مجله مهندسی ساخت و تولید ایران
سال دهم شماره 4 (تیر 1402)

Nowadays, for optimal control of oil pressure and reduction of energy consumption in hydraulic circuits used in fixed and moving machines, it is necessary to change the displacement volume of the pump proportional to the load on the moving part of the hydraulic actuator. For this purpose, in this paper, a displacement control valve with negative overlap is used in the axial piston pump structure. In order to evaluate the performance of the displacement control valve, the mathematical relations governing the axial piston pump were written in the frequency domain. Examining the presented mathematical model showed that the order of transform function of the axial piston pump in three different working conditions, including increase, decrease, and stabilization of the displacement volume is 7, 5, and 3, respectively. To evaluate the correctness of the presented mathematical model, the design and construction of the hydraulic power transmission system including the axial piston pump, fixed displacement hydraulic motor, and flow control valve without pressure compensator was carried out. The appropriate matching of the frequency response obtained from the experimental results with the results obtained from the mathematical model, especially at low frequencies, confirmed the validity of the presented mathematical model. Further investigations showed that the use of the displacement control valve to change the flow rate of the axial piston pump in three working conditions resulted in the stable operation of the pump in the hydraulic power transmission system.

Cutting with high accuracy is possible using wire electrical discharge machining or WEDM. Nonetheless, while machining parts, amplitude of vibration causes inaccuracy of cutting. The main topic of this research is investigating the factors affecting amplitude of vibration of the wire-tool in WEDM using mathematical governing equation of motion of wire electrode. Hence, machining and finding ways to reduce the amplitude of vibration is the main purpose of this research. The consequence of reducing amplitude of wire vibration is cutting with higher accuracy and having smoother finished surface. In this research, the governing equations of motion of the wire-tool vibration are obtained using the Euler-Bernoulli beam model, fixed at both ends and moving in axial direction. The wire undergoes different forces including the body force produced by electrical discharge, damping force caused by the dielectric fluid, thermal force produced in the machining area and the axial force. Thereafter, the partial differential equation of motion of the wire-tool is converted to an ODE equation using Galerkin's method and then it will be solved using fourth order Runge-Kutta method. The results of this research show that the amplitude of vibration can be decreased by increasing the axial force and the decreasing of electrical discharge frequency, wire length, temperature differences and reduction of the workpiece width. Also, the results show that increasing the temperature by 70 degrees in the axial force of 17.5N can lead to a 60% increase in the vibration amplitude of the wire. Also, the results show that increasing the temperature by 70 degrees in the axial force of 17.5N can lead to a 60% increase in the vibration amplitude of the wire.

Upgrading of the rail vehicles is in line with the policies of the Iran's twenty-year development vision document (Horizon 1404) in order to increase the share of railways in the transportation of goods up to 30%. The design of freight wagons with higher axial load, provides the possibility of increasing the load carrying capacity of the wagons, helps to achieve environmental goals through less CO2 emission, and causes a significant reduction in the transportation cost, which itself leads to more investment by the private sector in the Iran's rail vehicles. This paper presents a computational platform to analyze the mechanical strength of a long-sided freight wagon with an axle load of 25 tons, according to the requirements of EN 12663-2 standard, using the finite element method. Design requirements are described in detail and appropriate numerical models are developed for each requirement. The results of the simulations performed in all loading conditions have been compared with the limits defined in the standard and the correctness of the design has been ensured. Numerical results depict that among all load cases, lifting at one end, lifting the whole vehicle (load cases LC6 and LC7) and compressive force and vertical load (load case LC8) cases are the most sever ones, and induce higher local stresses; which could be reduced by reinforcing or making some geometrical changes in the underframe. In general, the outputs of this research will help the railways engineers to identify and optimize the high stress regions of the freight wagon underframe, under different loading conditions. Such modifications, not only optimize the weight and increase the strength and the load carrying capacity of the wagon, but also increase its useful life time and operational reliability.

Fiber metal laminates have garnered attention from the aviation and automotive industries due to their favorable mechanical properties. These laminates consist of thin metal layers and a fiber-reinforced epoxy layer. This study focuses on investigating and analyzing the impact of temperature and strain rate on GLARE 2/1 under bending conditions. GLARE 2/1 are composed of one layer of epoxy reinforced with glass fibers sandwiched between two layers of aluminum 2024. The samples were subjected to bending with loading rates of 0.03 and 0.3 1/s at temperatures of 25, 60, and 100 degrees Celsius.The force-displacement curves were extracted for three-point bending at different temperatures and strain rates. The deformation of the layers was observed using digital image correlation technology. The results indicate that, in GLARE 2/1 and at a constant loading speed, with increasing temperature, the maximum bending force decreases, this value decreased by 51% at a loading rate of 0.031/s and at 100 degrees Celsius compared to 25 degrees Celsius and this value decreased 30% at a loading rate of 0.3 1/s. Increasing the loading speed in GLARE 2/1 samples leads to a greater increase in the maximum bending force. The bending elastic coefficient at a loading rate of 0.3 1/s is higher than at a loading rate of 0.03 1/s at all temperatures. By utilizing the deformations obtained under different temperature and loading conditions, it is possible to control the deformation of GLARE 2/1 in forming processes.

In this research, by using an artificial bee colony optimization algorithm, the mechanical properties of chromium nanobeams have been identified in such a way that the error of the mathematical model in the interpretation of the experimental results be minimized. Since conventional continuous medium theories cannot correctly simulate the behavior of structures in the nanoscale, also, large deflections in nano dimensions are not far from expected, therefore, the mathematical modeling of the large deflections of the beam based on surface effects is considered to predict the behavior of chromium nanobeams. The mechanical properties of chromium nanobeam have been considered the value of elastic modulus, the value of residual surface stress and the values of support properties, that is, the value of initial slope of the beam at the support and the value of bending spring coefficient of the support. In this research, the effects of mechanical properties have been investigated separately and simultaneously on the behavior of nanobeams. It has been determined that all four parameters must be considered to simulate the exact behavior of the nanobeam. In addition, among the investigated mechanical properties, removing the support properties in the prediction of experimental deflections causes the most errors, and removing the surface effects causes the least errors. Furthermore, the error has been reduced by far compared to previous works.

In this research, the process of surface modification, fabrication, and examination of the mechanical and electrical properties of a semi-biodegradable composite prepared from polypropylene and hemp fiber fabric has been discussed. Production of composite samples was done by dissolving polypropylene polymer in a xylene solution and then combining it with fiber fabric under pressure and temperature curing of a hot press. To improve the interface between the fibers and the matrix and to improve the mechanical properties of the produced samples, the surface of the hemp fiber fabric was modified using a 6% sodium hydroxide solution for 12 hours. To determine the mechanical properties of the produced samples, two tensile and three-point bending tests were performed. The elastic modulus, yield stress, ultimate stress, elongation, and toughness were measured from the tensile test and were analyzed and investigated. The bending of the composite was obtained from the bending test. To determine the electrical properties of the composite, the dielectric constant test was performed using a network analyzer in the x band. The maximum tensile strength and Young's modulus obtained in this research are 8 MPa and 1.6 GPa respectively. The maximum dielectric constant and loss tangent of the produced samples in the x-band is equal to 3.48 and 0.24, respectively. Finally, to validate the results obtained in this research, the results of the tests have been compared with the results of other authorities in this field.