• Coupled systems mechanics
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• v.12 no.4
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• pp.297-313
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• 2023

This paper deals with delamination analysis of non-linear viscoelastic multilayered beam subjected to bending in the plane of the layers. For this purpose, first, a non-linear viscoelastic model is presented. In order to take into account the non-linear viscoelastic behaviour, a non-linear spring and a non-linear dashpot are assembled in series with a linear spring connected in parallel to a linear dashpot. The behaviours of the non-linear spring and dashpot are described by applying non-linear stress-strain and stress-rate of strain relationships, respectively. The constitutive law of the model is derived. Due to the non-linear spring and dashpot, the constitutive law is non-linear. This law is used for describing the time-dependent mechanical behaviour of the beam under consideration. The material properties involved in the constitutive law vary along the beam length due to the continuous material inhomogeneity of the layers. Solution of the strain energy release rate for the delamination is obtained by analyzing the balance of the energy with considering of the non-linear viscoelastic behaviour. The strain energy release rate is found also by using the complementary strain energy for verification. A parametric study is carried-out by using the solution obtained. The solutions derived and the results obtained help to understand the time-dependent delamination of non-linear viscoelastic beams under loading in the plane of layers.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.1
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• pp.97-107
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• 1995

Global postbuckling analysis is accomplished for one-dimensional and two-dimensional delaminations. A new finite element model, which can be used to model the global postbuckling analysis of one-dimensional and two-dimensional delaminations, is presented. In order to calculate the strain energy release rate, geometrically nonlinear analysis is accomplished, and the incremental crack closure technique is introduced. To check the effectiveness of the finite element models and the incremental crack closure technique, the simplified closed-form sloution for a through-the-width delamination with plane strain condition is derived and compared with the finite element result. The finite element results show good agreement with the closed-foul1 solutions. The present method was extended to calculate the strain energy release rate for two-dimensional delamination. For a symmetric circular delamination, the strain energy release rate shows great variation along the delamination front. and the delamination growth appears to occur perpendicular to the loading direction.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.911-920
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• 1989

It this study, beam-type bend specimen is used to evaluate the interlaminar fracture toughness of laminated composite under mixed-mode deformations. The specimen is loaded under three-point bending and hence produced mixed-mode deformations in the vicinity of the crack tip according to the variation of the thickness ratio on delamination plane. Total energy release rate is obtained by elementary beam theory considering the effect of shear deformation. The partitioning of total value into mode-I and mode-II components is also performed. The mixed-mode interlaminar fracture toughness is evaluated by experiments on specimens with several thickness ratios of delamination plane. As the part of delamination plane is thicker, the effect of shear deformation on total energy release rate is increased. Beam-type bend specimen men may be applied to obtain informations on the mixed-mode interlaminar fracture behavior of laminated composites.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.74-77
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• 2001

The impact response and damage of CLAS panel was investigated experimentally. The facesheet material used was RO4003 woven-glass hydrocarbon/ceramic and the core material was Nomex honeycomb with a cell size of 3.2mm and a density of 96 kg/$\textrm{m}^{3}$. The shield plane used was RO4003 and 2024-T3 aluminum. Static indentation and impact test was conducted to characterize the type and extent of the damage observed in two CLAS panels, and the performance of antenna used in a wireless LAN system. Correlation of peak contact force, residual indentation and the delamination area shows impact damage of the panel with an aluminum shield plane is larger than that of the panel with RO4003 shield plane, although tile former is more penetration resistant. The damage was observed by naked eye, ultrasonic inspection and cross sectioning. The shape and size of delamination was estimated by ultrasonic inspection, and the area of delamination linearly increases as impact energy increases. The performance of impact damaged antenna was estimated by measuring return loss and radiation pattern.

• Journal of the Korean Society for Advanced Composite Structures
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• v.1 no.1
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• pp.1-8
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• 2010

The dynamic instability analysis of delaminated composite structures subjected to in-plane pulsating forces is carried out based on the higher order shell theory of Sanders. In the finite element (FE) formulation, the seven degrees of freedom per each node are used with transformations in order to fit the displacement continuity conditions at the delamination region. The boundaries of the instability regions are determined using the method proposed by Bolotin. The numerical results obtained for skew plates and shells are in good agreement with those reported by other investigators. The new results for delaminated skew plate and shell structures in this study mainly show the effect of the interactions between the radius-length ratio and other various parameters, for example, skew angles, delamination size, the fiber angle of layer and location of delamination in the layer direction. The effect of the magnitude of the periodic in-plane load on the instability regions is also investigated.

