• Computers and Concrete
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• 제7권1호
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• pp.39-51
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• 2010

The system of pores of autoclaved aerated concrete (AAC) is described by the so-called cherry-pit model, a random system of partially interpenetrating spheres. For the simulation of fracture processes, the solid phase is approximated by an irregular spatial network of beams obtained by means of the so-called radical tessellation with respect to the pore spheres. FE calculations using standard software (ANSYS) yield the strain energies of the beams. These energies are used as fracture criterion according to which highly loaded beams are considered as broken and are removed from the network. The paper investigates the relationship between mean fracture strength and microstructure for structures close to real AAC samples and virtual structures with particular geometrical properties.

• Coupled systems mechanics
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• 제6권4호
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• pp.501-522
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• 2017

This paper introduces a numerical procedure to incorporate elasto-plastic local deformation effects in the dynamic analysis of beams. The appealing feature is that simple beam type finite elements can be used for the global model which needs not to be altered by the localized elasto-plastic deformations. An overlapping local sophisticated 2D membrane model replaces the internal forces of the beam elements in the predefined region where the localized deformations take place. An iterative coupling technique is used to perform this replacement. Comparisons with full membrane analysis are provided in order to illustrate the accuracy and efficiency of the method developed herein. In this study, the membrane formulation is able to capture the elasto-plastic material behaviour based on the von Misses yield criterion and the associated flow rule for plane stress. The Newmark time integration method is adopted for the step-by-step dynamic analysis.

• International Journal of Reliability and Applications
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• 제18권2호
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• pp.21-44
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• 2017

Accelerated life tests (ALTs) are frequently used in manufacturing industries to evaluate the reliability of products within a reasonable amount of time and cost. Test units are subjected to elevated stresses which yield quick failures. Most of the previous works on designing ALT plans are focused on tests that involve a single stress. Many times more than one stress factor influence the product's functioning. This paper deals with the design of optimum modified ramp-stress ALT plan for Burr type XII distribution with Type-I censoring under two stress factors, viz., voltage and switching rate each at two levels- low and high. It is assumed that usage time to failure is power law function of switching rate, and voltage increases linearly with time according to modified ramp-stress scheme. The cumulative exposure model is used to incorporate the effect of changing stresses. The optimum plan is devised using D-optimality criterion wherein the ${\log}_{10}$ of the determinant of Fisher information matrix is maximized. The method developed has been explained using a numerical example and sensitivity carried out.

• Structural Engineering and Mechanics
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• 제58권4호
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• pp.627-639
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• 2016

The analysis of thermally induced stresses in engineering structures is a very important and necessary task with respect to design and modeling of pressurized containers, heat exchangers, aircrafts segments, etc. to prevent them from failure and improve working conditions. So, the purpose of this study is to investigate elasto-plastic thermal stresses and deformations in a thin annular plate embedded into rigid container. To this end, analytical research devoted to mathematically and physically rigorous stress/strain analysis is performed. In order to evaluate the effect of logarithmic thermal gradients, commonly applied to structures which incorporate thin plate geometries, different thermal parameters such as temperature mismatch and varying constraint temperature were introduced into the model of elastic perfectly-plastic annular plate obeying the von Mises yield criterion with its associated flow rule. The results obtained may be used in sensitive to temperature differences aircraft structures where the thermal effects on equipment must be kept in mind.

• EDISON SW 활용 경진대회 논문집
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• 제5회(2016년)
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• pp.240-245
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• 2016

In this paper, stress contour plots depending on length, load, and diameter of the implant are presented. Depending on the condition and amount of cortical bone, process of implanting can be difficult and stress becomes important. Therefore deciding the right length and diameter of implant is critical. When analyzing stress in the implant, Von-mises yield criterion is often used; however, due to hardship of acquiring the actual material property of surrounding bones, simplified model of a implant was adapted in finite element analysis program of EDISON. The result acquired from EDISON program was then compared with results of different research papers.

• Tribology and Lubricants
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• 제21권3호
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• pp.136-141
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• 2005

Analytical model to calculate the contact fatigue life of rough surface is presented in this paper. The effect of surface roughness can be calculated by this model. Computational method and the theoretical basis are also discussed. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions; the subsurface stress field is obtained using rectangular patch solutions. Mesoscopic multiaxial fatigue criterion which can yield satisfactory results for non-proportional loading is then applied to predict fatigue damage. Suitable counting method and damage rule were used to calculate the fatigue life of random loading caused by rough surface. As a result of analysis the relationship between the life and the roughness as well as the most probable depth of the crack initiation is calculated.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1998년도 제2회 박판성형심포지엄 논문집 박판성형기술의 현재와 미래
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• pp.156-163
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• 1998

During an actual forming operation, a material may undergo considrably large changes in strain path, and these changes can significantly alter the forming limits. So, in this study, modified forming limit curves(FLCs) in complex strain path are determined with specially designed jig to give test specimens with desired prestrains in uniaxial or biaxial deformation mode. In another part of present study, theoretical prediction of FLCs is attempted with MK's theory and Hosford's yield criterion to give forming limit curves in positive minor strain region and with Hill's local necking theory in negative minor strain region. Comparison of these theoretical results with experimental ones will be mentioned for both linear and complex strain path.

• Structural Engineering and Mechanics
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• 제15권2호
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• pp.225-238
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• 2003

In the present study, the finite strip analysis of a box girder to simulate a ship's hull model is carried out to investigate its inelastic post-buckling behavior and to predict its ultimate flexural strength. Residual stresses and initial geometrical imperfections are both considered in the combined material and geometrical nonlinear analysis. The von-Mises yield criterion and the Prandtl-Reuss flow theory of plasticity are applied in modeling the elasto-plastic behavior of material. The Newton-Raphson iterative process is also employed in the analysis to achieve convergence. The numerical results agree well with the experimental data. The effects of some material and geometrical parameters on the ultimate strength of the structure are also investigated.

• 한국정밀공학회지
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• 제14권9호
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• pp.101-107
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• 1997

A sectional analysis of auto-body panel stamping is carried out by using the rigid-plastic FEM based on the membrane theory. The auto-body panel material is assumed to possess normal anisotropy and to obey Hill's new yield criterion and its associated flow rule. A method of contact treatment is proposed in which the skew boundary condition for arbitarily shaped tools is successively used during iteration. Deformation of each section of trunk-lid panel is simulated and composed to get the three-dimensional shape by using CAD technique. It was shown that the composition of the two-dimensional section analysis gives almost the same results as the full three-dimensional analysis.

• Steel and Composite Structures
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• 제51권4호
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• pp.377-389
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• 2024

In the present study, thermoelsatoplastic stresses and displacement for rotating hollow disks made of functionally graded materials (FGMs) has been investigated. The linear elastic-fully plastic condition is considered. The material properties except Poisson's ratio are assumed to vary in the radial direction as a power-law function. The heat conduction equation for the one-dimensional problem in cylindrical coordinates is used to obtain temperature distribution in the disk. The plastic model is based on the Tresca yield criterion and its associated flow rules under the assumption of perfectly plastic material behavior. Exact solutions of field equations for elastic and plastic deformations are obtained. It is shown that the elastoplastic response of the functionally graded (FG) disk is affected notably by the radial variation of material properties. It is also shown that, depending on material properties and disk dimensions, different modes of plastic deformation may occur.