• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.820-825
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• 1994

It is improtant to examine life or crack propagation behavior of structures because of its safety evaluation. The purpose of this study is to investigate the effect of crack-crack interaction to evaluate fatigue life and crack behavior. In this study, the behavior of the interaction of two cracks is studied by experiment. The vertical distance of two cracks is varied to make different interaction stress field. In addition, the effect of plastic zone is considered to examine crack propagation path and propagation rate.

• Geomechanics and Engineering
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• v.20 no.5
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• pp.421-432
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• 2020

Cutting of rocks is very common encountered in tunneling and mining during underground excavations. A deep understanding of rock-tool interaction can promote industrial applications significantly. In this paper, a distinct element method based approach, PFC^3D, is adopted to simulate the rock cutting under different operation conditions (cutting velocity, depth of cut and rake angle) and with various tool geometries (tip angle, tip wear and tip shape). Simulation results showed that the cutting force and accumulated number of cracks increase with increasing cutting velocity, cut depth, tip angle and pick abrasion. The number of cracks and cutting force decrease with increasing negative rake angle and increase with increasing positive rake angle. The numerical approach can offer a better insight into the rock-tool interaction during the rock cutting process. The proposed numerical method can be used to assess the rock cuttability, to estimate the cutting performance, and to design the cutter head.

• Structural Engineering and Mechanics
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• v.34 no.4
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• pp.475-490
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• 2010

It is the intention of this study to synthesize the effects of double-edge cracks on the dynamic characteristics of a beam. The stiffness matrix is first determined for a Timoshenko beam containing two same-line edge cracks. The presented model is then developed for elements with two parallel double-sided cracks, considering the interaction between the stress fields of adjacent cracks. Finally, a finite element code is implemented, to examine the influence of depth and location of double cracks, on the natural frequencies of the damaged system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.5 s.236
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• pp.754-761
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• 2005

The 40\% of wall thickness criterion which has been used as a plugging rule of steam generator tubes is applicable only to a single cracked tube. In the previous studies performed by authors, several global failure prediction models were introduced to estimate the failure loads of steam generator tubes containing two adjacent parallel axial through-wall cracks. These models were applied for thin plates with two parallel cracks and the COD base model was selected as the optimum one. The objective of this study is to verify the applicability of the proposed optimum global failure prediction model for real steam generator tubes with two parallel axial through-wall cracks. For the sake of this, a series of plastic collapse tests and finite element analyses have been carried out fur the steam generator tubes with two machined parallel axial through-wall cracks. Thereby, it was proven that the proposed optimum failure prediction model can be used as the best one to estimate the failure load quite well. Also, interaction effects between two adjacent cracks were assessed through additional finite element analyses to investigate the effect on the global failure behavior.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.67-70
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• 2008

This study is to analyzes the global behavior of frame structures with local cracks in structural members by frame analysis, using the stiffness matrix of cracked frame element. This local compliance is utilized to derive the stiffness matrix of the cracked frame element and the effects of interaction among multiple cracks are also examined. The proposed technique is applied to frame structures with local cracks. Analysis results confirm the possibility of quantitative analysis of a structure damaged with local cracks and the feasibility of the technique as a tool for analyzing the global behavior of frame structures, reflecting effects of local cracks.

• Structural Engineering and Mechanics
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• v.10 no.1
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• pp.81-92
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• 2000

This study is an investigation of the effect of cracks on the dynamical characteristics of a cantilever beam, having multiple open-edge transverse cracks. The flexibilities due to crack have been identified for several crack depths and locations. In the study the finite element method and component mode synthesis methods are used. Coupling the components is performed by a flexibility matrix taking into account the interaction forces. Each component is modelled by cantilever beam finite elements with two nodes and three degrees of freedom at each node. The results obtained lead to conclusion that, by using the drop in the natural frequencies and the change in the mode shapes, the presence and nature of cracks in a structure can be detected. There is some counter-evidence, however, that the effects due to multiple cracks may interact to make detection more difficult than for isolated cracks.

