• Journal of Welding and Joining
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• 제6권4호
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• pp.35-43
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• 1988

Welding residual stresses were calculated by two dimensional thermal elasto-plastic analysis using element method. Complicated plastic behavior during heat transfer was simulated with time. Fist, temperature distributions. To consider time varying behavior of material properties and loading and unloading processes, iterative calculation based on initial stiffness method was carried out. The method proposed by Yamata was used in time increment control which determined the accuracy of claculation. comparison with other caculated and experimental results shows fairly good agreement.

• 소성∙가공
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• 제22권3호
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• pp.171-177
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• 2013

Vacuum-assisted thermoforming is one of the critical steps for successful application of film insert molding (FIM) to make parts of complex shape. If the thickness distribution of the formed film is non-uniform, then cracking, deformation, warpage, and wrinkling can easily occur at the injection molding stage. In this study, the simulation of thermoforming was performed to predict the film thickness distribution, and the results were compared with experiments. Uniaxial tensile tests with a constant crosshead speed for various high temperatures were conducted to investigate the stress-strain behavior. An instance of yielding occurred at the film temperature of $90^{\circ}C$, and the film stiffness increased with increasing crosshead speed. Two types of viscoelastic models, G'Sell model, K-BKZ model, were used to describe the measured stress-strain relationship. The predicted film thickness distributions were in good agreement with the experimental results.

• Smart Structures and Systems
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• 제20권6호
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• pp.709-728
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• 2017

This disquisition proposes a nonlocal strain gradient beam theory for thermo-mechanical dynamic characteristics of embedded smart shear deformable curved piezoelectric nanobeams made of porous electro-elastic functionally graded materials by using an analytical method. Electro-elastic properties of embedded curved porous FG nanobeam are assumed to be temperature-dependent and vary through the thickness direction of beam according to the power-law which is modified to approximate material properties for even distributions of porosities. It is perceived that during manufacturing of functionally graded materials (FGMs) porosities and micro-voids can be occurred inside the material. Since variation of pores along the thickness direction influences the mechanical and physical properties, so in this study thermo-mechanical vibration analysis of curve FG piezoelectric nanobeam by considering the effect of these imperfections is performed. Nonlocal strain gradient elasticity theory is utilized to consider the size effects in which the stress for not only the nonlocal stress field but also the strain gradients stress field. The governing equations and related boundary condition of embedded smart curved porous FG nanobeam subjected to thermal and electric field are derived via the energy method based on Timoshenko beam theory. An analytical Navier solution procedure is utilized to achieve the natural frequencies of porous FG curved piezoelectric nanobeam resting on Winkler and Pasternak foundation. The results for simpler states are confirmed with known data in the literature. The effects of various parameters such as nonlocality parameter, electric voltage, coefficient of porosity, elastic foundation parameters, thermal effect, gradient index, strain gradient, elastic opening angle and slenderness ratio on the natural frequency of embedded curved FG porous piezoelectric nanobeam are successfully discussed. It is concluded that these parameters play important roles on the dynamic behavior of porous FG curved nanobeam. Presented numerical results can serve as benchmarks for future analyses of curve FG nanobeam with porosity phases.

• 대한기계학회논문집A
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• 제26권12호
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• pp.2492-2502
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• 2002

A rubber-like material model is generally characterized by hyperelasticity and formulated by a total stress-total strain relationship because the material shows nonlinear elastic behaviour under large deformation. In this study, a pressure potential obtained by a separately interpolated pressure is introduced to the non-linear finite element formulation incorporating with incompressible or almost incompressible condition of the material. The present formulation is somewhat different from the general formulation using the pressure computed in the displacement field. A non-linear finite element analysis program is developed for the plane strain and the axisymmetric contact problems of a rubber-like material. Various examples with rubber material are analyzed for its verification. The results about deformed shapes and stress distributions thought to be meaningful in comparison with a commercial program, MARC.

• Structural Engineering and Mechanics
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• 제47권6호
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• pp.839-856
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• 2013

Metallic annular discs with their outer boundary fully constrained are studied with newly derived semi-analytical solutions for the effects of thickness variations under thermal loading and unloading. The plane stress and axisymmetric assumptions were adopted, and the thickness of the disk depends on the radius hyperbolically with an exponent n. Furthermore, it is assumed that the stress state is two dimensional and temperature is uniform in the domain. The solutions include the elastic, elastic-plastic and plastic-collapse behavior, depending on the values of temperature. The von Mises type yield criterion is adopted in this work. The material properties, Young's modulus, yield stress and thermal expansion coefficient, are assumed temperature dependent, while the Poisson's ratio is assumed to be temperature independent. It is found that for any n values, if the normalized hole radius a greater than 0.6, the normalized temperature difference between the elastically reversible temperature and plastic collapse temperature is a monotonically decreasing function of inner radius. For small holes, the n values have strong effects on the normalized temperature difference. Furthermore, it is shown that thickness variations may have stronger effects on the strain distributions when temperature-dependent material properties are considered.

