• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.22 no.3
• /
• pp.540-544
• /
• 1998

Compliance calibration method is frequently used to determine $G_IC$ from the DCB composite specimen. However, the method requires at least 4 to 5 fracture test (loading-unloading) records. In this study, $G_IC$ of unidirectional graphite/epoxy DCB composites was determined from the elastic work factor approach which uses a single fracture test record. In order to inspect the validity of the elastic work factor approach, $G_IC$ determined from the elastic work factor approach was compared to that of determined from the compliance calibration method. It was shown that $G_IC$ determined from the elastic work factor approach was comparable to that determined from the compliance calibration method. That is, the elastic work factor approach can be used to determine $G_IC$ of unidirectional graphite/epoxy DCB specimen from a single fracture record.

• Composites Research
• /
• v.14 no.4
• /
• pp.8-14
• /
• 2001

The satellite system experiences severe mechanical loads during the launch period. Therefore, the positive margin of safety of the satellite system must be demonstrated for every possible mechanical loading conditions during the launch period. This paper presents modal and stress analysis results due to quasi-static loads for the satellite antenna system. The failure tendency fur the sandwich construction of the satellite antenna system has been studied with various lamination angles of unidirectional prepreg.

• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.244-249
• /
• 2004

In this paper, shielding effectiveness(SE) of the shielding paint of electromagnetic(EM) waves was investigated with actual experiments. The shielding paint used in this study were made of powder of conductive materials - Ag, Cu, Al, Sn, Ni. Cr, Graphite and Charcoal etc. with a solubility in oil and water. Also, the paper was used as a base sheet. The experiment was carried out by using a shielding evaluator(Shielding box) TR17302 with an ADVANTEST spectrum analyzer, model R3361C. It was found from the experimental results that silver, copper, nickel were good candidates as a shielding material against the EM waves with increasing the SE as the composite was laminated. The characteristics of the SE against the EM waves depended on a mode of preparation of specimen. The effects of density of particles on the SE were studied about the EM shielding paint. The SE strongly depended on the electric resistance by density of painting particles. SE increased as the density of particles was increasing.

• Journal of Ship and Ocean Technology
• /
• v.4 no.2
• /
• pp.38-57
• /
• 2000

This paper deals with reliability analysis of specially orthotropic plates subjected to transverse lateral pressure loads by using Monte Carlo simulation method. The plates are simply supported around their all edges and have a low short span to plate depth ratio with rectangular plate shapes. Various levels of reliability analyses of the plates are performed within the context of First-Ply-Failure(FPF) analysis such as ply-/laminate-level reliability analyse, failure tree analysis and sensitivity analysis of basic design variables to estimated plate reliabilities. In performing all these levels of reliability analyses, the followings are considered within the Monte Carlo simulation method: (1) input parameters to the strengths of the plates such as applied transverse lateral pressure loads, elastic moduli, geometric including plate thickness and ultimate strength values of the plates are treated as basic design variables following a normal probability distribution; (2) the mechanical responses of the plates are calculated by using simplified higher-order shear deformation theory which can predict the mechanical responses of thick laminated plates accurately; and (3) the limit state equations are derived from polynomial failure criteria for composite materials such as maximum stress, maximum strain, Tsai-Hill, Tsai-Wu and Hoffman.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2007.04a
• /
• pp.487-492
• /
• 2007

The enhancement of the service life of damaged or cracked structures is a major issue for researchers and engineers. The hierarchical void element with the integrals of Legend polynomials is used to characterize the fracture behavior of unpatched crack as well as repaired crack with bonded composite patches by computing the stress intensity factors and stress contours at the crack tip. The numerical approach is based on the v-version degenerate shell element including the theory of anisotropic laminated composites. Since the equivalent single layer approach is adopted in this study, the proposed element is necessary to represent a discontinuous crack part as a continuum body with zero stiffness of materials. Thus the aspect ratio of this element to represent the crack should be extremely slender. The sensitivity of numerical solution with respect to energy release rate, displacement and stress has been tested to show the robustness of hierarchical void element as the aspect ratio is increased up to 2000. The stiffness derivative method and displacement extrapolation method have been applied to calculate the stress intensity factors of Mode I problem.

