نصرالله بنی مصطفی عرب

In this paper, using analytical, numerical and experimental methods, the range of ballistic limit thickness and fragmentation behind the metal target for the PELE projectile has been investigated. PELE projectile consists of two parts: hard shell with high density and soft core with low density. The soft core is compressed inside the hard shell and upon impact, the hard shell penetrates the target. There are limited models to analyze the penetration and fragmentation of this projectile, and few researchers have addressed this issue. Considering the effect of target characteristics (thickness and material) on the rate of fragmentation and the failure to consider these parameters in the models presented so far, establishing a relationship between the main parameters (target, impact velocity and projectile), using two shock theories and the dynamic expansion of the spherical cavity and their combination with the cracking model have been investigated in this article. In parallel, the experimental tests of the impact of the PELE projectile on the metal target (gas gun - extraction of ballistic limit thickness) and also 3D simulation of finite elements (Auto Dyna software - extraction of shrapnel number) have been carried out in the impact velocity range of 312-780 m/s. According to the appropriate results of the shock wave method compared to the results of the dynamic expansion of the spherical cavity (smaller difference compared to the experimental and simulation results), the final ballistic performance range (the number of shrapnel according to the target thickness and impact velocity) of this method for the velocity range impact rates of 100 to 1000 meters per second were extracted.

In recent years, additive manufacturing has gained significant importance in the field of production. Most of the additive manufacturing technologies for metals involve melting and solidification processes, leading to metallurgical challenges. The friction stir additive manufacturing process is a novel solid-state method that does not face the common metallurgical challenges associated with the traditional melting methods. This process can be used for the production of aluminum-silicon carbide nanocomposites that find many applications in industries such as military, aerospace, automotive, etc. The primary objective of this research is to experimentally analyze the effect of tool rotational speed, tool traverse speed, and number of passes in friction stir additive manufacturing on the microhardness and wear amount of aluminum-silicon carbide nanocomposite manufactured by this method. To this end, the response surface method and Minitab software were used for experimental design, statistical analysis, and optimization of the parameters. Multi-objective optimization settings were selected to increase microhardness and reduce wear. The combinations of optimal values of the parameters were determined to achieve the optimization goals, and the results were validated. The optimization result with 0.87 desirability is obtained with a tool rotational speed of 1000 rpm, a tool traverse speed of 50 mm/min, and one pass. The predicted optimal responses of 104 Vickers for microhardness and 0.013 gr for wear had a small percentage of error compared to the experimental results.

7075 aluminum alloy, with a high strength-to-weight ratio and good impact strength, is one of the useful materials in the aerospace and automotive industries. However, this alloy has limitations such as poor formability, high spring back at low temperatures, and thermal distortion during hot forming. To overcome these limitations, a thermomechanical process including solution heat treatment, forming, and quenching in the die can be used. In this research, for producing a U-shape part with a depth of 30 mm, a 7075 sheet with a thickness of 2 mm was first subjected to solution heat treatment at a temperature of 480 ℃, and then was immediately transferred to a cooling die to be formed at a temperature of 4 ℃ under a hold time of 20 seconds. Finally, the part was artificially aged to improve its mechanical properties. A finite element simulation of the process using the ABAQUS software was also performed. Good dimensional accuracy and absence of rupture in the final U part, close agreement between the experimental and simulation results, an acceptable 25% reduction in elongation, very close tensile strength to the base material, and microhardness equal to 95% of the base material are the results of this research.

Polypropylene/ ethylene–propylene-diene monomer/ Nanoclay (PP/EPDM/ Nanoclay) nanocomposite with different loadings of clay content is used in many industries because of balance on the tensile and impact strengths. Laser welding, as a fabrication method, is applied to the butt-welding of these nanocomposites. The input parameters (clay content, laser power, scan velocity, and stand-off-distance) were varied to achieve the best responses (tensile strength of welds). Response surface methodology (RSM) was utilized to relate the input parameters and the response. The effects of all input parameters on the responses were investigated. Results demonstrated that increasing the clay content from 0 to 6 wt% and increasing stand-off-distance from 5 to 8 mm decreased the tensile strength from 9.6 MPa to 6.1 MPa and 9.19 MPa to 8.36 MPa, respectively. The models showed that laser power of 100 W, traverse speed of 400–750 mm min21, and stand-off-distance of 5 – 6.5 mm, led to weld strength from 8 to 9.9 MPa.

In this research the effect of different rotational speeds and different chosen materials for producing the Bobbin tool in friction stir welding process on hardness and impact resistance alterations for Aluminum 6061-T6 alloy is being studied. According to the results, the most desirable tool to accomplish this process should be from H13 hot-work steel and the pin length should be as long as the work piece thickness. The most optimized ratio between tool shoulders diameter and pin length is about 3 to 5. Accordingly, the designed tool for the mentioned process had 20 mm shoulder diameter, 6 mm pin diameter and 4 mm pin length. Results showed that increasing the rotational speed had desirable effect on connections outward quality and also cause raising the amount of consumed energy for breaking the work pieces and naturally it decreases the return angle of the projectile. Microstructure hardness tests showed that welding speed increasing caused welded zone grains size changing. So it will increase the weld hardness. Furthermore, joints macrostructure’s defects studied and determined that increasing rotational speed has good effect in decreasing these defects. Also in this research, the effect of using HSS tool steel as the bobbin tool material checked that despite better results in hardness tests in same speeds in compared with H13 hot-work steel, finally H13 chose as the bobbin tool material due to the better strength in most other speeds. 1500 rpms selected as the best rotational speed in terms of affect on mechanical properties.

