• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1057-1068
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• 2014

This paper proposes elastic-plastic constitutive relations for a composite material with two phases-inclusion and matrix phases-using a homogenization scheme. A thermodynamic framework is employed to develop non-local plasticity constitutive relations, which are specifically represented in terms of the second-order gradient terms of the internal state variables. A combined two back-stress evolution equation is also established and the degradation of the state and internal variables is expressed by continuum damage mechanics in terms of the damage factor. Then, deformation localization is analyzed; the analysis results show that the proposed model yields a wide range of shear band formation behaviors depending on the evolution of the specific internal state variables. The analysis results also show good agreement with the results of simplified Rice instability analyses.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.1
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• pp.82-93
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• 2019

In this paper, the ductile fracture criteria for a marine structural steel (EH36) are presented and validated. The theoretical background of the recently developed Hosford-Coulomb (HC) fracture strain model and the DSSE fracture strain model which was developed to apply to the shell elements is described. In order to accurately estimate the flow stress in the large strain range up to the fracture, the material constants for the combined Swift-Voce constitutive equation were derived by the numerical analyses of the smooth and notched specimens made from the EH36 steel. As a result of applying the Swift-Voce flow stress to the other notched specimen model, a very accurate load - displacement curve could be derived. The material constants of the HC fracture strain and DSSE fracture strain models were independently calibrated based on the numerical analyses for the smooth and notch specimen tests. The user subroutine (VUMAT of Abaqus) was developed to verify the accuracy of the combined HC-DSSE fracture strain model. An asymmetric notch specimen was used as verification model. It was confirmed that the fracture of the asymmetric specimen can be accurately predicted when a very small solid elements are used together with the HC fracture strain model. On the other hand, the combined HC-DSSE fracture strain model can predict accurately the fracture of shell element model while the shell element size effect becomes less sensitive.

• Journal of the Korean Society for Advanced Composite Structures
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• v.1 no.3
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• pp.41-48
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• 2010

In this paper, the analysis of impact damage behavior of a reinforced concrete structure that undergoes both a shock impulsive loading and an impact loading due to the air blast induced from an explosion is performed. Firstly, a pair of multiple loadings are selected from the scenario that an imaginary explosion accident is assumed. The RC structures strengthened with advanced composite materials (ACM) are considered as a scheme for retrofitting RC wall structures subjected to multiple explosive loadings and then the evaluation of the resistant performance against them is presented in comparison with the result of the evaluation of a RC structure without a retrofit. Also, in order to derive the result of the analysis similar to that of real explosion experiments, which require the vast investment and expense for facilities, the constitutive equation and the equation of state (EOS) which can describe the real impact and shock phenomena accurately are included with them. In addition, the numerical simulations of two concrete structures are achieved using AUTODYN-3D, an explicit analysis program, in order to prove the retrofit performance of a ACM-strengthened RC wall structure.

• Structural Engineering and Mechanics
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• v.74 no.1
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• pp.1-18
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• 2020

For the large deformation of shear walls under vertical and horizontal loads, there are difficulties in obtaining accurate simulation results using the response analysis method, even with fine mesh elements. Furthermore, concrete material nonlinearity, stiffness degradation, concrete cracking and crushing, and steel bar damage may occur during the large deformation of reinforced concrete (RC) shear walls. Matrix operations that are involved in nonlinear analysis using the traditional finite-element method (FEM) may also result in flaws, and may thus lead to serious errors. To solve these problems, a planar four-node element was developed based on vector mechanics. Owing to particle-based formulation along the path element, the method does not require repeated constructions of a global stiffness matrix for the nonlinear behavior of the structure. The nonlinear concrete constitutive model and bilinear steel material model are integrated with the developed element, to ensure that large deformation and damage behavior can be addressed. For verification, simulation analyses were performed to obtain experimental results on an RC shear wall subjected to a monotonically increasing lateral load with a constant vertical load. To appropriately evaluate the parameters, investigations were conducted on the loading speed, meshing dimension, and the damping factor, because vector mechanics is based on the equation of motion. The static problem was then verified to obtain a stable solution by employing a balanced equation of motion. Using the parameters obtained, the simulated pushover response, including the bearing capacity, deformation ability, curvature development, and energy dissipation, were found to be in accordance with the experimental observation. This study demonstrated the potential of the developed planar element for simulating the entire process of large deformation and damage behavior in RC shear walls.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.331-336
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• 2004

This paper is concerned with numerical simulation of hypervelocity impacts(HVIs) of a projectile on laminated composite plate targets using SPH method. A one-parameter visco-plasticity model and damage model is used to describe the HVIs response of composite materials. The numerical simulation was carried out for a steel projectile striking to aluminum plate targets and for an aluminum projectile striking to laminated graphite/epoxy (Gr/Ep) composite plate targets. Through the numerical simulation, comparison with the HVIs response of isotropic materials and composite materials is discussed.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.209-216
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• 2000

When subjected to earthquake shaking, saturated sandy soil may generate excess pore pressure. And a time may come when initial confining pressure will equal to excess pore pressure. Depending on the characteristics of the soil and the length of the drainage path, excess pore pressure was dissipated after earthquake. For this reason, it was induced settlement in grounds and fatal damage of various structures. In this study, settlement in silty sand grounds induced earthquake was evaluated using post-liquefaction constitutive equation between volumetric strain and shear strain from previous study. Using that, it was proposed that simplified estimation of settlement in silty sand grounds induced liquefaction.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1033-1036
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• 2008

