نشریه مهندسی مکانیک مدرس
سال بیست و دوم شماره 5 (اردیبهشت 1401)

In this study, the residual strength of the carbon/epoxy composite plates exposed to the thermal cycles and subjected to low-velocity impact was evaluated using an experimental procedure. Composite plates with a layup of [45/02/-45/902]s and thickness of 2.9 mm under three impact energy levels of 10J, 15J, and 20J and exposed to 200 thermal cycles in the range of -30 to 65° C went under low-velocity impact and compression after impact tests. In performing impact tests, a drop weight test device was used to investigate the behavior of damaged composites, force-time, force-displacement, and energy-time curves at all test temperatures were analyzed. Finally, the effect of temperature and associated damages at different levels of impact was evaluated using radiographic analysis and optical microscopy. Applying 200 thermal cycles in the temperature range of -30 to 65 ° C caused small cracks in the matrix and reduced the energy absorption of the samples. The highest drop in compressive strength is related to the highest impact energy, 20 J, which has a 31.12% decrease in strength. The thermal cycle at different impact energy levels of 10J, 15J, and 20J has led to an increase in the stiffness and compressive strength of the composite specimens. Finally, material parameters of the semi-empirical Caprino model to estimate the residual compressive strength of the carbon/epoxy plates under low-velocity impact and thermal cycles are obtained.

One of the forming pipes methods is the rotary draw bending process. Today, bending of thin-walled pipes with low radius of curvature is widely used in the automotive, military and aerospace industries, which is used to bend high-strength pipes. In this paper, at first the necessary models were created to simulate the bending process of the rotary pipe, and then the necessary mechanical and physical properties for stainless steel 304 and elastomers were determined. Then, experimental and numerical study of the forming force and changes in pipe wall thickness were performed. The process simulation was analytically performed using polyurethane elastomeric mandrels and nitrile rubber based on ABAQUS finite element software on 304 steel. The results show a good agreement between simulation and experimental results. Finally, the effects of process parameters including mandrel type, pipe diameter and bending radius were analyzed on the maximum forming force by factorial analysis. The results showed that the maximum forming force for both types of mandrel materials is obtained for pipes with small diameter and high curvature radius. Also, the bending forces increase 5 times by 30%increasing the bending radius, for pipes with smaller diameters. In addition, in equal diameter and radius of bending, the bending forces in the case of using polyurethane mandrel are 25% more than nitrile mandrel.

Digital Shearography is one of the new methods of non-destructive testing based on the laser beam which is used to measure the surface displacement derivatives. In this method, relying on the interference of two laser waves reflected from the object surface, the displacement gradient of the deformed sample can be measured directly. So that it is possible to evaluate the industrial parts in a non-contact and full-field way with a high speed and accuracy. One of the significant advantages of this method is the ability to detect subsurface defects in various materials, including composites. In this paper, samples with subsurface cracks made of composite materials reinforced with glass fibers and carbon fibers have been inspected by Digital Shearography testing. Also, the optimal values ​​of each main parameter such as shear distance and loading size for each material have been obtained using the Taguchi experiment design. The results show that for each type of material there is an optimal amount of loading amount and shear distance, which if applied, the best test results are obtained.

One of the problems in the experiment of breakup cryogenic liquid jet is the state of discharged cryogenic liquid jet from injector. In some applications, it is necessary jet to be in the sub-cooled condition. However, at atmospheric condition, the discharged cryogenic liquid jet becomes two-phase. In the present article, the methods for sub-cooling of the liquid nitrogen jet are investigated and a simple method to achieve this goal is used. With this method, which is based on holding at low pressure, a sub-cooled liquid nitrogen jet with a temperature of about 7 K lower than the saturation temperature was obtained. Then, the behavior of the liquid nitrogen jet at high pressure and atmospheric pressure is evaluated. High speed camera was used to observe the behavior of the jet. The speed of liquid jet is changed from 12 m/s to 34 m/s according to the Reynolds number from 90000 to 260000. When the liquid nitrogen jet is discharged into the environment under standard conditions, the jet becomes two-phase and expands. The larger the injector pressure difference, the greater the expansion of the jet; So that in the pressure difference of 6 and 13 bar, the diameter of the jet is 1.5 and 3.3 times the diameter of the injector, respectively. In the test speed range, under the conditions provided for the liquid and the environment, the breakup of the sub-cooled liquid jet leads to the production of very small droplets that are consistent with the expectation of such a liquid.

Due to the difficulties and limitations in grinding hard materials, the use of nanoparticles in the Minimum Quantity Lubrication method can be effective as an appropriate solution to improve the efficiency of lubricating fluids. In this study, the effect of using a combination of carbon nanotubes and copper nano oxide on the surface quality of Inconel 718 alloy during grinding by Minimum Quantity Lubrication has been investigated. The results showed that the use of nanoparticles in Rapeseed oil reduced the roughness and improved the surface health of the samples. The best surface topography with the least amount of pits and Furrows was obtained by combining nanoparticles with 3wt% in rapeseed oil, so that the surface roughness of the samples was reported 0.255 μm during this method, which is compared to the net use of CNT and CuO decreased by 14% and 3% respectively. Also, during the use of nanoparticles in minimum quantity lubrication, the amount of surface roughness compared to dry, flood and minimum quantity lubrication with rapeseed oil, decreased by about 35%, 13% and 18%, respectively.

Ultra-High molecular weight polyethylene (UHMWPE) fibers are among the strongest and lightest fibers available and are widely used in high-performance ballistic applications. Despite the great advancement of computational analysis in recent years, precise calculations have not been performed to identify the failure of these fibers due to the complexity of the material behavior to impact. In this research, using the most advanced finite element modeling method of composites (Abaqus-Explicit) has been used to study the composite behavior of these fibers subjected to high-velocity projectile impact. Fiber and matrix are designed using solid elements and 3D Hashin failure criterion was used to determine the behavior of the material. Since this criterion is not available in Abaqus, the VUMAT subroutine has been used to implement this criterion. Velocity diagrams and damage evaluation have been reported. To evaluate and validate this method, six samples of Ultra High Molecular Weight Polyethylene (UHMWPE) Composite panels, consisting of 20 and 45 layers, respectively, were experimentally studied by high-velocity projectiles at different velocities. The simulation results are in good agreement with the experimental results.