• Journal of Mechanical Science and Technology
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• v.17 no.6
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• pp.787-795
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• 2003

Mechanical properties of the materials used for transportations and industrial machinery under high strain rate loading conditions such as seismic loading are required to provide appropriate safety assessment to these mechanical structures. The Split Hopkinson Pressure Bar (SHPB) technique with a special experimental apparatus can be used to obtain the material behavior under high strain rate loading conditions. In this paper, dynamic deformation behaviors of the aluminum alloys such as A12024-T4, A1606 IT-6 and A17075-T6 under both high strain rate compressive and tensile loading conditions are determined using the SHPB technique.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.195-198
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• 2003

High temperature deformation and softening behavior of SAF 2507 super duplex stainless steel (SDSS) has been investigated in connection with an FEM analysis of hot forging process. Flow curves at various strain rates and temperatures were determined first from compression tests, and the kinetics of dynamic recrystallization were also formulated through the analysis of load relaxation test results. Applying the dynamic materials and proposed by Prasad et al., it was possible to determine the characteristics of deformation behavior effectively at a given condition of deformation. Constitutive relations and recrystallization kinetics formulated from the test results were then implemented in a commercial FEM code. Flow stress compensation formulated upon the volume fraction of recrystallization and adiabatic heating was found to improve significantly the FEA solutions in predicting the forming load and the distribution of recrystallized volume fraction after forging.

• Structural Engineering and Mechanics
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• v.19 no.1
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• pp.73-96
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• 2005

For the spatially coupled free vibration analysis of shear deformable thin-walled non-symmetric curved beam subjected to initial axial force, an exact dynamic element stiffness matrix of curved beam is evaluated. Firstly equations of motion and force-deformation relations are rigorously derived from the total potential energy for a curved beam element. Next a system of linear algebraic equations are constructed by introducing 14 displacement parameters and transforming the second order simultaneous differential equations into the first order simultaneous differential equations. And then explicit expressions for displacement parameters are numerically evaluated via eigensolutions and the exact $14{\times}14$ dynamic element stiffness matrix is determined using force-deformation relations. To demonstrate the accuracy and the reliability of this study, the spatially coupled natural frequencies of shear deformable thin-walled non-symmetric curved beams subjected to initial axial forces are evaluated and compared with analytical and FE solutions using isoparametric and Hermitian curved beam elements and results by ABAQUS's shell elements.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.181-185
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• 2001

This paper deals with the dynamic stability of a disc brake pad taking into account of its shear deformation and rotary inertia. A brake pad can be modeled as a beam like model subjected to distributed friction forces and having two translational springs. The study of this model is intended to provide a fundamental understanding of dynamic stability of drum brake pad. Governing equations of motion are derived from extended Hamilton's principle and their corresponding numerical solutions are obtained by applying the finite element formulation. The critical distributed friction force and the instability types are investigated bt changing two translational spring constants, rotary inertia parameter and shear deformation parameter. Also, the changes of eigen-frequencies of a beam determining instability types are investigated for various combinations of two translational spring constants.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.943-947
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• 2008

Dynamic response characteristics of a beam undergoing impulsive force are investigated using the wavelet transform method in this study. When an impulse is applied to an arbitrary position of a beam, it will generate a structural deformation wave. The characteristics of the wave are changing in the domain of time and space. The maximum amplitude of each natural frequency mode and the time to reach the maximum amplitude are obtained in this study. The effects of the location of impulse on the variations of the dynamic characteristics is also investigated.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.205-217
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• 2007

The behavior characteristics of underground structures are reported as they are not affected by their dynamic characteristics such as surface structures, but by dynamic characteristics of soil and rock surrounding the underground structures. Therefore, dynamic behavior of surrounding soil and rock dominates the dynamic behavior of the underground structure. The purpose of this paper is to analyze the dynamic response (longitudinal deformation and ovaling deformation) of the underground structure under earthquake loading. The dynamic responses of the underground structures were evaluated with varying earthquake conditions, soil conditions, and structural conditions using conventional closed-form solution of seismic behavior of underground structure. In addition, shaking table tests were conducted to simulate the earthquake loading and the dynamic behavior of the model was analyzed.

