• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.4
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• pp.501-507
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• 2007

In the first part of this study, the moving least squares finite difference method for solving solid mechanics problems was formulated. This second part verified the accuracy, robustness and effectiveness of the developed method through several numerical examples. It was shown that the method gives excellent convergence rate for elasticity problem. The solution process of elastic crack problems showed the easiness in discontinuity modeling and demonstrates the accuracy and efficiency in finding singular stress solution based on adaptive node distribution. The applicability to the engineering problem with abrupt change in displacement and stresses gradient fields is verified through a localization band problem. The developed method is expected to be extended to the various special engineering problems.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.4 no.1
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• pp.37-42
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• 2005

The localization of manufacturing technique development is actualizing for low cost with supplies of display devices. We need more high cutting technique because consumers want flat glasses of various sizes. Recently, most general two methods are normal wheel cutting and laser cutting, but both of them have some faults. First, the wheel cutting has cracks and sharp edges of sections. Second, it is easy for laser cutting to cut curved lines. however, it has thermal damage and low traverse speed. I suggest a new cutting method by high-wave frequency vibration wheel cutting(HFVC), which is good for quality improvement. Vertical cracks and crack depth is observed, after HFVC. When the average of the crack depth is $30{\mu}m$ and the average of the wallner liner depth is $200{\mu}m$, it has the most high quality of the sections in this experiment. As a result, when we consider between the normal wheel cutting method and the HFVC method, the latter has low cracks and good quality.

• Computers and Concrete
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• v.31 no.2
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• pp.151-161
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• 2023

This paper presents an investigation of variables that cause spurious cracking in numerical modeling of concrete fracture. Spurious cracks appear due to the approximate nature of numerical modeling. They overestimate the dissipated energy, leading to divergent results with mesh refinement. This paper is limited to quasi-static loading regime, homogeneous models, cracking as the only nonlinear mode of deformation and cracking only due to tensile loading. Under these conditions, some variables that can be related to spurious cracking are: mesh alignment, ductility, crack band width, structure size, mesh refinement and load increment size. Case studies illustrate the effect of each variable and convergence analyses demonstrate that, after all, load-increment size is the most important variable. Theoretically, a sufficiently small load increment is able to eliminate or at least alleviate the detrimental influence of the other variables. Such load-increment size might be prohibitively small, rendering the simulation unfeasible. Hence, this paper proposes two alternatives. First, it is proposed an algorithm that automatically find such small load increment size automatically, which not necessarily avoid large computations. Then, it is proposed a double simulation technique, in which the crack is forced to propagate through the localization zone.

• Tunnel and Underground Space
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• v.19 no.2
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• pp.158-166
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• 2009

As a basic study for investigating the development of the stress-induced crack in Hoek-Brown rock, a homogenization technique of elastic cracks is proposed. The onset of crack is monitored by Hoek-Brown empirical criterion, while the orientation of the crack is determined by the critical plane approach. The concept of volume averaging in stress and strain component was invoked to homogenize the representative rock volume which consists of intact rock and cracks. The formulation results in the constitutive relations for the homogenized equivalent anisotropic material. The homogenization model was implemented in the standard FEM code COSMOSM. The numerical uniaxial tests were performed under plane strain condition to check the validity of the propose numerical model. The effect of friction between the loading plate and the rock sample on the mode of deformation and fracturing was examined by assuming two different contact conditions. The numerical simulation revealed that the homogenized model is able to capture the salient features of deformation and fracturing which are observed commonly in the uniaxial compression test.

• Geomechanics and Engineering
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• v.18 no.1
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• pp.11-20
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• 2019

The purpose of this study was to propose a new approach for quantifying in situ rock mass damage, which would include a degree-of-damage and the degraded strength of a rock mass, along with its prediction based on real-time Acoustic Emission (AE) observations. The basic approach for quantifying in-situ rock mass damage is to derive the normalized value of measured AE energy with the maximum AE energy, called the degree-of-damage in this study. With regard to estimation of the AE energy, an AE crack source location algorithm of the Wigner-Ville Distribution combined with Biot's wave dispersion model, was applied for more reliable AE crack source localization in a rock mass. In situ AE wave attenuation was also taken into account for AE energy correction in accordance with the propagation distance of an AE wave. To infer the maximum AE energy, fractal theory was used for scale-independent AE energy estimation. In addition, the Weibull model was also applied to determine statistically the AE crack size under a jointed rock mass. Subsequently, the proposed methodology was calibrated using an in situ test carried out in the Underground Research Tunnel at the Korea Atomic Energy Research Institute. This was done under a condition of controlled incremental cyclic loading, which had been performed as part of a preceding study. It was found that the inferred degree-of-damage agreed quite well with the results from the in situ test. The methodology proposed in this study can be regarded as a reasonable approach for quantifying rock mass damage.

