• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.2
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• pp.25-31
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• 2005

The theory developed in a preceding paper [1] for poroelastic composite material behavior under thermal and gas diffusion is applied to thermo-chemical decomposition of a carbon-phenolic composite rocket nozzle liner under typical operating conditions. Specifically, the structural component simulated is the cowl ring for which distributions of pressure in the material pores, temperature and across-ply stress are presented. The results for particular composite designs show that across-ply failure occurs due to tensile stress in the material which is indicative of plylift. This prediction corroborates observations of plylift in a nozzle cowl. Simulations suggest designs to avoid plylift in the cowl zone.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.1
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• pp.41-51
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• 2006

This paper concerns the effect of lining interface adherence on the lining's load carrying capacity. A series of reduced scale laboratory tests and finite element anlayses were carried out with the aim of gaining insight into the effect of shotcrete lining adherence on the load carrying capacity of double shell lining. The results indicated among other things that the load carrying capacity of a double shell tunnel is significantly affected by the adherence between layers. Also revealed was that for cases with low lining layer adherence stress concentration may occur due to relative movement between the lining layers with this trend being more pronounced with increasing tunnel cover depth. Practical implications from the results of this study are discussed in great detail.

• Composites Research
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• v.31 no.5
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• pp.177-185
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• 2018

Fiber metal laminate (FML) is a type of hybrid composites which consist of metallic and fiber-reinforced plastic sheets. As the FML has a drawback of the delamination that is a failure of the interfacial adhesive layer, the nominal stresses and the energy release rates should be determined to identify the delamination behavior. However, it is difficult to derive the nominal stresses and the energy release rates since the operating temperature of the equipment is restricted. For this reason, the objective of this paper is to predict the mode-I nominal stress and the mode-I energy release rate of the adhesive layer using the inverse analysis based on the Levenberg-Marquardt method. First, the mode-I nominal stress was assumed as the tensile strength of the adhesive layer, and the mode-I energy release rate was obtained from the double cantilever beam test. Next, the finite element method was applied to predict the mode-I delamination behavior. Finally, the mode-I nominal stress and the mode-I energy release rate were predicted by the inverse analysis. In addition, the convergence of the parameters was validated by trying to input two cases of the initial parameters. Consequently, it is noted that the inverse analysis can predict the mode-I delamination behavior, and the two input parameters were converged to similar values.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.5 s.176
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• pp.1261-1270
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• 2000

This paper is concerned with the development of a general model for predicting material damping in laminates based on the strain energy method. In this model, the effect of interlaminar stress on damping is taken into accounts along with those of in-plane extension/compression and in-plane shear. The model was verified by carrying out the damping measurements on $90^0$ unidirectional composite beams varying length and thickness. The analytical predictions were favorably compared with the experimental data. The transverse shear($$\sigma$_{yz}$) appears to have a considerable influence on the damping behaviors in $90^0$ unidirectional polymer composites. However, the other interlaminar stresses($$\sigma$_{xz}$, $$\sigma$_z$) were shown to have little impact on vibration damping in $90^0$ laminated composite beam.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.652-657
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• 2008

A stress distribution of composite laminates patches is obtained by using the Kantorovich method when the substrate is under uniaxial load. The analysis is based on the stress function approach and uses the complementary virtual work principle. The three-dimensional stresses satisfy the traction free conditions at the free edges and the top surfaces of the patch. The stress of the bottom surfaces of the patch is obtained from equilibrium equation of patch and substrate. To demonstrate the efficiency and validity of the proposed analysis, numerical examples for cross-ply and quasi-isotropic laminates are included. The present method provides accurate stresses in the interior and near the free edges of composite laminate patches.

