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This paper examines the growth of cracks at a fastener hole containing intergranular cracking with a focus on ‘dome nut hole’ coupons that are representative of a critical location in the Royal Australian Air Force AP‐3C Orion wing. It is shown that crack growth under operational flight loads can be captured using the NASGRO formulation and that the scatter in these various tests can also be captured by allowing for small variations in the value of the cyclic stress intensity fatigue threshold. In this context, it is shown that crack growth can be captured using both a cycle‐by‐cycle analysis and also a United States Air Force ‘characteristic K’ approach. We also see that, for the operational load spectra considered, the crack growth history is approximately exponential so that the United States Air Force risk assessment computer program (PRobability Of Fracture) can be used to assess the risk of failure by fracture. The results of this study also suggest that, provided that intergranular cracking does not turn and break through to a free surface, it should have little effect on crack growth at a fastener hole.

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The AP-3C Orion aircraft is the oldest aircraft in the Royal Australian Air Force (RAAF) inventory. The planned fleet withdrawal has been extended far beyond the original design service objective. Continued safe and effective operation has required the development of a robust ageing aircraft management approach. A fundamental aspect was supplementing the structural certification basis with appropriate standards in the form of fatigue management requirements from Federal Aviation Regulations (FAR) 25.571 and Federal Aviation Administration Advisory Circular (FAA AC) 120-93. To develop and underpin the ageing aircraft management plan and transition to the supplementary fatigue management standards, the RAAF collaborated with the Original Equipment Manufacturer, Lockheed Martin Aeronautics Company, the United States Navy (USN) and other operators to form the P-3C Service Life Assessment Program (SLAP). This program provided Full Scale Fatigue Test (FSFT) data, associated analyses and analysis tools to support management in accordance with FAR 25.571. An important element of the ageing aircraft management plan included the introduction of a rigorous Safety By Inspection (SBI) maintenance regime to assure structural airworthiness. FAA AC 120-93 requires assessment of structural repairs to determine revised fatigue management and inspection requirements. Often, this information is derived using tailored analysis tools and detailed models on a case-by-case basis. This approach is specialized, expensive and usually occurs after the repair has been designed and installed. To avoid these limitations, the AP-3C Repair Assessment Manual (RAM) was developed to provide the repair designer with a design handbook approach to fatigue analysis. In conjunction with some simple Finite Element (FE) models, the RAM supports complete repair analysis prior to an aircraft leaving the maintenance venue. This paper will present the history of the SBI program, the genesis of the RAM and actual examples of assessing structural repairs on the P-3 platform using the RAM.

The oil-and-gas industry has become increasingly interested in drilling dynamics and vibration as causes of drilling inefficiency and reduced drilling performance. Generally, drillstring vibration is measured with shock-and-vibration sensors installed in measurement-while-drilling (MWD) tools, logging-while-drilling (LWD) tools, and rotary steerable systems (RSS). Although these tools provide valuable real-time and recorded-mode information on the dynamic conditions, they are not generally designed to capture continuous high-frequency (HF) mechanics and dynamics data, and burst data may miss important information about the evolution of the system response and state.A downhole mechanics measurement tool has been developed that makes a comprehensive suite of measurements of the drilling process, including forces, accelerations, rotational speed, pressures, and temperatures. In addition to providing information in real time, the tool has the capability to capture long durations of continuous data at frequencies between 50 and 2,000 Hz. The recorded-mode information obtained has provided significant insight into the response of the drilling system to starting rotation; drilling procedures and parameter modifications; and exposure to excitation from sources including, but not limited to, rig heave, bottomhole-assembly (BHA) component imbalance, and bit/rock interaction. A wide range of occurrences has been captured in which the drilling system switches from a dominant vibration mode, typically torsional (downhole rotation-velocity oscillations or stick/slip) into a different mode, such as axial (bit bounce) or lateral (whirl). Transitions between different types of whirl have also been recorded.Several cases were studied to investigate the evolution and response of drilling-system behavior on the basis of in-depth interpretation of relatively long durations (minutes to hours) of HF data sets in the operational context. The findings verify the value of using continuous HF vibration data to understand the drilling system and to increase drilling performance.