• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.23 no.5
• /
• pp.483-491
• /
• 2010

In this paper, ${\Delta}J$-integral is used to analyze fatigue crack growth of viscoelastic material. Using analytical integral value, the J-integral is calculated. So, reduction of calculation time and increase of accuracy are made possible. The stress intensity factor is calculated using the finite element method code. In difference with existed fatigue crack analysis using ${\Delta}K$, we were successfully able to analyze various load amplitude and the fatigue crack of load cycle only with two fatigue crack growth parameters and creep compliance. The analysis gives N-${\alpha}$ curve for simulation of crack growth, and the curve almost corresponds with test results.

• Journal of Korean Society on Water Environment
• /
• v.27 no.6
• /
• pp.885-895
• /
• 2011

The purpose of this study was evaluated on achievement of the Target water quality (TWQ) with Load Duration Curve (LDC) as well as materials collected through the implementation of Total Maximum Daily Load (TMDL), targeting 41 unit watersheds in the Nakdong River Basin in korea, and examines the adequacy of the LDC method to evaluate the TWQ by comparing methods through current regulations. It aims to provide basic materials for TMDL development in Korea. This determination resulted from the fact that the measured data placed on the LDC mean that they are beyond TWQ in a certain condition of water flow when actually measured load values were displayed in a form of LDC. In addition to water quality surveys, it is considered that information on the level of damage in a water body by water flow grade can be utilized as a basic material to identify compliance with the total admitted quantity, and establish rational plans to improve water quality. This information helps in the identification of the degree of damage in water quality according to water flow.

• Journal of the Korean Society of Safety
• /
• v.14 no.3
• /
• pp.18-24
• /
• 1999

This paper were performed to evaluate the elastic-plastic fracture toughness $J_IC$ by the unloading compliance method for 1/2 CT specimen of A5083-H112 aluminum alloy. A modified offset method for negative crack growth effect is presented and compared with Voss offset method. We found that the modified offset method presented can be used efficiently for a determination of the stable crack onset. The $J_IC$ by Voss offset method can be overestimated, but the suggested offset method showed a high reliability within 5% of tolerence from the results by the multi-specimen method.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.33 no.12
• /
• pp.1375-1382
• /
• 2009

The objective of this paper is to apply the load ratio method to the measurement of the crack length of the real scale pipe specimen. The load ratio method was modified and finite element analyses were performed to derive the relationship between the normalized compliance and the normalized crack length for the pipe specimen. In order to measure the crack length, the direct current potential drop method and the modified load ratio method were applied to the pipe test. The applicability of the modified load ratio method was confirmed by comparing the calculated crack length with the measured crack length from the pipe experiment.

• Journal of the Korean Society for Railway
• /
• v.8 no.2
• /
• pp.195-201
• /
• 2005

Mode II interlaminar fracture behaviors of carbon fabric/epoxy composites, which are applicable to tilting train carbodies, was investigated by the ENF (End notched flexure) test. The specimens were made of CF3327 plain woven fabric with epoxy and a starter delamination at one end was made by inserting Teflon film with the thickness of 12.5$mu$m or 25.0$mu$m. The equation for mode II interlaminar fracture toughness was suggested based on the effective crack length from the compliance of load-displacement curve. Mode II interlaminar fracture toughness was evaluated for several types of the specimens. Also crack propagating behaviors and fracture surfaces were examined through an optical travelling scope and a scanning electron microscope.

• Proceedings of the KSME Conference
• /
• 2001.06a
• /
• pp.658-662
• /
• 2001

Continuous fiber ceramic composites(CPCCs) having the advantages of ceramics resistance to heat, eroson can be applied in chemical reactors and engine. CFCCs has relatively high stiffness in spite of low weight. In particular, it exhibits greatly increased toughness, which serves to decrease its inherent damage characteristics of the brittle nature of monolithic ceramics. In this wort, tensile and flexural test for SCS6 fiber/ $Si_3N_4$ matrix composites were studied. An objective of this study is to obtain the basic quantities of mechanical properties for tension and flexural test and link these to the fracture resistance behavior. Then, we showed that wok of fracture concept was useful as a method for describing fracture restance behavior of CFCCs.

• Proceedings of the KSME Conference
• /
• 2000.11a
• /
• pp.328-332
• /
• 2000

Following the method described in ASTM E1737, J resistance curves are measured for Cr-Mo steel SA387, and Cr steel A240 which are used as piping materials in nuclear industry. Crack driving force diagrams are generated in order to find out instability points in crack growth. The $J_{appl}$ curves, which are used in the crack driving force diagram, are obtained from EPRI J estimation method and the finite element analysis. Crack growth instability points are plotted in load-crack length plane and the results are discussed.

• KSTLE International Journal
• /
• v.1 no.1
• /
• pp.48-51
• /
• 2000

Surface damage accumulation of alumina ceramics under the cyclic stress state was analyzed. The alternating stress state in repeat pass sliding contact was simulated by a synchronized biaxial (normal and tangential) repeated indentation technique. Wear debris formation mechanism through damage accumulation and fatigue grain failure in both alumina ceramic balls and flat disks was confirmed, and the contact induced surface degradation due to fatigue cracking accumulation was quantified by measuring vertical contact displacement. Variation of structural compliance (slope of load-displacement curve) of two contacting bodies was expressed as a variation of the apparent elastic property, called pseudo-elastic constant, of the contact system.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1999.05a
• /
• pp.32-38
• /
• 1999

Fatigue crack propagation behavior for block load in high strength aluminum alloys was investigated in this study. The materials used in this study are aluminum alloy 5052-H32. Initial crack was made by applying cyclic load to a through crack with chevron notch. Crack length was measured from calibration curve, which was plotted by known crack length and resistance of standard specimens. Load was obtained from linear regression formula. Unloading elastic compliance method was applied to check the crack closure and cracked area. The present study results can be usefully applied to predicting the change of crack propagation rate, the crack closure, and the delay of crack propagation.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.3
• /
• pp.497-505
• /
• 1992

본 연구에서는 최근에 개발된 직물 탄소섬유강화 복합재료의 파괴인성치를 정 량적으로 결정하고 파괴거동을 조사하고자 한다. 본 연구의 목적은 이 재료에 선형 탄성파괴역학의 적용여부를 알아보고, R곡선을 이용하여 균열의 생성점 및 불안정 파 괴점의 파괴인성치를 정확히 구하며, 주사형 전자현미경을 통해 파단면 및 균열 성장 시점을 관찰하여 파괴거동을 조사하는데 있다.