فهرست مطالب رامین مشک آبادی

Although bitumen makes up only a small portion of asphalt mixtures, it significantly impacts their performance. Over the past few decades, bitumen modifier additives, such as nano-silica, have been utilized to enhance asphalt performance. This research aims to investigate the influence of nano-silica on the mechanical properties of asphalt and bitumen mixtures. The study utilized crushed stone materials with grading No. 4 of the Iran Road Pavement code, 70-60 pure bitumen, and nano-silica in varying amounts (2%, 4%, and 6% by weight of bitumen). Marshall and resilient modulus tests were employed to evaluate the mechanical properties of asphalt mixtures, while Marshall's resistance ratio was used to assess moisture sensitivity. Additionally, tests on penetration degree, softening point, and elasticity were conducted to evaluate the effect of nanosilica on bitumen properties. The findings revealed that modification of bitumen with nanosilica led to decreased penetration, increased softening point, and reduced plasticity. Furthermore, the use of nano-silica improved Marshall strength and reduced Marshall's flow in asphalt mixtures, with a 6% addition of nano-silica increasing strength by 41% compared to the control sample. The addition of nano-silica also enhanced the moisture sensitivity of the mixtures and increased the resilient modulus by 95% compared to control asphalt samples.

The use of roller-compacted concrete in construction projects, such as road paving, parking lots, dam construction, and industrial pavement, is attributed to its quick implementation, relatively low cost, and sufficient strength without the need for steel bar. However, the brittle nature of roller-compacted concrete prompted an investigation into how steel fibers could improve its mechanical behavior. This research focused on the effect of steel fibers on fracture strength, compressive strength, and tensile strength of roller-compacted concrete. The study involved testing semicircular samples with edge cracks under three-point bending loading to simulate pure tension, pure shear, and their combination. Additionally, the compressive and tensile strength of roller-compacted concrete samples with steel fibers were evaluated at 7 and 28 days. The laboratory results showed that adding 0.1%, 0.3%, and 0.5% steel fibers improved the 28-day compressive strength by 12%, 15%, and 36%, respectively, and the tensile strength by 14%, 21%, and 39%, respectively. Moreover, the failure load of all samples increased in all loading modes with higher percentages of steel fibers, leading to greater resistance to crack growth. The study identified 0.3% of steel fibers as the most effective amount for improving the fracture resistance of roller-compacted concrete in different loading modes, while the optimal percentage for enhancing the compressive and tensile strength was determined to be 0.5%.

In previous researches, the properties of bitumen and asphalt mixture have been considered for investigation of thermal cracking. In these methods, the roles of different components of the asphalt mixture are not considered. The use of surface free energy and the basic characteristics of asphalt mixture can also be used in the investigation of thermal cracking. In this research, it has been tried to investigate the role of these basic properties of materials in the occurrence of these cracks along with the surface free energy parameters. For this purpose, surface free energy components have been measured for four types of aggregates and eight types of bitumen. Also, the bitumen creep stiffness and m-value were obtained from the bending beam rheometer tests. Asphalt film thickness, aggregate index and the specific surface area of the aggregates have been also determined. For thermal cracking potential, the semicircular bending test was used on 32 different combinations of asphalt mixtures at low temperature. Then, statistical methods have been used for assessing the relationship between the mentioned parameters and the semicircular bending test results. Statistical analysis shows that the basic characteristics of the materials, including the asphalt film thickness, the aggregate index, the free energy of cohesion, the free energy of adhesion, the ratio of basic to acidic components of the surface free energy and the specific surface area of the aggregate have a significant and positive effect on the cracking indices such as semicircular bending fracture energy and fracture toughness.

