the design of feasibility studies, the time of capital return for using a diesel generator was obtained more than three years and seven months. While this index in the condition of using diesel generator-photovoltaic was obtained less than a year, in this respect, this condition was in the first rank.

Because of the inherent structure of welded pipelines, the seam weld can be a potential source for initiation and propagation of crack that can eventually lead to failure of the structure. Due to the critical conditions in the welding region, the investigation of failure energy in gas transportation pipeline is very important for engineers and line designers. In this paper, the three-point bending test (according to the standard specimen of drop-weight tear test) was performed quasi-statically on the seam weld pipe and base metal of spiral seam weld pipe of API X65 steel from which force diagrams were extracted. The presence of sudden load drops in the force-displacement diagram of the specimen in the weld indicated the inhomogeneous structure of the weld. The diagrams of force-displacement, yield and ultimate force, amount of steady crack growth and fracture energy of the metal and seam weld specimens including initiation and propagation energy of crack were investigated and compared. Also, the ratio of the force drop to the ultimate force at the same displacement rate was investigated. The results showed that in seam weld compared to the base metal specimen, the yield force was higher and the ultimate force, the amount of steady crack, initiation and propagation energy of crack were lower. In addition, the lower ratio of force to ultimate force (at the same displacement) in the base metal also indicated a high resistance of the base to the crack propagation.

Prediction of the dynamic behavior of machining operations during the process is the main challenge of machining simulations. Therefore, the investigation of effective parameters in dynamic behavior is of great importance. Machining vibration is one of the most important factors. This article studied the vibration of the process by developing the dynamic model of the boring bar. The high length-to-diameter ratio of the boring tool and its flexibility cause machining vibrations. The amplitude of the tooltip vibrations is a function of the dynamic characteristic of the tool which can lead to the stability or instability of the process. Tool rigidity at low diameter to length ratios is high, and in most cutting conditions the process is stable. The impact test is used to extract the toolchr('39')s dynamic parameters and dynamic modeling of the process is developed inside the environment of ACIS software which is a powerful Boundary Representation (B-rep) solid modeling engine and it is proposed a novel method for simulating the dynamic equation of boring bar by using a solid modeling technique in a precise geometric environment. The mechanistic approach is used to modeling cutting mechanistic to develop the dynamic force model in the time domain. Also, dynamic time-domain parameters such as force, acceleration, and displacement in the Simulink environment are simulated. The results confirm that the presented geometrical model by considering the tool dynamics is well capable of estimating the force signal and the chip area changes.

One of the technologies considered for bioenergy production is microbial fuel cell. The microbial fuel cells are used as a novel method for wastewater treatment and power generation simultaneously. In this method, microorganisms appear as catalysts to convert chemical energy stored in organic matter into electrical energy under anaerobic conditions. In this study, a microbial fuel cell was designed and constructed using microorganisms existing in municipal wastewater to generate electricity. The structure of the current microbial fuel cell was single-chamber, into which added the wastewater. This chamber was adjacent to the anode and fed with anaerobic sludge, existing in municipal wastewater. In the constructed fuel cell, an air-cathode was used which was separated from the anode chamber by a proton exchange membrane. In order to measure voltage at different currents, a variable resistance and a digital multimeter with data storage capability were used. In this study, the developed potential differences due to changes in the type of microorganism, substrate, and the value of external resistance were investigated. Among the two types of substrates molasses and industrial vinasse investigated, industrial vinasse produced more voltage. The maximum current density of 312.7843mA/m2 was measured at 200 Ohm resistance and maximum power density at 600 Ohm resistance and current density of 201.41mA/m2 was measured 85.6010mW/m2.

This research is mainly focused on to study microstructure and mechanical properties of AA5051 aluminum alloy deformed by equal-channel angular pressing (ECAP) process at 200˚C and in BC routes and 4 four passes. The ECAP processing was carried out using die with an intersecting channel angle ‘ϕ’= 120° and corner angle ‘Ψ’= 20°. The results of uniaxial tensile test showed that tensile strength was found to be increased from 115MPa for annealed sample to 239MPa after four passes ECAP in route BC that shows that the strength in ECAP samples has increased. In addition, the percentage of elongation also decreased in initially passes and then increased slowly. Microstructure and grain refinement of specimens were investigated by optical microscopy and scanning electron microscopy and fractography were investigated by scanning electron microscopy. The grain size of annealed sample was 123μm and decreased to 18μm after four passes ECAP in route BC. The hardness also increased from 51HV in annealed sample to 90HV the fourth passes.