• Structural Engineering and Mechanics
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• 제28권3호
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• pp.295-316
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• 2008

In the present paper a mechanical model to predict the compressive response of high strength short concrete columns with square cross-section confined by transverse steel is presented. The model allows one to estimate the equivalent confinement pressures exercised by transverse steel during the loading process taking into account of the interaction of the stirrups with the inner core both in the plane of the stirrups and in the space between two successive stirrups. The lateral pressure distributions at hoop levels are obtained by using a simple model of elastic beam on elastic medium simulating the interaction between stirrups and concrete core, including yielding of steel stirrups and damage of concrete core by means of the variation in the elastic modulus and in the Poisson's coefficient. Complete stress-strain curves in compression of confined concrete core are obtained considering the variation of the axial forces in the leg of the stirrup during the loading process. The model was compared with some others presented in the literature and it was validated on the basis of the existing experimental data. Finally, it was shown that the model allows one to include the main parameters governing the confinement problems of high strength concrete members such as: - the strength of plain concrete and its brittleness; - the diameter, the pitch and the yielding stress of the stirrups; - the diameter and the yielding stress of longitudinal bars; - the side of the member, etc.

• Smart Structures and Systems
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• 제20권1호
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• pp.11-22
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• 2017

The long-term effect of ambient temperature on bridge strain is an important and challenging problem. To investigate this issue, one year data of strain and ambient temperature of a long-span cable-stayed bridge is studied in this paper. The measured strain-time history is decomposed into two parts to obtain the strains due to vehicle load and temperature alone. A linear regression model between the temperature and the strain due to temperature is established. It is shown that for every $1^{\circ}C$ increase in temperature, the stress is increased by 0.148 MPa. Furthmore, the extreme value distributions of the strains due to vehicle load, temperature and the combination effect of them during the remaining service period are estimated by the average conditional exceedance rate approach. This approach avoids the problem of declustering of data to ensure independence. The estimated results demonstrate that the 95% quantile of the extreme strain distribution due to temperature is up to $1.488{\times}10^{-4}$ which is 2.38 times larger than that due to vehicle load. The study also indicates that the estimated extreme strain can reflect the long-term effect of temperature on bridge strain state, which has reference significance for the reliability estimation and safety assessment.

• Nuclear Engineering and Technology
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• 제56권7호
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• pp.2859-2874
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• 2024

This paper presents the finite element deformation and failure simulation of a typical Korean high-power reactor vessel under a severe accident characterized by large break loss of coolant (LBLOCA) with in-vessel retention of molten corium through external reactor vessel cooling (IVR-ERVC) conditions. Temperature distributions calculated using Modular Accident Analysis Program Version 5 (MAAP5) as thermal boundary conditions were used, and ABAQUS thermal and structural analyses were performed. After full ablation, the temperature of the inner surface in the thinnest section remained high (920 ℃), but the stress remained relatively low (less than 6 MPa). At the outer surface, the stress was as high as 250 MPa; however, the resulting plastic strain was small owing to the low temperature of 200 ℃. Variations in stress, inelastic strain, and temperature with time in the thinnest section suggest that the plastic and creep strains are saturated owing to stress relaxation, resulting in low cumulative damage. Thus, the lower head of the vessel can maintain its structural integrity under LBLOCA with IVR-ERVC conditions. The sensitivity analysis of internal pressure indicates the occurrence of failure in the thinnest section at an internal pressure >9.6 MPa via local necking followed by failure due to high stresses.

• Computers and Concrete
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• 제20권5호
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• pp.605-616
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• 2017

Concrete filled steel tubular (CFST) composite girder is a new type of structures for bridge constructions. The existing design codes cannot be used to predict the thermal stress in the CFST truss girder structures under solar radiation. This study is to develop the temperature gradient curves for predicting thermal stress of the structure based on field and laboratory monitoring data. An in-field testing had been carried out on Ganhaizi Bridge for over two months. Thermal couples were installed at the cross section of the CFST truss girder and the continuous data was collected every 30 minutes. A typical temperature gradient mode was then extracted by comparing temperature distributions at different times. To further verify the temperature gradient mode and investigate the evolution of temperature fields, an outdoor experiment was conducted on a 1:8 scale bridge model, which was installed with both thermal couples and strain gauges. The main factors including solar radiation and ambient temperature on the different positions were studied. Laboratory results were consistent with that from the in-field data and temperature gradient curves were obtained from the in-field and laboratory data. The relationship between the strain difference at top and bottom surfaces of the concrete deck and its corresponding temperature change was also obtained and a method based on curve fitting was proposed to predict the thermal strain under elevated temperature. The thermal stress model for CFST composite girder was derived. By the proposed model, the thermal stress was obtained from the temperature gradient curves. The results using the proposed model were agreed well with that by finite element modelling.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.183-188
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• 2007

In this paper, we propose a 2D-FE model in single impact with combined physical factors to obtain a unique residual stress by shot peening. Applied physical parameters include elastic-plastic deformation of shot ball, material damping coefficients, strain rate, dynamic friction coefficients. Single impact FE model consists of 2D axisymmetric elements. The FE model with combined factors showed converged and unique distributions of surface stress, maximum compressive residual stress and deformation depth. Further, in contrast to the FE models with rigid shot and elastic deformable shot, FE model with plastic deformable shot produces residual stresses very close to experimental solutions by X-ray diffraction. We therefore validated the 2D FE model with combined peeing factors and plastic deformable shot. This FE model will be a base of the 3D FE model for residual stresses by multi-impact shot peening.