• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2008.10a
• /
• pp.304-307
• /
• 2008

In order to evaluate the effect of permanent softening behavior on springback prediction, 2D-draw bending simulations were compared with experiments for friction stir welded DP590 steel sheets. To account fur the nonlinear hardening behavior, the combined isotropic-kinematic hardening law was utilized with and without considering the permanent softening behavior during reverse loading. Also, the non-quadratic orthotropic yield function, Yld2000-2d, was used to describe the anisotropic initial-yielding behavior of the base sheet while anisotropic properties of the weld zone were ignored for simplicity.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.5 no.2
• /
• pp.59-64
• /
• 2001

The purpose of this work is to investigate the static strength, the stress distribution, and the failure process of quasi-isotropic composite laminates made of two different matrices when loading directions are changed. We carried out static tests of $[0/-60/+60]_s$ and $[+30/-30/90]_s$ laminates. Two types of matrices used are AS4/epoxy and AS4/PEEK. The damage mechanisms of the quasi-isotropic laminate, $[0/-60/+60]_s$, strongly depend on the load direction applied to the laminate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1996.04a
• /
• pp.106-112
• /
• 1996

In this paper, the propagation of elastic wave generated by loading impact to plates made of isotropic or anisotropic material was studied. And the influence of boundary conditions(free or clamped edge) upon the reflection of elastic wave of isotropic plate such as aluminum plate showed circular interferometric fringe pattern, whereas that of anisotropic plate such as epoxy composite laminates showed elliptical one. And the transverse displacement curves obtained from experiment and theory for both plates agreed well. Also, the waves reflected from the boundary edges showed much differences according to the boundary condition of edges.

• Structural Engineering and Mechanics
• /
• v.13 no.1
• /
• pp.103-116
• /
• 2002

A solution based on the linear three-dimensional theory of elasticity is developed for vibration and elastostatic problems of hollow toroids. The theory is developed for transversely isotropic toroids of arbitrary thickness, and has the potential to validate some vehicle and aircraft tire models in the linear range. In the semi-analytical method that is adopted Fourier series are written in the circumferential direction, forming a set of two-dimensional problems. These problems are solved using the differential quadrature method. A commercial finite element program is used to determine alternative solutions. For validation both problems of vibration and elastostatics are considered. Finally results are determined for local surface loading problems, and conclusions are drawn.

• Structural Engineering and Mechanics
• /
• v.2 no.1
• /
• pp.49-62
• /
• 1994

Based on the transfer matrix approach and integral transforms, a solution method is developed for the stress analysis of axisymmetrically loaded transversely isotropic elastic media with generalized interlayer and support conditions. Transfer functions (Green's functions in the transformed domain) are obtained in explicit integral form. For several problems of practical interest with different loading and support conditions, solutions are worked out in detail. For the inversion operation, an efficient technique is introduced to remedy the slow convergence of numerical integrals involving oscillating functions. Several illustrative examples are considered and numerical results are presented.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.10
• /
• pp.3211-3223
• /
• 1996

In this paper, the propagation of elastic wave generated by loading impact to plates made of isotropic of anisotropic material was studied. And the influence of boundary conditions (free or clamped edge) upon the reflection of elastic wave was anlyzed. Also, double exposure holographic interferometer using ruby pulse laser was formed in order to investigate transient waves. Before the elasitc wave was reflected from the edges, the elastic wave of isotropic plate such as aluminum plate showed circular interferometric fringe pattern, whereas that of anisotropic plate such as epoxy composite laminates showed elliptical one. And the transverse displacement curves obtained from experiment and theory for both plates agreed well. Also, the waves reflected from the boundary edges showed much differences according to the boundary condition of edges.

• Transactions of Materials Processing
• /
• v.18 no.4
• /
• pp.329-335
• /
• 2009

In order to better predict the springback for friction stir welded DP590 steel sheet, the combined isotropic-kinematic hardening was formulated with considering the permanent softening behavior during reverse loading. As for yield function, the non-quadratic anisotropic yield function, Yld2000-2d, was used under plane stress condition. For the verification purposes, comparisons of simulation and experiments were performed here for the unconstrained cylindrical bending, the 2-D draw bending tests. For two applications, simulations showed good agreements with experiments.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.1
• /
• pp.43-53
• /
• 2008

Surface edge crack in transversely isotropic piezoelectric material is analyzed. The concentrated antiplane mechanical and inplane electrical loadings are applied to an arbitrary point of the surface, where the impermeable crack boundary condition is imposed. Using Mellin transform the problem is formulated, from which Wiener-Hopf equations are derived. By solving the equations the solution is obtained in a closed form. Mechanical and electric intensity factors and energy release rate are obtained and discussed. This problem could be used as a Green's function to generate the solutions of other problems with the same geometry but of different loading conditions.

• International Journal of Aeronautical and Space Sciences
• /
• v.14 no.4
• /
• pp.350-355
• /
• 2013

Electrical resistance change measurements were performed, to detect fatigue damage of a quasi-isotropic CFRP and cross-ply CFRP laminates. A four-probe method was used to measure the exact electrical resistance change. A three-probe method was used to measure the electrical contact resistance change, during long cyclic loading. The specimen side surface was observed using a video-microscope to detect damage. The measured electrical resistance changes were compared with the observed damage. The results of this study show that the electrical resistance increase of the quasi-isotropic laminate was caused by a delamination crack between ${\pm}45^{\circ}$ plies. Matrix cracking caused a small electrical resistance increase of the cross-ply laminate, but the decreased electrical resistance caused by the shear-plastic deformation impedes matrix-cracking detection.

• Structural Engineering and Mechanics
• /
• v.39 no.2
• /
• pp.223-239
• /
• 2011

This paper presents a methodology to detect and locate damages and faults in orthotropic plate structures. A specific damage index based on dynamic mode shapes of the damaged and undamaged structures has been introduced. The governing differential equation on transverse deformation, the transverse shear force equations and the invariant expression for the sum of transverse loading of an orthotropic plate are employed to obtain the aforementioned damage indices. The validity of the proposed methodology for isotropic and orthotropic damage states is demonstrated using a numerical example. It is shown that the algorithm is able to detect damages for both isotropic and orthotropic damage states acceptably.