Today, due to the rapid increase in the bitumen price and environmental problems, the hot mix recycling is taken into consideration in the construction of asphalt pavements. From a technical point of view, fibers are materials that improve a number of behaviors of asphalt mixtures. The aim of this research is to investigate the technical properties of reclaimed asphalt pavement (RAP) in the presence of para-fibers in order to achieve a suitable combination of these parameters. For this purpose, a new approach was utilized to design the experiment, analyze the results and choose the appropriate asphalt mixture. This approach uses a two-level factorial design in the Design Expert software environment based on desirability functions. The results showed that in the mixture containing 50% RAP and 6% bitumen, increasing the fibers from zero to 0.2% increases the Marshall strength value by 17.4% and decreases the Marshal flow value by 3.8%. In the same mixture with 4% bitumen, with the increase of fibers from zero to 0.2%, Marshall's strength and flow increase by 1.8 and 21.5, respectively. The most air voids are related to the mixtures, containing 50% RAP, 4% bitumen and 0.2% fibers. The results for selected materials showed that the suitable combination for the production of reclaimed asphalt mixtures according to the design criteria in Iran Highway Asphalt Paving Code is 6% bitumen, 50% RAP and 0.2% para-fiber.

The use of microsurfacing layer can provide some good preventive characteristics for asphalt pavement surfaces. Various additives can be used to improve the properties of microsurfacing layers. One of these acceptable additives is latex adhesive. It is claimed that latex adhesive as a polymeric material can withstand environmental factors such as alkaline conditions, acidic conditions, the presence of leachate and oil spilled on road surfaces. In this study, the effect of using latex adhesive in different amounts (4 and 5 %) on wet adhesion properties, setting time, compatibility of materials, abrasion resistance in wet track abrasion and sand adhesion of microsurfacings have been investigated. For this purpose, laboratory samples with different amounts of cement (1.5 and 3 %) and bitumen (8, 10 and 12 %) were prepared and tested. The results showed that the use of latex adhesive improves the behavior of microsurfacing in different percentages of bitumen and cement.

Moisture damage in asphalt mixtures generally occurs due to the separation of bitumen from the surface of stone materials and due to the presence of water. This type of failure causes stripping and premature failures. Investigating the effective factors in this type of damage can be useful in improving the process of designing and producing asphalt mixtures. In the past years, significant research and efforts have been made to reduce these types of failures. In this article, the effect of adding Polytec 505, as a new material with complex amines that reduce the acidic nature of bitumen, on the moisture damage of asphalt mixtures has been investigated. For this purpose, two types of granite and lime aggregate and 60-70 bitumen have been used. The modified Lottman test was used to check the moisture damage, and pull-off tests were used to evaluate the cohesion properties of bitumen and the adhesion of bitumen to aggregate. The results show that the use of this additive causes an increase in the indirect tensile strength ratio of samples with granite and limestone aggregate, and as a result, the performance of these samples against moisture damage improves. This improvement increases with the increasing of this additive. The results of the Pull-off test show that the use of this additive improves the adhesion and cohesion of pull-off pull off test.

In this research, semi-solid powder processing was used to fabricate Al7075-CNT nanocomposite. The effect of process variables including compression time, semi-solid temperature and the CNT percent on the sample’s hardness and microstructure was investigated. The 1%-CNT nanocomposite is observed to be superior in hardness compared to the base alloy, but the 2%-CNT sample’s hardness was between the base alloy and 1%-CNT sample. It was observed that the compression time and semi-solid temperature do not have a significant effect on the sample’s hardness. Compression for 10 minutes and forming temperature of 620 °C were selected as the suitable variables. Microstructural examination showed that in 1%-CNT alloy, the reinforcing phase is completely penetrated in the aluminum matrix and there is no CNT accumulation on the sample’s surface unlike the 2%-CNT sample. Quantitative analysis showed that a proper percentage of CNT had the greatest effect on the hardness. Increasing the temperature from 600 to 620 °C by 10% and increasing the compression time from 5 to 15 minutes by 2% increased the hardness of 1%-CNT samples compared to the base alloy.

In this study, the strength of hot and warm asphalt mixtures containing 3% Sasobite in cold regions has been investigated using the principles of fracture mechanics. The effect of temperature and loading modes (tensile and shear) on the fracture toughness of the mixture was investigated using a semicircular samples with an edge crack under three-point bending. The coefficient of critical stress intensity was determined from the results of the fracture test and the shape coefficients were determined from finite element analysis in ABACUS software. In hot and warm asphalt mixtures containing 3% Sasobite, with decreasing temperature, the critical stress intensity coefficient increased in tensile and shear modes. The results showed that the hot asphalt mixture at temperatures of 0, -10 and -20 °C presents significant fracture resistance compared to the warm asphalt mixture in all loading modes. As the temperature decreases, the fracture toughness of both types of both asphalt mixtures increases.

