• Proceedings of the Korean Nuclear Society Conference
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• 1996.11b
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• pp.557-562
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• 1996

조사전 및 감시시험시 용접열영향부(heat affected zone, HAZ)의 인성평가를 위해 제작되는 샤피(Charpy) 충격시험편의 노치(notch) 위치에 대하여 현재의 규정에 대한 타당성을 검토하였다. 적용규정은 HAZ 시험편의 노치위치를 용접용융선(fusion line, FL) ＋ 모재측 0.8 mm 로 제한하고 있다. 그러나, 본 연구결과, 이 부위는 다층(multipass) 용접시 후속열이력에 의해 결정립이 미세화되어, 인장강도와 경도 및 충격인성이 모재나 용접부에 비하여 양호하게 나타났다. 한편, FL ＋ 4 mm 이상의 다른 위치에서는 강도와 경도 및 충격인성이 모두 모재와 용접부에 비하여 낮은 값을 보였다. 이는 다층용접에 의한 후속열이력 및 용접후열처리(post weld heat treatment, PWHT)에 의해 금속조직학적 영향을 받은 것으로 판단되었다. 일련의 시험결과로부터, 조 사전 및 감시시험용 샤피충격시험편의 HAZ 에 있어서의 노치위치에 대한 현재의 규정을 재검토할 필요가 있음을 제안하였다.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1818-1823
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• 2007

In this paper, notched bar tensile tests of Inconel 617 were performed at room ($20^{\circ}C$) and elevated ($800^{\circ}C$) temperature. Finite element analyses are also performed. It is found that, at the room temperature, smooth bar tensile test results could be used to simulate notched bar tensile tests. However, at the elevated temperature, notched bar tensile test results can not be simulated from smooth bar tensile test results. Metallurgical examination reveals that strength weakening results from many cavities over the specimens for smooth bar test at the elevated temperature. "True" tensile properties at the elevated temperature is found using FE simulations. It also suggests that cautious should be taken to determine tensile properties of Inconel 617 at elevated temperatures using smooth bar tests.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.322-327
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• 2003

In this study, the single notched specimen which was proposed the previous study was used to evaluate of the transverse tensile property of zircaloy cladding. The single notched specimen has notches which give stress intensity effect, so both FEM and experiment are needed for the same time. Take a coincidence of tensile behavior about both FEM and experiment, then obtain stress and strain from FEM only. The influence of notch was estimated by comparing the result of experimental, FEM. Then the relationship between stress-strain and displacement was evaluated.

• Composites Research
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• v.14 no.1
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• pp.1-7
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• 2001

In this study, damage evaluation of glass fiber reinforced thermoplastic composites was investigated with acoustic emission method. Specimens of 1.7mm thickness laminate were made from PET and 7 layers o171ass fabrics. Notch and impact loading were added to the specimen and normal tensile test and tensile test with the dead load were carried out. AE signal was measured as the functions of notch ratio to the width0 and impact energy in order to find out the correlation between fracture mode and AE parameters. The result has shown that low amplitude of AE signal was due to the microcrack of matrix and its growth, whereas the amplitude in the mid range was the response to the delamination and interfacial separation. In the range of high amplitude above 90dB. the fracture of glass fabric was found. Tensile strength decreased with increasing notch ratio to the width and impact energy because of tile effect or delamination, the cracking of matrix and stress concentration. In proportion to the size of damaged area. AE signal showed its wider range of frequency and energy as well as increased number of hits.

• Tunnel and Underground Space
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• v.9 no.4
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• pp.315-327
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• 1999

Rock fracture mechanics has been widely applied to blasting, hydraulic fracturing, rock slope and many other practical problems in rock engineering. But a measuring method for the fracture toughness of rock, one of the mort important parameters in fracture mechanics as an intrinsic property of rock, has not been yet well established. To obtain mode I rock fracture toughness, the more favorable disc-typed specimens such as CCNBD, SCB, chevron-notched SCB and BDT were used in this study. Rock fracture toughness under mixed-mode and mode II conditions was measured by using the STCA applied to the CCNBD specimen. Size effects such as specimen thickness, diameter and notch length on fracture toughness were investigated. From the mixed-mode results, fracture envelops were obtained by applying various regression curves. The mixed-mode results were also compared with three mixed-mode failure criteria. In each fracture toughness test, acoustic emission was measured to get the data for determining the load levels of different crack propagation patterns.

• Tunnel and Underground Space
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• v.26 no.5
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• pp.396-408
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• 2016

Rock fracture mechanics has been widely applied to various fields of rock and civil engineering. But most researches covered mode I behavior, though mode II behavior is dominant in rock engineering. Until now, there is only one ISRM suggested method for mode II toughness of rock. A new SCC (Short Core in Compression) mode II toughness test method was developed considering 1) application of confining pressure, 2) easiness of notch creation, 3) utilization of existing equipment, 4) simple test procedure. The stress intensity factors were determined by 3D finite element method considering line and distributed loading conditions. The tests with granite specimens were carried out using MTS 815 rock test system with a loading rate of 0.002 mm/s. The mean value of mode II fracture toughness of granite showed $2.33MPa{\sqrt{m}}$. Mode I toughness of the same granite was $1.12MPa{\sqrt{m}}$, determined by Brazilian disk test and $K_{IIC}/K_{IC}=2.08$. The smooth fracture surface with rock powder formation also supported mode II behavior of SCC method. The SCC method can be used for the determination of mode II fracture toughness of rocks based on the current results.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.5
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• pp.429-438
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• 2003

The effects of fiber orientation on acoustic emission(AE) characteristics have been studied for the unidirectional and satin-weave, continuous glass-fiber reinforced plastic(UD-GFRP and SW-GFRP) tensile specimens. Reflection and transmission optical microscopy was used for investigation of the damage zone of specimens. AE signals were classified as different types by using short time fourier transform(STFT) : AE signals with high intensity and high frequency band were due to fiber fracture, while weak AE signals with low frequency band were due to matrix and interfacial cracking. The feature in the rate of hit-events having high amplitudes showed a process of fiber breakages, which expressed the characteristic fracture processes of individual fiber-reinforced plastics with different fiber orientations and with different notching directions. As a consequence, the fracture behavior of the continuous GFRP could be monitored as nondestructive evaluation(NDE) through the AE technique.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.10
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• pp.140-148
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• 2019

Large cast iron structures are used in casings and pipes in shipsand chemical plants. Broken parts in the casings and pipescan result in failures even when stresses are below the yield strength of the part's materials. Fatigue failure of a large cast iron structure is inevitable due to the design constraints and low reliability of the material strength. A small structure can be repaired by welding, but a large structure cannot because it cannot be preheated slowly and uniformly. This study shows that a large structure can be repaired by a cold joint method using a crack repair screw. Large cast iron structures were manufactured by GC 300, and their design stress is below 3.5 MPa. The tensile strength on notched specimens repaired by crack repair screws was 8.2 MPa. Therefore, the safety factors of structures repaired by crack repair screws have a value above 2.3 and are considered to be high values.