• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.10b
• /
• pp.51-54
• /
• 2003

Internal defects such as chevron crack occasionally occur in the process of cold extrusion or cold drawing. It is known that the existence and property of inclusion greatly influences the generation of the internal crack. However, in the plastic working field, research about the effect of the inclusion on the fracture is not theoretically analyzed. This paper describes effects of the physical property of inclusion on the internal fracture generation in the process. Prediction of fracture was evaluated by critical damage value calculated by the equation of Cockcroft & Latham and its change by the inclusion physical property such as size and stiffness was investigated.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.05b
• /
• pp.417-420
• /
• 2006

Recently, the attention is paid to the problem of thermal crack by hydration heat according to the increase of high strength and mass concrete structures. At this point, various research has been carried out for the control of hydration heat in high strength and mass concrete. As a part of the research, it was investigated application of hydration heat reduction agent (HR) for the control of thermal crack by hydration heat in this study. To investigate the application, it was selected HR which can reduce hydration heat of concrete with effect in series I and II. Also, it was investigated the characteristics of hydration heat generation of low heat concrete using HR with binder types in seriesIII.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2001.10a
• /
• pp.111-115
• /
• 2001

Thermo-acoustic emission (AE) from composite laminates under the repetitive thermal cyclic loads have been quantitatively analyzed in consideration of AE source mechanisms. The repetitive thermal load brought about a large reduction, i.e. an exponential decrease in AE total ringdown counts and AE amplitudes. It was thought that generation of thermo-AE during the first thermal cycle was not caused by crack propagation but by secondary microfracturing due to abrasive contact between crack surfaces.

• Current Photovoltaic Research
• /
• v.2 no.1
• /
• pp.8-13
• /
• 2014

ZnSe/$Zn_3P_2$ heterojunctions with a substrate configuration were fabricated using a series of cost-effective processes. Thin films of ZnTe and $Zn_3P_2$ were successively grown by close-spaced sublimation onto Mo-coated glass substrates. ZnSe layers thinner than 100nm were formed by annealing the $Zn_3P_2$ films in selenium vapor. Surface selenization generated a high density of micro-cracks which, along with voids, provided shunt paths and severely deteriorated the diode characteristics. Annealing the $Zn_3P_2$ film at $300^{\circ}C$ in a $ZnCl_2$ atmosphere before surface selenization produced a dense microstructure and prevented micro-crack generation. The mechanism of micro-crack generation by the selenization was described and the suppression effect of $ZnCl_2$ treatment on the micro-crack generation was explained. ZnSe/$Zn_3P_2$ heterojunctions with low leakage current ($J_0$ < $1{\mu}A/cm^2$) were obtained using an optimized surface selenization process with $ZnCl_2$ treatment. However, the series resistance was very high due to the presence of an electrical barrier between the ZnTe and $Zn_3P_2$ layers.

• Corrosion Science and Technology
• /
• v.9 no.2
• /
• pp.57-66
• /
• 2010

Since nuclear power plants are being operated under high temperature and high pressure, on-line monitoring technique to detect corrosion could be more effective than off-line method in shut-off period. In this operating condition, electrochemical noise method may be suitable to monitor the corrosion. This paper aims the analysis on the relation between the cracking and electrochemical noise signal of Alloy 600 under U-bending. When electrochemical noise monitoring technique was used during SCC test, it was judge to be obvious that if cracks generate, its generation can be detected by electrochemical current noise. Cracking-related noise was defined as the noise showing 5~10 times greater than the average value of background noise bands. On the base of crack noise, crack initiation time was determined. From SCC test and electrochemical noise monitoring in $25^{\circ}C$, 0.1 M $Na_2S_4O_6$ solution (Reverse U-Bended Alloy 600 SE+), average crack initiation time was obtained as 9,046 seconds and from its initiation time, it could be defined that net crack propagation rate is the crack length divided by ${\Delta}T$(= total test period - crack initiation time). Therefore, average net crack propagation rate was obtained to be $1.18{\times}10^{-9}\;m/s$.

