• Journal of Aerospace System Engineering
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• v.14 no.spc
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• pp.1-6
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• 2020

The flaw tolerance evaluation requirement prescribed in Federal Aviation Regulation (FAR) §29.571 Amendment 55 was established in 2012. As a result, there are not many datas of flaw tolerance evaluation. This paper introduces the series of processes and evaluation methods carried out for certification based on the flaw tolerance evaluation. An initial flaws were artificially formed on the main rotor actuator and then the damage tolerance test was performed, which was twice life time of design requirements, to demonstrate that the main rotor actuator of the rotorcraft is sufficiently capable of flaw tolerance.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.17 no.2
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• pp.126-136
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• 2021

During operation of nuclear power plants, the fatigue assessment should be conducted repeatedly, considering changes of operating environments. For the case that cumulative usage factors (CUFs) may exceed the acceptance limit, flaw tolerance evaluation can be an alternative method to meet the regulatory requirements. In this respect, this paper analyzes the effects of the input variables for flaw tolerance evaluation based on ASME BPVC Section XI Appendix L. The reference analysis is performed for the example problem in NUREG/CR-6934. Then effects of the crack orientation, stress intensity factor solutions, thermal stress profiles, fatigue stress decomposition and fatigue crack growth curves are considered for the sensitivity analysis. The results show that the stress analysis considering the actual environment plays a crucial role in flaw tolerance evaluation.

• Journal of Aerospace System Engineering
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• v.14 no.spc
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• pp.22-30
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• 2020

Composite rotor blades for rotorcraft have an intrinsic vulnerability to foreign object impact from its inherent structural characteristics of insufficient strength in the thickness direction, which may easily lead to internal structure damage. Therefore, defects and strength reducing effects caused by foreign object impact should be considered in fatigue evaluation of composite blades. For this purpose, the flaw tolerant safe-life and fail-safe concepts were adopted in fatigue evaluation since 1980s, and recently those concepts have been replaced by the damage tolerance concept. In this paper, the relevant standards for fatigue evaluation are analyzed focusing on fiber reinforced composite rotor blades used in rotorcraft. In addition, fatigue evaluation procedure of composite blades considering impact damages is proposed by reviewing the practices implemented through domestic development projects.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1275-1282
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• 2012

Helicopter rotor systems are dynamically loaded structures with many composite components such as the main and the tail rotor blades. The fatigue properties of composite materials are extremely important to design durable and reliable helicopter rotor blades. The safe-life methodology has generally been used in the helicopter industry to substantiate dynamically loaded composite components. However, it cannot be used to evaluate the strength reducing effects of flaws and defects that may occur during manufacturing and operational usage. The damage tolerance methodology provides a proper means to overcome this shortcoming; however, it is difficult to economically apply it to every composite component. The flaw tolerant methodology is an equivalent option to the damage tolerance methodology for civil and military rotorcraft. In this study, the flaw tolerant safe-life evaluation is described and illustrated by means of successful application to substantiate the retirement time of composite rotor blades.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1181-1185
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• 1990

A failure evaluation diagram to evaluate fatigue fracture was developed. The relation between the fatigue limit and the threshold stress intensity factor for the short-cracked specimens of various materials including a piping carbon steel can be rationally predicted by the proposed method. It is shown that the coupled failure evaluation diagram for fatigue and ductile fracture is expecially useful for evaluation of the flaw tolerance as well as the margin of the safety of the pressure vessel and piping. Further, accumulation of fatigue data will be needed to construct an accurate fatigue failure evaluation diagram.