مجله مهندسی ساخت و تولید ایران
سال هشتم شماره 3 (خرداد 1400)

Due to the thermoelectric nature of the electrical discharge process, it is important to study the surface properties of the workpieces that are surface alloyed by this method. In this study, the effect of aluminum surface alloying process using Monell 400 electrode by electric discharge method on the workpiece surface mechanical properties has been investigated. To design the experiments, the pulse on time and pulse current were considered as input parameters and the surface residual stresses and Vickers indentation depth were considered as output parameters. In addition, the electromagnetic wave absorption of the surface alloyed layer was determined using the COMSOL simulation software. According to the obtained results, the Vickers indentation depth has the lowest value at the surface and with increasing distance from the surface, the amount of indentation depth increases. By increasing the pulse on time and pulse current, due to the increase in the amount of alloy elements (copper and nickel) diffusion to aluminum surface and thus improving the surface mechanical properties, the depth of the indentation decreases. Also, by examining the magnetic absorption in the surface layer using the simulation software, it was determined that the maximum amount of absorption of alloyed layer is in the range of 11-10.5 GHz.

Grinding burn is one of the most significant problems in grinding process with uncontrolled conditions and degrades the mechanical properties and performance of the part. The aim of the present study is to non-destructively evaluate the grinding burn phenomenon in steel parts. The parameters of the grinding process were changed to produce microstructural changes with different burn grades on the surface of steel parts. The results obtained from microscopic observations and micro-hardness tests revealed the occurrence of two types of burns including thermal softening (surface tempering) and re-hardening (formation of a hard white layer on the surface) burns. In the maximum burn grade, hardness of the surface increased from 600 HV to more than 900 HV, while hardness of 450 HV was obtained in the deeper layers due to thermal softening burn. In this study, the capability of two types of electromagnetic probes, measuring magnetic permeability and magnetic flux leakage, has been studied for detecting the grinding burn. The results show that the outputs of both probes were affected by the microstructural changes. Increase in tempered layer (due to thermal softening burn) enhances the magnetic permeability and reduces the flux leakage sensed by the probes. For the samples with re-hardening burn, effects of two opposing mechanisms (the surface hardening and softening) on the magnetic parameters have been assessed in the deeper layers. The present study indicates that utilizing the designed non-destructive probes, it is possible to detect the grinding burn, especially the thermal softening one, which happens more.

It is a fact that the shape of the bearing’s gap is one of the important elements of design. Also, experimental studies have shown that bearings with curved or rugged plates have better hydrodynamic performance. In the present paper, the effects of exponential gap-function as the sliding bearing’s gap have been studied on the bearing performance. For this purpose, new formulations of sliding bearing with a linear gap function have been developed. Then eroded slider bearing (since erosion provides curved surface) has been simulated. The governing equations are solved using the Finite Element Method (FEM) and the results have been presented. Besides, erosion adds debris to the oil which is simulated as additive nanoparticles in this study. The results of this analysis show that without considering solid nanoparticles, the load-bearing capacity force in the sliding bearing with exponential gap function increases 3.1% compared to the optimal linear gap. Furthermore, the nanoparticles analysis has shown that if the volume percentage of nanoparticles reaches 2%, the load-bearing capacity of sliding bearings shows an increase up to 13.1% compared to the optimal linear gap.

The main aim of this experiment is to determine the mechanical and microstructural of using Nano powder of Al2O3 besides stir welding of Al2024-T6 in multi-pass welding. Nanoparticles welded nine specimens and one particle-free in 1400 rpm rotational speed and 16 mm/min traveling speed. A combination of volume percentage of powder (3%, 5%, and 7%) and three different multi continuous passes (1, 2, and 4) is applied for Nano-rich specimens. The microstructure of joint, micro hardness and ultimate tensile strength (UTS) of the welded joint has been studied. It was observed that by increasing the particle volume from 3% to 7% average grain size increased extremely to 37% and UTS to 10%, and in the staid situation of welding passes, average micro hardness has 10% increase in shoulder affected zone. The result showed that the specimen with 7% of Nanoparticles in two passes has the highest mechanical and metallurgical properties and has a significant decrease (55%) in average grain size compared with a particle-free specimen. Meanwhile, UTS and average micro hardness of the same specimen was about 11% and 48% more than particle free.

In this paper, the effect of adding silica nanoparticles on the high- and room-temperature mechanical properties of the piston aluminum alloy is investigated. Aluminum alloy samples were fabricated by gravity-casting in the cast iron mold. However, nano-composite specimens were produced by stir-casting and with the addition of 1% of nano-SiO2-partiles to the melt. Due to the working conditions of the engine piston at high temperatures, tensile tests were performed at temperatures of 25, 250, 275 and 300°C and at a rate of 1 mm/min. After the tests, the sensitivity analysis was performed on the test results using the Minitab software. The experimental results showed that for all samples, the temperature increase had an effect on the yield stress, the ultimate tensile strength and the fracture strain. In aluminum alloy samples, increasing the temperature led to decrease in the yield stress and the ultimate tensile strength and the fracture strain increased. For nano-composite specimens, increasing the temperature enhanced the fracture strain and decreased the yield stress and the ultimate tensile strength. In general, mechanical properties of the nano-composite improved compared to the aluminum alloy. Therefore, the elastic module at 25°C increased as 23% and the elongation at this temperature decreased as 18%. These improvements at 300°C was the increase of 58% and the decrease of 25%. The improvement in the yield stress was 4% and 9% at 25 and 300°C respectively, by adding nano-particles.

Laser shock peening (LSP) process is a modern technology that can be used to improve fatigue life by inducing compressive residual stresses on the surface and along the thickness of peened parts.The aim of this study is to improve fatigue life of parts due to apply this process in order to generate compressive residual stresses (CRS) on samples with stresses concentration .The main objective of this paper is to investigate the effect of LSP parameters include scanning pattern and laser pulse energy on maximum compressive residual stress (MCRS) and depth of CRS around a hole in a 5mm thickness using both finite element technique and experimental results.The specimen material is AA7075-T6 .This material is used in the aerospace industry due to its high strength and high fatigue resistance. Slitting method is used to determine the residual stresses. The results show that elaborate application of LSP could efficiently be used for stress concentration points and improve fatigue strength.