• 건축구조
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• v.15 no.2
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• pp.38-46
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• 2008

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.163-168
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• 1991

During Compression molding of polymeric composite materials, the flow characteristics should be obtained. Understanding the flow states may be useful for determination of optimum molding conditions, charge pattern etc. So far, for obtaining the flow analysis, no-slip boundary condition was applied on the mold surface. However, The study under consideration of the slip was conducted by Barone and Caulk. They have introduced the nondimensional parameter which is the ratio of viscous to friction resistance and governs the frictional condition. But the method for determining the parameter could not be proposed. In our work, the parameter which explains the interfacial friction is measured under a variety of molding conditions. Two-dimensional rectangular part and circular hollow disk are simulated with the measured parameter using the finite element method. Effects of the parameter on shapes of flow fronts are also presented.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.1
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• pp.22-28
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• 2010

To detect the damage in composite structure, nondestructive evaluation techniques are widely used. Tapping test is perhaps the most common technique used for the detection of damage in composite laminates. The method is accomplished by tapping the inspection area with light hammer-like device. The tapping test has the ability that indicates damages in a structure due to a localized change of stiffness. The change in vibration signature may be detected by measurement of the dynamic contact force during impact. In this study, it has been shown that the characteristics of impact force histories from a structure during tapping are changed by the presence of damage such as surface crack and delamination. And impact response analysis has been performed on composite rotor blade with crack to investigate the effect of damage.

• Composites Research
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• v.12 no.6
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• pp.31-42
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• 1999

In aerospace industry, the improvement of structural performance of fight structure without increasing weight has great advantage. In this study. an innovative design method to increase the buckling load and tension failure load at the same time without increasing the weight of composite plates was investigated. By using the curvilinear fiber format a method to increase the buckling load and tension failure load simultaneously was investigated for composite plates with central hole with finite element method. It was investigated how much gain can be obtained with curvilinear fiber format for the plates with different hole size and different stacking sequence. And, for the cases studied, the failure mechanism was also investigated. For the manufacturing of the curvilinear fiber format, smoothly and continuously changing fiber path is necessary. In this study, a simple method to find the smoothly changing fiber path by using the fiber angles obtained with finite element method was presented.

• Journal of Korean Society of Steel Construction
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• v.13 no.1
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• pp.41-52
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• 2001

In this paper the analysis of laminate composite folded plates with arbitrary angle connection like box girder is studied by finite strip method Total stiffness of laminated plate is obtained by integration of the stiffness in each layer or lamina through laminate thickness and total stiffness in each layer or lamina through laminate thickness and total tiffness matrix is obtained by substitutionto equilibrium equation derived from the minimum total potential energy theorem. The assumed displacement functions for a finite strip method in plate or box girder analysis are combinations of one-way polynomial functions in the transverse direction and harmonic functions in the span-wise direction. Finite strip method with the merits of the simplification in modeling and the reduction of analytical time is accurate in the analysis of laminate composite folded plates shaped like box firders.

• Composites Research
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• v.28 no.5
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• pp.277-284
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• 2015

This paper presents a method to detect the fiber property variation of laminated GFRP plates from natural frequency response data. The combined finite element analysis using ABAQUS and the inverse algorithm described in this paper may allow us not only to detect the deteriorated elements from the mirco-mechanical point of view but also to find their numbers, locations, and the extent of damage. To solve the inverse problem using the combined method, this study uses several natural frequencies instead of mode shapes in a structure as the measured data. Several numerical results show that the proposed system is computationally efficient in identifying fiber stiffness degradation for complex structures such as composites with various layup sequences.

• Composites Research
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• v.26 no.1
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• pp.36-41
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• 2013

In this study, low velocity impact analysis on composite sandwich structure was performed. Sandwich structure configuration is made of Carbon-Epoxy face sheets and foam cores. For validating study, the results of an experimental and a finite element method analysis were compared previously. From the finite element method analysis results of sandwich panel, it was confirmed that the results of analysis was reasonable. Impactor velocity to initiate damage was estimated, and in order to investigate the damage at the predicted velocity, impact analysis using finite element method was performed. According to the impact analysis results of sandwich panel, it was confirmed that the damage was generated at the estimated impact velocity. Finally, The comparison of the numerical results with those measured by the experiment showed good agreement.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.3
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• pp.22-30
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• 2012

This study deals with an enhanced assumed strain (EAS) three-dimensional element for free vibration analysis of laminated composite and sandwich structures. The three-dimensional finite element (FE) formulation based on the EAS method for composite structures shows excellence from the standpoints of computational efficiency, especially for distorted element shapes. Using the EAS FE formulation developed for this study, the effects of side-to-thickness ratios, aspect ratios and ply orientations on the natural frequency are studied and compared with the available elasticity solutions and other plate theories. The numerical results obtained are in good agreement with those reported by other investigators. The new approach works well for the numerical experiments tested, especially for complex structures such as sandwich plates with laminated composite faces.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.4
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• pp.1146-1153
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• 1996

The properties of FRP(fiber-reinforced plastics) depend not only on the characteristics of the matrix but also on the structure of fiber mat and the fiber type of reinforcement. Therefore it is very important to study the characteristics of reinforcement and matrix. In this paper, a method is proposed which can be used to measure the mean coeffcient of separation for the press molding of FRP, and the mean equivalent coefficient of separation is obtained from the separation coefficient. And the relationship between the mean equivalent coefficient of separation and the structure of fiber mat is discussed. The effects of corrlelation coefficient between separation and orientation on the mean equivalent coefficient are also presented.

• Composites Research
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• v.20 no.6
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• pp.21-27
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• 2007

Low-velocity impact damage in a composite stiffened panel was detected using built-in piezoelectric active sensor arrays. Using these piezoelectric active sensors, various diagnostic signals were generated to propagate Lamb waves through the structure and the responses were picked up to detect changes in the structure's vibration signature due to the damage. Three algorithms - ADI(Active Damage Interrogation), TD RMS (Time Domain Root Mean Square) and STFT (Short Time Fourier Transform) - were examined to express the features of the signal changes as one damage index. From damage detecting tests, two impact induced delaminations were detected and the location was estimated with the algorithms and diagnostic signals.