مجله مهندسی ساخت و تولید ایران
سال هشتم شماره 9 (آذر 1400)

Hot deformation behavior and microstructure evaluation of ATI425 alloy with initial martensite microstructure in single-phase and two-phase region in the temperature range of 700-1100˚C and strain rate of 0.001-1s-1 were investigated. The flow curves of the alloy in the α/β region and β-single phase showed that the flow softening of the alloy is the result of spheridization of alpha plates and dynamic recovery and dynamic recrystallization in the α/β phase and β single phase, respectively. In the α/β phase region at low temperatures and low strain rates, the splitting of the alpha plates and the penetration phenomenon are the main causes of alpha plate sphericity and the structure modification mechanism. Kinetic analysis of the alloy was calculated after removing the effect of adiabatic heat and friction. The activation energies for the ATI425 alloy were calculated to be 403.226 kj/mol and 201.038 kj/mol in the α/β and β regions, respectively. The linear relationship between the Zener-Holman parameter and the stress indicates that the flow stress follows the predicted trend of the equation. The process map extracted at 0.5 strain showed that the three zones, instability, safe zone and peak zone with power dissipation efficiency 0 -0.30%, 30-40% and above 40%.

Transporting molten metals is one of challenges in industries. Dangers for human, oxidation, torbulance and reduction of equipment life are problems of the transportation. Electromagnetic pumps have solved problems of using molten containers and also mechanical pumps. In this paper, by examining the effect of main parameters in the design of a direct current electromagnetic pump with a rectangular cross section (magnetic field size, electric current applied to the fluid, channel height and width) by the surface response method, the pump output including flow velocity and The Lorentz force is optimized. The results show that the amount of electric current applied to the fluid has the greatest effect on the response surfaces. It is also found that changing the channel width had little effect on responses. However, reducing the channel height has a positive effect on the response levels. By creating a magnetic field of 0.3 Tesla and a current of 12 amps on a channel with dimensions of 30 X 10 mm, the fluid with a velocity of 0.27 m⁄s is displaced by a volumetric force of 5000N⁄m^3. The method used in this paper optimized the output parameter of the pump. Experimental tests verify the results of simulations, including the maximum pumping height, pump flow and fluid velocity in the pump.

In the railway transportation system, frogs play a crucial role. Frogs provide flexibility in the transportation system due to their intersecting different paths. During the transition of the rail, contact and impact forces are applied to the main body and nose of the frog, causing degradation and wear. Furthermore, impact forces cause extensive wheel damage and higher maintenance costs. As a result, the frog's wear resistance needs to be improved in order to prevent unusual plastic deformations and wear degradation under cyclic loadings. Explosive work-hardening is one of the most effective and cost-effective methods for increasing the hardness of Hadfield's steel to match the properties of railway materials. The hardness of the frog's running surface is between 320 and 390 HBW, according to relevant Standards. The experimental results were validated against FE analysis after calculating optimal explosive energy using a numerical approach, and then the DOI were adopted based on numerical results. According to the FE model, the critical thickness of explosive material is 4 mm, and increasing the thickness of explosive plate significantly increased the hardness. Furthermore, the FEM results revealed that the 5- and 7-mm thicknesses of explosive plate produced the best results in the rail hardening process. The hardness of railway frogs was increased from 161 HBW to 326 HBW and 347 HBW, respectively, by using 7 mm thick explosive plate in the hardening process.

Nanocomposite foam has small cells due to the presence of reinforcing materials in nanoscale and the presence of neutral gas as a blowing agent . In the foaming process, there are four variables to control the process of saturation time, saturation pressure, foaming time and foaming temperature. In this study, foam temperature, foam time and weight percentage of hydroxyapatite nanoparticles were considered as variables. Nanocomposite samples were prepared by solvent casting. The samples are saturated in a tank with a constant pressure of 3.5 MPa by neutral CO2 gas and after 6 hours the samples are taken out of the tank and separately into hot glycerin under one of the temperature conditions of 90, 110 and 120% with a time of 5 , 37.5 and 70 seconds were placed. The temperature of glycerin and the storage time of the sample inside it are called the temperature and time of the foam. The aim of this study was to prepare porous nanocomposite samples with polylactic acid / polyethylene glycol background and hydroxyapatite nanoparticles with 3% and 5% by weight by mass method, to reduce the density and create a suitable cell diameter inside the samples. The results showed that with increasing foam time from 5 to 70 seconds and foam temperature from 90 to 120 ° C, the density decreases and the cell diameter increases. Increasing the nanoparticles to 3% decreases the density and increases the cell diameter and values of 5% increases the density and decreases the cell diameter.

This paper presents a novel Contactless Hybrid Static Magnetostrictive Force-Torque sensor using Galfenol. Initially, the sensor's design principles in axial force and torque measurements are described. The magneto-mechanical properties of used materials, such as B-H curves and magnetic permeabilities are measured under various mechanical preloads and magnetic fields and improved in some cases. These properties are used in finite element method. The sensor is evaluated numerically using COMSOL Multiphysics® software based on the obtained experimental results. Afterward, the sensor is fabricated based on finite element method results and experimentally tested in different electrical currents and excitation frequencies. Sensitivity, repeatability and linearity errors are presented separately in force and torque measurements in optimal operating condition of the sensor. Then, the finite element method results are verified with the experimental results. Finally, the performance characteristics of the sensor in optimal conditions are presented and it is found that the sensitivity increases while increasing the electrical current (or magnetic field) and frequency. The maximum sensitivities for axial load and torque measurements are obtained at 0.7349 mV/kgf and 2.24 mV/N.m, respectively.

Today, due to the importance of reducing the time between design and production, the use of methods such as fused deposition modeling (FDM), is considered as a good alternative compared to reduction production methods. Poly lactic acid (PLA) is used as a biocompatible polymer in many engineering and medical fields. Improving the long-term load bearing capacity of such products is one of the essential criteria to ensure the proper performance of these components. In this study, in order to improve the fatigue life and creep resistance of samples made of poly lactic acid polymer during the fused deposition modeling, to evaluate the effect of layer height, layer thickness, infill percentage and infill pattern on fatigue behavior. And creep resistance of the samples was investigated. Also, in order to benefit from statistical analysis, the response surface methodology has been used. Analysis of variance (ANOVA) showed that the percentage of filling and layer thickness had the greatest effect on increasing the fatigue life and reducing the creep rate of the samples. The results showed that layering based on layer height of 0.1 mm, layer thickness of 0.3 mm, infill percentage of 75% using honeycomb pattern had the highest fatigue life and creep resistance of the samples.