• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1997.04a
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• pp.164-169
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• 1997

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.507-510
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• 2001

Brittle failure mechanism has been well known as growth of initial micro-damage, that causes macro crack and failure in the end. Several precise criteria are suggested recently, based on experiments values in a whole load range. Among them, Mohr-Coulomb's criterion is used widely these days, but it has a big error compared with the real failure behavior since it does not show reciprocal actions of stresses. In this study, a new brittle failure criterion is proposed, which includes the effects of brittle damage evolution by taking a brittle damage parameter specifically. Comparisons between the proposed model and the previous ones are also given.

• Journal of Korean Society of Steel Construction
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• v.10 no.1 s.34
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• pp.85-99
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• 1998

This paper describes an experimental study to examine collapse causes of the lifting cable due to brittle failure of an fitting anchor under the lifting works. Also, in this study an collapse mechanism that was obtained from stress analysis was compared with an actual collapse procedure. Fractographical analysis as well as chemical component test, tension test and Charpy V-Notch impact test for the fractured steel members were carried out. And then, its results were compared with that of normal steel members. Circumferential surface flaws were developed at internal facets of the fitting anchor before tensile stress occurred. Hence, a higher stress than nominal stress was occurred at flaws by stress concentration at the crack tip. Also, stress intensity factor of members increased by crack size of the potential flaws. Because the stress intensity factor at the crack tip was greater than critical values(fracture toughness), brittle fracture occurred under the lifting works. It is judged that the main collapse of the lifting cable is due to brittle fracture of the fitting anchor.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.97-104
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• 2007

An investigation has been made on the relationship between characteristics of Acoustic Emission (AE) signal in welding flaw and the stress corrosion defect in-service for the high pressure pipe steel. In order to tackle the problem of welding flaw in high pressure pipe, specimens were made by the aid of the application of both corrosion liquid usage and a quenching method after local heating. The amplitude of signal was $60{\sim}75\;dB$ in the territory which is suspected for defect, and the specimens which only have welding flaw showed gradients of 0.034, 0.034, 0.035. Moreover, there is a certain increase in gradient even though the differences are very slight. That is, corrosion specimens showed new gradients of 0.040, 0.039, 0.041 which put welding flaw and corrosion mechanism together. After pressurizing 3 minutes, AE signal has been detected from welding flaw easily in each part of the section. It is possible to predict the occurrence and also prevent the damage of stress corrosion crack which has characteristics of cleavage fracture.

• Journal of the KSME
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• v.19 no.4
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• pp.291-294
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• 1979

본 강좌에서는 취성파괴의 사고와 그 원인, 재료의 강도와 구조설계, 재료의 이상강도와 결함 크 랙의 변형과 파괴인성의 개요, 탄성파괴역학의 개요 등을 기술하겠다.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.3
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• pp.40-46
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• 2001

An integrated analysis for the thermo-elastic deformation, fatigue, wear and brittle damage evolution of the shrink-fitted die with multi stress-ring of dissimilar materials is presented. A simple numerical algorithm for the moving elastic boundaries characterizing the contacts of the insert and multi stress-rings is presented. The initial stress distribution in the die due to shrink-fit is considered and the traction at the die surface contacting with the work piece is obtained by analyzing the elasto-plastic deformation of work piece. Elastic analysis of the separate-type die is performed and then the evolution of brittle damage, wear and fatigue life are predicted. This integrated analysis is applied to the extrusion die with two layers of stress-rings and the results are discussed in detail.

• The Journal of Engineering Geology
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• v.9 no.3
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• pp.243-251
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• 1999

Granitic rock, by its nature, contains numerous micro-discontinuities including grain boundary, microcracks, microcavities and mineral cleavages. The brittle fracture of rock is a progressive procedure in which the failure occurs with prior microcracking. In this paper, initiation, propagation and interaction of microcracks are considered to be the dominant, controlling micromechanisms of macroscopic failure. The authors show a few patterns of microcrack initiation and propagation by using sequential photographs of water-saturated granite taken under triaxial compressive state. The failure process was observed directly and continuously by a newly developed triaxial compressive test system.

• Journal of the KSME
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• v.28 no.4
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• pp.322-327
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• 1988

용접구조물의 파괴는 단순 역학적인 차원을 넘어서 재료공학적 검토와 시공상의 각종 변수를 고려해야만 정확하게 이해할 수가 있으며 방지할 수 있다. 용접도중에 발생되는 미소파괴(균열) 는 적절한 재료의 선정과 적당한 시공법으로 해결할 수 있으며, 사용도중 발생되는 거시적 파 괴는 사용조건에 유의하고 발생된 용접결함을 제거할 수 있다면 방지할 수 있다. 결론적으로 용접구조물의 파괴는 용접도중에 결함을 발생시키지 않는 방법으로 방지하는 것이 가장 효과적 이기 때문에 시공법의 선정 및 실시는 충분한 검토와 주의가 필요하다. 용접품의 파괴현상을 해석하는 데는 현재까지 잘 연구되어진 각종 파괴역학적 및 피로역학적 해석이 적용될 수 있 으나 용접부의 불균일한 조직형성에 따른 기계적 성질의 불균일성과 잔류응력 등을 추가로 고 려해야 하는 것이 약간 다를 뿐이다. 현재 용접부의 취성 및 피로파괴에 대한 다방면의 연구가 활발하게 이루어지고 있는 형편이며 향후에는 용접구조물의 수명예측을 포함한 가족 파괴해석 기술이 확립될 것으로 생각된다.

• Journal of Welding and Joining
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• v.5 no.1
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• pp.34-41
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• 1987

To explore the possible application of thermal analysis technique as a probe for finding weld defects, Hydrogen trapping phenomena in Heat Affected Zone (HAZ) of the AISI 5160 spring steel were investigated. HAZ was divided into five parts, which were used as thermal analysis specimens. Two types of trap sites were found in HAZ, ferrite/cementin interface and microvoid. The thermal analysis peak due to the ferrite/cementite interface increased its height toward the weld deposit. The thermal analysis peak due to the microvoid was the highest where the grain size was the smallest. The correspondence between the cold cracking and hydrogen trap nature is also discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.220-223
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• 1998

The failure of die often occurs as a result of growth of microcracks - referred as a brittle damage. In this study, an analysis of brittle damage evolution cupled with elastic finite element analysis of die deformation is presented. A local transformation from the tractions of a workpiece mesh to those of a die mesh is developed. The brittle damage is defined as a vector considering the shape of common microcracks in the brittle metals and the damage function suggested by Krajcinovic is utillized. Applications of the proposed model to modeling damage evolution in the extrusion die and forging die are given and the characteristics of brittle damage evolution in die are in detail examined.