• Structural Engineering and Mechanics
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• v.25 no.6
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• pp.733-751
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• 2007

The metis element method (Hung 1978) has been applied to analyse free edge interlaminar stresses and delamination in composite laminates, which are subjected to extension and bending. The paper recalls Lekhnitskii's solution for generalized plane strain state of composite laminate and Wang's singular solution for determination of stress singularity order and of eigen coefficients $C_m$ for delamination problem. Then the formulae of metis displacement finite element in two-dimensional problem are established. Computation of the stress intensity factors and the energy release rates are presented in details. The energy release rate, G, is computed by Irwin's virtual crack technique using metis elements. Finally, results of interlaminar stresses, the three stress intensity factors and the energy release rates for delamination crack in composite laminates under extension and bending are illustrated and compared with the literature to demonstrate the efficiency of the present method.

• Structural Engineering and Mechanics
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• v.6 no.2
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• pp.143-159
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• 1998

The objective of this present work is to estimate the failure loads, associated maximum transverse displacements, locations and the modes of failure, including the onset of delamination, of thin, square symmetric laminates under the action in-plane positive (+ve) shear load. Two progressive failure analyses, one using the Hashin criterion and the other using a Tensor polynomial criterion, are used in conjunction with finite element method. First order shear deformation theory along with geometric non-linearity in the von Karman sense have been employed. Variation of failure loads and failure characteristics with five type of lay-ups and three types of boundary conditions has been investigated in detail. It is observed that the maximum difference between failure loads predieted by various criteria depends strongly on the laminate lay-up and the flexural boundary restraint. Laminates with clamped edges are found to be more susceptible to failure due to transverse shear (ensuing from the out of plane bending) and delamination, while those with simply supported edges undergo total collapse at a load slightly higher than the fiber failure load. The investigation on negative (-ve) in-plane shear load is in progress and will be communicated as part-II of the present work.

• Composites Research
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• v.22 no.1
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• pp.1-8
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• 2009

In this paper low-velocity impact response and damage of composite laminates is analytically investigated. A modified displacement field of plate considering initially loaded in-plane strain is proposed. From the displacement field a finite element equation on structural behavior of composite laminate is newly induced and a computational program is coded. Numerical results using the FEM code is compared with the numerical ones from reference. Additional numerical analysis is performed on another impact condition and effect of initial in-plane load is reviewed. Potential delamination damage area in the first inter-ply surface from bottom of laminate is approximated and effect of initial in-plane load and impact condition is also reviewed.

• Composites Research
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• v.35 no.2
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• pp.106-114
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• 2022

Carbon fiber-reinforced plastic, well known high specific strength and high specific stiffness, have been widely used in the aircraft industry. Mostly the CFRP structure is fabricated by lamination of carbon fiber or carbon prepreg, which has major disadvantage called delamination. Delamination is usually produced due to absence of the through-thickness direction fiber. In this study, three-dimensional carbon preform woven in three directions is used for fabrication of aircraft wing unit structure, a part of repeated structure in aircraft wing. The unit structure include skin, stringer and rib were prepared by resin transfer molding method. After, the 3D structure was compared with laminate structure through compression test. The results show that 3D structure is not only effective to prevent delamination but improved the mechanical strength. Therefore, the 3d preform structure is expected to be used in various fields requiring delamination prevention, especially in the aircraft industry.

• Journal of Aerospace System Engineering
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• v.1 no.1
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• pp.25-35
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• 2007

In this paper, the interlaminar crack problems of a fiber metal laminate (FML) under generalized plane deformation are studied using the theory of anisotropic elasticity. The crack is considered to be embedded in the matrix interlaminar region (including adhesive zone and resin rich zone) of the FML. Based on Fourier integral transformation and the stress matrix formulation, the current mixed boundary value problem is reduced to solving a system of Cauchy-type singular integral equations of the 1st kind. Within the theory of linear fracture mechanics, the stress intensity factors are defined on terms of the solutions of integral equations and numerical results are obtained for in-plane normal (mode I) crack surface loading. The effects of location and length of crack in the 3/2 and 2/1 ARALL, GLARE or CARE type FML's on the stress intensity factors are illustrated.