Showing papers by "Ramin Sedaghati published in 2018"

A comprehensive review of finite element modeling of orthogonal machining process: chip formation and surface integrity predictions

Abstract: Finite Element (FE) modeling of machining processes has received growing attention over the last two decades. Since machining processes operate at severe deformation conditions, involving very high strain, strain rate, stress, and temperature, the modeling procedure is still a challenging task even with new advanced software and computers. Therefore, most of the published research works were mainly performed for the simplest configuration of machining known as orthogonal cutting, in which a plane strain deformation state is assumed. This configuration leads to reducing the number of elements in the FE model and the computational time of the solution, compared to conventional machining processes (turning, milling, and drilling). Nevertheless, FE modeling of orthogonal turning is still considered as an open-ended subject as most of the phenomena involved in the orthogonal turning process, which also exist in other machining operations, are not fully well understood. The present review article deals with finite element modeling of orthogonal machining process. The paper consists of several related parts. First, the fundamentals of the FE simulation of orthogonal turning process are briefly described. Then, a detailed review on the FE prediction of machining characteristics including chip morphology, cutting forces, cutting temperature, tool wear, and burr formation is provided. Also, the FE prediction of surface integrity characteristics including residual stresses and microstructural changes is discussed. The influence of input model and parameters including thermal, material, and frictional models as well as size and arrangement of elements on machining and surface integrity characteristics are explained as well. Both technical and statistical aspects of the FE simulation of orthogonal turning are treated. Since there is no review paper thoroughly and specifically discussing the methods and findings of the finite element simulation of turning operations, the present article can be used as a reference for researchers who are active and/or interested in this filed.

Finite element analysis and response surface method for robust multi-performance optimization of radial turning of hard 300M steel

Abstract: 300M steel is commonly used in the automotive and aerospace industries due to its high strength and fatigue life. Residual stresses induced by machining of these materials can greatly affect the fatigue life. The present research aims mainly to develop an optimization strategy to identify optimal cutting parameters to improve machining characteristics and residual stresses induced by radial orthogonal turning 300M steel. To achieve this, first, a predictive finite element tool is developed to model cutting temperature, cutting and thrust forces, and residual stresses. Orthogonal turning experiment is conducted to measure machining forces, chip thickness, and residual stresses to validate the developed finite element model. The validated model is then used to construct response functions (meta models) using combined design of experiment and response surface method for practical and efficient implementation of the optimization problem. Finally, the developed response functions are utilized to formulate various multi-objective optimization problems. A hybrid optimization algorithm combining genetic algorithm and sequential quadratic programming method is employed to solve optimization problems in order to identify optimal cutting conditions and tool geometry. The results show that for unconstrained optimization problems, the percentage improvement in the total objective function is greater than that of constraint optimization ones. For multi-objective optimizations, it is found that weighting factors affect the optimum values of the total objective function more than those of the machining parameters. Since very few efforts were exerted to perform finite element modeling, experimental tests, and multi-performance optimization of machining characteristics and residual stresses induced by orthogonal turning 300M steel, the present results can be utilized as a reference for future works along this filed.

Free in-plane vibration of curved beam structures: A tutorial and the state of the art:

Abstract: The study of free in-plane vibration of curved beams, using different beam theories, is more challenging than that of straight beams, since the structural deformations in curved beams depend not on...

