فهرست مطالب s. m. hossein seyedkashi

Double-layer sheet forming methods are developed in various industries due to their dual properties and wide application. In this paper, the numerical and experimental investigation of the bowing defect in the flexible roll forming process of double-layer sheets have been discussed. Numerical analysis has been conducted using Abaqus finite element software and experimental tests using a single-station flexible roll forming machine. After validation of the numerical model, the effects of significant parameters on the bowing defect in the flexible roll forming process, including the forming angle, sheet thickness, sheet wing length, and the displacement of sheet layers have been investigated using full factorial design of experiments method and finite element simulations. The results were analyzed using the Analysis of Variance statistical method. The results showed that with increase of the forming angle and wing length, the amount of bowing defect increases while it decreases with the increase of the thickness of the sheet. Also, the arrangement of layers is also effective in the occurrence of the bowing defect. The results showed that the bowing defect in the Al-Cu layer material increased from 2.152 to 2.646 mm with the increase of the wing length from 18 to 25 mm.

In friction stir welding process, a non-consumable rotary tool is used which consists of a pin and a shoulder. The tool/workpiece friction results in stirring, plastic deformation, and joining. It is the shoulder penetration which leads to thinning of the upper sheet and remaining of a hole. In this study, a stationary shoulder was used to investigate the spot welding of a non-alloyed aluminium sheet to address the mentioned drawback. The aim was to investigate the effects of tool rotational speed with two levels of 1000 and 2000 rpm, tool shoulder diameter with two levels of 20 and 24 mm, and plunge depth with two levels of 3 and 3.5 mm on the microhardness, strength, and microstructure of the welded samples. Feed rate and dwell time were constantly set to 20 mm/s and 10s, respectively. Optimization was carried out in three modes including maximum strength, maximum hardness, and a combination of the maximum strength and hardness. In the first mode, the maximum strength was 1389.51 N in the specimen welded with a tool rotational speed of 2000 rpm, plunge depth of 3 mm, and tool shoulder diameter of 24 mm. In the second mode, the highest micro-hardness value was 91.33 HV in the specimen that was welded with a tool rotational speed of 1000 rpm, plunge depth of 3.5 mm, and tool shoulder diameter of 20 mm. Finally, in the third mode, the combination of the highest strength and micro-hardness values were 1389.51 N and 85.66 HV, respectively.

In this paper, a new production method of aluminium/steel double-layered wire is proposed using a modified friction stir extrusion process. The core and coating were made of St37 steel and aluminium alloy, respectively. For extruded specimens, the effects of the main process parameters including tool rotational speed and feed rate were investigated on adhesion strength and surface cracks. The tool rotational speed was studied at two levels of 300 and 600 rpm, and the feed rate at two levels of 4 and 12 mm/min. Pull-out test was carried out using a tensile test machine to evaluate the adhesion strength. Surface cracks were evaluated by the liquid penetrant test. The results suggest that the modified friction stir extrusion process can be used successfully to produce dissimilar double-layered wires. With the right combination of tool rotational speed and feed rate levels, a dissimilar double-layered wire can be produced with a high adhesion strength and good surface quality. No cracks were observed in specimens produced with the feed rate of 12 mm/min and rotational speed of 600 rpm. The maximum adhesion strength was 2867.13 N that was achieved with a tool rotational speed of 300 rpm and feed rate of 12 mm/min.

The addition of nanoparticles to the multilayer sheets improves the properties and performance of these laminates. In this research, the deformation process in metal-nanocomposite laminates including polypropylene matrix reinforced with nanoclay and glass fibers as core layer and annealed aluminum 1050A as the skin layer has been investigated using experimental method. In this regard, the effect of different weight percentages of nanoclay relative to the base phase, including 1, 3, 5 and 7 wt% on the values of drawing depth and maximum drawing force in the stamping process has been measured. In order to determine the effects of adding nanoclay particles, the results of deformation of metal/nanocomposite laminates are compared with metal/composite laminate including pure polypropylene reinforced with glass fibers. The results show the ability to perform stamping process of metal/nanocomposite laminates. It was observed that in general, with the addition of different percentages of nanoclay particles, drawing parameters including the maximum drawing force and the drawing depth have changed. Also, the failure mechanisms in all samples are crack growth in layers and delamination of layers. Addition of nanoclay particles has no effect on the principle of failure mechanism in the stamping process of metal/composite laminates and only affects the values of the process parameters.

Metal sandwiches are a new class of ultra-lightweight materials made from a porous metal core and two outer metal plates. High strength and high energy absorption capacity, resistance to heat, and also fast and inexpensive recyclability make these materials ideal for use in many industries including automotive, aerospace, oil, energy and construction industries. Considering the advantages of friction stir welding, the connection of these plates using this welding technology can be used industries for welding of bimetal sandwiches. In this research, feasibility of using frictional stir welding to prepare metal sandwiches with a core of aluminum foams and copper covers was investigated. The investigated parameters were tool rotational speed, in three levels of 2000, 2500 and 3000 rpm, and tilt angle in two levels of 5 and 7 degree. The cross-sections of the joints were investigated for weld quality which confirmed a successful joining. Tensile tests were carried out to evaluate the joint strength. It was concluded that the effect of tool rotational speed on the weld strength is much higher than the effect of tilt angle and has a reverse relation with tensile strength. The best strength which was 18.8 MPa was obtained with a tool rotational speed of 2000 rpm and a tilt angle of 5 degree.

Non-destructive test is one of the techniques that is used to ensure the health of concrete structures. In order to retrofit concrete columns, it is necessary to know the number of reinforcement steel bars embedded in concrete and their cover to the concrete surface. In this paper, for the purpose of obtaining the reinforcement cover to surface of concrete in concrete columns, finite element simulation is performed by using Maxwell software and a special type of measuring probe is designed and fabricated. When a conductor such as reinforcement steel bar approaches the coil and ferrite core, the reinforcement bars interacts with low frequency electromagnetic waves, and by measuring of these waves’ effects from the concrete surface, the location of the reinforcement can be estimated. The designed probe was tested on different reinforcement covers with various frequencies and the recorded results were evaluated. The reinforcement cover can be estimated from the inductance variation and the ohmic resistance of the coil while the frequency and voltage are kept constant. Effects of the reinforcement cover to the concrete surface and frequency on the ohmic resistance and inductance of the probe are evaluated by using three-level full factorial designs and a regression model from effective parameters is prepared. Finally, the neural network is employed to estimate the reinforcement cover with different values of frequency, the reinforcement cover to concrete surface and the ohmic resistance of probe.

In the present study, a 3D finite element model was developed using DEFORM commercial software to analyse the material flow and phase transformation, as two key phenomena affecting the joint properties in friction hydro-pillar processing of 1045 steel alloy. The microstructure changes significantly due to the high temperature and strain rate. The final microstructure was intergranular pearlite and grain boundary allotriomorphic ferrite. Pearlite was the dominant phase at the final microstructure; thus, its volume fraction was used to validate the model where a good agreement was obtained with the experiment. According to the model, the pearlite volume fraction varies from 100% to 70% moving from the bottom of the stud to the top. The model suggests an inverse relation between the strain rate and pearlite volume fraction. The highest temperature which was experienced in the welding step was 1490 ºC while it dropped to 890 ºC in the forging step. Downward and then radial material flow was detected in the welding step while upward extrusion of material was the dominant material flow pattern during the forging step. Flash was formed mainly in the forging step from stud side material.