One of the conventional recycling methods of asphalt mixture is the reuse of reclaimed asphalt with cement as a method for treatment of the base layer and its replacement in pavement layers. In this research, cold recycled asphalt mixture with using emulsified asphalt binder has been investigated through response surface method. In this regard, the technical and economical aspects of fabricated samples of recycled cold asphalt mixtures using crushed asphalt materials, cationic emulsified binder and Portland cement (type II) were investigated. Marshal strength and flow, bulk specific gravity and air voids of mixture were determined by experiments. By performing analysis of variance on the proposed models and determining the effective parameters, mathematical equations between independent and dependent parameters were developed and the effect of the parameters was investigated. Finally, an optimum mix design, which has 60% desirability, was suggested for cold recycled asphalt. Results showed that emulsified binder and cement content have significant effect on the marshal strength. Also, water exhibit a significant effect on the flow of asphalt mixtures.

The defectless microstructure of metal matrix composites, the uniform distribution of particles and their good properties are determined by the production parameters and the base material and reinforcement. In this study, high-energy planetary ball mill was used to fabricate Al6063-SiC composite powder. Aluminum chips were milled with different time and ball to powder weight ratio (BPR) in high energy planetary ball mill. The resulting powder was mechanically alloyed by adding different weight percentages of silicon carbide (SiC) and BPRs at different times. During the milling process under argon atmosphere, stearic acid was used as a process control agent (PCA) to prevent excessive cold welding and agglomeration of the powder. After mechanical alloying, the effect of alloying time, BPRs and weight percentage of silicon carbide, on the obtained composite powder were examined morphologically by particle size analysis (PSA), field emission scanning electron microscope (FESEM), and the fuzzy compounds by X-ray diffraction (XRD) spectroscopy. According to the X-ray diffraction pattern of the samples, grain size was calculated using the Williamson-Hall model. The results of mechanical milling and alloying process have shown that in short milling times with high BPRs composite powder with finer particle size could be achieved. Also, the presence of silicon carbide reinforcing particles accelerates the process of mechanical alloying and further reduces the particle size.

In previous studies, the effect of different types of polyethylene on the performance of asphalt mixtures has been investigated. In this research, the mixing design of asphalt mixtures containing high density polyethylene has been analyzed and modeled based on the conventional and the response surface methods for limestone and granite aggregates. For this purpose, the volumetric and strength behavior of laboratory-made samples have been measured and statistically analyzed. In the optimization process,, the optimal amount of binder and polyethylene has been extracted according to the criteria of the asphalt pavement regulations for Iranian roads and with the desirability approach. Experimental results show that the optimal conditions for limestone aggregate are 6.1% binder and 4% polyethylene with a desirability of 0.909. However, these values for granite aggregate are 5.9% binder, 4% polyethylene with a desirability of 0.962. The polyethylene additive increases the Marshall strength and specific weight of the samples for both materials. The higher percentage of additive has the greater effect on these parameters. Analysis of variance shows that polyethylene percentage has a significant effect on Marshall flow. By increasing the amount of additive from zero to four percent, the flow value decreases.

The recent increase in bitumen prices and environmental considerations has expanded the use of recycled asphalt mixtures. These mixtures are prepared with different percentages of recycled and new materials including bitumen and aggregate. Sometimes it is necessary to examine the effect of different laboratory parameters quickly and with a smaller number of samples. In this paper, the Taguchi method with 3 effective factors including the percentage of recycled materials (in three levels of 0, 25 and 50%), type of recycled materials (in two levels of two different sources) and the percentage of bitumen (in 3 levels of 4, 5 and 6%) was used to design experiments for rapid analysis of laboratory samples. The strength and volumetric characteristics of asphalt mixtures were determined and analyzed using Minitab software in L18 orthogonal array. The effect of each of the input parameters on the obtained results was determined by signal-to-noise ratio and analysis of variance. The results showed that the percentage of recycled materials significantly affects the strength and volumetric behavior of recycled mixtures. Contrary to expectations, the effect of the source of recycled materials is less than other input parameters.

