• Earthquakes and Structures
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• v.3 no.1
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• pp.59-81
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• 2012

A ductility inverse-mapping method for SDOF systems including passive dampers is proposed which enables one to find the maximum acceleration of ground motion for the prescribed maximum response deformation. In the conventional capacity spectrum method, the maximum response deformation is computed through iterative procedures for the prescribed maximum acceleration of ground motion. This is because the equivalent linear model for response evaluation is described in terms of unknown maximum deformation. While successive calculations are needed, no numerically unstable iterative procedure is required in the proposed method. This ductility inverse-mapping method is applied to an SDOF model of bilinear hysteresis. The SDOF models without and with passive dampers (viscous, viscoelastic and hysteretic dampers) are taken into account to investigate the effectiveness of passive dampers for seismic retrofitting of building structures. Since the maximum response deformation is the principal parameter and specified sequentially, the proposed ductility inverse-mapping method is suitable for the implementation of the performance-based design.

• Journal of Biosystems Engineering
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• v.18 no.3
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• pp.262-269
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• 1993

Stress relaxation behaviors of the cucumber under bending moment were tested with UTM at three levels of loading rate and initial deflection ratio. Sample cucumber was selected from three cultivars of cucumber, Cheongjangmadi, Baekdadagi, and Gyeousalicheongjang, because these cultivars are the most popular grown cultivars in Korea. When the bending moment was applied to the cucumber sample, the effective span between simple supports was held a constant value of 116mm with consideration of the selected sample length. The objectives of this study were to develop the rheological models such as linear and nonlinear models of the stress relaxation for the cucumber samples, and to investigate the effects of loading rate and initial deflection ratio on the stress relaxation behavior of the cucumber. The results of this study may be summarized as follows : 1. Stress relaxation behavior of the cucumber could be well described by the generalized Maxwell model for each level of deflection ratio. But the stress relaxation behavior of the sample was found to be initial deflection ratio and time dependent, and it was represented the nonlinear viscoelastic model as a function of initial deflection ratio and time. 2. Stress relaxation behavior of the cucumber samples was very highly affected by the loading rate and the initial deflection ratio. The more loading rate and initial deflection ratio resulted in the more initial bending stress and after stress relaxation progressed more rapidly. 3. At the same test conditions, it was found that the stress relaxation rate of Cheongjangmadi was faster than that of other cultivars.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.11
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• pp.1202-1208
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• 2009

An inverse finite element (FE) model parameter estimation algorithm can be used to characterize mechanical properties of biological tissues. Using this algorithm, we can consider the influence of material nonlinearity, contact mechanics, complex boundary conditions, and geometrical constraints in the modeling. In this study, biomechanical experiments on macro and micro samples are conducted and characterized with the developed algorithm. Macro scale experiments were performed to measure the force response of porcine livers against mechanical loadings using one-dimensional indentation device. The force response of the human liver cancer cells was also measured by the atomic force microscope (AFM). The mechanical behavior of porcine livers (macro) and human liver cancer cells (micro) were characterized with the algorithm via hyperelastic and linear viscoelastic models. The developed models are suitable for computing accurate reaction force on tools and deformation of biomechanical tissues.

• Korean Journal of Food Science and Technology
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• v.26 no.2
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• pp.103-109
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• 1994

Changes in the rheological properties and the linear viscoelasticity of fish protein gel upon the thermal processing were studied by using mathematical models with stress-relaxation data. The linear viscoelasticity of surimi gel was observed in the range of the true strain $0.105{\sim}0.693$ and cross-head speed $50{\sim}250\;mm/min$ applied in this study. The results of the generalized Maxwell analysis showed that the magnitudes of elastic elements $(E,\;E_e)$ were increased, but the viscous element $({\eta}) $was decreased, as the cross-head speeds and strain levels were increased. Compared to the protein gel heated directly at $90^{\circ}C$ without preheating, the protein gel pretreated at $4^{\circ}C$ and $40^{\circ}C$ showed the higher elastic modulus, but showed different trends in the viscous component, depending on the rheological model applied. Thus, the approaching methods and curve fitting of two mathematical models of stress-relaxation to describe the viscoelastic properties of fish protein gel were discussed.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.2
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• pp.127-153
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• 2012

