• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.4
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• pp.267-274
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• 2024

Hydrogen embrittlement fracture poses a challenge in ensuring the structural integrity of materials exposed to hydrogen-rich environments. This study advances our comprehension of hydrogen-induced fracture through an integrated numerical modeling approach. In addition, it employs a ductile fracture model named the Gurson-cohesive model (GCM) and hydrogen diffusion analysis. GCM is employed as a fracture model that combines the Gurson model to illustrate the continuum damage evolution and the cohesive zone model to describe crack surface discontinuity and softening behavior. Moreover, porosity and stress triaxiality are considered as crack initiation criteria . A hydrogen diffusion analysis is also integrated with the GCM to account for hydrogen enhanced decohesion (HEDE) mechanisms and their subsequent impacts on crack initiation and propagation. This framework considers the influence of hydrogen on the softening behavior of the traction-separation relationship on the discontinuous crack surface. Parametric studies explore the sensitivity to diffusion properties and hydrogen-induced fracture properties. By combining numerical models of hydrogen diffusion and the ductile fracture model, this study provides an understanding of hydrogen-induced fracture and thereby contributes significantly to the ongoing efforts to design materials that are resilient to hydrogen embrittlement in practical engineering applications.

• Computers and Concrete
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• v.24 no.1
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• pp.51-61
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• 2019

Compressive ability is one of the most important mechanical properties of concrete material. The compressive failure process of concrete is pretty complex with internal tension, shear damage and friction between cracks. To simulate the complex fracture process of concrete at meso level, methodology for meso-structural analysis of concrete specimens is developed; the zero thickness cohesive elements are pre-inserted to simulate the crack initiation and propagation; the constitutive applied in cohesive element is established to describe the mechanism of crack separation, closure and friction behavior between the fracture surfaces. A series of simulations were carried out based on the model proposed in this paper. The results reproduced the main fracture and mechanical feature of concrete under compression condition. The effect of key material parameters, structure size, and aggregate content on the concrete fracture pattern and loading carrying capacities was investigated. It is found that the inner friction coefficient has a significant influence on the compression character of concrete, the compression strength raises linearly with the increase of the inner friction coefficient, and the fracture pattern is sensitive to the mesostructure of concrete.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.11
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• pp.919-926
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• 2014

In this paper, the effect of material properties on fracture behavior was studied using cohesive zone model and extended finite element method. The rectangular tensile specimen with a central inclined initial crack was modeled by plane stress elements. In the CZM modeling, cohesive elements were inserted between every bulk elements in the predicted crack propagation region before analysis, while in the XFEM the enrichment to the elements was added as needed during analysis. The crack propagation behavior was examined for brittle and ductile materials. For thin specimen configuration, wrinkle deformation was accounted for by geometrically nonlinear post-buckling analysis and the effect of wrinkling on the crack propagation was investigated.

• Nuclear Engineering and Technology
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• v.53 no.3
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• pp.974-987
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• 2021

This paper presents ductile fracture simulation of full-scale cracked pipe for nuclear piping materials using the cohesive zone model (CZM). The main objective of this study is to investigate the applicability of CZM to predict ductile fracture of cracked pipes with various crack shapes and under quasi-static/dynamic loadings. The transferability of the traction-separation (T-S) curve from a small-scale specimen to a full-scale pipe is demonstrated by simulating small- and full-scale tests. T-S curves are calibrated by comparing experimental data of compact tension specimens with finite element analysis results. The calibrated T-S curves are utilized to predict the fracture behavior of cracked pipes. Three types of full-scale pipe tests are considered: pipe with circumferential through-wall crack under quasistatic/dynamic loadings, and with 360° internal surface crack under quasi-static loading. Computational results using the calibrated T-S curves show a good agreement with experimental data, demonstrating the transferability of the T-S curves from small-scale specimen.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.337-340
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• 2005

The effect of residual stress on fatigue crack growth was investigated in terms of finite element analysis. Simulations were performed on a CT specimen in plane strain. An interface-cohesive element that accounts for damage accumulation due to fatigue along the notch direction has been used. Numerical results show that fatigue crack growth rate slows down when compressive residual stress field exists in front of the crack tip.

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.79-84
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• 2003

A fictitious crack model was used to analyze fatigue crack growth under the influence of residual stress. In the fictitious crack model, crack is represented in terms of the separation of two adjacent interfaces and the constitutive equation between the separation and traction is assumed. The effect of fatigue loading was included in the constitutive equation by considering damage accumulation in the cohesive zone. To investigate the effect of the residual stress on the fatigue crack growth, we calculated the residual stress distribution due to transient heat flux to the specimen by finite element method. Fatigue crack growth was simulated by the fictitious crack model with repeated loading. The mode-I crack growth rates were compared for the cases with and without the compressive residual stress around the crack tip. It was observed that the mode-I crack growth can be suppressed by compressive residual stress.