Thermex is a thermo-mechanical process which is used as an in-line operation after rolling process. By using this process, the yield strength of the rebar reaches to at least 500 MPa. Due to the importance of using high-strength rebars, in the present study, the influences of the process parameters on the rebar’s mechanical properties are investigated using experimental techniques. Considering four effective factors including water flow rate, Thermex pressure, rolling speed and different furnace temperatures, standard tensile tests were performed. The required experiments according to Taguchi method were designed and then the effect of mentioned parameters on the mechanical properties (yield strength, ultimate strength and ductility) of the rebar was studied. Statistical investigation includinf signal to noise (S/N) ratio and analysis of variance (ANOVA) showed that all the mentioned parameters have s significant influence on the mechanical properties. Based on the results, the optimal values of the parameters were determined to achieve optimal conditions of strength and ductility.

The effect of size distribution of metal powder particles on the density and strength of fabricated parts under high velocity impact loading has been investigated in this paper. Experiments have been performed on aluminum powder using gas gun apparatus. To do so, pure aluminum powder with three different sizes has been compacted and both density and strength of compacts have been compared. The obtained results show that the coarsest particle size, has the maximum value of density. To evaluate the effect of mixing powder particles with different size distributions on properties of compacts, three initial powders with different weight ratios have been mixed together. The obtained results show that the density of composite part increases as the content of powder with greater particle sizes increases, but this has no particular effect on strength. Next, a mathematical modelling using neural network method has been presented to predict the density of compacts. Through this method, obtained experimental values are used as input by the neural network method. Comparison of values predicted using this model with those obtained by experiments, represents an appropriate level of adjustment.

The safety is one of the important part of traffic engineering and road lighting issue, which aims to achieve a degree of visibility for drivers, so that a quick, accurate, and convenient visibility can be achieved. The driver's visibility can prevent some accidents caused by road traffic at night. In this paper, the linear programming method is used to locate and optimize the lighting system in Ahar - Tabriz, Sarab - Bostanabad and Maragheh - Hashtrood roads. A model was designed based on maximizing the benefit /cost ratio. In order to calculate the savings due to the reduction of accidents by using lighting systems, the approximate average cost of a fatal accident was calculated in the country. Also, the amount required to install the lighting system in different parts was defined. The constraints for this model are the allocated budget for the installation of lighting systems. In order to analyze the model, WinQSB2 software was used to obtain optimal sections for the installation of the lighting system. Based on this research, the ranges of 44 + 500 to 45 + 500 and 54 +500 to 55+500 of Ahar-Tabriz road with a profit ratio of 8.26 and 8.07 in all budget scenarios and segmentation at the top of other components were determined as the optimal sections. The 09 + 500 and 10 + 500 Kilometers of Maragheh-Hashtrood road with a profit ratio of 5.13 was also ranked next.

In the present study, the effects of defects in the honeycomb structure on the capability of the energy absorption are investigated using the finite element method in ABAQUS software. By simulation using quasi-static analysis, the effects of the geometric dimensions of the defect and different geometries of honeycomb cells on the energy absorption of the structure have been investigated. In the analysis, for each case three percent of defects, including 0, 10 and 30% were studied. The results show that the honeycomb structure with A-type cell geometry is completely destroyed, which can be due to the asymmetry of the structural cells. In the other two models, the structure retains its overall shape and by systematic modification of the cells, they have the ability to absorb energy during the collision. Also, the results show that the defects in these structures have a significant effect on their energy absorption capacity in which by increasing the defects, the energy absorption capacity decreases.

Trusses is one of most usable structures in engineering. Truss is combination of bar elements created. Triangle shape is most stable possible are formed by bar elements in truss. In this research, effects of variations in internal angles, elastic modulus, diameters and loading on truss members and displacement in joints were evaluated. For this purpose, 45 models in Sigma/w analyzed. Results of present study showed that with decreasing elastic modulus in members, vertical and horizontal displacement in joints increase. Also, horizontal displacement in supports with two freedom degree is more than supports including one freedom degree.

