• Journal of Mechanical Science and Technology
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• v.17 no.6
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• pp.796-804
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• 2003

The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service failures occur from cracks subjected to mixed-mode loading. Hence, it is necessary to evaluate the fatigue behavior under mixed-mode loading. Under mixed-mode loading, not only the fatigue crack propagation rate is of importance, but also the crack propagation direction. In modified range 0.3$\leq$a/W$\leq$0.5, the stress intensity factors (SIFs) of mode I and mode II for the compact tension shear (CTS) specimen were calculated by using elastic finite element analysis. The propagation behavior of the fatigue cracks of cold rolled stainless steels (STS304) under mixed-mode conditions was evaluated by using K$\_$I/ and $_{4}$ (SIFs of mode I and mode II). The maximum tangential stress (MTS) criterion and stress intensity factor were applied to predict the crack propagation direction and the propagation behavior of fatigue cracks.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.3
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• pp.120-126
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• 2006

In this paper, we investigated the characteristics of fatigue fracture on TB(Tailored Blank) weldment by comparing the fatigue crack propagation characteristics of base metal with those of TB welded sheet used for vehicle body panels. We also investigated the influence of center crack on the fatigue characteristic of laser weld sheet of same thickness. We conducted an experiment on fatigue crack propagation on the base metal specimen of 1.2mm thickness of cold-rolled metal sheet(SPCSD) and 2.0mm thickness of hot-rolled metal sheet(SAPH440) and 1.2+2.0mm TB specimen. We also made an experiment on fatigue crack propagation on 2.0+2.0mm and 1.2+1.2mm thickness TB specimen which had center crack. The characteristics of fatigue crack growth on the base metal were different from those on 1.2+2.0mm thickness TB specimen. The fatigue crack growth rate of the TB welded specimens is slower in low stress intensity factor range$({\Delta}K)$ region and faster in high ${\Delta}K$ region than that of the base metal specimens.

• Journal of Ocean Engineering and Technology
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• v.14 no.1
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• pp.23-28
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• 2000

The fatigue crack growth behavior of the cold-rolled STS 304 steel developed for membrane material of LNG storage tank was examined experimentally at 293K, 153K and 111K. The fatigue crack growth rate(do/dN) tends to increase as the stress ratio (R) increases over the testing temperature when compared at the same stress intensity factor range($\Delta$K). The effect of R on do/dN is more explicit at low temperatures than at room temperature. The resistance of fatigue crack growth at low temperatures is higher compared with that at room temperature which is attributed to the extent of strain-induced martensitic transformation at the crack tip. The temperature dependence of fatigue crack growth resistance is gradually vanished with an increase in $\Delta$K which correlates with a decreasing fracture toughness with decreasing temperature. Fractographic examinations reveal that the differences of the fatigue crack growth characteristics between room and low temperature are mainly explained by the crack closure and the strengthening due to the martensitic transformation.

• Journal of Welding and Joining
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• v.6 no.3
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• pp.27-36
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• 1988

In fabrication of various welded structures made of high strength steels, the occurence of hydrogen assisted cracking and embrittlement in HAZ is prime importance. The present work was carried out to clarify the effect of chemical compositions, especially B and/or Ti addition on the cold cracking susceptibility and HAZ embrittlement in low crabon equivalent steel. Tests results showed that the addtio of optimum boron content in steel with low Pem value i.e., below 0.20 % was the best way to improve the weldability as well as the mechanicla properties of $60kg/mm^2$ grade quenched and tempered high strength steels.

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

• Journal of the Korean Wood Science and Technology
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• v.17 no.1
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• pp.55-68
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• 1989

This experiment was carried out to investigate the crack of coated Nitrocellulose Lacquer on flatand edge-grained boards of Quercus acutissima, ring-porous wood, and Betula platyphylla var. japonica, diffuse-porous wood, by variations of moisture contents at 7, 13 and 21%. Cold check system was used as an accelerating method for crack development, in which one cycle of the system consisted of 10 replications of each unit cycle, $60^{\circ}C$ for 4hr followdd by $-20^{\circ}C$ for 4hr. The analysis of Nitrocellulose Lacquer characteristics was made by means of water permeation measurement, F.T.I.R. spectroscopy, N.M.R. spectroscopy, gel permeation chromatography, gas chromatography, and D.S.C. The results obtained were as follows: 1. The number of cracks increased with the increasing moisture content of board. 2. The crack of coated film on flat-grained board was fewer in number than on edge-grained board. 3. The crack occurred in Quercus acutissima was more numerous on edge-grained board but less frequent on flat-grained board compared with that in Betula platyphylla var. japonica, respectively. 4. The cold crack vertically developed to the grain both in Quercus acutissima and Betula platyphylla var. japonica. 5. Water permeability in intermediate coated film was lower than in under and top coated film, but the difference was not confirmed between under and top coated film.

• Proceedings of the KWS Conference
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• 1998.10a
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• pp.313-316
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• 1998

• Proceedings of the KWS Conference
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• 2006.05a
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• pp.109-111
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• 2006

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.348-350
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• 2007

• Journal of Biosystems Engineering
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• v.33 no.3
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• pp.167-172
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• 2008

The objective of this study was to investigate the adequate storage method that was able to maintain the high quality of rough rice according to storage methods and period. The quality change of the rough rice during the storage period was evaluated by storage method such as cooling bin using winter cold air, ordinary temperature bin, freezing, refrigeration and indoor storage. Moisture content, brown rice whiteness, hardness, crack ratio and germination ratio were measured in this study. Moisture content of rough rice stored in cooling bin using winter cold air and ordinary temperature bin were decreased by 0.07% and 0.42%, respectively, which were lower than the other storage method. The hardness of brown rice increased in order of storage method such as winter cooling bin, normal bin, freezing storage, refrigeration storage and indoor storage. Crack ratio by indoor and ordinary temperature bin storage were increased by 2.68% and 3.63%, respectively, whereas cooling bin using winter cold air, refrigeration and freezing storage showed below 1.0%. The highest germination rate was found in cooling bin using winter cold air. As a result, cooling bin using winter cold air can be evaluated for the adequate storage method of rough rice.