نشریه مهندسی مکانیک مدرس
سال یازدهم شماره 3 (پاییز 1390)

In this paper, Pythagorean-hodograph (PH) quintic spline curves constructed by several connected PH curves with C2 continuity are used to designing the toolpath in machining operation. To generate the toolpath commands, the acceleration/ deceleration phase of motion and the middle regions of the toolpath are devised by time-dependent and constant velocity interpolation algorithms, respectively. In the aforementioned interpolation algorithm, the exponential functions are employed to modify the feedrate profile and subsequently using the Pattern Search algorithm (PSA), the proposed feedrate profile is optimized to maintain the maximum jerk within allowable physical limits. Finally, high speed CNC machining for two cases of open and closed C2 PH quintic spline curves along with the commonly used feed forward/feedback controller is simulated in Simulink-Matlab software and the contouring error is studied and analyzed.

Carbon Nanotube (CNT) dimensions and interphase region are the important parameters that affect on the mechanical behavior of CNT/Polymer composites. In this study, a new analytical model is established to predict the modulus of these structures. Considering the influence of CNT dimensions (diameter and length) an interphase region, the elastic modulus of nanocomposite is determined. In this new model, a nanotube with hollow cylindrical structure is modeled as a transversely isotropic solid nano-fiber. Moreover, interphase region and its van-der Waals interaction is simulated as an isotropic hollow cylindrical solid that its mechanical properties is derived using the continuum mechanics. To predict the modulus of nano-composites, a representative volume element (RVE) containing a transversely isotropic solid nano-fiber, isotropic solid interphase region and the matrix is employed using Halpin-Tsai model. Finally, the results of the proposed analytical model are compared with various available experimental results. The proposed model is simple and the results obtained by the model are in good agreement with available experimental results.

The spring-back of a work-piece during machining operation causes dimensional error of the work-piece. In the present study, the spring-back of work-piece in ultrasonic-vibration assisted turning and conventional turning has been modeled. It is illustrated that the reaction of the work-piece in high frequency vibration cutting is similar to a static behavior, whereas the spring-back in this process is theoretically and experimentally smaller than the conventional cutting leading to smaller error. A method has also been proposed to obtain the errors caused by rigid assumption of the spindle assembly used for correction of the results.

In this paper, considering a half car model with 3-DOF, the effects of vehicle velocity, wheelbase, and the vibration parameters of the passenger seat on the statistical characteristics of the vehicle body and the seat responses are investigated. In the previous studies, 2-DOF model was generally used for vibration analysis of the vehicle under the road random excitation. However, science these models ignore the DOF corresponding to the seat, they are not suitable for ride comfort analysis. Here, in order to overcome this shortage and make it possible to study the ride comfort, considering an additional DOF for the seat, a half car 3-DOF model has been used. Moreover, in order to investigate the Root Mean Square Acceleration Response (RMSAR) of the vehicle body and the seat, a mathematical relation is proposed for the power spectral density (PSD) of the actual highway- type road excitation. Finally, by applying the proposed PSD, the ride comfort of a special passenger car (Samand) has been studied. The results show that the range of variations of RMSAR of the vehicle body and that of the seat are completely different from each other, and by choosing reasonable values for the stiffness and damping coefficients of the seat, one can improve the ride comfort.

In this paper, free vibration analysis of moderately thick smart FG rectangular plate is presented on the basis of Mindlin plate theory. This structure is composed of a host FG plate and two bonded piezoelectric layers. The plate has two opposite edges simply supported (i.e., Levy-type rectangular plates). The closed circuit piezoelectric layers can be used as an actuator. According to a power-law distribution of the volume fraction of the constituents, material properties vary continuously through the thickness of host plate. Using Hamilton's principle and Maxwell electrostatic equation, six complex coupled equations are introduced. These equations are exactly solved introducing the new potential and auxiliary functions as well as using separation of variables method. The accuracy of the frequencies is verified by the available literature and the finite element method. The present exact solution can accurately predict not only the out of plane, but also the in-plane modes of FG plate. Finally, the effects of various parameters such as boundary conditions, gradient index and thickness of piezoelectric layers on the natural frequency are investigated.

In the present paper, three different samples of alumina used as nanoparticles in the ethylene glycol suspension of alumina with volumetric concentration in the range. These samples have different surface properties, shape and size. The use of Al2O3/EG nanofluids as coolants in a double-tube heat exchanger has been studied under laminar flow conditions. The hot solvent inlet heat exchanger must be cooled down with a specified amount. At first, heat transfer relations between hot solvent and nanofluids as coolants have been investigated theoretically. Subsequently, heat transfer area and flow rate of coolant are optimized by using the nanofluids. In the present paper, heat transfer coefficient, overall heat transfer coefficient, friction factor, pressure drop and pumping power for Al2O3/EG nanofluids calculated.

The purpose of this paper is the study of tensile and bending behavior of polyamide with nano clay by different modifier and corrections in the work condition. Many previous studies about behavior mechanical had been done in standardize condition or after dried samples. However result of this research is not proper for applied design. In this research polyamide is mixed with three kinds of nano clay, By the way of melt intercalated with 9, 7, 5, 3, 1 percents. The samples were tested by X-ray diffraction, for clarifying nano composite morphology. After that tensile and bending tests were done on standard samples. Results show that mechanical property can be improved by added any kind of nano clay to polyamide. Nanocomposites have exfoliated structure if nano clay had more compatibility to polyamide. Moduli tensile and bending were improved with increase nano clay concentration. Although CL30B have best exfoliated structure therefore has most modules in beading and tensile.

Several numerical methods have been emerged to analyze the engineering problems. Boundary Element Method (BEM) is an important method for solving the partial differential equation in engineering problems. The Poison equation is an applicable equation in various engineering problems. General solution of this equation is obtained based on BEM by definition of the two integrals on the domain boundaries, and one integral in the internal domain which is a drawback for this method. To remove this disadvantage, Dual Reciprocity Method (DRM) is suggested. For example, in analysis of the welding heat transfer problems in transient zone where not homogeneous part is involved time dependent terms, is solved by this method. The calculation of the welding zone temperature history is a significant step for the thermal loading and residual stress analysis of the process. In this work, welding temperature history is obtained using the DRM. The Method and its theory are explained. Then, the code validation is carried out by common heat transfer problems. The welding temperature history is studied for a specific case by the created code. Because of the method simplicity and low time and error in computation process, the application of DRM is recommended.