• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.73-78
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• 2002

Ships and ocean structures are generally under random loading. Various type of variable-amplitude loading affects fatigue crack growth and fatigue life. However interaction effects due to irregularity of loading including random loading have not explained exactly and it is difficult to examined fatigue crack growth behaviour and fatigue life for this reason. Therefore in this paper crack growth tests with constant-amplitude loading including a single overload were conducted to measure plastic zone size near crack tip of DENT specimen. And the observed plastic zone sized were discussed in terms of crack growth rate. As a result of this the effect the plastic rue size due to the overload is examined on the effect on crack growth rate and, consequently, fatigue life.

• Journal of Welding and Joining
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• v.14 no.2
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• pp.79-89
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• 1996

일정진폭하중과 과대하중비 2.5의 단일 인장과대하중에 의한 4140강 용접부 의 피로균열성장거동을 실온과 -45.deg.C의 저온에서 피로시험과 파면관찰을 통하여 고찰하였다. 이때, 용접부 미시조직의 영향을 평가하기 위해 모재(parent metal), 열영향부(as-welded HAZ), 열처리된 열영향부(PWHT HAZ)로 나누어 응력비 0과 0.5로 CT시험편을 이용하여 피로시험을 실시하였다. 피로균열성장거동은 재료의 미시조직과 온도변화보다는 응력비에 크게 영향을 받았으며, 단일 과대하중에 의한 피로균열성장 지연효과가 모든 재료에서 상당히 크게 나타났다. 전자현미경에 의한 피로파면 관찰 결과, 실온에서는 연성의 스트라이에이숀과 -45.deg.C에서는 의벽개파면과 같은 피로 균열성장거동을 나타내고 있다.

• Journal of Welding and Joining
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• v.6 no.1
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• pp.46-52
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• 1988

Retardation or delay in fatigue crack growth due to overloads are important for the accurate prediction of fatigue lives of structural materials. In this study, retardation of fatigue crack growth in Al 6061-T6 weldments and heat affected zones (HAZ) after single overload cycle had been investigated. Retardation in both weldments and HAZ was observed. It was concluded that retardation in both weldment and HAZ was greater than in base metal due to microstructural change and crack branching and crack closure were major governing factor in retardation.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.3
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• pp.45-53
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• 2003

Ships and ocean structures are subjected to random loads caused by irregular waves. The irregularity of amplitude from random loading affects on fatigue crack growth and fatigue life. However the effects of irregularity of loading on fatigue including random loading have not been explained exactly. Therefore in this paper crack growth tests on DENT specimens under constant-amplitude loading including a single tensile overload are conducted to investigate the effect of overload on crack growth rate. The size of plastic zone and crack growth rate before and after a single tensile overloading are measured using ESPI system. Crack growth retardation model that is characterized by crack growth length and the size of plastic zone was proposed and compared with test result. From the research, the validity of proposed model is examined on crack growth retardation, and consequently fatigue life.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.11
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• pp.6399-6405
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• 2014

An external overload or impact is an important factor affecting the safety of large-scale structures. The proposal of this paper is the development of a system for detecting overload and impulse using a single PVDF film sensor. In large-scale structures, the load causes the structure to be deformed and the impulse generates vibration on the structure. Generally, low frequency deformation or bending of a structure is measured with a strain gauge and the high frequency vibration is detected by an accelerometer. On the other hand, a single sensor that can detect both deformation and vibration has not been developed. In this study, the development of a detection system integrated with a polyvinylidene fluoride (PVDF) film sensor, amplifier, and software was attempted to monitor deformation and impact through a single sensor. The system was verified by the possibility of detecting overload and impulse, and the two filtered signals of the PVDF were compared with a conventional strain gauge and an accelerometer.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.213-219
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• 2003

Acoustic emission behavior during fatigue crack growth test was investigated under various loading condition. To describe the acoustic emission activity, counts rate (d/dn) was related with SIFR (stress intensity factor range, K). Results indicated that SIFR could be divided into two parts according to its relationship with counts rate. For $K<25_{MPa\sqrt{m}}$, counts rate was increased as the SIFR increased. However, for values greater than $25_{MPa\sqrt{m}}$ , decreasing behavior was shown. This behavior of counts rate corresponding SIFR was keeping the same trend regardless of load range or crack length. Acoustic emission response to the single overload was sudden drop and slow recovery in counts rate like crack growth retardation. Under variable loading condition, counts rate of each loading block was same as that of constant amplitude loading. Overall experimental data was somewhat scattered since sensitive characteristics of acoustic emission method. However, these empirical relations indicated that counts rate was uniquely correlate with single parameter, SIFR.