• Korean Journal of Materials Research
• /
• v.3 no.2
• /
• pp.166-174
• /
• 1993

Abstract The crack resistance of PSG(Phosphosilicate Glass) and PE-SiN(Plasma Enhanced CVD S${i_2}{N_4}$)films deposited on aluminium thin films on Si substrate was analyzed in this study. PSG was deposited by AP-CVD and PE- SiN by PE-CVD. All the films underwent repeated heat cycles at 45$0^{\circ}C$for 30 min. Crack formation and development were examined between each heat cycle. The crack behavior was found to be closely related to the stresses in the films. The stress induced by the difference in thermal expansion behavior between the passivation layers and underlying aluminum film may cause the crack. Crack resistance decreases as the thickness of PSG films increases due to the high tensile stress of the films. Phosphorus in the PSG films releases tensile stress and consequently the stress of the films tends to show compressive stress. As a result, crack resistance increased as the concentratin of P in the PSG films increased. Crack resistance in the PE-SiN films also increased with compressive stress. An experimental model to predict crack generation in the PSG and PE-SiN films during heat cycle was suggested.

• Nuclear Engineering and Technology
• /
• v.47 no.1
• /
• pp.102-114
• /
• 2015

Background: A technique developed to produce artificial intergranular stress corrosion cracks in structural components was applied to thick, forged alloy 600 base and alloy 182 weld metals for use in the qualification of nondestructive examination techniques for welded components in nuclear power plants. Methods: An externally controlled procedure was demonstrated to produce intergranular stress corrosion cracks that are comparable to service-induced cracks in both the base and weld metals. During the process of crack generation, an online direct current potential drop method using array probes was used to measure and monitor the sizes and shapes of the cracks. Results: A microstructural characterization of the produced cracks revealed realistic conformation of the crack faces unlike those in machined notches produced by an electrodischarge machine or simple fatigue loading using a universal testing machine. Conclusion: A comparison with a destructive metallographic examination showed that the characteristics, orientations, and sizes of the intergranular cracks produced in this study are highly reproducible.

• Structural Engineering and Mechanics
• /
• v.19 no.6
• /
• pp.639-652
• /
• 2005

In this paper, a full-scale K-joint specimen was tested to failure under cyclic combined axial and in-plane bending loads. In the fatigue test, the crack developments were monitored step by step using the alternating current potential drop (ACPD) technique. Using Paris' law, stress intensity factor, which is a fracture parameter to be frequently used by many designers to predict the integrity and residual life of tubular joints, can be obtained from experimental test results of the crack growth rate. Furthermore, a scheme of automatic mesh generation for a cracked K-joint is introduced, and numerical analysis of stress intensity factor for the K-joint specimen has then been carried out. In the finite element analysis, J-integral method is used to estimate the stress intensity factors along the crack front. The numerical stress intensity factor results have been validated through comparing them with the experimental results. The comparison shows that the proposed numerical model can produce reasonably accurate stress intensity factor values. The effects of different crack shapes on the stress intensity factors have also been investigated, and it has been found that semi-ellipse is suitable and accurate to be adopted in numerical analysis for the stress intensity factor. Therefore, the proposed model in this paper is reliable to be used for estimating the stress intensity factor values of cracked tubular K-joints for design purposes.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.32 no.4
• /
• pp.376-387
• /
• 2012

Based on the nonlinear spring model coupled with perturbation method, 2nd harmonic waves generated by oblique incident ultrasound on nonlinear crack interface were calculated and investigated. Reflected and transmitted waves from the interface were determined and analyzed at various angle of incidence for the cracks with different interfacial stiffness in order to estimate the 2nd harmonic generation of incident ultrasound. It was shown in computer simulation that the 2nd harmonic components changed much with the increase of incidence angle in both reflected and transmitted wave, but became very small when the incident angle approached toward 90 degree. It can be concluded that the 2nd harmonic component of reflected wave has a meaningful amplitude as much as the transmitted 2nd harmonic wave from partly closed crack.

• Economic and Environmental Geology
• /
• v.52 no.6
• /
• pp.587-593
• /
• 2019

This study were subjected to accelerated weathering test under freeze-thaw and pressure conditions to observe initiation and propagation of cracks using CLSM. Applied stress was set at 50 MPa, 55 MPa, 70 MPa for 3 samples each by using compressor and freeze-thaw experiment was conducted while samples maintained that condition. In freeze-thaw experiments, a temperature range was set to -20~40℃ which was 1 cycle for 6 hours. The freeze-thaw cycle was composed of time which reached to set temperature for 1 hour and holding time for 2 hours. On the basis of this cycle, surface of samples was observed by CLSM after each 20 freeze-thaw cycle. From this research, according to increase freeze-thaw cycle, there were 7, 10, 19 each cracks and High pressured sample's accumulate length was longer than low pressured sample's. High pressured sample's crack velocities were also faster than low pressured sample's which were calculated by accumulate length and freeze-thaw cycle.