مجله مهندسی ساخت و تولید ایران
سال دهم شماره 6 (شهریور 1402)

In this study, a nanocomposite based on polyvinyl chloride (PVC)/nitrile butadiene rubber (NBR)/Graphene nanoplates was prepared by melt mixing method. The response surface methodology (RSM) was employed to investigate the effect of weight percentages of NBR elastomer and graphene nanosheets on the mechanical properties (tensile strength and elongation at break) of the PVC/NBR/graphene nanocomposite. Mathematical relationships for the mechanical properties of the nanocomposite were presented using analysis of variance (ANOVA) table, and the degree of influence of each material parameter on the mechanical properties was studied. The comparison of mathematical relationships and experimental results showed low error. Additionally, the microstructure of the samples was examined using scanning electron microscope (SEM) to confirm the results. The results showed that by increasing the weight percentage of graphene nanosheets from 0 to 2% and decreasing NBR from 40 to 20% weight percentage in the nanocomposite, the tensile strength increases while the elongation at break decreases. By optimizing the mechanical properties to achieve maximum tensile strength (15.4 MPa) and maximum elongation at break (107.6%), the weight percentages of graphene nanosheets and NBR will be respectively 0.81 and 35.18%.

In recent years, with the increase in competition between automobile companies and the establishment of government laws to further reduce fuel consumption and, as a result, the requirement to reduce vehicle weight, the third generation of advanced strength steels have received much attention in the automotive industry due to their better tensile strength and ductility than the first generation and lower cost than the second generation. In this research, a new candidate of the third generation of advanced high-strength steels, with the name of 112HR, was design, production, and introduced and its mechanical properties were investigated and compared with SAPH440 steel, which is currently used in the domestic car industry and in the car cabin. Uniaxial tensile test was performed in three directions of rolling, perpendicular to rolling and 45-degree angle to rolling. 112HR steel with a tensile strength of 1190 MPa and an increase in length of 54.5% and a ductility index of more than 60 GPa% has shown better properties than SAPH440 steel with a tensile strength of 450 MPa and elongation of 43%. But in the tensile test of grooved sample and hole expansion, which is a three-dimensional stress, 112HR steel performed worse, so that the cavity expansion rate of SAPH440 steel was about 3.76 times higher than that of 112HR steel. The reason for this difference is the transformation properties of austenite to martensite during deformation in 112HR steel and the low shear strength of martensite. The transformation of austenite to martensite was confirmed by X-ray diffraction and optical and electron microscopic investigations in 112HR steel.

Perforated thin-walled tubes have always been the focus of researchers as an appropriate energy absorption alternative. In this research, the energy absorption capability of perforated thin-walled tubes with irregular pattern has been compared with thin-walled tubes without holes and regular holes. In this regard, cylindrical thin-walled tubes made of aluminum alloy 6061 have been used under axial loading. At first, the process was modeled using the finite element simulation, and the accuracy of the numerical results was verified using the experimental results. Then, using Taguchi's L16 orthogonal array, the effect of geometrical parameters on the energy-to-weight ratio of the perforated thin-walled tubes with irregular pattern was investigated. Afterward, the optimal arrangement was obtained to achieve the maximum energy-to-weight ratio using the signal-to-noise analysis. Finally, experimental tests were carried out on the tube with the optimal arrangement, the tube without holes and the tube with regular holes. By comparing the energy absorption ability of various tubes, it was found that with the optimal arrangement, the energy-to-weight ratio increases by 19 and 26%, respectively, compared to the non-perforated and regular perforated tubes. Also, using the new proposed pattern, the initial force to average force is reduced by 17 and 19%, respectively, compared to the non-perforated and regular perforated samples.

In this research, the impact resistance behavior at low speed is analyzed for two types of common metal materials, steel and aluminum, and two types of epoxy composite materials reinforced with carbon fibers and glass, and the results related to the analyzes of metal and composite materials, including Von Mises stresses and strains, maximum shear stress and impact strain energy were compared in these materials. Based on the obtained results, steel with high Von Mises and shear stress and low Von Mises strain and shear strain had better performance than aluminum and composite materials. The steel sample bearing 23815 MPa had the highest von Mises stress and the composite sample reinforced with carbon fibers bearing 4763 MPa had the lowest von Mises stress. The highest Von Mises strain is in the carbon fiber composite sample compared to other metal and composite samples. This increase is about 870% more than the steel sample. This indicates the weakness of these materials in bearing shock loads. Also, the glass fiber reinforced composite sample has better performance compared to the carbon fiber reinforced epoxy composites. The reason for this is the better energy absorption properties of glass fibers compared to carbon fibers.

Friction stir spot welding (FSSW) is one of the types of solid state welding methods for joining parts and light metals, especially aluminum and copper alloys. In this research, the effect of important parameters of the FSSW welding process, such as rotational speed and tool stop time, on the mechanical and micro- hardness properties of dissimilar connections of aluminum alloy 6061 to commercial pure copper has been investigated. Also, the effect of the placement of the sheets on the mechanical properties has been studied. The results show that by increasing the rotational speed of the tool from 1250 to 1600 rpm and the stopping time of the tool from 5 to 10 seconds, the tensile and bending strength of all welded samples increases. Also, at rotational speeds less than 1250 rpm due to the reduction of frictional heat generation, and higher than 1600 rpm due to excessive heat generation, the quality of connections has decreased. The results of micro- hardness measurement show that in various welding parameters, increasing the rotational speed and stopping time of the tool caused the creation of fine grains and recrystallization found in the stir zone and other areas, which is due to the heat produced due to friction and severe material change in shape. The obtained results show that at high aluminum and low copper, the yield strength and ultimate tensile strength reach their highest value, of 142 MPa and 188 MPa respectively.

Grain refinement through dynamic recrystallization is one way to improve the mechanical properties of high nitrogen austenitic stainless-steel ingots during hot rolling. In this paper, by using simulation based on the finite element method and experimental results, the effect of conventional rolling and gradient temperature rolling on the microstructural evolution of Nitronic 50 austenitic stainless-steel ingot during hot rolling is investigated. The results of simulations showed that strain in the center of the ingot be increased under a gradient temperature, while the maximum strain value in the conventional rolling is on the surface. The microstructural results obtained from optical microscopy for gradient temperature rolling showed strain value in the center is more than the surface. The temperature difference between the center and the surface leads to a significant reduction in the strength center of the ingot against the surface. The difference in average grain size of dynamic recrystallized for gradient temperature in the surface and center was less than 3μm. The existence of primary grains (68μm average grain size) and bulged grain boundaries in the center of ingot and refinement and small grains in the surface area (8.5μm) in conventional rolling (1000℃) showed that dynamic recrystallization, due to low effective strain and temperature, has not occurred in the center of the ingot. The almost uniform distribution of austenite grains in the direction of ingot thickness for gradient temperature rolling showed that this method is an appropriate method for hot rolling of austenitic steel ingots compared to conventional conditions.