• Computational Structural Engineering
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• v.8 no.4
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• pp.107-115
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• 1995

The long term behavior of the Waste Isolation Pilot Plant(WIPP), a nuclear waste repository currently under construction near Carlsbad at New Mexico, depends upon the fracture and deformation behavior of bedded rock salt. Although many numerical analyses of the WIPP have been conducted, to our knowledge none have included the ability to simultaneously predict the effects of fracture and nonlinear deformation of the salt continuum. We are in the process of developing a finite element program to simulate the effects of nonlinear fracture mechanics and nonlinear continuum behavior of rock salt simultaneously.

• Coupled systems mechanics
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• v.4 no.3
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• pp.211-235
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• 2015

In this work we present a one-dimensional damage model capable of representing the dynamic fracture for elastodamage bar with combined hardening in fracture process zone - FPZ and softening with embedded strong discontinuities. This model is compared with another one we recently introduced (Do et al. 2015) and it shows a good agreement between two models. Namely, it is indicated that strain-softening leads to a sensitivity of results on the mesh discretization. Strain tends to localization in a single element which is the smallest possible area in the finite element simulations. The strain-softening element in the middle of the bar undergoes intense deformation. Strain increases with increasing mesh refinement. Strain in elements outside the strain-softening element gradually decreases to zero.

• Structural Engineering and Mechanics
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• v.6 no.5
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• pp.485-496
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• 1998

Standard finite element wave propagation codes are useful for determining stresses caused by the impact of one body with another; however, their applicability to a laminated system such as architectural laminated glass is limited because the important interlayer delamination process caused by impact loading is difficult to model. This paper presents a method that allows traditional wave propagation codes to model the interlayer debonding of laminated architectural glass subject to low velocity, small missile impact such as that which occurs in severe windstorms. The method can be extended to any multilayered medium with adhesive bonding between the layers. Computational results of concern to architectural glazing designers are presented.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.1 s.256
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• pp.70-76
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• 2007

Elastic-plastic fracture mechanics is popularly used for integrity evaluation of major components, however, it is not easy to extract standard specimens from operating facility. This paper examines how ductile fracture toughness is characterized by a small punch testing technique in conjunction with finite element analyses incorporating a damage model. At first, micro-mechanical parameters constituting Rousselier model are calibrated for typical nuclear materials using both estimated and experimental load-displacement (P-$\delta$) curves of miniaturized specimens. Then, fracture resistance (J-R) curves of relatively larger standard CT specimens are predicted by finite element analyses employing the calibrated parameters and compared with corresponding experimental ones. It was proven that estimated results by the proposed method using small punch specimen is promising and might be used as a useful tool for ductile crack growth evaluation.

• Journal of Welding and Joining
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• v.25 no.1
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• pp.63-69
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• 2007

Once assessment of material failure characteristics is captured precisely in a unified way, it can bedirectly incorporated into the structural failure assessment under various loading environments, based on the theoretical backgrounds so called Local Approach to Fracture. The aim of this study is to develop a numerical fatigue test method by continuum damage mechanics applicable for the assessment of structural integrity throughout crack initiation and structural failure based on the Local Approach to Fracture. The generalized elasto-visco-plastic constitutive equation, which can consider the internal damage evolution behavior, is developed and employed in the 3-D FEA code in order to numerically evaluate the material and/or structural responses. Explicit information of the relationships between the mechanical properties and material constants, which are required for the mechanical constitutive and damage evolution equations for each material, are implemented in numerical fatigue test method. The material constants selected from constitutive equations are used directly in the failure assessment of material and/or structures. The performance of the developed system has been evaluated with assessing the S-N diagram of stainless steel materials.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.17-25
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• 2001

This paper briefly describes the new engineering method, called the enhanced reference stress method, to estimate J (or $C^*$) for non-linear fracture mechanics analysis of defective components, recently proposed by authors. The proposed method offers significant advantages over existing methods in terms of its accuracy, simplicity and robustness. Examples of application of the proposed method to typical piping integrity problems such as through-wall cracked pipes under combined loading, and surface cracked pipes under internal pressure and bending are given. Excellent agreements between the FE J and $C^*$ results and those of the proposed method provide sufficient confidence in the use of the proposed method. One notable point is that the proposed method can be used to estimate J (or $C^*$) along the crack front of surface cracks. Moreover simplicity of the proposed method makes it easy to extend to more complex problems. Thus the proposed method is attractive to assess the significance of defects under practical situations.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.215-220
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• 2001

The objective of this study is to examine the fracture characteristics of concrete at early ages such as critical stress intensity factor, critical crack-tip opening displacement, fracture energy based on the concepts of the effective-elastic crack model and the cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By varying strength and age, load-crack mouth opening displacement curves were obtained and the results were analyzed by linear elastic fracture mechanics. The results from the test and analysis showed that critical stress intensity factor and fracture energy increased, and critical crack-tip opening displacement decreased with concrete age from 1 day to 28 days. The obtained fracture parameters at early ages may be used as a fracture criterion and an input data for finite element analysis of concrete at early ages.

• Structural Engineering and Mechanics
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• v.75 no.6
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• pp.685-699
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• 2020

Polygonal finite element provides a great flexibility in mesh generation of crack propagation problems where the topology of the domain changes significantly. However, the control of the discretization error in such problems is a main concern. In this paper, a polygonal-FEM is presented in modeling of crack propagation problems via an automatic adaptive mesh refinement procedure. The adaptive mesh refinement is accomplished based on the Zienkiewicz-Zhu error estimator in conjunction with a weighted SPR technique. Adaptive mesh refinement is employed in some steps for reduction of the discretization error and not for tracking the crack. In the steps that no adaptive mesh refinement is required, local modifications are applied on the mesh to prevent poor polygonal element shapes. Finally, several numerical examples are analyzed to demonstrate the efficiency, accuracy and robustness of the proposed computational algorithm in crack propagation problems.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.839-844
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• 1998

The purpose of this study is to analyze the interface debonding failure on RC beams strengthened with carbon fiber sheet(CFS). The behavior of damaged RC beams strengthened with CFS is analytically investigated using both linear elastic fracture mechanics (LEFM) approach and the finite element method. This study includes the investigation of the separation mode by interface fracture of the strengthening materials due to the interfacial shear and normal stresses.

• Structural Engineering and Mechanics
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• v.6 no.4
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• pp.467-471
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• 1998

A mathematical model is developed to predict the fatigue notch factor of butt welds subject to number of parameters such as weld geometry, residual stresses under dynamic combined loading conditions (tensile and bending). Linear elastic fracture mechanics, finite element analysis, dimensional analysis and superposition approaches are used for the modelling. The predicted results are in good agreement with the available experimental data. As a result, scatters of the fatigue data can be significantly reduced by plotting S-N curve as ($S{\cdot}K_f$) vs. N.