• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.5
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• pp.309-316
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• 2022

This paper presents nonlinear numerical analysis results which were compared with the tested tensile strengths of CFRP(Carbon Fiber Reinforced Plastic) laminates with 14 different stacking sequences. The composite laminate coupons were cured under an autoclave pressure using resin-impregnated unidirectional tapes. The nonlinearity of the matrix was considered for the analysis, which was obtained from lamina tests. The Hashin failure criteria and progressive failure analysis were used for the nonlinear finite element analysis. The comparison results show that the current approach is acceptable to predict the tensile strengths of the CFRP laminate coupons with various stacking sequences and no damage. However, it is not acceptable to predict the tensile strengths of the laminate specimens with a center hole.

• Composites Research
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• v.12 no.1
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• pp.47-58
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• 1999

This paper describes the results of experiments to analyze the free vibration of the laminated composite and hybrid composite plates with various shapes and boundary conditions. The materials of specimens were the carbon fiber reinforced plastic (CFRP), the glass fiber reinforced plastic (GFRP), the GFRP-Aluminum hybrid composite and the CFRP-CFRP hybrid composite. The natural frequencies and nodal patterns of plates with various shapes were experimentally obtained by impact exciting test using an impact hammer and an accelerometer. The experimental results were presented with normalized frequency parameters. The effects of composite material properties, fiber orientation angles, various geometrical shapes and boundary conditions on the vibration characteristics of composite plates were evaluated. To compare and verify these experimental results, the finite element analysis was carried out, and was well agreed with experimental results.

• Korean Journal of Crystallography
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• v.13 no.2
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• pp.69-72
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• 2002

The interlaminar problems near the free edge of composite laminates are analyzed in this paper. CFRP specimen (［+40/-40］s) and interleaved specimen (［+40//-40］s) with non-woven carbon tissue (NWCT) are discussed under tensile loading condition. The symbol “//”means that the NWCT is located between the CFRP interfaces. The NWCT has carbon short fibers which are discretely distributed with the in-plane random orientation. It was reported/sup 3)/ that the Mode Ⅱ interlaminar fracture toughness of CFRP laminates with NWCT is increased largely and the Mode I interlaminar fracture toughness is not changed significantly. Mode Ⅲ interlaminar fracture toughness is also an important factor in composite structures. But it is not easy to experimentally investigate the Mode Ⅲ interlaminar fracture toughness. The objective of this work is to study the effect of the NWCT and to fundamentally understand the Mode Ⅲ interlaminar shear characteristics of laminated composites with NWCT in the vicinity of a free edge by using finite element method analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.812-815
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• 2002

This paper deals with the buckling and vibration analysis of plate with a hole. We knew that in this paper, as aspect ratio rises in design parameter, the buckling strength and the natural frequency of laminated composite plate decrease and as diameter of hole for width of plate rises, the buckling strength decrease but the natural frequency increase. Also this paper compared the CFRP laminated composit plate with the hybrid composite plate, and proposed that the hybrid composite plate is stronger than the CFRP composite plate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.11
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• pp.1239-1243
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• 2014

This paper presents the application of carbon-fiber-reinforced polymer (CFRP) for the damage absorption and optimal design of portable smart devices to close in life. CFRP specimens are subjected to a tensile test to estimate their mechanical properties in terms of the stacking angles. Further, the screw reverse torque and screw torque at each stacking angle are determined using a torque tester after tapping holes on the CFRP specimens. Two experiments are performed for comparing their results in order to determine optimal conditions. In the tensile test, a woven specimen is found to have the highest strength and stiffness. In the case of the woven specimen, no difference is observed even when it is applied to prevent loosening of the coating. And average result value was excellent.

• Composites Research
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• v.29 no.5
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• pp.299-305
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• 2016

This paper presents a method to detect the fiber property variation of laminated CFRP plates using the bivariate Gaussian distribution function. Five unknown parameters are considered to determine the fiber damage distribution, which is a modified form of the bivariate Gaussian distribution function. To solve the inverse problem using the combined computational method, this study uses several natural frequencies and mode shapes in a structure as the measured data. The numerical examples show that the proposed technique is a feasible and practical method which can prove the location of a damaged region as well as inspect the distribution of deteriorated stiffness of CFRP plates for different fiber angles and layup sequences.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.2
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• pp.81-88
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• 1997

Impact behavior of carbon fiber reinforced plastics (CFRP) laminates were evaluated with tension test and compact tension test. A steel ball launched by an air gun collides against CFRP laminates to generate impact damage of relatively low energy. The static tensile and fracture toughness tests were performed to evaluate the residual strength and the AE behavior of impact-damaged laminates. As a results, it was found that the static strength, the fracture toughness and the AE-event count were decreased with increasing of impact velocity and delamination area, and to have a different strength ratio and fracture toughness ratio for each stacking method. And also, it was confirmed that strength and fracture toughness of impact-damaged CFRP laminates could be evaluated and analyzed quantitatively by AE techniques.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.364-369
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• 2003

Crack propagation and AE characteristics of CFRP plain woven laminate composites are examined with acoustic sensor by AEDSP 32/16 board in PC system. AE signals are measured during the fracture behavior tests. The purpose of study is the estimation of the crack extension behavior effected between three kinds of fiber orientation for plain woven CFRP laminate composite and the relationship between AE characteristics and load-displacement curves and crack extension length.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.63-67
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• 1999

This paper presents the optimization of CFRP laminated rectangular plates using fuzzy theory. In optimization, thickness of CFRP lamina and fiber angle are taken as design variables, and total thickness of the plates is minimized under Tsai-Hill failure criterion. The uncertainties are entered by introducing fuzzy material strengths and then the objective and constraints are represented by a membership function of their own according to the intersection method. Various design results are presented for the CFRP laminated composites plates.

• Journal of the Korean Society for Precision Engineering
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• v.34 no.2
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• pp.95-99
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• 2017

The recent development of core techniques in the IT industry can be summarized as a technical advancement for safety and convenience, and mechanical technology for being "eco-friendly" and lightweight. Under these circumstances, research of lightweight material has become attractive. In this study, CFRP (Carbon Fiber Reinforced Plastic) laminate specimens are subjected to a tensile test using the UTM(Universal Testing Machine, AG-IS 100 kN) to estimate their mechanical properties in terms of the Hole machining impact evaluation. The FEM (Finite Elements Method) analysis method is applied and the material properties obtained from basic experiments such as the Tensile test, the compressive test, and the shear test. CFRP materials properties from a previous study, as well as a finite element analysis program for Hole machining CFRP was compared with the experiments.