• Composites Research
• /
• v.26 no.3
• /
• pp.195-200
• /
• 2013

This study aims to detecting and analyzing the defects of damaged carbon fiber reinforced composites after impacts, particularly focusing on barely visible impact damages. The impact test was progressed by a drop-weight machine and applied to introduce simulated damages on laminated composites used in aircrafts. Various nondestructive testing (NDT) techniques were applied to identify the defects on the specimens with different levels of impact energies. Based on the measurements data, the levels of the barely visible impacts, and the applicability and effectiveness of the detection methods were discussed. Generally, the results demonstrated that their inner damages contained bigger footprints than those on the surfaces. However, when the damage energy was low, it was found that the inner damage size could be smaller than those appeared on the surfaces.

• Journal of the Korean Society of Industry Convergence
• /
• v.26 no.1
• /
• pp.201-209
• /
• 2023

Recently, fiber-reinforced composites have been widely used in various industrials fields. In this study, the mechanical behavior, especially fracture behavior, of biomimetic fiber-reinforced composites subjected to pressure loading was analyzed using finite element analysis (FEA). The fiber alignments in the biomimetic composites formed a helicoidal structure, wherein a stacking sequence involved a gradual rotation of each ply in the multi-layered laminated composites. For comparison, cross-ply composite samples with fibers arranged at 0° and 90° were prepared and analyzed. In addition, the mechanical behavior was analyzed based on combinations of the stacking sequence of carbon-fiber composites and glass-fiber composites. The FEA results showed that, when compared with the cross-ply samples, the mechanical properties of the biomimetic composites were considerably improved under pressure loading, which was applied to one side of the composites. Thus, the biomimetic helicoidal structure significantly improved the mechanical properties of the composites. Placing materials having high elasticity and strength in the outermost layers (the layer of the side on which pressure was applied and the opposite side layer) of the composites also significantly contributed to improving the mechanical properties of the composites.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.15 no.3
• /
• pp.491-499
• /
• 2002

A p-version finite element model based on degenerate shell element is proposed tot the analysis of orthotropic laminated plates. In the nonlinear formulation of the model, the total Lagrangian formulation is adopted with large deflection and moderate rotation being accounted tot in the sense of yon Karman hypothesis. The material model is based on the Huber-Mises yield criterion and Prandtl-Reuss flow rule in accordance with the theory of strain hardening yield function, which is generalized lot anisotropic materials by introducing the parameters of anisotropy. The model is also based on extension of equivalent-single layer laminate theory(ESL theory) with shear deformation, leading to continuous shear strain at the interface of two layers. The integrals of Legendre polynomials are used for shape functions with p-level varying from 1 to 10. Gauss-Lobatto numerical quadrature is used to calculate the stresses at the nodal points instead of Gauss points. The validity of the proposed P-version finite element model is demonstrated through several comparative points of iew in terms of ultimate load, convergence characteristics, nonlinear effect, and shape of plastic tone.

• Journal of Aerospace System Engineering
• /
• v.15 no.1
• /
• pp.86-94
• /
• 2021

PCB-based deployable solar panel is mainly used for CubeSat due to its lightweight and easy of electrical connection. However, as the size of solar panel increases, there is a limit to ensuring the structural safety of solar cells due to excessive dynamic displacement under launch vibration environment. In previous mechanical designs, for the minimization of dynamic deflection, panel stiffness is increased by applying additional stiffeners made of various materials such as aluminum or composite. However, it could have disadvantages for CubeSat design requirements due to limited mass and volumes. In this study, a high-damping 6U solar panel was proposed. It had superior damping characteristic with a multi-layered stiffener laminated with viscoelastic acrylic tapes. Basic characteristics of this solar panel were measured through free-vibration tests. Design effectiveness of the solar panel was validated through qualification-level launch vibration test. Based on test results, vibration characteristics of a typical PCB solar panel and the high-damping laminated solar panel were predicted and a comparative analysis was performed.

• Journal of Advanced Marine Engineering and Technology
• /
• v.37 no.8
• /
• pp.862-868
• /
• 2013

The mechanics of woven fabric-based laminated composites is complex. Then, many researchers have studied woven fabric CFRP materials but fracture resistance behaviors for composites have not been still standardized. It also shows the different behavior according to load and fiber direction. Therefore, there is a need to consider fracture resistance behavior in conformity with load and fiber direction at designing structure using woven CFRP materials. In this study, therefore, the tensile strength and resistance for plain-weave CFRP composite materials were investigated under various different angle condition(load to fiber angle: $0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$). Tensile strength and fracture toughness tests were carried out under mode I transverse crack opening load by using compact tension specimens.