• Computers and Concrete
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• v.23 no.4
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• pp.235-243
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• 2019

The discontinuous Galerkin method (DGM) has become widely used as it possesses several qualities, such as a natural ability to dealing with discontinuities. DGM has its major success related to fluid mechanics. Its major importance is the ability to deal with discontinuities and still provide high order of approximation. That is an important advantage when simulating cracking propagation. No remeshing is necessary during the propagation, since the crack path follows the interface of elements. However, DGM comes with the drawback of an increased number of degrees of freedom when compared to the classical continuous finite element method. Thus, it seems a natural approach to combine them in the same simulation obtaining the advantages of both methods. This paper proposes the application of the combined continuous-discontinuous Galerkin method (CDGM) to crack propagation. An important engineering problem is the simulation of crack propagation in concrete structures. The problem is characterized by discontinuities that evolve throughout the domain. Crack propagation is simulated using CDGM. Discontinuous elements are placed in regions with discontinuities and continuous elements elsewhere. The cohesive zone model describes the fracture process zone where softening effects are expressed by cohesive zones in the interface of elements. Two numerical examples demonstrate the capacities of CDGM. In the first example, a plain concrete beam is submitted to a three-point bending test. Numerical results are compared to experimental data from the literature. The second example deals with a full-scale ground slab, comparing the CDGM results to numerical and experimental data from the literature.

• Geomechanics and Engineering
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• v.31 no.4
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• pp.395-407
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• 2022

In this paper, cracks with different angles are prefabricated in rock specimens to study the fracture characteristics of rock based on CT images. The rock specimens are prepared for compression tests according to the standard recommended by ISRM (International Society for Rock Mechanics). The effects of different angles on rock mechanical properties and crack propagation fracture modes are analyzed. Then, based on the cohesive element method and CT images, the relationship between porosity and Young's modulus as well as the fracture property is explored by the numerical modelling. In the modelling, the distribution of Young's modulus is determined by the CT image through the field variable method. The results show that prefabricated cracks reduce the mechanical properties of rock. The closer the angles of the prefabricated crack is, the greater the Young's modulus of the rock sample is. The failure process of each specimen with prefabricated cracks is formed by the initiation and propagation of crack, and the angle of the prefabricated crack will affect the type of extended crack. As part of the numerical model proposed in this paper, the microstructure of rocks is reflected by CT images. The numerical results verify the effectiveness of the cohesive element method in the study of crack propagation for rock. The rock model in this paper can be used to predict engineering disasters such as collapse and landslide caused by rock fracture, which means that the methodology adopted in this paper is comprehensive and important to solve rock engineering problems.

• International journal of steel structures
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• v.18 no.5
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• pp.1754-1760
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• 2018

The present article showcases a temperature dependent cohesive zone model (CZM)-based fi nite element simulation of drop weight tear test (DWTT), to analyse fracture behavior of pipeline steel (PS) at different temperatures. By co-relating the key CZM parameters with known mechanical properties of PS at varying temperature, a temperature dependent CZM for PS is proposed. A modified form of Johnson and Cook model has been used for the true stress-strain behavior of PS. The numerical model, using Abaqus/CAE 6.13, has been validated by comparing the predicted results with load-displacement curves obtained from test data. During steady-state crack propagation, toughness parameters (such as CTOA and CTOD) were found to remain fairly constant at a given temperature. These toughness parameters, however, show an exponential increase with increase in temperature. The present paper offers a plausible approach to numerically analyze fracture behavior of PS at varying temperature using a temperature dependent CZM.

• Computers and Concrete
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• v.1 no.3
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• pp.227-248
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• 2004

A combined experimental-computational study of a double edge-notched stone specimen subjected to tensile loading is presented. In the experimental part, the load-deformation response and the displacement field around the crack tip are recorded. An Electronic Speckle Pattern Interferometer (ESPI) is used to obtain the local displacement field. The experimental results are used to validate a numerical model for the description of fracture using finite elements. The numerical model uses displacement discontinuities to model cracks. At the discontinuity, a plasticity-based cohesive zone model is applied for monotonic loading and a combined damage-plasticity cohesive zone model is used for cyclic loading. Both local and global results from the numerical simulations are compared with experimental data. It is shown that local measurements add important information for the validation of the numerical model. Consequently, the numerical models are enhanced in order to correctly capture the experimentally observed behaviour.