مجله مهندسی ساخت و تولید ایران
سال هفتم شماره 6 (شهریور 1399)

Plasma spark sintering is an effective method for producing nanostructured metal materials. In this process, a graphite die is usually used. The limitation of graphite die is using this die at higher pressure of 100 MPa. In this research, the simultaneous effect of the pressure and type of die (graphite die with a pressure of 40 MPa and Inconel die with a pressure of 250 MPa) on the microstructure and the properties of nanostructured silver in the spark plasma sintering process were evaluated. The first nanostructured powder with a 47nm crystallite was transformed into two nanoscale silver pieces using two different dies and pressures. Changes in the crystallite size of the powder and the bulks, the percentage of dislocations and the strain of the nanostructured silver bulks were calculated using the X-ray diffraction results. Microstructure and micro hardness of samples were also investigated using FESEM and micro hardness tests, respectively.The results indicate that the increase in crystallite size was 6% in a specimen prepared with a graphite die and 40 MPa pressure and reduce 53% in a crystallite size of a sample prepared in an Inconel die with a pressure of 250 MPa. The change in the type of mold and the applied pressure has no effect on the density of the bulk samples, but the hardness of the sample in the case of Inconel die conditions is increased by 40% compared to the sample prepared in graphite die.High temperature pressure tests show superplasticity behavior nanostructured silver at high temperature.

Corrosion is a type of irreversible destruction of a metal by chemical or electrochemical reaction with ambient. The loss of materials caused by corrosion in metallic structures is a widespread and urgent problem in various industries including petroleum, gas, aerospace, construction, mining, and manufacturing. Pipes used in the oil and gas industry as well as aluminum pipes used for heat transfer in cooling systems are subject to corrosion. Therefore, the evaluation and detection of corrosion, progressive damage, is of particular importance both qualitatively and quantitatively. In this study, a new electromechanical impedance measurement method was used to detect corrosion inside an aluminum tube. Defects or changes in the structure integrity cause changes in the mechanical impedance of the structure which shown as the alteration in the piezoelectric electrical impedance, due to the piezoelectric coupling characteristics. For this study, a circular corrosion cross-section with insulation of the surrounding environment on the inner wall of the tube was created by the corrosive acid solution in a period of 180 minutes until the tube was pierced. Measurement of impedance spectrum in the range of 10-20 kHz was performed to monitor changes in impedance shape as a result of corrosion progress in steps of 20 minutes. Comparing the impedance spectrum at each step with healthy state, changes in amplitude and resonance frequencies revealed and extracted quantitatively. Experimental results from the scalar damage criteria increased linearly with increasing corrosion depth, indicating the effectiveness of this method in real-time detection of corrosion damage in the pipe.

Bonded joints are widely used in industries such as automotive, wind turbine blade, and aircraft because of their ability to adhere dissimilar materials. It is significant to study manufacturing factors such as surface preparation and curing procedures in order to improve load carrying capacity and durability of the joint. In this paper, the influences of these procedures are investigated on the strength of metal-to-metal, metal-to-composite, and composite-to-composite bonded lap joints subjected to quasi-static and fatigue four-point bending tests. Sandpapering and acid-etching are selected as mechanical and chemical surface preparation methods, and three curing procedures of no post-cure, post-curing with gradual, and sudden cooling are applied. Results showed that, for similar conditions, metal-to-composite and metallic joints achieved the highest and lowest values of maximum quasi-static loads, respectively. Besides, for all joints types, mechanical surface preparation method achieved higher maximum quasi-static load and fatigue life in compare to chemical one. Maximum quasi-static load in the metal-to-composite joint showed less dependency to gradual cooling than with metallic one, and in the composite joint depends strongly to curing procedure. It is also revealed that fatigue life of the metal-to-composite joints improved for gradual cooling after post-curing. Finally, it is concluded that the metal-to-composite joints have superior quasi-static and fatigue behavior in compare with others, and the mechanical surface treatment and second curing procedure are suitable. Microscopic observations of failure surfaces showed that the metal-to-composite joints led to the cohesive failure mode which is appropriate for future repairing purposes of a bonded joint

Nowadays, thin-walled energy absorbers have been widely used in different industrial applications. Many studies have also been performed to optimize behavior and application of such elements with geometrical triggers. In this paper, the effect of geometrical triggers on deformation and energy absorption of three-layer Al/Polypropylene/Steel deep drawn samples is investigated. To this end, the sandwich panel from two metal sheets of Steel and Aluminum as the skins and a Polypropylene layer as the core was fabricated. These three layers were bonded to each other applying a polymeric granular cohesive and under hot pressing technique to produce three-layer sandwich panels with two different core thicknesses. The sandwich panels were then deep drawn and converted to three-layer cups for crushing energy absorption tests. The quasi-static crushing tests were performed to evaluate the absorbed energy in fabricated samples. These tests were also done in order to studying the effects of core thickness and geometrical triggers (like notch and hole) on the samples body on the absorbed energy. The results show that increasing the core thickness from 1 to 2 mm enhances the capacity of energy absorption by about 6%. In addition, notch triggers with 45 degree in the samples wall could increase the energy absorption up to 8%.

Composite materials are used widely in military, nuclear, vehicle, and aerospace industries because of the high strength-to-weight ratio. One of the biggest challenges about these materials is the behavior of them under impact or high strain rate loadings. In this research, the effect of the low-velocity impact on the hybrid-laminated Kevlar-Basalt composites is investigated. These composites plates are made by Hand-layup method. The samples made of six type of stacking sequence contains sandwich hybrid, intercalated and not hybrid. All of the samples have 13 layers and same thickness. To apply an impact load to specimens, Drop-weight test setup is used. The experimental tests have been done for 40J applied energy. The aim of this research is to comparison the destruction rate of the different samples and select the best and most resistance one. In addition to experiential testing, all specimens are simulated in finite element software ABAQUS and have been analyzed. At the end, experimental and numerical results are compared. The results show that the composite hybridization has very excellent effect on their impact properties. The absorbed energy of the samples that have hybridized with intercalated configuration is more than other samples.

Shoes are used in daily activities to protect the human foot against applied forces from the ground. One of the most important parts of shoes which absorb the incoming forces is the outsole. The aim of the present research is to investigate the efficiency of three different materials in fabricating outsoles. Outsoles made of styrene butadiene rubber (SBR), polyurethane (PU), and polyvinyl chloride (PVC) were fabricated with the same geometry and without shoe treads. Then, they were tested by the PEDAR system in order to determine the plantar pressure exerted by each outsole, and they were also tested in terms of fatigue, hardness, and uniaxial compression tests, and after the modeling they were analyzed by finite element method (FEM) software. In static and dynamic states, the outsole made of PVC, SBR, and PU reduces the pressure by 44%, 65%, and 59%, respectively on average compared to barefoot posture. SBR in stress (in static and dynamic states) and strain (in static and dynamic states) have 39.06% and 98.75% better performance on average respectively compared to PVC. In addition, SBR outperformed PU in stress (in static and dynamic states) and strain (in static and dynamic states) by 3.45% and 8.5% respectively. To fabricate outsoles, multilayer outsoles should be used in order to concurrently benefit from the positive characteristics of several materials.