• Composites Research
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• v.18 no.1
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• pp.30-37
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• 2005

The bending strength characteristics and local deformation behaviors of honeycomb sandwich composites were investigated using three-point bending experiment and finite element simulation with a real model of honeycomb core. Two kinds of cell sizes of honeycomb core, two kinds of skin layer thicknesses, perfect bonding specimen as well as initial delamination specimen were used for analysis of stress and deformation behaviors of honeycomb sandwich beams. Various failure modes such as skin layer yielding, interfacial delamination, core shear deformation and local buckling were considered. Its simulation results were very comparable to the experimental ones. Consequently, cell size of honeycomb core and skin layer thickness had dominant effects on the bending strength and deformation behaviors of honeycomb sandwich composites. Specimens of large core cell size and thin skin layer showed that bending strength decreased by $30\~68\%$.

• Composites Research
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• v.29 no.2
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• pp.45-52
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• 2016

An understanding of the failure mechanisms of the adhesive layer is decisive in interpreting the performance of a particular adhesive joint because the delamination is one of the most common failure modes of the laminated composites such as the fiber metal laminates. The interface between different materials, which is the case between the metal and the composite layers in this study, can be loaded through a combination of fracture modes. All loads can be decomposed into peel stresses, perpendicular to the interface, and two in-plane shear stresses, leading to three basic fracture mode I, II and III. To determine the load causing the delamination growth, the energy release rate should be identified in corresponding criterion involving the critical energy release rate ($G_C$) of the material. The critical energy release rate based on these three modes will be $G_{IC}$, $G_{IIC}$ and $G_{IIIC}$. In this study, to evaluate the fracture behaviors in the fracture mode I and II of the adhesive layer in fiber metal laminates, the double cantilever beam and the end-notched flexure tests were performed using the reference adhesive joints. Furthermore, it is confirmed that the experimental results of the adhesive fracture toughness can be applied by the comparison with the finite element analysis using cohesive zone model.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.973-987
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• 2018

Most of the previous seismic analyses have been carried out by separating the ground and structures, and there is a lack of comparative study on the dynamic behavior of high-rise and low-rise buildings. Therefore, in this study, the sensitivity analysis was performed with selected parameters by using a finite element analysis program in order to grasp the dynamic behavior of high-rise and low-rise buildings. As a result, it was turned out that the horizontal displacement, the interstory drift ratio, and the bending stress of a high-rise building were more affected by a long seismic wave than a low-rise buildings. Also, the weak parts of a high-rise and low-rise building were more affected by type of seismic wave than the ground conditions. Therefore, it is inferred that it will be helpful for seismic designs to consider the influence of ground conditions and seismic wave type on buildings.

• Composites Research
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• v.34 no.6
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• pp.337-344
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• 2021

In this study, the progressive failure behavior of the composite fan blade dovetail element under tensile loading is numerically investigated through finite element(FE) simulation. The accuracy of prediction by FE simulation is verified through tensile testing. The dovetail element is one of the joints for coupling the fan blade with the disk in a turbofan engine. The dovetail element is usually made of a metal material such as titanium, but the application of composite material is being studied for weight reduction reasons. However, manufacturing defects such as drop-off ply and resin pocket inevitably occur in realizing complex shapes of the fan blade made by composite materials. To investigate the effect of these manufacturing defects on the composite fan blade dovetail element, we performed numerical simulation with FE model to compare the prediction of the FE model and the tensile test results. At this time, the cohesive zone model is used to simulate the delamination behavior. Finally, we found that FE simulation results agree with test results when considering thermal residual stress and through-thickness compression enhancement effect.

• Composites Research
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• v.22 no.2
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• pp.18-23
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• 2009

Failure of Kevlar29/Phenolic composite plate under high velocity impact of FSP(Fragment Simulation Projectile) is investigated using a non-linear explicit finite element code, LS-DYNA. Composite laminate and impactor are idealized by solid element and interface between laminas are modeled by tied-break element in LS-DYNA. Interaction between impactor and laminate is simulated face-to-face eroding contact algorithm. When the stress level meets a failure criteria, the layer in the element is eroded. Numerical results are verified by existing test results.