مجله مهندسی ساخت و تولید ایران
سال نهم شماره 7 (مهر 1401)

In the lathe process with a length-to-diameter ratio of more than four, due to the low rigidity of the tool, a lot of vibration is created and the machining quality of the surface is reduced. For this reason, controlling and reducing the vibration of the lathe tool is always important. In this paper, the lateral vibration of a long lathe tool equipped with a dynamic absorber and the effect of various parameters are investigated. For this purpose, first, the equations governing the lateral vibration of the system are extracted and solved using the hypothetical modes method. Then, the effect of adsorbent presence and its main parameters such as adsorbent position, adsorbent stiffness, and adsorbent length on the vibration of the tool inside the lathe are studied and results are presented in the form of diagrams. The results show that the addition of adsorbent increases the natural frequency of the tool by 10% and the closer the adsorbent is to the tip of the tool, the better the performance. Also, as the stiffness of the absorber spring increases, the steady-state performance range of the lathe increases and the tool begins to vibrate at higher frequencies. In addition, by increasing the absorber length to 175 mm, the distance between the two absorber intensification frequencies increases, which indicates an increase in the area of stable performance and dynamic stiffness, and from lengths greater than 175 mm, this behavior decreases.

In the Past, monolithic armor plates were used to protect people and equipment. Today, the use of armored plates with unique designs (a combination of base plate & perforated plate) is considered. This new design is a structure consisting of at least two plates, one with a hole and the other monolithic (without holes), and they are placed in such a way that the perforated plate is placed in front of the monolithic plate (base plate) and this combination generally prevents the projectiles from penetrating and damaging the protected target. Experimental and numerical studies performed on these structures showed that this combination of plates has up to 31% less weight compared to integrated armored plates with the same ballistic protection capability. In the performed experiments, it was found that the edge effect causes deviation in the projectile path and erosion in the projectile sharp point, which in total prevents the projectile from penetrating the base plate and passing through it. The distance between the perforated & base plate was also studied, in which it was found that in order to have a proper effect of perforated plate, at least a distance greater than the length of the projectile between the two plates should be considered. By comparing the results obtained from experimental and numerical studies performed using LS-DYNA software, a good convergence between the results has been observed.

Quenching-partitioning (Q-P) is one of the methods of producing advanced high strength steels (AHSS). The principles of the mentioned thermal process are based on carbon penetration from martensite to residual austenite (γR) and stabilization of γR. In this research, the alloy with the chemical composition of 0.054 wt% Al, 1.5 wt% Si, 2.2 wt% Mn, 2.2 wt% Mn, 0.21 wt% Fe, containing 0.08% Ti as a micro-alloy in an induction melting furnace in VIM was cast as an ingot. The said ingot was homogenized for 3 hours at a temperature of 1200 °C. The homogenized ingot was rolled into a sheet with a thickness of 1.5 mm by hot and cold rolling processes. The prepared sheet was subjected to Q-P heat treatment and direct quenching (D-Q) and was compared in terms of microstructure and mechanical properties. The comparison of the effect of the mentioned operations on the microstructure and mechanical properties of steel was done by scanning electron microscope (SEM), X-ray analysis (XRD), micro-hardness measurement, and metallography. The obtained results showed that the sample subjected to Q-P heat treatment has better formability and strength than the D-Q sample. The strength and formability of the sample obtained from Q-P were reported as 1062 MPa and 24.52% respectively, and the strength and formability of the sample obtained from D-Q were reported as 1484 MPa and 15.21% respectively.

Friction stir processing is widely used for improvement of properties and microstructure of Aluminum, Copper and Magnesium alloys but investigation on steels are limited. Due to the fact that steel alloys, in addition to aluminum, copper and magnesium alloys, have good engineering properties and vast applications in the industry, they need to be processed by friction-stirring process. In this regard, the present research examines the effect of frictional stirring process on grain size, hardness and wear resistance of Ck45 steel due to the number of passes and tool design. In this research, it was shown that the friction-stirring method can be an effective method to increase the hardness and wear resistance of this steel in such a way that increasing the number of passes causes more heat generation per unit length and also affects the grain size, hardness and probably atomic penetration. In general, with the increase in the number of passes, the size of the grains in the stirring area becomes larger, while the final hardness and wear resistance are determined under the joint effects of grain size and hardness. The results indicate that the hardness has increased by 42% and the amount of wear has decreased by 85% compared to the original sample by the frictional stirring process.Keywords

In this article, the study of the time history of the displacement of the central point of single-layer graphene nanosheets under the passage of moving mass has been studied. In order to analyze the passage of the nanoparticle on the graphene sheet, the non-local theory of elasticity was used and finally the governing equations were extracted by the special function expansion method. Also, by using molecular dynamics simulation, the time history of the displacement of the central point of single-layer graphene sheets under different boundary conditions and the passage of metal nanoparticles with different geometries (such as square cubes, spheres and blades) along the length and through the middle of these sheets, including There are parameters that are effective in changing the behavior of graphene, and the results of theoretical calculations have been compared with the relevant molecular dynamics simulations. In addition, the results of the molecular dynamics simulation for a single-layer graphene sheet have been compared with the results of the corresponding non-local elasticity theory, and a non-local coefficient has been proposed for the model. As a result, the comparison of the results obtained from the relevant theory and simulation will provide more confidence to validate the response of the graphene sheet.

Grain size refining down to sub-micrometer range using severe plastic deformation methods is known as an effective strengthening mechanism in metals and alloys. However, metals with low formability such as titanium are subjected to cracking and fracture when they are severely deformed. As a result, attempts to impose intense plastic strain to them which is essential for grain refinement are generally not successful. In the present study commercially pure titanium was severely deformed by equal channel angular pressing. In order to enhance the formability, a larger channel of 105˚ was selected instead of common angle of 90˚and the effect ECAP temperature (300, 250, and 200 ˚C), pressing speed (10, 1, 0.1, 0.01 mm/s), and the initial microstructure on the formability of titanium was investigated. The results indicate that by lowering the pressing speed the formability is improved. Also, the use of a larger channel angle provides the possibility of reducing the processing temperature by 150 ˚C compared to previous researches, such that the titanium bars were processed at a temperature of 250 ˚C safely and without cracking up to 10 passes. Moreover, it was seen that the initial equiaxed microstructure shows much better formability than lamellar one. Light microscopy observations of the microstructure of the processed bars indicate that cracks nucleate and grow from the regions in which the material experienced higher amounts of strain.