• Journal of Korean Society of Steel Construction
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• v.15 no.2
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• pp.137-145
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• 2003

In this study, direct tensile fatigue tests of the PS bar were performed in terms of diameter, minimum stress level, and maximum stress level. In the static test, the stress - strain curve and ultimate streng th of the PS bar were determined. Results of the fatigue test indicate that the diameter of the PS bar was not influenced by fatigue life. Minimum stress also had quite an influence on the fatigue of the PS bar. Thus, the fatigue characteristic equation was proposed in terms of stress range and minimum stress through statistical process. Strains on specimen that loaded direct tension were measured in the fatigue test, with the secant modulus of elasticity calculated from measured strains. The strain development consisted of three different stages, i.e., rapid increases during the initial fatigue life, uniform increases during the middle stage, and rapid increases until failure. The secant modulus of elasticity decreased during the fatigue life with increasing strain. However, stress level seemed to have no influence on the secant modulus of elasticity.

• Bulletin of the Society of Naval Architects of Korea
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• v.30 no.1
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• pp.49-55
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• 1993

구조물의 피로파괴 현상과 이에 대한 제어기술의 현황을 선형파괴역학적 접근방법을 중심으로 간략히 정리하였다. 현재까지의 연구결과들이 결집되므로써 피로파괴 제어기술 분야의 기초기술은 거의 정립된 단계에 이른 것으로 보여진다. 그러나 구조물의 사용환경은 고응력, 고온 또는 초저온 등으로 더욱 가혹해지는 경향이 있고 고장력강과 복합재료 등 신소재의 사용범위 확대에 의한 경량화 구조설계의 실현, 그리고 생산성 향상을 위한 용접구조물의 보편화 등에 따라 파괴역학의 적용분야는 점차 확대되고 있으며 이를 뒷받침하기 위한 기초 및 응용연구의 필요성도 더 커지고 있다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.9-16
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• 1991

The concept of damage is all-pervasive in structural engineering. It can be considered a state variable and defined to vary from 0(no damage) to 1(failure). Thus, the factor of safety against failure, the most important aspect of a structure, cannot be assessed without evaluating the damageability of a structure under load. It is the objective of the research reported herein to study the behavior of concrete under repeated load applications. Concrete is known to deteriorate under such loading, i.e., it suffers damage of increasing degree. Its response to future loading is a function of the amount of damage sustained during previous load exposures. The same can be said about reinforced concrete members and entire structures, but here we wish to consider only plain concrete and express some of its material properties as functions of the degree of sustained damage. The work described herein is based on the stipulation that the energy dissipation capacity of plain concrete is a material property and the damage accumulates in direct proportion to the degree to which the energy dissipation capacity is being exhausted, in some analogy to both high- and low-cycle failure behavior of materials.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.864-869
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• 1998

파단전 누수균열을 일으키는 가장 주요한 파손 형태는 피로파손으로 사료되어, 하나로 일차냉각계통 배관의 피로파손 가능성에 대한 정량적인 해석을 수행하였다. 하나로 일차냉각계통 배관은 발전로에 비해 저온, 저압이므로 ASME Class 3 로 분류되어 설계 완료되었지만 Class 3 절차에 의해서는 피로해석을 구체적으로 수행할 수 없어, 본 연구의 피로해석에 서는 Class 1 절차에 따라 피크응력강도의 범위를 보수적으로 계산하여 피로누적계수를 산정하였다. 일차냉각계통 배관 중에서 피로파괴 가능성이 가장 큰 것으로 예상되는 고응력 지점을 배관응력해석 결과로부터 선택하여 피로해석을 수행하였다. 선택된 분기관 연결부, 앵커 지점 및 butt 용접부의 피로누적계수들이 모두 1 보다 훨씬 작았으므로 열평창과 OBE 지진하중으로 인한 일차냉각계통 배관의 피로파손 가능성은 매우 희박한 것으로 나타났다. 따라서 냉각재 상실시 파단전 누수균열 개념을 적용하기 위한 일차냉각계통 배관의 피로파손에 대한 배관의 건전성은 충분히 입증된 것으로 판단된다.

