• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.6
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• pp.981-987
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• 1997

Modern helicopter rotor blades with non-homogeneous cross section composed of anisotropic material rquire highly sophisticated structural analysis. Variation in cross section geometry makes this task of analysis more complicated. Since rotor blades generally are much longer than their lateral dimensions, one-dimensional models seem feasible, at least from a computational point of view. Therefore determination of the principal coordinate system is very important to remove the structural coupling for one-dimensional beam modelling. In this study, shear center, and principal direction. The method will be verified by comparing the results with confirmed experimental results.

• Composites Research
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• v.12 no.6
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• pp.1-7
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• 1999

The change of the coefficients of thermal expansion(CTE) of Carbon/Epoxy was investigated for the temperature variation and a prediction model for the change of CTE was proposed. Elastic properties and CTEs in the principal material directions were measured in the range of room temperature to cure temperature and characterized as functions of temperature. By applying the characterized properties to the classical lamination theory, a computational method to predict the change of CTEs of a general laminate for temperature variation was proposed. the coefficients of thermal expansion of laminates with various stacking sequences were measured and compared with those predicted. Good agreements between the predicted results and the experimental data show that the c hanges of CTEs of a general laminate for temperature variation can be predicted well by using the proposed method.

• Composites Research
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• v.18 no.1
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• pp.38-44
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• 2005

In this paper, the group velocity dispersion curves of the $S_o$ symmetric mode in unidirectional CFRP plate was calculated as varying the propagating direction. The group velocity curve was obtained with the group velocities of the $S_o$ symmetric mode corresponding to 0.2 MHz-mm under the first cut-off frequency in the dispersion curves, and corrected by introducing the slowness curve. The velocities of the $S_o$ symmetric mode in the unidirectional CFRP plate were measured as varying the propagating direction and compared with the col?rotted group velocity curve. The measured velocities were good agreement with the corrected group velocity curve except near the fiber direction which was called the cusp region. It implies that the direction of the group velocities incline toward the fiber direction of the unidirectional CFRP plates when the propagation direction is not accorded with the principal axis. It is supposed that this phenomenon rerults from the preferential propagating the energy toward the direction with the faster propagation velocity.

• Journal of the Korean Society for Nondestructive Testing
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• v.7 no.2
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• pp.42-47
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• 1988

The off-axis tensile strength of the unidirectional carbon fiber reinforced plastic and the residual strength of impact damaged CFRP were measured and compared with the stress wave factor (SWF) of the specimens. The SWF values were measured to be decreased with the strength reduction in both cases and found to be useful for the nondestructive strength evaluation of unidirectional CFRP. The failure behaviour of the unidirectional CFRP during off-axis tensile testing was also monitored by acoustic emission(AE) method. The AE energy release showed the characteristic feature depending on the off-axis angle and this result was analyzed to be caused by the difference of the expected failure mode depending on the off-axis angle. The failure mode of CFRP was found to be analyzed by investigation of the peak amplitude distribution of AE.