• Interaction and multiscale mechanics
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• v.4 no.3
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• pp.173-185
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• 2011

A multiscale modeling scheme that addresses the influence of the nanoparticle size in nanocomposites consisting of nano-sized spherical particles embedded in a polymer matrix is presented. A micromechanics-based constitutive model for nanoparticle-reinforced polymer composites is derived by incorporating the Eshelby tensor considering the interface effects (Duan et al. 2005a) into the ensemble-volume average method (Ju and Chen 1994). A numerical investigation is carried out to validate the proposed micromechanics-based constitutive model, and a parametric study on the interface moduli is conducted to investigate the effect of interface moduli on the overall behavior of the composites. In addition, molecular dynamics (MD) simulations are performed to determine the mechanical properties of the nanoparticles and polymer. Finally, the overall elastic moduli of the nanoparticle-reinforced polymer composites are estimated using the proposed multiscale approach combining the ensemble-volume average method and the MD simulation. The predictive capability of the proposed multiscale approach has been demonstrated through the multiscale numerical simulations.

• Computers and Concrete
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• v.21 no.5
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• pp.593-605
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• 2018

A nonlinear finite element modeling approach is developed to assess the behavior of a dowel bar embedded on a single concrete block substrate, subjected to monotonic loading. In this approach, a discrete representation of the steel reinforcing bar is considered, using beam finite elements with nonlinear material behavior. The bar is connected to the concrete embedment through nonlinear Winkler spring elements. This modeling approach can only be used if a new constitutive model is developed for the spring elements, to simulate the deformability and strength of the concrete substrate. To define this constitutive model, an extensive literature review was conducted, as well as 3 experimental tests, in order to select the experimental data which can be used in the calibration of the model. Based on this data, an empirical model was established to predict the global dowel response, for a wide range of bar diameters and concrete strengths. This empirical model provided the information needed for calibration of the nonlinear Winkler spring model, valid for dowel displacements up to 4 mm. This new constitutive model is composed by 5 stages, in order to reproduce the concrete substrate response.

• Computers and Concrete
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• v.3 no.4
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• pp.197-212
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• 2006

Modeling of physically non-linear behavior becomes more and more important for the analysis of SFRC structures in practical applications. From this point of view we will present an effective, three-dimensional constitutive model for SFRC, that is also easy to implement in commercial finite element programs. Additionally, the finite element analysis should only require standard material parameters which can be gained easily from conventional experiments or which are specified in appropriate building codes. Another important point is attaining the material parameters from experimental data. The procedures to determine the material parameters proposed in appropriate codes seem to be only approximations and are unsuitable for precise structural analysis. Therefore a finite element analysis of the test itself is used to get the material parameters. This process is also denoted as inverse analysis. The efficiency of the proposed constitutive model is demonstrated on the basis of numerical examples and their comparison to experimental results. In the framework of material parameter identification the idea of a new, indirect tension testing procedure, the "Modified Tension Test", is adopted and extended to an easy-to-carry-out tension test for steel fiber reinforced concrete specimens.

• Advances in concrete construction
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• v.5 no.3
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• pp.221-240
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• 2017

The modeling of the mechanical behavior of quasi-brittle materials is still a challenge task, mainly in failure processes when fracture and plasticity phenomena become important actors in dissipative processes which occur in materials like concrete, as instance. Many homogenization-based approaches have been proposed to deal with heterogeneous materials in the last years. In this context, a computational homogenization modeling for concrete is presented in this work using the concept of Representative Volume Element (RVE). The material is considered as a three-phase material consisting of interface zone (ITZ), matrix and inclusions-each constituent modeled by an independent constitutive model. The Representative Volume Element (RVE) consists of inclusions idealized as circular shapes symmetrically and nonsymmetrically placed into the specimen. The interface zone is modeled by means of cohesive contact finite elements. The inclusion is modeled as linear elastic and matrix region is considered as elastoplastic material. A set of examples is presented in order to show the potentialities and limitations of the proposed modeling. The consideration of the fracture processes in the ITZ is fundamental to capture complex macroscopic characteristics of the material using simple constitutive models at mesoscopic level.

• Nuclear Engineering and Technology
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• v.45 no.1
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• pp.89-98
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• 2013

In recent years steel-concrete composite shear walls have been widely used in enormous high-rise buildings. Due to high strength and ductility, enhanced stiffness, stable cycle characteristics and large energy absorption, such walls can be adopted in the auxiliary building; surrounding the reactor containment structure of nuclear power plants to resist lateral forces induced by heavy winds and severe earthquakes. This paper demonstrates a set of nonlinear numerical studies on I-shaped composite steel-concrete shear walls of the nuclear power plants subjected to reverse cyclic loading. A three-dimensional finite element model is developed using ABAQUS by emphasizing on constitutive material modeling and element type to represent the real physical behavior of complex shear wall structures. The analysis escalates with parametric variation in steel thickness sandwiching the stipulated amount of concrete panels. Modeling details of structural components, contact conditions between steel and concrete, associated boundary conditions and constitutive relationships for the cyclic loading are explained. Later, the load versus displacement curves, peak load and ultimate strength values, hysteretic characteristics and deflection profiles are verified with experimental data. The convergence of the numerical outcomes has been discussed to conclude the remarks.

