• Journal of the Korean Society for Precision Engineering
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• v.13 no.5
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• pp.30-37
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• 1996

The objective of this research is to explore the analysis and test method for the reliable design and fabrication of a high precision dynamically tuned gyroscope. The tuning frequency is decided by the calculation of mass moment of inertia of rotor and gimbal and the stiffness of flexures. Due to the complex geometry of the flexure, calculation of the stiffness of the suspension flexure is difficult. In this paper, three analytical methods for obtaining the stiffness of the flexure are porposed and a special testing method is used for checking the accuracy of the computed results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1826-1832
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• 2000

A modelling method for the bending vibration analysis of rotating cantilever beams employing finite element method is presented in this paper. Different from the conventional modelling method in wh ich only Cartesian deformation variables are used, a non-Cartesian deformation variable is introduced and approximated to derive the equations of motion. Numerical results obtained by using the presented modelling method are compared to those obtained by using other methods in the related literature, and the accuracy of the presented method is verified through the comparison study. The presented modelling method is superior to other previous methods in a sense that several advantages of the previous methods are incorporated into the presented method.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.2
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• pp.202-206
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• 2011

Works on the strength and stiffness in the structural members are carried out widely with various material and cross-sections with ever increasing safety concerns, they are presently applied in various fields including railroad trains, air crafts and automobiles. In addition to this, problem of lighting structural members became important subject by control of exhaust gas emission, fuel economy and energy efficiency. So, Light weight of member structures is necessary for the high performance and various functions. In this study, the CFRP flat and circular member was manufactured by CFRP prepreg sheet in autoclave. Carbon FRP is an anisotropy material whose mechanical properties change with its fiber orientation angle, so this study apply to the effects of the fiber orientation angle on the bending characteristics of the member. Each CFRP flat and circle are compared by strength and stiffness.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.994-999
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• 2003

A modeling method for the modal analysis of a rotating cross-ply composite beam based on Timoshenko beam theory is presented. To analyze the composite beam exactly, the effects of shear deformation and rotary inertia are included. Linear differential equations of motion are derived using the assumed mode method. For the modeling, hybrid deformation variables are employed and approximated to derive the equations of motion. The effects of the dimensionless angular velocity and the slenderness ratio parameter on the variations of modal characteristics are investigated

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.92-99
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• 2006

Design capability for high safety vehicle with light weight is crucial to enhancing competitive power in vehicle market. The structural foam can contribute to restraining section distortion in body members undergoing bending collapse at vehicle crash. In this study, first, the validation of analysis model including structural foam model for simulating fracture behavior was discussed, and the bending collapse characteristics of five representative section types were analyzed and compared. Next, with changing the laminate foam shape, load carrying capability and absorbed energy were observed. The results suggests a design strategy of body members filled with laminate foam, leading to effectively elevating bending collapse characteristics with weight increase in the minimum.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.42-47
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• 2003

Nonlinear models for a thin ring rotating at a constant speed are developed. The geometric nonlinearity of displacements is considered by adopting the Lagrange strain theory for the circumferential strain. By using Hamilton’s principle, the coupled nonlinear partial differential equations are derived, which describe the out-of-plane and in-plane bending, extensional and torsional motions. The natural frequencies are calculated from the linearized equations at various rotational speeds. Finally, the computation results from the nonlinear models are compared with those from a linear model. Based on the comparison, this study recommends which model is appropriate to describe the behavior of the rotating ring.

• Computational Structural Engineering
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• v.8 no.4
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• pp.87-97
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• 1995

For the same configuration of two-dimensional finite element models, 6-node element exhibits stiffer bending stiffness than 8-node element. This is true in the relation between 16-node element and 20-node element for three-dimensional model. This stiffening phenomenon comes from the elimination of several mid nodes from full-node elements. Therefore, this may be called 'relative stiffness stiffening phenomenon'. It seems that there are a couple of ways to correct the stiffening effect, however, we could find only one effective method-the method of modification of Gauss sampling points-which passes the patch test and does not alter other kinds of stiffness, such as extensional stiffness. The quantity of modification is a function of Poisson's ratios of the constituent materials. We could obtain two modification equations, one for plane stress case and the other for plane strain case. This method can be extended to 3-dimensional solid elements. Except the exact plane strain cases, most 3-dimensional plates could be modeled successfully with 16-node element modified by the equation for the plane stress case. The effectiveness of the modification method is checked by applying it to several examples with excellent improvements. In numerical examples, beams with various boundary conditions are subjected to static and time-dependent loads. Free and forced motion analyses of beams and plates are also tested. The beam and plate may be composed of isotropic multilayers as well as a single layer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.12
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• pp.1013-1020
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• 2017

In this study, the failure prediction of composite laminates under flexural loading is investigated. A FEA(finite element analysis) using 2D strain-based interactive failure theory. A pregressive failure analysis was applied to FEA for stiffness degradation with failure mode each layer. A three-point bending test based on the ASTM D790 are performed for cross-ply $[0/90]_8$ and quasi-isotropic $[0/{\pm}45/90]_{2s}$ laminated composites. The accuracy of the applied failure theory is verified with the experimental results and other failure criteria such as maximum strain, maximum stress and Tsai-Wu theories.

• Composites Research
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• v.22 no.6
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• pp.39-44
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• 2009

The effect of exposure times on the aging characteristics of carbon fiber/epoxy composite ring specimen was evaluated using an accelerating aging tester. Combined exposure conditions, such as temperature, moisture, and ultraviolet, were applied up to 3000 hours. Tensile properties and flexural properties including the effect of curvature were evaluated on the specimens subject to various exposure times through a material testing system. Their aging surfaces were observed through a scanning electron microscope. According to the results, tensile modulus was little affected by the exposure times. However, tensile strength, at the early stage of the exposure times, increased due to physical aging and curing reaction, but tensile strength slightly decreased due to degradation as the exposure times increased. The flexural modulus and flexural strength increased at the early stage of the exposure times, but slightly decreased as the exposure times increased. Aging surfaces of the specimens examined using the scanning electron microscope revealed a different morphology in various exposure times and provided useful information for identifying the degradation in mechanical properties of the composite subject to various exposure times.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.11-18
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• 1991

Stiffened plate structure, which is generally used in the various structural design to develope the load carrying capacity, is classified in two groups; one is the plate stiffened with stiffeners, the other is corrugated plate. In the studies on those structures, the studies on the stiffened plates with stiffeners have been much studied with both quantities and qualities according to requirements of the minimum-weight structural design and the development in many industrial fields, especially automobile, ship and aerospace fields, but the studies on the corrugated plates are undeveloped in comparison with the stiffened plates, and also the analytical stiffness on the corrugated plates remains as the imperfect. In the present studies, the analytical method on the stiffness of corrugated plates made by folding is proposed, and the stiffness equation of corrugated plates with some angle is derived and generalized. The purpose of the present study is to contribute to the design of corrugated plates and to determine the optimum aspect ratio for parameters that decide the aspect of corrugated plates.