• Computers and Concrete
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• v.17 no.3
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• pp.407-421
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• 2016

This paper presents numerical modeling of the structural behavior of CFRP (carbon fiber reinforced polymer) strengthened RC (reinforced concrete) beams under four-point bending. Simulation of debonding at the CFRP-concrete interface was focused, as it is the main failure mode of CFRP strengthened RC beams. Here, cohesive layer was employed to model the onset of debonding, which further helps to describe the post debonding behavior of the CFRP strengthened RC beam. In addition, the XFEM approach was applied to investigate the effects of crack localization on strain field on CFRP sheet and rebar. The strains obtained from the XFEM correlate better to the test results than that from CDP (concrete damaged plasticity) model. However, there is a large discrepancy between the experimental and simulated loaddisplacement relationships, which is due to the simplification of concrete constitutive law.

• Advances in concrete construction
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• v.1 no.2
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• pp.137-149
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• 2013

The first part of this two-part paper discussed some basic considerations on bond strength and its effect on strain localization and plastic deformation capacity of cracked structural concrete, and analytically evaluated the impacts of the hardening behavior of reinforcing steel and concrete quality on the basis of the Tension Chord Model. This second part assesses the impacts of the most frequently encountered construction details of existing concrete structures which may not satisfy current design code requirements: bar ribbing, bar spacing, and concrete cover thickness. It further evaluates the impacts of the additional structure-specific features bar diameter and crack spacing. It concludes with some considerations on the application of the findings in practice and an outlook on future research needs.

• Journal of Industrial Technology
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• v.19
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• pp.197-208
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• 1999

The process of localization of cracks and movement of the fracture process zone(FPZ) was studied using the acoustic-emission(AE) techniques. The rate of AE events and sources of AE activity were studied for mortar and rock specimens loaded in uniaxial compression. A series of transducers could be used to detect and AE activity. Based on the time differences between detection of the event at different transducers, source of AE activity could be detected. The rate of AE events increased sharply before peak load. The highest rate occurred just after peak load was attained. The effective crack length estimated from the modified linear-elastic fracture mechanics seemed consistent with the optical and AE measurements.

• Structural Engineering and Mechanics
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• v.72 no.1
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• pp.19-30
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• 2019

The mechanical behavior of Fiber Reinforced Cementitious Composites (FRCC) under direct shear is studied through experiment and analytical simulation. The cementitious composite considered contains 55% replacement of cement with fly ash and 2% (volume ratio) of short discontinuous synthetic fibers (in the form of mass reinforcement, comprising PVA - Polyvinyl Alcohol fibers). This class of cementitious materials exhibits ductility under tension with the formation of multiple fine cracks and significant delay of crack stabilization (i.e., localization of cracking at a single location). One of the behavioral parameters that concern structural design is the shear strength of this new type of fiber reinforced composites. This aspect was studied in the present work with the use of Push-off tests. The shear strength is then compared to the materials' tensile and splitting strength values.

• Coupled systems mechanics
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• v.7 no.6
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• pp.669-690
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• 2018

This paper deals with numerical modeling of dynamic failure phenomena in rate-sensitive brittle and/or ductile materials. To this end, a two-dimensional continuum viscodamage-embedded discontinuity model, which is based on our previous work (see Do et al. 2017), is developed. More specifically, the pre-peak nonlinear and rate-sensitive hardening response of the material behavior, representing the fracture-process zone creation, is described by a rate-dependent continuum damage model. Meanwhile, an embedded displacement discontinuity model is used to formulate the post-peak response, involving the macro-crack creation accompanied by exponential softening. The numerical implementation in the context of the finite element method exploiting the second-order mid-point scheme is discussed in detail. In order to show the performance of the model several numerical examples are included.