• Advanced Composite Materials
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• v.16 no.1
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• pp.11-30
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• 2007

Since delamination often propagates at the interfacial layer between a surface skin and a foam core, a crack arrester is proposed for the suppression of the delamination. The arrester has a semi-cylindrical shape and is arranged in the foam core and is attached to the surface skin. Here, energy release rates and complex stress intensity factors are calculated using finite element analysis. Effects of the arrester size and its elastic moduli on the crack suppressing capability are investigated. Considerable reductions of the energy release rates at the crack tip are achieved as the crack tip approached the leading edge of the crack arrester. Thus, this new concept of a crack arrester may become a promising device to suppress crack initiation and propagation of the foam core sandwich panels.

• Structural Engineering and Mechanics
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• v.34 no.1
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• pp.97-107
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• 2010

Nonlinear thermoelastic static response characteristics of laminated composite conical panels are studied employing finite element approach based on first-order shear deformation theory and field consistency principle. The nonlinear governing equations, considering moderately large deformation, are solved using Newton-Raphson iterative technique coupled with the adaptive displacement control method to efficiently trace the equilibrium path. The validation of the formulation for mechanical and thermal loading cases is carried out. The present results are found to be in good agreement with those available in the literature. The adaptive displacement control method is found to be capable of handling problems with multiple snapping responses. Detailed parametric study is carried out to highlight the influence of semicone angle, boundary conditions, radius-to-thickness ratio and lamination scheme on the nonlinear thremoelastic response of laminated cylindrical and conical panels.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.3
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• pp.80-93
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• 1996

A 2-dimensional FEM/GEM program was developed under the plane strain assumption using linear line elements for analyzing stretch/draw forming operations of an arbitrarily shaped draw-die. FEM formulation adopted a new algorithm for solving force equilibrium as well as non-penetration condition simultaneously. Also, a rigid-viscoplastic material model with Hill's normal anisotropic yield condition and rate-sensitive hardening law is assumed, along with the Coulomb friction law in the contact regions. For the case of numerical divergence at nearly final forming stages, geometric force equilibrium method(GEM) is also introduced. The developed program was tested by simulating the forming processes of cylindrical punch/open die, and the drawing processes of automotive oilpan and hood inner panel in order to verify the usefulness and validity of FEM/GEM formulation. The numerical simulation verified the validity and robustness of developed program.

• Advances in aircraft and spacecraft science
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• v.8 no.4
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• pp.345-372
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• 2021

The analysis of nonlinear vibrations, buckling, post-buckling, flutter boundary determination and post-flutter behavior of a homogeneous curved plate assuming cylindrical bending is conducted in this article. Other assumptions include simply-supported boundary conditions, supersonic aerodynamic flow at the top of the plate, constant pressure conditions below the plate, non-viscous flow model (using first- and third-order piston theory), nonlinear structural model with large deformations, and application of mechanical and thermal loads on the curved plate. The analysis is performed with constant environmental indicators (flow density, heat, Reynolds number and Mach number). The material properties (i.e., coefficient of thermal expansion and modulus of elasticity) are temperature-dependent. The equations are derived using the principle of virtual displacement. Furthermore, based on the definitions of virtual work, the potential and kinetic energy of the final relations in the integral form, and the governing nonlinear differential equations are obtained after fractional integration. This problem is solved using two approaches. The frequency analysis and flutter are studied in the first approach by transferring the handle of ordinary differential equations to the state space, calculating the system Jacobin matrix and analyzing the eigenvalue to determine the instability conditions. The second approach discusses the nonlinear frequency analysis and nonlinear flutter using the semi-analytical solution of governing differential equations based on the weighted residual method. The partial differential equations are converted to ordinary differential equations, after which they are solved based on the Runge-Kutta fourth- and fifth-order methods. The comparison between the results of frequency and flutter analysis of curved plate is linearly and nonlinearly performed for the first time. The results show that the plate curvature has a profound impact on the instability boundary of the plate under supersonic aerodynamic loading. The flutter boundary decreases with growing thermal load and increases with growing curvature.

• Journal of the Korean Society of Safety
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• v.30 no.3
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• pp.107-113
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• 2015

The goal of this paper is to investigate structural integrity factors of RMI(reflective metal insulation) to confirm the design requirements in nuclear power plant. Currently, a glass wool insulation is using now, but it will gradually be replaced with the reflective metal insulation maded by stainless steel plates. The main function of an insulation is to minimize a heat loss of vessel and pipes in RCS(reactor coolant system). It has to maintain structural a integrity in nuclear power plant life duration. In this study, the structural integrity analysis was carried out both multi-plate and outer shell plate by using a static analysis and experimental test. First, inner multi-plate has a self support structure for being air space. Because the effect of total static weight in multi-layer plate is low, a plate collapse possibility is not high. Considering optimum thin plate pressing process, it has to pre-check the basic physical properties. Second, the outer segment thickness and stiffener shape are verified by the numerical static analysis, and sample test for both type of panel and cylindrical pipe model.