Trusses is one of most usable structures in engineering. Truss is combination of bar elements created. Triangle shape is most stable possible are formed by bar elements in truss. In this research, with using statistical analyses methods effects of per parameters such as material, diameter of bar, applied force to joints, combination of interior angles in vertical and horizontal displacement in Pratt truss have been evaluated. For this purpose, 45 models in Sigma/w analyzed. Then, statistical analyses on data’s by using SPSS program have been performed and continuity of parameters with considering of displacement in joints was evaluated. In finally, a relationship for estimation of maximum displacement in joints of truss has proposed. Results of this study showed that in single parameter mode, a scenario with combination bar diameter, elastic modulus and angles between elements results much better than scenario with considering force in joints. According to results of Pearson test it can be explained that maximum displacement in joints have liner direct relationship with diameter, elastic modulus, applied force and angle between elements.

Metallic alloys exhibit rheological behavior similar to non-Newtonian fluids in the semi-solid temperature range. This behavior can be described using rheological models. In this study, the viscosity of semi-solid 7075 aluminum alloy was measured by using the results of load-displacement signals obtained from two different experiments: parallel plate compression and backward extrusion. The obtained data were used to determine the parameters of the Cross model in a wide range of shear rates. The effects of temperature (solid fraction) and shear rate were studied on the viscosity of the alloy. The results showed that with increasing temperature and decreasing the solid fraction the resistance to flow decreases, resulting in a reduced amount of applied forces. This reduction in applied forces results in reducing the viscosity. It was observed that the behavior of semi-solid alloy is shear thinning in which the viscosity decreases with increasing shear rate. Also, the calculated viscosity values of the four parameters Cross model were in good agreement with the obtained experimental results in a wide range of shear rates. The simulation results showed a good agreement of the presented model for predicting the rheological properties and flow behavior of the semi-solid alloy in a wide range of shear rates.

The quality of parts in green sand mold casting mostly depends on the green sand properties such as compressive strength، permeability، mould hardness، etc. These parameters depend on input parameters like water، size and shape of the sand، percentage of bentonite and so on. The compressive strength of sand of different moisture contents which is required for modeling، obtained by experimental tests، and a research method، based on Artificial Neural Network (ANN). The predicted values of the compressive strength obtained by the ANN and new experiments found to be in good agreement with each other and showed that by using Artificial Neural Networks one can estimate the compressive strength of green sand precisely before molding.

Gas tungsten arc welding (GTAW), is one of the important methods used in industry and it is an arc welding process that uses a no consumable tungsten electrode to produce the weld. GTAW is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminum, magnesium, and copper alloys. In this research the authors have designed and manufactured an automatic welding arm in which its feed is controlled by a microcontroller. In different conditions like feed, ampere and pre-heat temperature practical tests have done and tensile strength of the welded parts has measured. Then by using this data an artificial neural network designed and tested. The inputs of the network are adjustable parameters of the welding process and the output is the tensile strength. The results show that by using neural networks we can determine the tensile strength precisely before the process.

The Finite Element Method (FEM) is one of advanced methods in modeling of solid mechanics used in the design and analyzing of prosthesis in the human body. One of the important factors in designing a femur (the linkage between basin and knee) which is under complicated stresses is to minimize the amount of the stress in the components of the prosthesis due to the body weight. In this research the authors have used prosthesis of two different substances to investigate the affect of the materials in the fatigue analyze. The other important factor is to apply a suitable linkage between prosthesis and bone called cement in order to prevent the slip of stem shape in the femur. In finite element analyze we have used contact elements for modeling the surfaces in contact. For the contact surface of stem shape and femur we have considered three cases: Bonded, slippage with the coefficient of friction 0, 0.22. We have used Genetic Algorithms (GA) method to optimize the shape of prosthesis. The results have been compared with the results presented by Charnley which shows an improvement in the shape of prosthesis. The optimized angle is about 132 degrees.