• Journal of the Korean earth science society
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• v.30 no.1
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• pp.19-32
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• 2009

Paleostress was interpreted by analyzing the healed microcracks and the secondary fluid inclusions in quartz of the Jurassic granites distributed in the southwestern Ogcheon Folded Belt, South Korea. The most dominant direction of healed microcracks in the study area was oriented $N30^{\circ}W$, and $N70^{\circ}W$ direction was also recognized. The formation temperatures of fluid inclusions were ranged $380-550^{\circ}C$ and the age of healed microcrack formations might have been approximately 166-200 Ma. Comparing the paleostress orientation obtained from the direction of healed microcracks to the formation age of healed microcracks estimated from the secondary fluid inclusions, it is considered that granitic rock body in study area was subject to a maximum horizontal principal stress along the NNW-SSE and WNW-ESE directions in the early Jurassic to middle Jurassic.

• Journal of the Korean Society of Safety
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• v.14 no.1
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• pp.208-215
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• 1999

The creep behavior of a rapidly solidified and consolidated Al-9.45wt%Fe-4.45wt%Cr alloy were investigated in the stress range 40 to 115 MPa and temperature range 300(0.53Tm) to 441$^{\circ}C$(0.66Tm). It is of use to available aerospace and automobile industries for the improved performance of materials used at high temperature. Because Al alloys with improved creep resistance offer the potential for lower weight and reduced costs in aerospace and automobile components (e.g., structural members and engine parts) through the replacement of heavier and more costly materials, the safety in use at high temperature is good. The alloy is characterized by high stress exponents and activation energies for creep, which are greatly dependent on the stress and temperature. Because the creep stress is seen to cause a strongly significant enhancement of coarsening, the coarsening rate of the dispersed particles in all crept specimens is faster than that in isothermally annealed specimens. Dislocations connecting dispersoids are observed more cofrequently in crept specimens with higher stress and lower temperature. The creep strain rates in the power law creep regime were found to be predicted much better by the Shorty and Rosler/Arzt equation with the inclusion of a threshold stress and dislocation detachment mechanism. The dispersoids in this alloy were acting a source of void nucleation that finally leaded to ductile fracture within the grain so called intergranular. Each void was initiated, grown and failed at the dispersoids in the aluminium matrix. Grain boundary accommodation of the slip produced, which result in initiation of the void and then final transgranular fracture. Therefore, it was confirmed that these dispersoids played an important role in the fracture mechanism by the formation of $Al_{13}Fe_4$, $Al_{13}Cr_2$ and $Al_2O_3$.

• Journal of Korean Society of Steel Construction
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• v.23 no.2
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• pp.199-210
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• 2011

The cables in cable-stayed bridges are under high stress and are very sensitive to vibration due to their small section areas compared with other members. Therefore, it is reasonable to evaluate the cable impact factor by taking into account the dynamic effect due to moving-vehicle motion. In this study, the cable impact factors were evaluated via moving-vehicle-load analysis, considering the design parameters, i.e., vehicle weight, cable model, road surface roughness, vehicle speed, longitudinal distance between vehicles. For this purpose, two steel composite cable-stayed bridges with 230- and 540-m main spans were selected. The results of the analysis were then compared with those of the influence line method that is currently being used in design practice. The road surface roughness was randomly generated based on ISO 8608, and the convergence of impact factors according to the number of generated road surfaces was evaluated to improve the reliability of the results. A9-d.o.f. tractor-trailer vehicle was used, and the vehicle motion was derived from Lagrange's equation. 3D finite element models for the selected cable-stayed bridges were constructed with truss elements having equivalent moduli for the cables, and with beam elements for the girders and the pylons. The direct integration method was used for the analysis of the bridge-vehicle interaction, and the analysis was conducted iteratively until the displacement error rate of the bridge was within the specified tolerance. It was acknowledged that the influence line method, which cannot consider the dynamic effect due to moving-vehicle motion, could underestimate the impact factors of the end-cables at the side spans, unlike moving-vehicle-load analysis.