نشریه علوم کاربردی و محاسباتی در مکانیک
سال بیست و ششم شماره 2 (بهار و تابستان 1394)

Actually a new mechanism presented for automatic control of angular velocity of a rotary axis is a complete power transmission system. This system can produce an almost constant output speed for different values of the angular velocity input, and can be employed as a suitable coupling between tractor P.T.O. shaft and agricultural machineries. This system is quite mechanical. In this study, equations of force, torque and power of the mechanism were extracted and mechanism performance were modeled. The equations of motion of mechanism are non-holonomic dynamical and differential algebraic equations with an index of three. Modeling results showed that changing the input velocity in the range of -30% to 50%, variations of output velocity would less than 10%.

In the present paper, based on the classical plate theory, buckling analysis of piezoelectric coupled FGM rectangular plates is investigated. By assuming the transverse distribution of electric potential to be a combination of a parabolic and a linear function of thickness, the equiblirium equations for buckling analysis of plate with surface bonded piezoelectric layers are established. The Maxwell’s equation and all boundary conditions including the conditions on the top and bottom surfaces of the plate for closed and open circuited and Levy type of boundary conditions are satisfied. Numerical results show that, the critical buckling load for open circuit is more than that of closed circuit. Furthermore, the critical buckling loads increase by increasing the thickness of piezoelectric layers.

In a laser forming process, the temperature gradient across the sheet thickness produces the final bending angle. Metallic foams cannot be formed by any mechanical processes due to occurrence of failure during deformation. In this article, closed-cell aluminium foams are irradiated by a laser beam. Experiments are carried out by varying laser power, scan velocity and the number of scan passes to specify their effect on the bending angle. Design of experiment with the response surface methodology and analysis of variance are utilized to analyze parameter effects. At last, an equation is derived for prediction of bending angle.

In this paper, the heat shocks in the heat flux profile are estimated with known temperature distribution using Kalman filtering. For this task, the temperature distribution is calculated and artificial noise is added to adequately simulate the real temperature measurements. Next by using Kalman filtering, estimation of online heat flux is assessed which appears as heat shocks in the discussed problem. Results indicate that the present method can accurately estimate jumps in the heat flux.

In this paper, free vibration of rectangular functionally graded material (FGM) plates with distributed patch mass is analyzed. Properties of these plates like Young’s modulus and density vary continuously throughout the thickness direction. The plate is defined by power-law, sigmoid or exponential function. The boundary condition of the plate is assumed to be simply supported and the equation of motion is obtained by using of Hamilton principle and third order shear deformation theory. The effects of different parameters such as the plate and mass dimensions and mass ratio on the natural frequencies of the plate are analyzed. Compared to previous results, our results are very accurate in similar cases.

A method for error estimation of isogeometric analysis of plane stress problems, based on stress recovery by using the super convergent properties of the Gauss points, was introduced. In this paper, a different approach for improvement of stresses based on the satisfaction of equilibrium equations by taking into consideration of two elasticity problems is followed and the effect of the number of the Gauss quadrature points is studied. In this approach, the equilibrium equations are satisfied for each patch of the isogeometric analysis model and it has been shown that the recovered stresses are more accurate than the previous method where the super-convergent properties were used. To demonstrate the performance and efficiency of the method a couple of elasticity problems are considered and the obtained results are compared with the previous method and exact solutions. The results indicate that the suggested method can be employed for error estimation and stress recovery in the isogeometrical analysis method.

This work outlines the influence of microstructure and grain size on surface hardening within high efficiency deep grinding (HEDG). To do this, different samples with various microstructure and grain size are prepared through specific heat treatments, then they are undergone the grinding operation with constant operating conditions. Finally, the variations of microhardness are recorded. It is observed that by increasing the primary hardness of material the surface hardening amount is increased. But this trend is not observed for super hard material and instead, hardening percent is decreased after a critical primary hardness. This hardening amount is more than for fine grain materials in comparison with coarse grain materials. The rolled samples show the same manner like non-rolled samples. It is found that grinding in direction of elongated grains, resultes in increasing superficial hardening in comparison with that of grinding is perpendicular to elongated grains.

The present work is focused on the computational method for simulation of the rubber vulcanization process in injection molding machines. The main innovation of the work is the calculation of the curing time in a rubbery part using the modification of curing kinetic model. For solving the curing equations, the computer code is developed in “UDF” module of the Fluent. The parameters of curing model, specific heat and viscosity of the rubber are obtained from the experiment. In order to evaluate the experimental curing time, a mechanical compression test is performed on the rubbery part at different times. Predicted mold filling and curing times are compared with experimental data, which confirmed the accuracy and applicability of the method.

Impact energy absorption systems in various industries such as automotive and railway have a particular importance to minimize the impact on passengers and enhance vehicle safety. This paper focuses on the bending collapse behavior of thin-walled energy absorber with circular and square cross sections. The theory that is applied is global energy equilibrium and the prevalent bending collapse mode for obtaining the relationship is considered. On the same basis, obtained relations are compared with the published results for the bending strength of tubular structures which were derived from experimental and analytical studies. Subsequently by using the derived bending strength formula, simplified models for circular and square tubes is introduced. The main advantage of these simplified models as a critical modeling technique is dramatically reducing the time of computer simulation in early design stages with the results close to the original model. For this purpose, by axial crash simulation of curved tube by using nonlinear dynamic finite element software LS-DYNA, the results are compared to verify the efficiency of the proposed simplified model and the accuracy of the derived relationship for tube’s bending strength.

Many of the mechanical structures are employed in high temperature conditions. Any variation of temperature may cause considerable side effects such as the creation of thermal stress or deformation. When a structure is composed of slender members such as beams or columns, one of the main problems concerning the rise of temperature is the incidence of thermal buckling. The continuing rise of temperature beyond the onset of thermal buckling level, continually affects the dominant forces and deformations. To study the post buckling phenomenon, following the introduction of different small deformation methods of thermal buckling analysis, a through large deformation scheme is developed to analyze the buckling of a simply supported column. For the case of large deformation analysis the validity of the results is evaluated by comparing with the results obtained by using of the small deformation theory, the linear and nonlinear simulations of ABAQUS software as well as the experimental data. The results characterize the deflection of a beam with uniformly distributed load by different solution techniques as well as the effect of temperature on the mid span deflection of a post buckled beam. Based on the obtained results, the validity of different methods is evaluated.

Besides the braking force error, the dynamic and geometric parameters of a truck affect its safety during the braking process. In this paper, the effect of dynamic and geometric parameters and the way of loading on the dynamic behavior of a truck in the presence of the braking force error is studied. To this end, some dynamic parameters of the truck have been obtained experimentally and applied to the truck governing equations of motion. Then, by using the realistic assumption in which the velocity of the truck decreases with a constant rate during the braking process, the governing equations are solved using a numerical technique. Finally, the load distribution on the truck as well as the dynamic and geometric parameters which affect the truck lateral deviation, are discussed and the results are presented in appropriate figures. The results show that the best load distribution for decreasing the effect of braking force imbalance on lateral deviation, can be achieved when the mass center approaches the front axis.