In this paper, the analysis of impact damage behavior of a reinforced concrete structure that undergoes both a shock impulsive loading and an impact loading due to the air blast induced from an explosion is performed. Firstly, a pair of multiple loadings are selected from the scenario that an imaginary explosion accident is assumed. The RC structures strengthened with glass fiber reinforced polymer (GFRP) composites are considered as a scheme for retrofitting RC wall structures subjected to multiple explosive loadings and then the evaluation of the resistant performance against them is presented in comparison with the result of the evaluation of a RC structure without a retrofit. Also, in order to derive the result of the analysis similar to that of real explosion experiments, which require the vast investment and expense for facilities, the constitutive equation and the equation of state (EOS) which can describe the real impact and shock phenomena accurately are included with them. In addition, the numerical simulations of two concrete structures are achieved using AUTODYN-3D, an explicit analysis program, in order to prove the retrofit performance of a GFRP-strengthened RC wall structure.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.26-36
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• 2001

Smart sensors and actuators have recently been developed. In this study, first, small-diameter fiber Bragg grating (FBG) sensors developed by the author, whose cladding and polyimide coating diameters were 40 and $52{\mu}m$, respectively, were embedded inside a laminate without resin-rich regions around sensors and the deterioration of mechanical properties of the composite laminate. The small-diameter FBG sensor was embedded in $0^{\circ}$ ply of a CFRP laminate for the detection of transverse cracks in $90^{\circ}$ ply of the laminate. The reflection spectra from the FBG sensor were measured at various tensile stresses. The spectrum became broad and had some peaks with an increase of the transverse crack density. Furthermore, the theoretical calculation reproduced the change in the spectrum very well. These results show that the small-diameter FBG sensors have a potential to detect the occurrence of transverse cracks through the change in the form of the spectrum, and to evaluate the transverse crack density quantitatively by the spectrum width. On the other hand, shape memory alloy (SMA) films were used to suppress the initiation and growth of transverse cracks in CFRP laminates. Pre-strained SMA films were embedded between laminas in CFRP laminates and then heated to introduce the recovery stress in SMA films and compressive stresses in the weakest plies ($90^{\circ}$ ply). The effects of recovery stresses are demonstrated in the experiments and well predicted using the shear-lag analysis and the nonlinear constitutive equation of SMA films.

• Journal of the Korean GEO-environmental Society
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• v.25 no.7
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• pp.5-19
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• 2024

During the blasting process, a fracture zone is formed in the vicinity of the blast hole. Any damage that extends beyond the excavation boundary line necessitates the implementation of an additional support system to assure safety. Typically, fracture zone radius is estimated from blast hole pressure using theoretical methods due to its simplicity. However, linear charge concentration (kg/m) is used for tunnel blasting. This paper compiles Swedish experimental datasets to estimate the radius of fracture zones based on linear charge concentration. Further numerical analyses are performed in LS-DYNA for coupled single-hole blasting. The Riedel-Hiermaier-Thoma (RHT) model has been selected as the constitutive model for this investigation. The numerical model is validated against small-scale laboratory tests. Parametric studies are conducted to predict fracture zones in granite and sandstone rocks using two kinds of explosives, PETN and AFNO. The analyses evaluate ten types of blast hole sizes, ranging from 17 to 100 mm. The results indicate that granite has a larger fracture zone than sandstone, and the PETN explosive predicts more damage than ANFO. Smaller blast holes exhibit smaller fracture zones in comparison to larger blast holes. Wave propagation is more rapidly attenuated in granite than in sandstone. Subsequently, the predicted fracture zone outcomes are compared with the empirical dataset. Fracture zones of medium blast hole diameter align well with the experimental data set. A predictive equation is derived from the data set, which may be used to evaluate blast design to manage fracture zones beyond the excavation line.

• Geomechanics and Engineering
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• v.23 no.3
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• pp.245-259
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• 2020

Tunnels have become an indispensable part of metro cities. Blast resistance design of tunnel has attracted the attention of researchers due to numerous implosion event. Present paper deals with the non-linear finite element analysis of rock tunnel having shear zone subjected to internal blast loading. Abaqus Explicit schemes in finite element has been used for the simulation of internal blast event. Structural discontinuity i.e., shear zone has been assumed passing the tunnel cross-section in the vertical direction and consist of Highly Weathered Granite medium surrounding the tunnel. Mohr-Coulomb constitutive material model has been considered for modelling the Highly Weathered Granite and the shear zone material. Concrete Damage Plasticity (CDP), Johnson-Cook (J-C), Jones-Wilkins-Lee (JWL) equation of state models are used for concrete, steel reinforcement and Trinitrotoluene (TNT) simulation respectively. The Coupled-Eulerian-Lagrangian (CEL) method of modelling for TNT explosive and air inside the tunnel has been adopted in this study. The CEL method incorporates the large deformations for which the traditional finite element analysis cannot be used. Shear zone orientations of 0°, 15°, 30°, 45°, 60°, 75° and 90°, with respect to the tunnel axis are considered to see their effect. It has been concluded that 60° orientation of shear zone presents the most critical situation.