• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.157-160
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• 2006

Carbon fiber reinforced polymer (CFRP) laminates can be used more efficiently in strengthening applications by applying prestress to the CFRP laminates. A key problem for prestressing with CFRP laminates is anchoring the laminates. These may include fracture to the CFRP laminates due to excessive gripping force or slippage of the CFRP laminates out of the anchorage zone caused by low friction between the anchor device and the lamiantes. The main objective of this study is the development of an applicative wedge-type anchorage system for prestressed CFRP laminates through experimental study. The experimental parameters were the type of anchorage and the effect of elastic modulus of tab. The test results showed that the developed anchor assures 100% CFRP laminate strength.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.420-425
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• 2000

The room-temperature shapes of cured unsymmetric composite laminates have out-of-plane warping after autoclave processing. In addition, they exhibit two stable room-temperature configurations due to snap-through phenomena when the side length of laminates exceeds a critical value. The cured shapes of unsymmetric laminates are influenced by many environmental factors. Experiments show that the effect of too-plate cannot be ignored and has significant influence on the cured shape of unsymmetric laminates. In this present study, approximations to the strain fields are used in the expression for the total potential energy and the Rayleigh-Ritz method is applied. The slippage effects resulting from the interaction between the laminates and the tool-plate are considered. By introducing a dimensionless slippage coefficient and correlating the corresponding value with experimental results, the influence of processing parameters is investigated. Modeling is extended to predict curvatures of plate configurations with various aspect ratio.

• Advanced Composite Materials
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• v.18 no.3
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• pp.251-264
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• 2009

Nonlinear mechanical behaviors of unidirectional carbon fiber-reinforced plastic (CFRP) laminates using cup-stacked carbon nanotubes (CSCNTs) dispersed epoxy are evaluated and compared with those of CFRP laminates without CSCNTs. Off-axis compression tests are performed to obtain the stress-strain relations. One-parameter plasticity model is applied to characterize the nonlinear response of unidirectional laminates, and nonlinear behaviors of laminates with and without CSCNTs are compared. Clear improvement in stiffness of off-axis specimens by using CSCNTs is demonstrated, which is considered to contribute the enhancement of the longitudinal compressive strength of unidirectional laminates and compressive strength of multidirectional laminates. Finally, longitudinal compressive strengths are predicted based on a kink band model including the nonlinear responses in order to demonstrate the improvement in longitudinal strength of CFRP by dispersing CSCNTs.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.279-282
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• 2005

This study investigates the flexural behavior and strengthening performance of RC beams strengthened by prestressed CFRP laminates through static bending tests. Tests on RC beams strengthened with prestressed CFRP laminates were carried out for both cases where the CFRP laminates were bonded or not and the corresponding effects on the strengthening performances of RC beams were examined. Experimental results revealed that RC beams strengthened with prestressed CFRP laminates presented increased crack load and yield load according to the level of prestress. Premature debonding occurred before the RC beam strengthened with bonded prestressed CFRP laminates reaches the maximum load, and the specimen presented similar behavior to the one exhibited by the specimen with unbonded laminates.

• Journal of the Korean Society of Safety
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• v.12 no.2
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• pp.27-36
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• 1997

This paper evaluates the static and fatigue bending strengths of CFRP (carbon fiber reinforced plastic) laminates subjected to hygrothermals. The specimens which had different stacking composition, orthotropic and quasi-isotropic laminated plates, were prepared for this experiment. A steel ball launched by the air gun collides against CFRP laminates to generate impact damages, and the 3-point fatigue bending test is carried out by using the impacted laminates to investigate the influence of hygrothermals on the effect on the residual bending fatigue strength of CFRP laminates.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1991.10a
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• pp.121-126
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• 1991

In his recent book, D.H. Kim proposes to use the quasi-isotropic constants by Tsai for the preliminary design of the composite primary structures for the civil construction. Such structures generally require a large number of laminae layers. Simple equations which can predict "exact" values of the buckling strength, the natural frequency of vibration, and the deflection for the special orthotropic laminates are presented. Many laminates with certain orientations lave decreasing values of B$\_$16/ and B$\_$26/ as the number of plies increases. Such laminates, with D$\_$16/=D$\_$26/\longrightarrow0, including the laminates with anti-symmetric configurations can be solved by the same equation for the special orthotropic laminates. If the quasi-isotropic constants are used, the equations for the Isotropic plates can be used. Use of some coefficients can produce "exact" value for laminates with such configuration.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.1-4
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• 2001

A new non-destructive fatigue prediction model of the composite laminates is developed. The natural frequencies of fatigue-damaged laminates under extensional loading are related to the fatigue lift of the laminates by establishing the equivalent flexural stiffness reduction as a function of the elastic properties of sublaminates. The flexural stiffness is derived by relating the $90^{\circ}$-ply elastic modulus reduction, and using the laminate plate theory to the degraded elastic modulus and the intact elastic modulus of other laminate. The natural frequency reduction model, in which the dominant fatigue mode can be identified from the sensitivity scale factors of sublaminate elastic properties, provides natural frequency vs. fatigue cycle curves for the composite laminates. Vibration tests were also conducted on $[\textrm{90}_{2}\textrm{0}_{2}]_s$ carbon/epoxy laminates to verify the natural frequency reduction model. Correlations between the predictions of the model and experimental results are good.

• Journal of Industrial Technology
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• v.19
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• pp.227-233
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• 1999

Simple equations which can predict "exact" values of the natural frequency of vibration for the special orthotropic laminates are presented. Many laminates with certain orientations have decreasing values of $B_{16}$ and $B_{26}$ as the number of plies increases. Such laminates, with $D_{16}=D_{26}{\rightarrow}0$, including the laminates with anti-symmetric configurations can be solved by the same equation for the special orthotropic laminates. If the quasi-isotropic constants are used, the equations for the isotropic plates can be used. Use of some coefficients cab produce "exact" value for laminates with such configurations. Natural frequencies of the plate with varying aspect ratios is presented.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.275-278
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• 2004

In this paper, the fracture strength of the surface damaged laminates was predicted by applying the fracture strengths of the unflawed and flawed laminates. For prediction, the theoretical equation about the fracture strength of laminates was simplified applying classical laminate theory and was applied to the surface damaged laminates. Lagace's and Tsai's experimental data were used for verifying the theoretical equation. Moreover, to verify the theoretical prediction, an experiment was performed. Surface unflawed laminate and flawed laminates were fabricated and the experiments were made and these results were compared with theoretical predictions. The specimens' fiber direction was same to the tensile direction and the theoretical predictions and the experimental results were showed good agreement. Therefore, by this equation, the fracture strength of structures made of composites will be able to be predicted when the surface of the structures was damaged.

• Journal of the Korean Society of Safety
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• v.18 no.2
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• pp.34-39
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• 2003

In this paper, when CF/PEEK laminates for high efficiency space structure are subjected to FOD(Foreign Object Damage), the effects of temperature change on the impact damages(interlaminar separation and transverse crack) of CF/PEEK laminates and the relationship between residual lift and impact damages are experimentally investigated. Composite laminates used in this experiment are CF/PEEK orthotropic laminated plates, which have two-interlaces [$0^{\circ}_4/90^{\circ}_8/0^{\circ}_4$]. A steel ball launched by the air gun collides against CF/PEEK laminates to generate impact damages. And then CF/PEEK specimens with impact damages are observed by a scanning acoustic microscope under room and high temperatures. In this experimental results, various relations are experimentally observed including the delamination area vs. temperature change, the bending strength vs. impact energy and the residual bending strength vs. impact damage of CF/PEEK laminates.