نشریه مکانیک مواد پیشرفته و هوشمند
سال دوم شماره 2 (پیاپی 4، تابستان 1401)

Phononic crystals are inhomogeneous structures which are created by periodic arrangement of inclusions in an elastically different host material. By removing of a row of inclusions, phononic crystal waveguide can be obtained. In this research, effects of structural defects on a phononic crystal heterostructure waveguide have been investigated. The heterostructure is composed of square and triangular phononic crystals (periodic arrangement of steel inclusions in epoxy host). To analyze the structure, displacement based finite difference time domain method has been used. The simulation shows that a stub attached vertically to the heterostructure waveguide induces dips in the transmission spectrum. Also, the frequency range of the transmission was limited to a narrow frequency domain of 104 Khz in the cavity-containing waveguide. Finally, the simulation showed that the effect of the cavity that is inserted at the side of the waveguide is insignificant.Phononic crystals are inhomogeneous structures which are created by periodic arrangement of inclusions in an elastically different host material

In the present article, the design and construction of a 3D photocopier is discussed. This device has two main units: 3D scanner unit and 3D printer unit. Today, the need to use 3D scanners in various applications such as quality control, reverse engineering, and computer aided design and production is growing. This machine will be able to take 3D scanning and after processing the scanned image, sends a 3D model to the 3D printer unit for printing and makes a copy model of that part. One of the salient advantages of this design is its use in reverse engineering. It can make a copy model with the desired fit of a workpiece without the need for a measurement process to determine the dimensions, followed by the design process, which in many cases due to the apparent complexity of the workpiece is long, difficult and time consuming, in the least make time. It is possible to repair or change the part after taking the scan, and then send it to the 3D printer unit. Scanning the piece uses the photogrammetric method. 3D printers work with different mechanisms and technologies, the printer movement mechanism is inspired by the delta robot mechanism and printing technology, and extrusion (melting) of raw materials has been selected. The rules and principles of designing and building a 3D printer are explained. It is stated how the observance of these principles and rules will be effective in increasing the accuracy and quality of manufactured parts.

Tube hydroforming is widely used in the production of structural parts of an Automobile. One of the characteristics of the parts produced by this process is the high strength-to-weight ratio. Low-pressure tube hydroforming is one of the proposed methods to solve tube hydroforming problems such as the need for high fluid pressure and sealing problems. The method of performing low-pressure hydroforming of the tube is like to compressing a solid object, in which, unlike high-pressure hydroforming, the upper mold is not fixed during the process and moves and presses the tube at the same time as internal pressure is applied to the tube. In this paper, the low-pressure hydroforming process of AA6063 aluminum tube is performed and the round section of the tube is transformed into a rectangular cross section by the hydroforming process. Also, the thickness distribution and the values of the radius of the formed corner are investigated under three different loading paths. The results show that by increasing the internal pressure, a smaller corner radius can be achieved but the thinning increases. Also, the maximum flat surface of the upper part is obtained when the upper mold is displaced after the internal pressure reaches its maximum value.

The deep drawing process is a widely used method for producing metal sheet parts. The main cost of the die in this method is to make the matrix. Using rubber matrix saves construction time and production cost. Controlling the deformation of rubber and blank is one of the important issues in this method. Therefore, in this article, a comparison has been made between the parts produced by metal and rubber dies. In the following, three-dimensional simulations have been performed using the finite element method and hyper elastic model. The simulation results showed that placing an intermediate ring between the rubber and the blank causes a significant improvement in the production parts and better control of the behavior of the blank and rubber during deformation. For verification, a die with rubber components and also a die with a metal matrix were made, and experimental tests were performed for the steel material. The dies were made based on the primary spacing technique instead of the spring and blank holding system. The maximum percentage of thinning, the percentage of equivalent plastic strain, shrinkage, tearing, and the force on the metal mandrel have been investigated and compared in two types of dies for steel workpieces

Nosing is one of the methods of forming metal pipes, during this process, a metal shell or pipe is guided by a press into a mold that has the shape of the final piece. This method is used to make pressure tanks and CNG cylinders. In this research, the simulation of the nosing process of a steel pipe has been carried out, and then, in order to validate the results of the simulation, it has been compared with experimental tests. Then, with the help of response surface method, a series of experiments were designed and in order to investigate the effect of parameters of thickness, slope of preform pipe wall and friction coefficient between pipe and mold, as well as their interactive effects on the percentage of nosing, analysis of variance method was used. According to the obtained results, the thickness and slope of the preform pipe wall have the greatest effect on the nosing percentage compared to the friction coefficient between the pipe and the mold. A regression equation to predict the percentage of nosing is expressed based on the effective parameters, and finally, the optimal percentage of nosing for the regression equation obtained by the genetic algorithm is obtained.

One of the most attractive modern machining methods is electrical discharge machining, which was introduced in the late 1960s. Electric discharge machining with wires has a number of uses, including high accuracy machining of all conductive materials such as metals, metal alloys, graphite, and ceramics, as well as aerospace, automotive, and other industries. In order to increase the rate and reduce surface roughness and gap width, optimal cutting parameters play a crucial role in selecting output parameters. In this study, input parameters (discharge, pulse duration, pulse frequency, wire speed, wire tension, and dielectric current velocity) were compared to output variables (cutting rate, surface filter, and width). The sensitivity analysis shows that pulse duration parameters, wire speed, and discharge flow are most effective parameters for cutting rate, and pulse duration parameters, dielectric rate, and discharge flow are most effective parameters for surface roughness, as well as pulse duration, wire speed, and discharge current for gap width. Pulse duration with 72%, wire speed with 14%, and discharge current with 10% has the greatest impact on the chip removal rate.

Refineries and petrochemical industries, due to the presence of all-metal equipment and acidic environment, have high corrosion. This study investigated the effect of ultrasonic shock on the corrosion behavior of 316 stainless steels in order to the increasing use of stainless steels in this industries. The aim of this study was to investigate the effect of ultrasonic stress relief method on increasing the strength of parts in corrosive environments. It should be noted that the residual stress in the samples is created by welding. In this study, first the considered sample is De-tensioning using ultrasonic vibration at a frequency of 20 kHz, then the obtained results are compared with the results of samples without De-tensioning operation and also thermal De-tensioning operation. XRD method used to measure the residual stress. The obtained results show that in ultrasonic method and heat treatment, the amount of residual stress is reduced by 58.7% and 54.3%, respectively. It has also been observed that the use of ultrasonic waves has increased the life of the sample in a corrosive environment.