This paper presents an advanced computational method for the prediction of the responses in the frequency domain of general linear dissipative structural-acoustic and fluid-structure systems, in the low-and medium-frequency domains and this includes uncertainty quantification. The system under consideration is constituted of a deformable dissipative structure that is coupled with an internal dissipative acoustic fluid. This includes wall acoustic impedances and it is surrounded by an infinite acoustic fluid. The system is submitted to given internal and external acoustic sources and to the prescribed mechanical forces. An efficient reduced-order computational model is constructed by using a finite element discretization for the structure and an internal acoustic fluid. The external acoustic fluid is treated by using an appropriate boundary element method in the frequency domain. All the required modeling aspects for the analysis of the medium-frequency domain have been introduced namely, a viscoelastic behavior for the structure, an appropriate dissipative model for the internal acoustic fluid that includes wall acoustic impedance and a model of uncertainty in particular for the modeling errors. This advanced computational formulation, corresponding to new extensions and complements with respect to the state-of-the-art are well adapted for the development of a new generation of software, in particular for parallel computers.

• Computers and Concrete
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• v.7 no.4
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• pp.365-386
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• 2010

This paper presents the physical formulation of a 1D material model suitable for seismic applications. It is written within the framework of thermodynamics with internal variables that is, especially, very efficient for the phenomenological representation of material behaviors at macroscale: those of the representative elementary volume. The model can reproduce the main characteristics observed for concrete, that is nonsymetric loading rate-dependent (viscoelasticity) behavior with appearance of permanent deformations and local hysteresis (continuum plasticity), stiffness degradation (continuum damage), cracking due to displacement localization (discrete plasticity or damage). The parameters have a clear physical meaning and can thus be easily identified. Although this point is not detailed in the paper, this material model is developed to be implemented in a finite element computer program. Therefore, for the benefit of the robustness of the numerical implementation, (i) linear state equations (no local iteration required) are defined whenever possible and (ii) the conditions in which the presented model can enter the generalized standard materials class - whose elements benefit from good global and local stability properties - are clearly established. To illustrate the capabilities of this model - among them for Earthquake Engineering applications - results of some numerical applications are presented.

• International Journal of Highway Engineering
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• v.17 no.3
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• pp.77-83
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• 2015

PURPOSES : In this study, a fracture-based finite element (FE) model is proposed to evaluate the fracture behavior of fiber-reinforced asphalt (FRA) concrete under various interface conditions. METHODS : A fracture-based FE model was developed to simulate a double-edge notched tension (DENT) test. A cohesive zone model (CZM) and linear viscoelastic model were implemented to model the fracture behavior and viscous behavior of the FRA concrete, respectively. Three models were developed to characterize the behavior of interfacial bonding between the fiber reinforcement and surrounding materials. In the first model, the fracture property of the asphalt concrete was modified to study the effect of fiber reinforcement. In the second model, spring elements were used to simulated the fiber reinforcement. In the third method, bar and spring elements, based on a nonlinear bond-slip model, were used to simulate the fiber reinforcement and interfacial bonding conditions. The performance of the FRA in resisting crack development under various interfacial conditions was evaluated. RESULTS : The elastic modulus of the fibers was not sensitive to the behavior of the FRA in the DENT test before crack initiation. After crack development, the fracture resistance of the FRA was found to have enhanced considerably as the elastic modulus of the fibers increased from 450 MPa to 900 MPa. When the adhesion between the fibers and asphalt concrete was sufficiently high, the fiber reinforcement was effective. It means that the interfacial bonding conditions affect the fracture resistance of the FRA significantly. CONCLUSIONS : The bar/spring element models were more effective in representing the local behavior of the fibers and interfacial bonding than the fracture energy approach. The reinforcement effect is more significant after crack initiation, as the fibers can be pulled out sufficiently. Both the elastic modulus of the fiber reinforcement and the interfacial bonding were significant in controlling crack development in the FRA.