نشریه مهندسی مکانیک مدرس
سال بیست و یکم شماره 10 (مهر 1400)

These days, investigation on using acoustofluidic microchannels in separation of microparticles and cells is under consideration. Working under optimum efficiency, these microchannels should be designed and manufactured truly. In this work, a new methodology for designing and manufacturing of acoustofluidic microchannels are explained. Then, a metallic microchannel with 2-nodes of pressure wave based on this method was developed. For mass production purpose, a low cost and reliable method which is CNC micromachining is used. Also, to conduct the heat generated by the wave, this microchannel was made out of aluminum and then polishing technique is applied. Then, the performance of this microchannel in agglomerating of human blood cells and BT-20 breast cancer cells to nodal lines was experimentally studied. The results showed that the applied design and manufacturing technique are suitable. Although some tests were performed to find temperature rise of microchannel due to damping effect, it was found that true design method and also using metals with high thermal conductivity can prevent the temperature increase to the point beyond which living cells will be hurt.

In present study, hydrostatic tube cyclic extrusion compression process is introduced as a novel severe plastic deformation process for grain refining and improving mechanical properties of tubular components. Also, this process has the potential to produce relatively long and large tubes. In this process, because of the utilization of pressurized hydraulic fluid between the tube and die, there is nearly no contact friction. This leads to a significant reduction in pressing load. In this research, after applying hydrostatic tube cyclic extrusion compression process on pure copper tube, the microstructure evolution and the mechanical properties improvement were examined. The results denoted that this process was successfully performed on pure copper tube. In this way, the microstructure and mechanical properties were improved significantly. For example, after this process, the ultimate strength of pure copper, the yield strength and the value of hardness became 1.57, 1.85 and 1.86 times higher, respectively, and a low loss of ductility was achieved. Also, after this process, an ultrafine cellular microstructure with average size of about 990 nm were observed. While, the average value of grain size for the unprocessed tube was about 40 μm. The stages of the formation of the observed microstructure are as follows: the creation of a high density of dislocations, the dislocations coalescence with each other and the formation of tangled structures, the formation of ordered arrangements of dislocations and low angle boundaries, the formation of dislocation cells to diminish strain energy, the creation of new dislocations and their movement to boundaries.

Sandwich panels which can be used as an explosion shield are important structures for absorbing explosion energy. Crushing and plastic deformation of the core with the plastic bending of the faces are the main factors in absorbing the explosion energy in this sandwich panel. Structural components undergo permanent deformation after explosion and energy absorption. In this paper, the energy absorption of the structure and the deformation of circular metal sandwich panels with tubular core under explosion load have been investigated analytically, numerically and experimentally. The tubes are arranged radially and symmetrically in the core constructions. The experiment have been performed by making sandwich panels under free blast load in order to evaluate and validate analytical and numerical results. The analytical solution is performed using the energy method by balancing the kinetic energy and the plastic work which is done by the different components of the sandwich panels. Numerical solution is performed in ABAQUS finite element software and the pressure function is generated by CONWEP method. The amount of energy absorbed by the structure and different parts of it is obtained. There is good agreement between the results in different ways.

The grinding process is one of the most important and widely used machining processes to achieve the desired surface quality and dimensional accuracy. Since the undeformed chip thickness is not a constant value in the grinding process and is changing independently and momentarily for each abrasive, the determination of the undeformed chip thickness accurately is essential to determine the grinding forces and surface topography of the grinding wheel. Previous studies on grinding forces were mainly regardless of the micro-mechanisms between the abrasive and the workpiece. On the other hand, only the average values ​​of forces could be calculated by determining the average value for undeformed chip thickness. In this study, a new analytical model with the approach of kinematic-geometric analysis of abrasive grain trajectory is presented to determine the undeformed chip thickness and subsequent grinding forces. This model predicts the components of normal and tangential grinding forces (including sliding, plowing, and cutting forces) accurately and in detail based on the instantaneous undeformed chip thickness obtained from the kinematic analysis of abrasive movement and micro-mechanisms between abrasive and the workpiece. In the end, experimental tests were performed to validate the theoretical model.

In this paper, an asymmetric breakup of non-Newtonian droplet (with power law behavior) in a new geometry (network junction) has been investigated. The geometry can break an initial droplet into six unequal size droplets. The research method is numerical simulation with Volume of Fluid (VOF) algorithm. The numerical results are compared with the results of a benchmark problem and a very good agreement is seen. The results showed that in areas close to the wall, mixing of materials of inside droplet is performed better, which is important in industrial applications of droplet based flows, especially in pharmaceutical and chemical industries. The results showed that the maximum vorticity magnitude in the K1 branch (the lowest output branch in the system) is 26, 44 and 28 % more than the maximum vorticity magnitude of the branches of K2, K3 and K4 (K4 is the highest output branch is in system). Also, maximum effective viscosity in the K1 branch is 27, 29 and 24 % less than the maximum effective viscosity in the K2, K3 and K4 branches, respectively. Therefore, K1 branch has the best performance in mixing of the material of inside droplet among the output branches. It was also revealed that the pressure of inside of droplet (both before and after breakup) is constant along the channel width.

In this study, the effect of multidirectional forging (MDF) was studied on the microstructure and mechanical properties of Ti-modified SiP/ZA22 composite containing 4 and 8 wt. % Si. The forging process was performed at 100 °C by two and five passes. Based on the obtained results, Ti modification refined the coarse primary dendrites, and reduced the size of primary Si (SiP) particle as well as grains. Applying MDF also gradually eliminated the dendritic structure, promoted fine distribution of SiP particles, second phases, and porosities in the microstructure. According to the image analysis results, the average size of SiP particles in as-cast composite reduced from 25 and 30 μm to about 6 and 7 μm, respectively in 5-pass MDFed composites containing 4 and 8 wt. % Si. The mechanical properties results also showed work softening during the MDF where after two-pass MDF the hardness and tensile strength of the base sample reduced by 30 and 25%, while its elongation and toughness improved by 120 and 325%, respectively. In MDFed composites, the presence of SiP particles maintains the hardness and strength. According to the results, in the case of 2-pass MDFed composite containing 4 wt. % Si the hardness and tensile strength reduced by 18 and 2%, respectively, but the elongation and toughness increased by 25 and 175%, respectively.