Dynamic Response
J. Akbari; H. Valaei; M. F. Sepahvand
Abstract
Finite-element modeling of structures using elements without rotational degrees of freedom (DOFs) is usually stiffer than their physical behavior. Therefore, the stiffness of a structural system will be smoothed by adding rotational DOFs in the numerical model. In the traditional displacement-based ...
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Finite-element modeling of structures using elements without rotational degrees of freedom (DOFs) is usually stiffer than their physical behavior. Therefore, the stiffness of a structural system will be smoothed by adding rotational DOFs in the numerical model. In the traditional displacement-based finite-element method, adding drilling rotations is not easy. The main contribution of this paper is performing dynamic analyses using the finite strip element with added drilling rotations to the elements. For this purpose, any quadrilateral area is divided into two independent sets of orthogonal strips comprising truss and Bernoulli-Euler beam elements. Then, by using new shape functions, mass, damping, stiffness matrices, and equivalent nodal forces are derived. Finally, time history analysis for plane stress or strain type problems for direct earthquake records is performed using the developed formulations. The numerical studies show that the results of the finite strip element method using coarse meshes are competitive with the results of the finite-element method using fine meshes. This advantage is valuable in time-consuming computational problems, e.g., dynamic or nonlinear analyses.
Finite Elements Method (FEM)
Farshid Ahmadi; Rohollah Mohammadi
Abstract
Abstract The first step of implanting teeth is to drill a hole in the jaw bone. Excessive temperature produced during drilling is one of the destructive factors for bony tissue. If the temperature generation during surgical drilling exceeds the critical temperature, it could lead to osteonecrosis. This ...
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Abstract The first step of implanting teeth is to drill a hole in the jaw bone. Excessive temperature produced during drilling is one of the destructive factors for bony tissue. If the temperature generation during surgical drilling exceeds the critical temperature, it could lead to osteonecrosis. This research intends to study drilling parameters such as drilling speed, feed rate, cooling condition and tool geometry by FEM method in order to achieve the most appropriate drilling conditions. Three dimensional modeling of lower jaw bone from the CT scan images was made by Mimics 10.01 software. In order to place the drill bit on the mandibular model, two teeth were removed from the final part of model by CATIA V5R20 software. DEFORM-3D (Version 10.2) was used for mandibular cortical bone drilling simulation. For this purpose, drill bits with different geometrical parameter including point angles of 90, 70, and 118 degrees and helix angles of 20, 23, and 30 degrees were designed in the software. The simulations were carried out using different feed rates (60, 90, 120 and 200 mm/min) and rotational speeds (200, 400, 800, and 1200 rev/min). The simulation results showed that the most appropriate conditions for the lowest temperature was as follows: 70 degrees for drill bit point angle, 23 degrees for helix angle, 200 mm/min for feed rate, and 200 rev/min for rotational speed. Also, by using coolant the maximum temperature reduced by approximately 12 degrees. The results also suggest that the rotational speed of 200 rev/min and feed rate of 200 mm/min have the largest thrust force in drilling area. The finite element results were validated by available experimental data.
Manufacturing Processes
Saman Khalilpourazary; jamal ahmadi
Abstract
Reaming is a common finishing process for improving the drilled holes surface quality. Choosing an appropriate finishing method in drilling process has a significant effect on the surface quality of holes and in decreasing the process total cost and time. In this study, four similar holes were drilled ...
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Reaming is a common finishing process for improving the drilled holes surface quality. Choosing an appropriate finishing method in drilling process has a significant effect on the surface quality of holes and in decreasing the process total cost and time. In this study, four similar holes were drilled on the AISI 4340 workpiece with different two pair feed rates. The drilling process was performed with a conventional cutting fluid, an emulsion of water and ECOCOOL 3015 GS-W. The surface roughness values after drilling process were measured using a portable roughness tester. Then, two distinct sizes of alumina micro-particles were used in the cutting fluid discretely to perform finishing process of the holes with a specific cylindrical tool. A comparison of the surface roughness measurements after the finishing process showed a significant decrease in the arithmetic surface roughness and ten-point mean roughness values of the drilled holes. The values were very close to the surface roughness limits in reaming process of the holes.