• Journal of Korea Multimedia Society
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• v.15 no.8
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• pp.1038-1047
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• 2012

The SIP(Session Initation Protocol) is an application layer protocol that is used to establish, release, and change the call session of the IP telephony. In the SIP signalling networks, when the number of the UA(User Agent) requested the call session increase, the number of messages to be processed by SIP proxy server increase. It often will be caused the overload of the SIP proxy server. In this paper, we proposed the overload control method with a normal queue and a delay queue in the SIP proxy server. When it is estimated the overload of the server by the excess of the high threshold in the normal queue, new INVITE messages will be put into the delay queue to reduce the load of the server. It results in some delay of the call session from the INVITE message. Subsequently when the number of messages in the normal queue is reduced below the low threshold, the INVITE messages in the delay queue is processed. The simulation results showed that the number of the retransmission messages by our proposed method was 45% less than the one by the method with single queue. The results also showed that the average call success rate by the proposed method was 2% higher than the one by the method with single queue.

• Journal of Advanced Navigation Technology
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• v.21 no.6
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• pp.529-536
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• 2017

The general ground control system has control and information display functions for the operation of a single unmanned aerial vehicle. Recently, the function of the single ground control system extends to the operation of multiple UAVs. As a result, operators have been exposed to more diverse tasks and are subject to task overload due to various factors during their mission. This study proposes an adaptive ground control system that reflects the operator's condition through the task overload measurement of multiple UAV operators. For this, the ground control software is developed to control multiple UAVs at the same time, and the simulator with six degree-of-freedom aircraft dynamics is constructed for realistic human-machine-interface experiments by the operators.

• Journal of the Korean Society for Precision Engineering
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• v.9 no.3
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• pp.140-148
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• 1992

The effect of mechanical, properties in the plastic zone near the crack-tip was investigated, under various controlled loading conditions, i.e., ${\Delta}K$ increasing, ${\Delta}K$ decreasing, and single overload test. For both ${\Delta}K$ decreasing test and ${\Delta}K$ increasing test with constant stress ratio, it is found that the ratio of material constant m'( ${\Delta}K$ decreasing test) to material constant m( ${\Delta}K$ increasing test) is larger than 1 for n<0.1, and it is equal to 1 for 0.10.2. A modified crack growth rate equation based on Forman's equation which applied stable region of fatigue crack propagation in ${\Delta}K$ decreasing test is proposed. Within the limit of this single overload test, an empirical relation between among the retardation ratio (Nd/ $N^{*}$), the strain hardening exponent (n) and the percent peak load (%PL) has been established.established.

• Animal cells and systems
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• v.14 no.2
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• pp.91-98
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• 2010

Male rats were given a single injection of iron, and temporal changes in iron content and iron-induced effects were examined in heart cellular fractions. Over a period of 72 h, the contents of total and labile iron, reactive oxygen species, and NO in tissue homogenate, nuclear debris, and postmitochondrial fractions were mostly constant, but in mitochondria they continuously increased. An abrupt decrease in membrane potential and NAD(P)H at 12 h was also found in mitochondria. The respiratory control ratio was reduced slowly with a slight recovery at 72 h, suggesting uncoupling by iron.While the ATP content of tissue homogenate decreased steadily until 72 h, it showed a prominent increase in mitochondria at 12 h. Total iron and calcium concentration also progressively increased in mitochondria over 72 h. Enzyme activity of the oxidative phosphorylation system was significantly altered by iron injection: activities of complexes I, III, and IV were reduced considerably, but complex II activity and the ATPase activity of complex V were enhanced. A reversal of activity in complexes I and II at 12 h suggested reverse electron transfer due to iron overload. These results support the argument that mitochondrial activities including oxidative phosphorylation are modulated by excessive iron.