مجله مهندسی ساخت و تولید ایران
سال هشتم شماره 7 (مهر 1400)

The friction drilling process is a new process for producing cylindrical holes. In this process, a conical tool made of tungsten carbide is used and a bush is created along with a hole in the back of the part after drilling. The advantages of this new process include reducing drilling time and no chip production. In this paper, the friction drilling process is performed by combining ultrasonic vibrations. To perform the above process, a suitable ultrasonic horn was designed and made also a conical tool made of tungsten carbide with optimal angles was used for drilling. St37 steel material type was selected for workpiece. To investigate the effects of ultrasonic vibrations on the friction drilling process, micro-hardness tests, surface roughness test, corrosion test, and metallographic imaging (light microscope images and SEM images) were used. The results of this study indicated that the ultrasonic vibrations assisted friction drilling process increases the micro-hardness about 13 percent at special rotational speeds and vibrations intensities. Also, the corrosion resistance of the workpiece increased by about 57 percent in the case of applying vibrations of 96 W / cm2 intensity. According to the metallographic imaging, it was observed that the grain size and the amount of cavities of the workpiece are reduced due to the application of ultrasonic vibrations and these results is expressed qualitatively and comparatively.

The use of lattice structures has always been envisaged by researchers and various industries because of their unique mechanical properties and low weight. One of the main challenges in this area is the manufacturing process of these structures, particularly in mass production and commercialization. Pyramid-metal tubular lattice structures are among the most optimal lattice structures for energy absorption. The connection of tubes to metal plates is one of the main challenges in the construction of these types of structures. In this research, rather than using metal molds and fixtures, the toothed appendages are created by cutting the ends of the tube and place them in the holes of the plates in order to fix the position of the tubes in the brazing process. Mechanical locking of tubes and plates enhances connection strength and structural stiffness. In this study, specimens have been made with various geometries and the effect of geometrical parameters such as the length to diameter ratio of the tube and its angle of orientation on energy absorption were investigated. The manufacturing process used in this research was very efficient and none of the samples were damaged at the joint. Increasing the orientation angle from 45 to 55 increases the specific energy uptake by up to 40%.

In the present study, failure strength of the type-IV CNG fuel tank under burst pressure test in both constant and variable thicknesses was analized using finite element simulation. Afterward, optimal fiber twist angle was optimized to achieve maximum resistance to burst pressure in both models. To this end, the test specifications stated in NECE R 110: 2016 standard and von Mises yield criterion were used to determine the critical area which is prone to failure in the tank. The simulation results showed that the separation occurred in the lower flange of the tank and the location of the low curvature shell in the tank with the constant and variable thicknesses, respectively. Validation of presented finite element simulation for prediction of burst pressure in both design modes, including constant and variable thicknesses, using the technique of comparison with experimental results showed that an acceptable agreement was established between the experimental and numerical results. Also, the results showed that the optimal fiber twist angle to achieve maximum resistance to burst pressure for both design cases (constant and variable thicknesses) was 23° (670 bar) and 15° (780 bar), respectively. Finally, applying the results of this study can lead to a 22% increase in the failure strength of the type-IV composite tank.

In this paper, using fiber path geometry, shell geometry, lattice geometry and classical shell theory, the stiffness coefficients of a composite conical shell and a composite lattice conical shell are obtained. The results in determining the buckling strength in this method have been compared with the experimental results and a good agreement has been seen between the results. The stiffness coefficients are obtained as a function of the position of each point of the shell relative to the axis of the conical shell generator. The value of all stiffness coefficients at each point of the unreinforced shell relative to its generating axis decreases from the location of the small edge to the location of the large edge of the conical shell. Changes in the thickness of the shell and the angle of placement of the fibers on the shell relative to the axis of the cone generator cause the stiffness of the shell to vary along the axis of the generator. Therefore, the stiffness of the whole conical lattice structure varies in the direction of its generator. It can be seen that although the analysis of the buckling strength of the conical shell by the equivalence method is not completely accurate, but it provides a detailed description of the manner and ratio of changes in stiffness of the lattice shells along the axis of its generator. The coefficients equivalent like the coefficients of a filament wound composite laminated conical shell vary by the direction of its generating axis.

The main purpose of this study is experimental and numerical investigation on failure of resistance spot welded Al6061-T6 joint under tensile-shear test using damage model. Today using aluminum alloys in automobiles’ structure is increases to reduce weight and fuel consuming. The strength of an automobile’s structure completely depends on the quality of the strength and the quality of the welded joints. So, study the strength of these welded joints is very essential to obtain safe structures. In this study Gurson-Tevergaard-Needleman (GTN) model is utilized to study the failure of welded joint. A finite element (FE) model is developed to simulate failure of the welded joint under tensile-shear test. To validate the FE model, 7 series of samples are welded with different welding parameters (minimum 5.72 mm and maximum 8.41 mm) to obtain altered nugget size. The comparison between experimental and FE model results’ shows that the different between results is approximately 2% and the GTN model has a good reliability to predict the failure force. In addition the results show that the FE model can predict truly the starting of failure in the welded joint.

In the present study, the finite element method was used to study the effects of geometric parameters on superconductive behavior of new geometries Z- Shape of shape memory alloy stent for application in the trachea using a radial loading(crimping) test. The material model used to describe the properties of a shape memory material based on the Helmholtz free thermodynamic energy (Aurichio model). In this numerical study by creating a new design of the stent and by choosing different mechanical properties and changing its geometric parameters, the mechanical performance of the stents was evaluated using finite element analysis with empirical verification. The modified geometric parameters are the thickness, number of vertices and angles between the stents. Reducing the thickness of the stents from 0.3 to 0.2 in the same of angle between the length and the number of bends of the stent causes reducing the stiffness = 37.87%, reducing the radial mechanical strength to open ducts (COF) = 50%, reducing the radial force = 38.35% and increasing displacement = 0.2%. The stents with lower thickness have a better mechanical performance due to more complete mechanical hysteresis loop, less radial mechanical strength to open ducts(COF), more radial resistive mechanical strength related to ducts(RRF), less radial force, less stiffness, more displacement, less stress ,high strain at stent critical points, and high martensite formation at less strain.