• Journal of Mechanical Science and Technology
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• v.18 no.3
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• pp.419-431
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• 2004

The dynamic response of a cracked functionally graded piezoelectric material (FGPM) under transient anti-plane shear mechanical and in-plane electrical loads is investigated in the present paper. It is assumed that the electroelastic material properties of the FGPM vary smoothly in the form of an exponential function along the thickness of the strip. The analysis is conducted on the basis of the unified (or natural) crack boundary condition which is related to the ellipsoidal crack parameters. By using the Laplace and Fourier transforms, the problem is reduced to the solutions of Fredholm integral equations of the second kind. Numerical results for the stress intensity factor and crack sliding displacement are presented to show the influences of the elliptic crack parameters, the electric field, FGPM gradation, crack length, and electromechanical coupling coefficient.

• Structural Engineering and Mechanics
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• v.75 no.6
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• pp.659-674
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• 2020

The present paper employs nonlocal strain gradient theory (NSGT) to study buckling behavior of functionally graded magneto-electro-thermo-elastic (FG-METE) nanoshells under various physical fields. NSGT modeling of the nanoshell contains two size parameters, one related to nonlocal stress field and another related to strain gradients. It is considered that mechanical, thermal, electrical and magnetic loads are exerted to the nanoshell. Temperature field has uniform and linear variation in nanoshell thickness. According to a power-law function, piezo-magnetic, thermal and mechanical properties of the nanoshell are considered to be graded in thickness direction. Five coupled governing equations have been obtained by using Hamilton's principle and then solved implementing Galerkin's method. Influences of temperature field, electric voltage, magnetic potential, nonlocality, strain gradient parameter and FG material exponent on buckling loads of the FG-METE nanoshell have been studied in detail.

• Journal of Welding and Joining
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• v.20 no.3
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• pp.84-90
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• 2002

The strength and the life of welded components are affected extensively by the residual stresses distributed around their weldments not only under static loads, but also fatigue loads. The residual stress can be superimposed with externally applied loads, so that unexpected deformations and failures of members will be occurred. These residual stresses are not kept constant, but relaxed or redistributed during in service. Under static loads the relaxation takes place when the external stress superimposed with the residual stress exceeds locally the yield stress of material used. It is shown that under fatigue loads the residual stress is considerably relieved by the first or flew cycle loading, and then gradually relaxed with increasing loading cycles. In this study the phenomenon and mechanism of the stress relaxation by mechanical means were investigated and a model to predict quantitatively the residual stress relaxation for the case of static and fatigue loading condition was proposed.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.442-447
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• 2001

The process and results of the Coupled Loads Analysis performed in the course of the development of the KOMPSAT-1 were introduced in this paper. The process of performing the Coupled Loads Analysis was explained. The finite-element model of KOMPSAT-1 was explained. The load cases analyzed were introduced. With the results obtained from the Coupled Loads Analysis, it was confirmed that the KOMPSAT-1 was safe from the loads transmitted from the launch vehicle during launch vehicle flight.

• Coupled systems mechanics
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• v.12 no.5
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• pp.409-418
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• 2023

A coupled algorithm is proposed which first considers the creation of porous structure of the material and then the simulations of response of mechanical components with porous structure to a variable load history. The simulations are carried out by the Prandtl operator approach in the finite element method (FEM) which enables structural simulations of mechanical components subjected to variable thermomechanical loads. Temperature-dependent material properties and multilinear kinematic hardening of the material can be taken into account by this approach. Several simulations are then performed for a tensile-compressive specimen made of a generic porous structure and mechanical properties of Aluminium alloy AlSi9Cu3. Variable mechanical load history has been applied to the specimens under constant temperature conditions. Comparison of the simulation results shows a considerable elastoplastic stress-strain response in the vicinity of pores whilst the surface of the gauge-length of the specimen remains in the elastic region of the material. Moreover, the distribution of the pore sizes seems more influential to the stress-strain field during the loading than their radial position in the gauge-length.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1262-1269
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• 2003

