• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.5
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• pp.493-504
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• 2008

This paper presents a computation of nonlinear elastic strains that may occur in the leaflet of the Edwards MIRA mechanical heart valve by the applied high blood pressure using the finite element analysis methodology. By adopting numerical analysis techniques of the commercial finite element analysis code, NISA, structural analyses of the Edwards MIRA mechanical heart valve are performed for the slight variation of leaflet thickness to get the elastic strains occurring in the leaflet while the high blood fluid pressures are applied to the leaflet surface in order that the maximum stress occurring in the leaflet may be less than the yield stress of the leaflet material(Si-Alloyed PyC). And so, only the geometric non-linearity is assumed because large geometric nonlinear elastic strains are expected rather than material nonlinear strains due to the applied high blood pressure. Computed linear and nonlinear elastic strains are compared to make sure the non-linearity of the computed elastic strain. The comparison result shows that large elastic strains occur clearly in the very thin leaflets as high blood pressures are applied. However, only the linear elastic strains occur for low blood pressures, and also for thick leaflets even for the high blood pressures. Hence the nonlinear structural analysis is very required in the structural design of a mechanical heart valve.

• Advances in aircraft and spacecraft science
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• v.2 no.1
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• pp.57-76
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• 2015

We investigated complex damped modes in beams in the presence of a viscoelastic layer sandwiched between two elastic layers. The problem was solved using two approaches, (1) Rayleigh beam theory and analyzed using the Ritz method, and (2) by using 2D plane stress elasticity based finite-element method. The damping in the layers was modeled using the complex modulus. Simply-supported, cantilever, and viscously supported boundary conditions were considered in this study. Simple trigonometric functions were used as admissible functions in the Ritz method. The key idea behind sandwich structure is to increase damping in a beam as affected by the presence of a highly-damped core layer vibrating mainly in shear. Different assumptions are utilized in the literature, to model shear deformation in the core layer. In this manuscript, we used FEM without any kinematic assumptions for the transverse shear in both the core and elastic layers. Moreover, numerical examples were studied, where the base and constraining layers were also damped. The loss factor was calculated by modal strain energy method, and by solving a complex eigenvalue problem. The efficiency of the modal strain energy method was tested for different loss factors in the core layer. Complex mode shapes of the beam were also examined in the study, and a comparison was made between viscoelastically and viscously damped structures. The numerical results were compared with those available in the literature, and the results were found to be satisfactory.

• Structural Engineering and Mechanics
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• v.62 no.5
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• pp.551-565
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• 2017

Based on the strain gradient theory (SGT), vibration analysis of an embedded micro cylindrical shell reinforced with agglomerated carbon nanotubes (CNTs) is investigated. The elastic medium is simulated by the orthotropic Pasternak foundation. The structure is subjected to magnetic field in the axial direction. For obtaining the equivalent material properties of structure and considering agglomeration effects, the Mori-Tanaka model is applied. The motion equations are derived on the basis of Mindlin cylindrical shell theory, energy method and Hamilton's principal. Differential quadrature method (DQM) is proposed to evaluate the frequency of system for different boundary conditions. The effects of different parameters such as CNTs volume percent, agglomeration of CNTs, elastic medium, magnetic field, boundary conditions, length to radius ratio and small scale parameter are shown on the frequency of the structure. The results indicate that the effect of CNTs agglomeration plays an important role in the frequency of system so that considering agglomeration leads to lower frequency. Furthermore, the frequency of structure increases with enhancing the small scale parameter.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.3
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• pp.199-209
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• 2009

This paper deals with the three-dimensional finite element analysis of failure behavior of UHPFRC I-beam under monotonic load. Different from the constitutive law of normal and high strength concrete, an elastic-plastic fracture model that considers the tensile strain hardening is proposed to describe the material properties of UHPFRC. A multi-directional fixed crack criterion with tensile strain hardening is defined in the tensile region, and Drucker-Prager criterion with an associated flow rule is adopted in the compressive region. The influence of span, prestressing force and section on the behavior of UHPFRC I-beam are investigated. The comparison of the numerical results with the test results indicates a good agreement.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.94-97
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• 1999

The study has been performed for the relation between die and product in closed die upsetting by the experiment. the strain of die has been given by the simple experiment using the strain gauge located at the outer surface of die and the deformation history of die and product has been given by the experiment and Lame's formula. the product with accurate dimension and shape can be obtained by analysing elastic deformation of die during upsetting process. The deformation of die during metal forming process has been given by the experiment and lame's formula. The product with accurate dimension and shape can be obtained by analysing elastic deformation of die during upsetting process. The deformation of die during metal forming process has been usually predicted by the experience of industrial engineers of finite element analysis. But it is difficult to predict the dimension of product at unloading and ejected states. The study has given useful result for the deformation history of die and product through the experiment and Lame's formula at closed die upsetting and can be applied in the die design for product with accurate dimension.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.2
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• pp.239-246
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• 2003