• The Journal of Korea Robotics Society
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• v.14 no.3
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• pp.191-195
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• 2019

This paper presents a rope modeling and verification for the robotic platform of the wall cleaning robot (ROPE RIDE). ROPE RIDE has the characteristics of climbing up and down using a rope fixed on the roof like traditional workers. In order to perform a stable operation with a wall cleaning robot, it is necessary to estimate the position of the robot in a vertical direction. However, due to the high coefficient of extension and nonlinearity of the climbing rope, it is difficult to predict the behavior of the rope. Thus, in this paper, the mathematical modeling of the rope was carried out through the preliminary experiment. Extensive experiments using different types of rope were used to determine the parameters of the constitutive equation of climbing ropes. The validity of the determined parameters of various ropes was verified through the experiment results.

• Transactions of Materials Processing
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• v.26 no.1
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• pp.18-27
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• 2017

A comparative study was performed on strain-compensated Arrhenius-type constitutive models established with two regression methods: polynomial regression and regression Kriging. For measurements at high temperatures, experimental data of 70Cr3Mo steel were adopted from previous research. An Arrhenius-type constitutive model necessitates strain compensation for material constants to account for strain effect. To associate the material constants with strain, we first evaluated them at a set of discrete strains, then capitalized on surrogate modeling to represent the material constants as a function of strain. As a result, disparate flow stress models were formed via the two different regression methods. The constructed constitutive models were examined systematically against measured flow stresses by validation methods. The predicted material constants were found to be quite accurate compared to the actual material constants. However, notable mismatches between measured and predicted flow stresses were revealed by the proposed validation techniques, which carry out validation with not the entire, but a single tensile test case.

• KCI Concrete Journal
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• v.13 no.1
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• pp.69-78
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• 2001

The inelastic behavior of a reinforced concrete columns is influenced by a number of factors : 1) level of axial load, 2) tie spacing, 3) volumetric ratio of lateral steel, 4) concrete strength, 5) distribution of longitudinal steel, 6) strength of lateral steel, 7) cover thickness, 8) configuration of lateral steel, 9) strain gradient, 10) strain rate, 11) the effectively confined concrete core area, and 12) amount of longitudinal steel. A new constitutive model of a confined concrete is suggested in order to investigate the nonlinear behavior of the reinforced concrete columns under concentric loading. The developed constitutive model for the confined concrete takes into account the effects of effectively confined area as well as the horizontal and longitudinal distributions of the confining pressures. None of the existing models incorporated these two main effects at the same time. A total of different six constitutive models for the behavior of the confined concrete under concentric compression were compared with the sixty-one test results reported by different researchers. The superiority of the developed model in its accuracy is demonstrated by evaluating the error function, which compares the weighted averages for the sum of squared relative differences in peak compressive strength and corresponding strain, stress at strain equal to 0.015, and total area under stress-strain curve up to strain equal to 0.015.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.9 no.3
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• pp.191-197
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• 2009

Up to now, a number of models have been proposed and discussed to describe a wide range of inelastic behaviors of materials. The fatal problem of using such models is however the existence of model errors, and the problem remains inevitably as far as a material model is written explicitly. In this paper, the authors define the implicit constitutive model and propose an implicit viscoplastic constitutive model using neural networks. In their modeling, inelastic material behaviors are generalized in a state space representation and the state space form is constructed by a neural network using input-output data sets. A technique to extract the input-output data from experimental data is also described. The proposed model was first generated from pseudo-experimental data created by one of the widely used constitutive models and was found to replace the model well. Then, having been tested with the actual experimental data, the proposed model resulted in a negligible amount of model errors indicating its superiority to all the existing explicit models in accuracy.

• Computational Structural Engineering
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• v.10 no.4
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• pp.229-238
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• 1997

Mechanical behavior of asphalt concrete that accounts for viscoelasticity and damage evolution under cyclic loading conditions is modeled and presented in this paper. An elastic-viscoelastic correspondence principle in terms of pseudo variables is applied to separately evaluate viscoelasticity and time-dependent damage growth in asphalt concrete. A microcrack growth law, which is commonly employed in linear viscoelastic fracture mechanics, is successfully used for describing the damage growth in the body. A constitutive equation in terms of stress and pseudo strain is first established for controlled-strain mode, and then transformed to controlled-stress constitutive equation by simply replacing stress and pseudo strain with pseudo stress and strain. The transformed constitutive equation in terms of pseudo stress satisfactorily predicts the mechanical behavior of asphalt concrete all the way up to failure under controlled-stress modes.