• Geomechanics and Engineering
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• v.14 no.1
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• pp.29-42
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• 2018

This paper presents the results of an empirical study in which square rock-like blocks containing two parallel pre-existing rough non-persistent joints were subjected to uniaxial compression load. The main purpose of this study was to investigate uniaxial compressive strength and deformation modulus of jointed specimens. Response Surface Method (RSM) was utilized to design experiments and investigate the effect of four joint parameters, namely joint roughness coefficient (JRC), bridge length (L), bridge angle (${\gamma}$), and joint inclination (${\theta}$). The interaction of these parameters on the uniaxial compressive strength (UCS) and deformation modulus of the blocks was investigated as well. The results indicated that an increase in joint roughness coefficient, bridge length and bridge angle increased compressive strength and deformation modulus. Moreover, increasing joint inclination decreased the two mechanical properties. The concept of 'interlocking cracks' which are mixed mode (shear-tensile cracks) was introduced. This type of cracks can happen in higher level of JRC. Initiation and propagation of this type of cracks reduces mechanical properties of sample before reaching its peak strength. The results of the Response Surface Methodology showed that the mutual interaction of the joint parameters had a significant influence on the compressive strength and deformation modulus.

• Interaction and multiscale mechanics
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• v.5 no.3
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• pp.169-185
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• 2012

The concrete bridge is likely to produce fatigue cracks during long period of service due to the moving vehicular loads and the degeneration of materials. This paper deals with the time-frequency analysis of a coupled bridge-vehicle system. The bridge is modeled as an Euler beam with breathing cracks. The vehicle is represented by a two-axle vehicle model. The equation of motion of the coupled bridge-vehicle system is established using the finite element method, and the Newmark direct integration method is adopted to calculate the dynamic responses of the system. The effect of breathing cracks on the dynamic responses of the bridge is investigated. The time-frequency characteristics of the responses are analyzed using both the Hilbert-Huang transform and wavelet transform. The results of time-frequency analysis indicate that complicated non-linear and non-stationary features will appear due to the breathing effect of the cracks.

• Progress in Superconductivity and Cryogenics
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• v.22 no.3
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• pp.7-12
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• 2020

Electromechanical properties of REBCO CC tapes are known to be limited by defects (cracks) that form in the brittle REBCO layer. These defects could be inherently acquired during the CC tapes' manufacturing process, such as slitting, and which can be initiated at the CC tapes' edges. If propagated and long enough, they are believed to cause critical current degradation and can substantially decrease the delamination strength of CC tapes. Currently, commercially available CC tapes from various manufacturers utilize different growth techniques for depositing the REBCO layers on the substrates in their CC tapes preparation. Their epitaxial techniques, unfortunately, cannot perfectly avoid the formation of particles, in which sometimes acts as current blocking defects, known as outgrowths. Collective research regarding the composition, size, and formation of these particles for various CC tapes with different deposition techniques are particularly uncommon in a single study. Most importantly, these particles might interact in one way or another to the existing cracks. Therefore, systematic investigation on the interactions between the cracks' development mechanism and particles on the REBCO superconducting layers of practical CC tapes are of great importance, especially in the design of superconducting devices. Here, a proper etching process was employed for the CC tapes to expose and observe the REBCO layers, clearly. The scanning electron microscope, field emission scanning microscope, and energy-dispersive x-ray spectroscopy were utilized to observe the interactions between cracks and particles in various practical CC tapes. Particle compositions were identified whether as non-superconducting or superconducting and in what manner it interacts with the cracks were studied.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.10 s.253
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• pp.1255-1260
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• 2006

To maintain the structural integrity of steam generator tubes, 40% of wall thickness plugging criterion has been developed. The approach is for the steam generator tube with single crack, so that the interaction effect of multiple cracks can not be considered. Although, recently, several approaches have been proposed to assess the integrity of steam generator tube with two identical cracks whilst actual multiple cracks reveal more complex shape. In this paper, the coalescence pressure of steam generator tube containing multiple cracks of different length is evaluated based on the detailed 3-dimensional (3-D) elastic-plastic finite element (FE) analyses. In terms of the crack shape, two collinear axial through-wall cracks with different length were considered. Furthermore, the resulting FE coalescence pressures are compared with FE coalescence pressures and experimental results for two identical collinear axial through-wall cracks to quantify the effect of crack length ratio on failure behavior of steam generator tube with multiple cracks. Finally, based on 3-D FE results, the coalescence evaluation diagrams were proposed.