On sound insulation of pyramidal lattice sandwich structure

Abstract: Pyramidal lattice sandwich structure (PLSS) exhibits high stiffness and strength-to-weight ratio which can be effectively utilized for designing light-weight load bearing structures for ranging from ground to aerospace vehicles. While these structures provide superior strength to weigh ratio, their sound insulation capacity has not been well understood. The aim of this study is to develop numerical and experimental methods to fundamentally investigate the sound insulation property of the pyramidal lattice sandwich structure with solid trusses (PLSSST). A finite element model has been developed to predict the sound transmission loss (STL) of PLSSST and simulation results have been compared with those obtained experimentally. Parametric studies is then performed using the validated finite element model to investigate the effect of different parameters in pyramidal lattice sandwich structure with hollow trusses (PLSSHT), revealing that the pitching angle, the uniform thickness and the length of the hollow truss and the lattice constant have considerable effects on the sound transmission loss. Finally a design optimization strategy has been formulated to optimize PLSSHT in order to maximize STL while meeting mechanical property requirements. It has been shown that STL of the optimal PLSSHT can be increased by almost 10% at the low-frequency band. The work reported here provides useful information for the noise reduction design of periodic lattice structures.

Development, optimization, and control of a novel magnetorheological brake with no zero-field viscous torque for automotive applications:

Abstract: The significant energy loss due to viscous torque generation in the absence of the applied magnetic field is the main obstacle in the practical realization of magnetorheological brake in the automo...

Dynamic analysis of an SDOF helicopter model featuring skid landing gear and an MR damper by considering the rotor lift factor and a Bingham number

Abstract: The present study addresses the performance of a skid landing gear (SLG) system of a rotorcraft impacting the ground at a vertical sink rate of up to 4.5 ms−1. The impact attitude is assumed to be level as per chapter 527 of the Airworthiness Manual of Transport Canada Civil Aviation and part 27 of the Federal Aviation Regulations of the US Federal Aviation Administration. A single degree of freedom helicopter model is investigated under different values of rotor lift factor, L. In this study, three SLG versions are evaluated: (a) standalone conventional SLG; (b) SLG equipped with a passive viscous damper; and (c) SLG incorporated a magnetorheological energy absorber (MREA). The non-dimensional solutions of the helicopter models show that the two former SLG systems suffer adaptability issues with variations in the impact velocity and the rotor lift factor. Therefore, the alternative successful choice is to employ the MREA. Two different optimum Bingham numbers for compression and rebound strokes are defined. A new chart, called the optimum Bingham number versus rotor lift factor '', is introduced in this study to correlate the optimum Bingham numbers to the variation in the rotor lift factor and to provide more accessibility from the perspective of control design. The chart shows that the optimum Bingham number for the compression stroke is inversely linearly proportional to the increase in the rotor lift factor. This alleviates the impact force on the system and reduces the amount of magnetorheological yield force that would be generated. On the contrary, the optimum Bingham number for the rebound stroke is found to be directly linearly proportional to the rotor lift factor. This ensures controllable attenuation of the restoring force of the linear spring element. This idea can be exploited to generate charts for different landing attitudes and sink rates. In this article, the response of the helicopter equipped with the conventional undamped, damped, and MREA based SLG are numerically simulated using three sets of Bingham numbers. Namely, an underestimated, optimum, and overestimated Bingham number for every stroke. The simulation results depict that the only feasible solution is when the MREA generates the optimum damping force corresponding to the optimum Bingham numbers. Under this circumstance, the MREA utilizes the available energy absorption stroke to attain a soft landing. Furthermore, in the rebound stroke, the optimum damping force resettles the helicopter to its equilibrium position and prevents oscillations after the end of the rebound stroke.

Linear and Nonlinear Viscoelastic Behavior of MR Fluids: Effect of Temperature

Abstract: This study aims to investigate the influence of temperature on the linear and nonlinear rheological behavior of a MR fluid, MRF 132DG, using a rotational rheometer. The experiments were designed to obtain properties of the fluid under oscillatory shear strain in the amplitude and frequency sweep modes, while maintaining different constant temperatures (−5, 0, 20 and 50 °C). The data were used to evaluate the storage and loss moduli under different levels of magnetic flux density considering the linear as well as nonlinear viscoelastic regions. The critical strain amplitudes were further obtained. Results showed enhanced linear viscoelastic region with increasing magnetic field density. Moreover, the effects of temperature and magnetic field on the frequency dependency of the fluid properties are illustrated for small and large amplitudes of shear strains.