In structural optimization, static loads are generally utilized although real external forces are dynamic. Dynamic loads have been considered in only small-scale problems. Recently, an algorithm for dynamic response optimization using transformation of dynamic loads into equivalent static loads has been proposed. The transformation is conducted to match the displacement fields from dynamic and static analyses. The algorithm can be applied to large-scale problems. However, the application has been limited to size optimization. The present study applies the algorithm to shape optimization. Because the number of degrees of freedom of finite element models is usually very large in shape optimization, it is difficult to conduct dynamic response optimization with the conventional methods that directly threat dynamic response in the time domain. The optimization process is carried out via interfacing an optimization system and an analysis system for structural dynamics. Various examples are solved to verify the algorithm. The results are compared to the results from static loads. It is found that the algorithm using static loads transformed from dynamic loads based on displacement is valid even for very large-scale problems such as shape optimization.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1675-1680
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• 2010

Flow Accelerated Corrosion (FAC) occurring during in-service conditions results in localized wall-thinning in the feeder pipes of CANDU. The wall-thinning of the feeder pipes is the main degradation mechanisms affecting the integrity of piping systems. In this paper, we assess the integrity of wall-thinned feeder pipes by limit load analysis. The limit loads for wall-thinning feeder pipes subjected to in-plane bending and internal pressure were determined on the basis of finte element limit analyses. The limit loads are determined from the results of limit analyses of elasticperfectly-plastic materials using the large geometry change. Closed-form approximations of limit load solutions for wall-thinning feeder pipes subjected to in-plane bending and pressure are proposed.

• Structural Engineering and Mechanics
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• v.69 no.4
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• pp.439-455
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• 2019

This research deals with thermo-electro-mechanical buckling analysis of the sandwich nano-beams with face-sheets made of functionally graded carbon nano-tubes reinforcement composite (FG-CNTRC) based on the nonlocal strain gradient elasticity theory (NSGET) considering various higher-order shear deformation beam theories (HSDBT). The sandwich nano-beam with FG-CNTRC face-sheets is subjected to thermal and electrical loads while is resting on Pasternak's foundation. It is assumed that the material properties of the face-sheets change continuously along the thickness direction according to different patterns for CNTs distribution. In order to include coupling of strain and electrical field in equation of motion, the nonlocal non-classical nano-beam model contains piezoelectric effect. The governing equations of motion are derived using Hamilton principle based on HSDBTs and NSGET. The differential quadrature method (DQM) is used to calculate the mechanical buckling loads of sandwich nano-beam as well as critical voltage and temperature rising. After verification with validated reference, comprehensive numerical results are presented to investigate the influence of important parameters such as various HSDBTs, length scale parameter (strain gradient parameter), the nonlocal parameter, the CNTs volume fraction, Pasternak's foundation coefficients, various boundary conditions, the CNTs efficiency parameter and geometric dimensions on the buckling behaviors of FG sandwich nano-beam. The numerical results indicate that, the amounts of the mechanical critical load calculated by PSDBT and TSDBT approximately have same values as well as ESDBT and ASDBT. Also, it is worthy noted that buckling load calculated by aforementioned theories is nearly smaller than buckling load estimated by FSDBT. Also, similar aforementioned structure is used to building the nano/micro oscillators.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.1
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• pp.55-60
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• 2010

The honeycomb composite joint structure designed for application to a tilting KTX railroad car body is subjected to bending loads of a cantilever type. Honeycomb sandwich composite panel-joint attached in the real tilting car body was fabricated and sectioned as several beam-joint specimens for the bending test. The fracture behaviors of these specimens under static loads were different from those under cyclic loads. Static bending loads caused shear deformation and fracture in the honeycomb core region, while fatigue cyclic bend loading caused delamination along the interface between the composite skin and the honeycomb core, and/or caused a fracture in the welded part jointed with the steel under-frame. These fracture behaviors could occur in other industrial honeycomb composite joints with similar sub-structures, and be used for improving design parameters of a honeycomb composite joint structure.

• Coupled systems mechanics
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• v.9 no.4
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• pp.311-323
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• 2020

This paper deals with the effect of the mode shapes on the dynamic response of a multi-storey frame subjected to moving train loads which are modelled as loads of constant intervals with constant velocity using the finite element method. The multi-storey frame is modelled as a number of Bernoulli-Euler beam elements. First, the first few modes of the multi-storey frame are determined. Then, the effects of force span length to beam length ratio and velocity on dynamic magnification factor (DMF) are evaluated via 3D velocity-force span length to beam length ratio-DMF graphics and its 2D projections. By using 3D and 2D graphics, the directions of critical speeds that force the structure under resonance conditions are determined. Last, the mode shapes related to these directions are determined by the time history and frequency response graphs. This study has been limited by the vibration of the frame in the vertical direction.