Nowadays, the use of polymer composite materials in various industries has been increased due to their good mechanical properties, lightness, sound and thermal insulation and corrosion resistance. Over the past two decades, carbon fiber reinforced polymer (CFRP) materials have been widely used in aerospace and automotive industries. These materials may be subjected to impact during manufacturing or service period and a lsmal impact region may be produced in them. This small defect can reduce the mechanical properties of the structure and lead to its failure. Therefore, it is necessary to use a method for defect detection in these materials. In this study, a polymer composite sample made of carbon fiber in polyester resin was made and subjected to impact test. To consider the repeatability of the defect detection process, the sample was subjected to four various impact tests and the defect areas were evaluated using penetrant-enhanced X-ray radiography and ultrasound immersion pulse-echo C-scan. The image obtained from the penetrant-enhanced X-ray method was scanned using a digital scanner, and the image of the ultrasound C-scan test was calibrated, taking into account the step of scanning.The areas of the defect region were obtained using Imagej software. The results show that these methods are able to detect and measure the impact area in the composite sample and Ultrasonic C-scan method detect impact area more accurately.

Welding plays an important role in manufacturing and it is a reliable and efficient joining process in which the coalescence of metals is achieved by fusion. Nowdays welding is as the main and most common process for joint of metals. Among the welding methods, Laser Beam Welding) has the potential of welding very small and precise components. Localized heating with solidification of the melt, makes the connection between parts. In this thesis, laser spot welding process, which is one of the varieties of LBW process, is studied. In fact the laser spot welding is a simple type of laser welding that is widely used in various industries. The low strength of joints can damage structures. Therefore it is important that the strength of the joint be estimated and optimized. In this research, investigation and optimization of the laser spot welding process using design of experiments and response surface method is considered. Three parameters (peak power, pulse duration and thickness) of the process at three levels were the input factors. Material of sheets that was used in this research is AISI 304 stainless steel. The response or output factor was tensile - shear strength. Minitab16 software was used for design of experiments and analysis of the results. Finally, results showed that increase the peak power until 4250 watt and pulse duration until 3/5 millisecond provide the most tensile - shear strength (2200 Kg), and Square of thickness has the most negative effect on tensile shear strength of the joint.

In this paper, ultrasonic lap welding process has been used for welding of standard specimens of polypropylene composites reinforced with glass fiber with 4 mm thickness. The tensile-shear strength and appearance properties of welds under was used different conditions of time, pressure and vibration amplitude and glass fiber content were investigated. To investigation the relationship between input variables and appearance properties of welds and weld strength, the response surface method to decrease the number of experiments and costs considering four factors at three levels. Based on experimental observations, effects of input parameters on appearance of welds were clearly evaluated. The results indicated that amplitude and pressure had the most and the least significant effect on the tensile-shear strength of these composites respectively. Best appearance condition of welds (which has least weld defects) was resulted at an amplitude of 33 µm, welding time of 0.4s, pressure of 1.5 bar and glass fiber content of 10%. Increase of welding pressure, time and glass fiber content in composites has negative effects on welds appearance status and causes weld defects increase.

Nowadays welding is the most important and the most common joining processfor Metals (and sometimes other metals). Among the existing methods for welding, ressistance welding uses heat and pressure simultaneously, In this thesis, effect of the process parameters on torsional strength of resistance projection welds in sheet metal and nut with different thickness has been investigated. Welding time, welding current and electrode force are the most important factors affecting the quality of a the weld. The Minitab16 software and response surface method have been used to conduct experiments to find the effect of the above parametrs on torsional strength.

Engineering components during service are exposed to destructive phenomena such as wear which may lead to their destruction. For their protection and reduction of costs of replacement of these defective components and also increasing productivity, attention is given to welding processes for depositing a wear-resistant layer on the components. In this research, the effect of welding current on last layer weld quality deposited on carbon steel by shielded metal arc welding process using Fe-based hardfacing electrodes is investigated. The chemical composition of the weld deposit layers was studied by quantometery. Optical and scanning electron microscopes, energy dispersive X-ray fluorescence and X-ray diffraction were used for microstructural studies. Microhardness and pin on disk wear tests were also employed for microhardness and wear resistance evaluations. The metallography and X-ray diffraction results show presence of martensite and retained austenite in the microstructure of the last deposited weld layer. The results of chemical analysis and microhardness and wear-resistant tests show that increasing the current increases weld dilution which leads to reduction of alloying elements affecting hardness and wear resistance of the weld deposit and hence these properties decrease slightly. Evaluation of the worn surfaces shows that the wear mechanism on the last deposited layer is of abrasive wear type.

In this study, the effect of heat input on microstructure and mechanical properties of magnesium alloy, AZ91, were investigated. The butt welding was carried out at three different heat inputs (269, 452, and 657 J/mm), using a tungsten arc welding process under the protection of inert gas (GTAW). Microstructure observation with optical (OM) and scanning electron, microscopes (SEM) showed that with an increase of the heat input, the grains both in the fusion zone and the heat-affected zone coarsen and the width of the heat-affected zone increased. Moreover, an increase of the heat Input up to 657 J/mm resulted in a decrease of the continuous β-Mg17Al12 phase and an increase of the granular (particularly in weld area) and randomly dispersed. The results of tensile tests show that at high heat input the welding strength will decrease to 114 MPa, due to creation of gas voids in the welding area. This value is 21% less than that observed for lower heat input (269 J/mm).