This paper proposes engineering estimation equations of elastic-plastic J and COD fur axial through-wall cracked pipes under internal pressure. Based on detailed 3-D FE results based on deformation plasticity, the plastic influence functions for fully plastic J and COD solutions are tabulated as a function of the mean radius-to-thickness ratio, the normalized crack length. and the strain hardening. Based on these results, the GE/EPRI-type J and COD estimation equations are proposed and validated against the 3-D FE results based on deformation plasticity. For more general application to general stress-strain laws or to complex loading, the developed GE/EPRI-type solutions are re-formulated based on the reference stress concept. Such a reformulation provides simpler equations for J and COD, which are then further extended to combined internal pressure and bending. The proposed reference stress based J and COD estimation equations are compared with elastic-plastic 3-D FE results using actual stress-strain data for Type 316 stainless steels. The FE results for both internal pressure cases and combined internal pressure and bending cases compare very well with the proposed J and COD estimations.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.5 no.4
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• pp.19-30
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• 2002

The stability of slope using root-pile like to the reinforcements is affected by the interaction behavior mechanism of soil-reinforcements. Through the studying on the interaction in joint of its, therefore, the control roles can be find out in installed slope. In study, the stress level ratio based on the insert angle of installed reinforcements in soil used to numerical analysis, which was results from the duty direct shear test in Lab. The maximum shear strain variation on the reinforcements was observed at insert angle, which was approximately similar to the calculated angle based on the equation proposed by the Jewell. The elasto-plastic joint model on the contact area of soil-reinforcements was presumed, the reinforced soil assumed non-linear elastic model and the reinforcements supposed elastic model, respectively. The finite element analysis of assumed models was performed. The shear strain variation of non-reinforced state obtained by the FEM analysis including elasto-plastic joint elements were shown the rationality of general limit equilibrium analysis for the slope failure mode on driving zone and resistance zone, which based on the stress level step according to failure ratio. Through the variation of shear strain for the variation of inserting angle of reinforcements, the different mechanism on the bending and the shear resistance of reinforcements was shown fair possibility.

• Transactions of Materials Processing
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• v.13 no.6 s.70
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• pp.540-545
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• 2004

Ever since the ideal forming theory has been developed for process design purposes, application has been limited to sheet forming and, fur bulk forming, to two-dimensional steady flow. Here, application for the non-steady case was performed under the plane-strain condition based on the theory previously developed. In the ideal flow, material elements deform following the minimum plastic work path (or mostly proportional true strain path) so that the ideal plane-stram flow can be effectively described using the two-dimensional orthogonal convective coordinate system. Besides kinematics, fur a prescribed final part shape, schemes to optimize a preform shape out of a class of initial configurations and also to define the evolution of shapes and boundary tractions were developed. Discussions include the two problematic issues on internal tractions and the non-monotonous straining. For demonstration purposes, numerical calculations were made for a bulk part under forging.

• Advances in concrete construction
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• v.11 no.4
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• pp.347-356
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• 2021

To address the limitation of the commonly used steam curing of reactive powder concrete (SC-RPC) in engineering, a preparation technology of normal curing reactive powder concrete (NC-RPC) is proposed. In this study, an experimental comparative research on the mechanical properties of NC-RPC and SC-RPC under uniaxial tension is conducted. Under the premise of giving full play to the ultra-high performance of RPC, the paper tries to explore whether normal curing can replace steam curing. The results show that various mechanical indexes of NC-RPC (e.g., tensile strength, ultimate tensile strain, elastic modulus and deformation performance) could basically reach the mechanical index values in steam curing at 28d age, some performance is even better at a longer age. So it affirms the feasibility of normal curing. In this paper, the influence of normal curing age on the tensile properties of RPC is discussed, and the relationship between each index and age is introduced in detail. Based on the experimental data, the tensile mechanism of RPC is analyzed theoretically, and two kinds of tensile constitutive models for RPC are proposed, one is curvilinear model, and another one is polygonal line model. The validity of the two models is further verified by the test results of others.

• Fashion & Textile Research Journal
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• v.18 no.6
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• pp.733-745
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• 2016

This paper provides a review of wearable textile strain sensors that can measure the deformation of the body surface according to the movements of the wearer. In previous studies, the requirements of textile strain sensors, materials and fabrication methods, as well as the principle of the strain sensing according to sensor structures were understood; furthermore, the factors that affect the sensing performance were critically reviewed and application studies were examined. Textile strain sensors should be able to show piezoresistive effects with consistent resistance-extension in response to the extensional deformations that are repeated when they are worn. Textile strain sensors with piezoresistivity are typically made using conductive yarn knit structures or carbon-based fillers or conducting polymer filler composite materials. For the accuracy and reliability of textile strain sensors, fabrication technologies that would minimize deformation hysteresis should be developed and processes to complement and analyze sensing results based on accurate understanding of the sensors' resistance-strain behavior are necessary. Since light-weighted, flexible, and highly elastic textile strain sensors can be worn by users without any inconvenience so that to enable the users to continuously collect data related to body movements, textile strain sensors are expected to become the core of human interface technologies with a wide range of applications in diverse areas.