• Composites Research
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• v.32 no.6
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• pp.327-334
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• 2019

The delamination is a special mode of failure occurring in composite laminates. Several numerical studies with finite element analysis have been carried out on the delamination behavior of unidirectional composite laminates. On the other hand, the fracture for the multi-directional composite laminates may occur not only along the resin-fiber interface between plies known as interply or interlaminar fracture but also within a ply known as interyarn or intralaminar fracture accompanied by matrix cracking and fiber bridging. In addition, interlaminar and intralaminar cracks appear at irregular proportions and intralaminar cracks proceeded at arbitrary angle. The probabilistic analysis method for the prediction of crack growth behavior within a layer is more advantageous than the deterministic analysis method. In this paper, we analyze the crack path when the mode I load is applied to the cross-ply carbon/epoxy composite laminates and collect and analyze the probability data to be used as the basis of the probabilistic analysis in the future. Two criteria for the theoretical analysis of the crack growth direction were proposed by analyzing the stress field at the crack tip of orthotropic materials. Using the proposed method, the crack growth directions of the cross-ply carbon/epoxy laminates were analyzed qualitatively and quantitatively and compared with experimental results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.49-55
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• 2002

In this paper, we present the simulation monitoring of strain and temperature during and after the cure of unsymmetric composite laminate using fiber optic sensors. Fiber Bragg grating/extrinsic Fabry-Perot interferometric (FBG/EFPI) hybrid sensors are used to measure those measurands. The characteristic matrix of the sensor is analytically derived and measurements can be done without sensor calibration. A wavelength-swept fiber laser is utilised as a lighr source. Two FBG/EFPI sensors are embedded in a graphite/epoxy unsymmetric cross-ply composite laminate in different directions and different locations. We perform a real time monitoring of fabrication strains and temperatures at two points of the composite laminate during cure process in an autoclave. Also, the thermal strains and temperatures of the fabricated laminate are measured in a thermal chamber. Through these experiments, we can provide a basis for the efficient smart processing of composite and know the thermal behavior of unsymmetric cross-ply composite laminate.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.6
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• pp.219-225
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• 2011

Advanced composite structures are too difficult for such design engineers for construction and some simple but accurate enough methods are necessary. The simply supported laminated plates are analyzed by the specially orthotropic laminates theory. This method, however, may be too difficult for some practising engineers. In this paper, the result of analysis for such plate by means of the beam theory with unit width is reported. The plate aspect ratio considered is from 1 : 1 to 1 : 5. Most of the bridge and building slabs on girders have large aspect ratios. For such cases further simplification is possible by neglecting the effect of the longitudinal moment terms($M_x$) on the relevant partial differential equations of equilibrium. In this paper. the influence of the aspect ratio on the natural frequency of the specially orthotropic laminated plates is studied and it is concluded that the method used is sufficiently accurate for engineering purposes. The result of this paper can be used for simply supported laminated plates analysis.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.595-603
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• 1989

Free vibration of orthotropic laminated composite conical shells with constant thickness are considered. Governing frequency equations are derived based on the Flugge theory and Galerkin method is applied for the numerical analysis. Comparisons are made between present results and others for the isotropic conical shells and numerical results are obtained based on these results for the specially orthotropic laminated composite conical shells with simply supported edges. Variations of frequency parameter on the change of material properties, stacking sequences, stacking number, geometrical parameters and orthotropic parameters are considered in the analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.2
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• pp.189-196
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• 2009

This paper presents the subparametric finite element model formulated by partial-linear layerwise theory for the analysis of laminate composites. The proposed model is based on refined approximations of two dimensional plane for orthotropic thick laminate plate as well as thin case. Three dimensional problem can be reduced to two dimensional case by assuming piecewise linear variation of in-plane displacement and a constant value of out-of-plane displacement across the thickness. The integrals of Legendre polynomials are chosen to define displacement fields and Gauss-Lobatto numerical integration is implemented in order to directly obtain maximum values occurred at the nodal points of each layer without other extrapolation techniques. The validity and characteristics of the proposed model have been tested by using orthotropic multilayered plate problem as compared to the values available in the published references. In this study, the convergence test has been carried out to determine the optimal layer model in terms of central deflection and stresses. Also, the distribution of displacements and stresses across the thickness has been investigated as the number of layer is increased.

• Composites Research
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• v.14 no.3
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• pp.1-9
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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 life 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-ply elastic modulus reduction, and using the laminate plate theory to the degraded elastic modulus and the intact elastic modulus of other laminates. 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 $[{90}_2/0_2]_s$ carbon/epoxy laminates to verify the natural frequency reduction model. Correlations between the predictions of the model and experimental results are good.

• Journal of Korean Society of Steel Construction
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• v.18 no.1
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• pp.93-100
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• 2006

A simple but precise method of calculating the natural vibration frequencies of composite laminated plates with all-simple support and under axial loadings is presented herein. This method uses deflection influence surfaces, which can be obtained by any method for vibration analysis and member due to the inertia force under resonance condition. Beginning with an initially guessed mode shape, the exact mode shape is obtained by the process similar to iteration. In this paper, equations are given for the case of special orthotropic laminates. The same equations, however, can be used for any laminate as long as ${B_1_6}$, ${B_2_6}$, ${D_1_6}$, and ${D_2_6}$ are negligible as the number of plies increases. Some laminates that possess such properties are presented in the paper.

• Composites Research
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• v.31 no.2
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• pp.69-75
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• 2018

In this study, a grid panel structure in which the woven CFRP composites were stacked in the orthogonal array was proposed and the mechanical properties were analyzed and studied. The grid parts were fabricated by cutting prepregs and laminating them. The grid panel structure was fabricated by co-curing with lower laminate plate in auto-clave process. The behavior of the proposed grid panel structure was evaluated by tests under tensile, compressive, shear, and bending loads. The effect of increasing the stiffness of the orthogonal grid structure was verified through these tests. In addition, the finite element model was constructed and compared with the test results, confirming the validity and reliability of the test and analysis.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.929-936
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• 1986

Free vibration characteristics of laminated orthotropic circular cylindrical shells with clamped free boundary condition are investigated. The solution is obtained through a direct solution procedure with axial mode displacements represented as simple Fourier series expressions. On the basis of the thin shell theories of Sanders, Love, Loo, Morley and Donnell, the 4*$ frequency determinant is derived and is expressed in a unified form. Various numerical examples determining the natural frequencies of circular cylindrical shells with isotropic material and also with layers of orthotropic elastic material arbitraily laminated either symmetrically or anti-symmetrically about the shell middle surface. The results obtained compared very well with some available experimental and numerical results.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.3
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• pp.299-308
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• 2001

This paper presents the three-dimensional (3-D) study of the natural vibration of cantilevered laminated composite plates. The Ritz method is used to obtain stationary values of the associated Lagrangian functional with displacements approximated by mathematically complete polynomials satisfying the boundary conditions at the clamped edge exactly. The accuracy of the 3-D model is established through a convergence study of non-dimensional frequencies followed by a comparison of the converged 3-D solutions with analytical and experimental findings in the existing literature. A wide scope of 3-D frequency results explain the influence of a number of geometrical and material parameters for cantilevered laminated plates, namely aspect ratio (a/b), width-to-thickness ratio (a/h), orthotropy of material, number of plies (NP), fiber orientation angle(θ), and stacking sequence.