• Structural Engineering and Mechanics
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• v.66 no.2
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• pp.249-262
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• 2018

In this paper, reaction of functionally graded (FG) thick nanoplates resting on a viscoelastic foundation to a moving nanoparticle/load is investigated. Nanoplate is assumed to be thick by using second order shear deformation theory and small-scale effects are taken into account in the framework of Eringen's nonlocal theory. Material properties are varied through the thickness using FG models by having power-law, sigmoid and exponential functions for material changes. FG nanoplate is assumed to be on a viscoelastic medium which is modeled using Kelvin-Voight viscoelastic model. Galerkin, state space and fourth-order Runge-Kutta methods are employed to solve the governing equations. A comprehensive parametric study is presetned to show the influence of different parameters on mechanical behavior of the system. It is shown that material variation in conjunction with nonlocal term have a significant effect on the dynamic deformation of nanoplate which could be used in comprehending and designing more efficient nanostructures. Moreover, it is shown that having a viscoelastic medium could play an important role in decreasing these dynamic deformations. With respect to the fresh studies on moving atoms, molecules, cells, nanocars, nanotrims and point loads on different nanosctructures using scanning tunneling microscopes (STM) and atomic force microscopes (AFM), this study could be a step forward in understanding, predicting and controlling such kind of behaviors by showing the influence of the moving path, velocity etc. on dynamic reaction of the plate.

• Structural Engineering and Mechanics
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• v.70 no.3
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• pp.325-337
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• 2019

In the present article, cross ply laminated composite plates are considered and a simple sinusoidal shear deformation model is tested for analyzing their flexural, stability and dynamic behaviors. The model contains only four unknown variables that are five in the first order shear deformation theory (FSDT) or other higher order models. The in-plane kinematic utilizes undetermined integral terms to quantitatively express the shear deformation influence. In the proposed theory, the conditions of zero shear stress are respected at bottom and top faces of plates without considering the shear correction coefficient. Equations of motion according to the proposed formulation are deduced by employing the virtual work principle in its dynamic version. The analytical solution is determined via double trigonometric series proposed by Navier. The stresses, displacements, natural frequencies and critical buckling forces computed using present method are compared with other published data where a good agreement between results is demonstrated.

• Journal of Welding and Joining
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• v.21 no.3
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• pp.68-77
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• 2003

It is important to understand the characteristics of material strength and fracture under the dynamic loading like as earthquakes to assure the integrity of welded structures. The characteristics of dynamic strength and fracture in structural steels and their welded joints should be evaluated based on the effects of the strain rate and the service temperature. It is difficult to predict or measure temperature rise history with the corresponding stress-strain behavior. In particular, material behaviors beyond the uniform elongation can not be precisely evaluated, though the behavior at large strain region after the maximum loading point is much important for the evaluation of fracture. In this paper, the coupling phenomena of temperature and stress-strain fields under the dynamic loading was simulated by using the finite element method. The modified rate-temperature parameter was defined by accounting for the effect of temperature rise under the dynamic deformation, and it was applied to the fully-coupled analysis between heat conduction and thermal elastic-plastic behavior. Temperature rise and stress-strain behavior including complicated phenomena were studies after the maximum loading point in structural steels and their undermatched joints and compared with the measured values.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.3
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• pp.116-126
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• 2010

The Korean rolling stock safety regulation stipulates that the collision deceleration of a car body should be maintained under average 5g and maximum 7.5g during train collisions. One-dimensional dynamic model of a full rake train, which is made up of nonlinear springs/bars-dampers-masses, is often used to estimate the collision decelerations of car bodies in a basic design stage. By the way, the previous studies have often used some average force-deformation curve for energy absorbing structures in rolling stock. Through this study, we intended to analyse how much the collision deceleration levels are influenced by the initial peak force modeling in the one-dimensional force-deformation curve. The numerical results of the one-dimensional dynamic model for the Korean High-Speed Train show that the initial peak force modeling gives significant effect on the collision deceleration levels. Therefore the peak force modeling of the force-deformation curve should be considered in one-dimensional dynamic model of a full rake train to evaluate the article 16 of the domestic rolling stock safety regulations.