• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.2
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• pp.129-136
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• 2017

This study aims to assess the damage tolerance of the wing structure of aged aircraft with long-term service through the fatigue crack growth analysis and tests. For the fatigue-critical locations (FCL) W2 and W4 in the wing structure, the fatigue stress spectrum was derived based on a previous study. Thereafter, a crack propagation analysis for the FCLs was conducted using the commercial software $NASGRO^{TM}$. The algorithm for the fatigue stress spectrum was verified. Fatigue crack growth tests were then performed for two types of specimens: Type #1 was extracted from the wing structure of aged aircraft, and Type #2 was made of the same material as the wing structure. By comparing the experimental results of these specimens, we assessed the damage tolerance of the wing structure of aged aircraft with service time.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.638-644
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• 2020

This study examines cracks that occur under the load of an aircraft. The life of aircraft vulnerability structures was analyzed and structural fitting improvements were made. Structural integrity and safety have been achieved through preemptive life expectancy and life management of aircraft structures. The crack size inspection capability of the aircraft under analysis is 0.03inch, compared with 0.032inch, which is the lowest of the three vulnerable parts. In addition, the fatigue life analysis results in approximately 1450 operating hours, the lowest of the three vulnerable parts relative to the aircraft's required life of more than 15000 operating hours, which increased the repeat count of the aircraft's initial and re-inspection times, and hence raised the resulting costs and manpower consumption. Finally, the features were improved through structural fitting of the identified three weak parts. The lowest critical crack size was secured at 0.13 through increased structural resistance to generated cracks and increased aircraft safety. The lowest structural fatigue life for cracks occurring during aircraft operation is 25000 operating hours, which are analyzed above the required structural life, resulting in more optimized improvements than the repair costs and excessive fitting range caused by cracks and fractures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.9
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• pp.1185-1191
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• 2010

Aged aircraft have several cracks as a results of long-term service, and these cracks affect the safety and decrease the rate of operation of the aircraft. To solve these problems, crack propagation analysis should be performed to determine the service life at fatigue critical location(FCL). It is, however, almost impossible to obtain the stress spectrum, which is crucial for crack propagation analysis of the FCLs of wing structure of aged aircraft. In this study, to analyze the fatigue crack propagation behavior at the FCL of an aged aircraft, first finite element analysis is performed for a 3D geometry model of the aircraft wing structure, which is obtained using CATIA based on the paper drawings. Then, the transfer function and stress-spectrum of the FCL are derived using the load factor data and the FEA results. Finally, the crack propagation rates of the FCL are evaluated using the commercial software, NASGRO 6.0.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.16-24
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• 2009

In this study, fatigue crack growth rate of a cracked railway bogie frame under variable amplitude loading is predicted by applying linear elastic fracture mechanics. For this purpose, we find the critical points by reference surveying on cracked railway bogie frames. And we make an effective load history by synthesizing the dynamic load measured from the critical points of railway bogie frame during commercial line operation and the static load calculated from structural analysis. Crack growth analyses are performed at the 3 critical points under the commercial operation loading condition by assuming an initial crack size as 40 mm. and the results are compared with the experimental results from Japanese railway bogie frame crack growth case. From the analysis results, we find that around 500,000 km operating distance is necessary to bring crack growth from the initial crack to unstable crack. And it takes around 3.8 normal operating years. We conclude that it is enough time to detect the crack between normal maintenance period.