• Structural Engineering and Mechanics
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• v.66 no.6
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• pp.713-727
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• 2018

Thin-walled mental tubes under lateral crushing are desirable and reliable energy absorbers against impact or blast loads. However, the early formations of plastic hinges in the thin cylindrical wall limit the energy absorption performance. This study investigates the energy absorption performance of a simple, light and efficient energy absorber called the ring stiffened tube. Due to the increase of section modulus of tube wall and the restraining effect of the T-stiffener flange, key energy absorption parameters (peak crushing force, energy absorption and specific energy absorption) have been significantly improved against the empty tube. Its potential application in the offshore blast wall design has also been investigated. It is proposed to replace the blast wall endplates at the supports with the energy absorption devices that are made up of the ring stiffened tubes and springs. An analytical model based on beam vibration theory and virtual work theory, in which the boundary conditions at each support are simplified as a translational spring and a rotational spring, has been developed to evaluate the blast mitigation effect of the proposed design scheme. Finite element method has been applied to validate the analytical model. Comparisons of key design criterions such as panel deflection and energy absorption against the traditional design demonstrate the effectiveness of the proposed design in blast alleviation.

• Applied Biological Chemistry
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• v.19 no.4
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• pp.183-188
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• 1976

In order to establish methods of potato processing for mixed cooking with rice as main dish, the size and shape of potato granules and favorable ratio of potato granules to rice for cooking were studied preliminary. As the results cylindrical shaped potato granule of around 6mm in diameter and $10{\sim}13mm$ in length are more favorable than rectangular shape for mixed cooking according to panel test. Mixed cooking of 30% of treated potato granules with rice is the most favorable in the point of palatability.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.2
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• pp.21-28
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• 1987

The paper describes the analysis of large displacement problems including instability phenomena. The element used in this is a degenerated isoparametric shell element with eight nodes. Total Lagrangian formulation has been adopted in this study using Newton-Raphson iteration method with incremental load. The linear stability analyses performed usually for the initial position can be repeated at several advanced fundamental states on the non-linear buckling path. Thus a current estimate of the failure load is given. The numerical examples of a cylindrical panel under uniform load, simply supported plate under axial load, and clamped plate under uniform load are carried out. The examples applying degenerated isoparametric elements to bifurcation buckling and nonlinear collapse problems are also performed.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.5
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• pp.933-940
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• 2010

A numerical analysis for the space frame structure under ballistic and blast loads was performed using LS-DYNA, a commercial code. The space frame structure was developed to be adapted to the ground vehicle in the future and it was designed to build with Al7039 frames and lightweight multi-layered panels for the purpose of weight reduction and shock mitigation. The analyses have done for side impacts by a cylindrical projectile and Comp. C-4 explosive representing major threats to the vehicle. The deformed shape of the panel section and stresses as well as accelerations of the frames calculated from LS-DYNA were compared to the test results to validate the analysis model. The internal energies for panels and frames from LS-DYNA were also compared to each other to discern their role in absorbing the ballistic and blast impact.

• Steel and Composite Structures
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• v.50 no.1
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• pp.63-75
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• 2024

In this paper, the modified couple stress theory (MCST) and first order shear deformation theory (FSDT) are employed to investigate the free vibration and bending analyses of a three-layered micro-shell sandwiched by piezoelectric layers subjected to an applied voltage and reinforced graphene nanoplatelets (GPLs) under external and internal pressure. The micro-shell is resting on an elastic foundation modeled as Pasternak model. The mixture's rule and Halpin-Tsai model are utilized to compute the effective mechanical properties. By applying Hamilton's principle, the motion equations and associated boundary conditions are derived. Static/ dynamic results are obtained using Navier's method. The results are validated with the previously published works. The numerical results are presented to study and discuss the influences of various parameters on the natural frequencies and deflection of the micro-shell, such as applied voltage, thickness of the piezoelectric layer to radius, length to radius ratio, volume fraction and various distribution pattern of the GPLs, thickness-to-length scale parameter, and foundation coefficients for the both external and internal pressure. The main novelty of this work is simultaneous effect of graphene nanoplatelets as reinforcement and piezoelectric layers on the bending and vibration characteristics of the sandwich micro shell.