جستجوی مقالات مرتبط با کلیدواژه "تنش کوپل" در نشریات گروه "مکانیک"

The aim of this paper is the investigation of fully developed flow of Newtonian and non-Newtonian fluids in two-dimensional microchannel based on a completely consistent couple stress theory and the calculation of the length scale parameters of these fluids. Therefore, the analytical solutions of the velocity and flow rate are obtained for Newtonian and power law non-Newtonian fluids. Afterward, the characteristic material length of Newtonian water and non-Newtonian blood fluids are calculated using the obtained relations and experimental data. Comparing characteristic material length for water and blood can perceive that the characteristic length scale depends on the fluid type. The blood velocity profile is calculated based on the couple stress theory using the obtained length scale and compared with the results of classical Navier Stokes theory. These results show the difference between the obtained values of the couple stress and classical theories increases by increasing the flow rate. This increase in the difference means decreasing of precision of classical theory for investigating flow through a microchannel. Comparing the calculated and experimental velocity profiles for water shows a good agreement between theoretical and experimental results.

Size dependent behavior of materials appears for a structure when the characteristic size such as thickness or diameter is close to its internal length-scale parameter. In these cases, ignoring this behavior in modeling may leads to incorrect results. In this paper, strong effects of the size dependence on the static and dynamic behavior of the electrostatically actuated micro-beams have been studied. The equilibrium positions or fixed points of the gold and nickel micro-beams have been determined and shown that for a given DC voltage, there is a considerable difference between the fixed points gained using the classic beam theory and the modified couple stress theory. In addition, it has been shown that the static and dynamic pull-in voltages gained using the couple stress theory are several times higher than those gained using the classic beam theory. Some previous studies have applied the classic beam theory in their models and introduced a considerable hypothetical value of residual stress to match their experimental and incorrect theoretical results. It has been shown that using the modified couple stress theory decreases considerably the difference with the experimental results.