Advanced Materials Research Vols. 891-892

Abstract: The material properties of single crystal (SC) superalloys are orientation-dependent. To fully exploit the material capacity, the life modeling needs to consider the anisotropy. In the present study the life modeling of SC nickel-base superalloys is considered by employing the modified Mücker's anisotropic theory in which a Hill type function is utilized for describing the anisotropic failure. Strain-controlled low cycle fatigue (LCF) experiments of SC nickel-base superalloys at different crystallographic orientations (i.e. [00, [01 and [11) under high temperatures (i.e. 760°C) are carried out to verify the modeling availability for the modified Mücker's anisotropic theory. Further, based on the stress-strain field obtained by the anisotropic elastoplastic constitutive model coupled with the finite element method (FEM), the modified Mücker's anisotropic theory is employed to predict the fatigue life for SC flat plate with a hole.

Abstract: Marine grade alloys are extensively being used in high speed vessels such as patrol crafts, ferries and crew boats, where a reduction of the structural weight is critical to achieve higher speeds [1]. The use of aluminium has forced marine industry engineers to develop methods to design against fatigue failure. This has largely been addressed by the development of design standards, analysis techniques and the improvement of quality control and construction methods [2]. Nevertheless, even with these advancements there is a continued need for the development and improvement of aluminium analysis methods and guidelines [3].

Abstract: This paper illustrates a technique that may be used to evaluate the risk of structural failure of each aircraft in a fleet when a crack has been detected in a particular member aircraft, or the risk of failure for that member has become too high. When a crack is detected, the calculated risk of failure for other aircraft in the fleet will increase significantly, and the aircraft operators need to decide which aircraft should be temporarily grounded for unscheduled inspection and which ones be allowed to fly. The proposed method applies the Bayesian inference to update the risk assessment by updating the equivalent initial flaw size distribution, which is one of the key inputs for risk analysis. To illustrate the method, a hypothetical fleet aircraft is considered and the single flight probability of failure of each aircraft in the fleet is revised after the occurrence of a failure in one fleet aircraft.

Abstract: Early airplanes were designed using purely static conditions and mainly tested only with simple wing tests. But despite the significant advances in design, manufacturing and testing capabilities, structural failures may still occur. Thus new concepts are required to ensure safe operations over the lifetime of an airframe. In 1952 Juerg Branger developed a concept for a fatigue simulator at the Federal Swiss Aircraft Factory (F+W). The Pilatus P3 trainer became the first airplane to be tested in Emmen, Switzerland to demonstrate the safety of the airframe over a lifetime of 2500 FH. This first test demonstrated the importance of full scale fatigue tests to ensure the structural integrity of the airframe. Due to the intense usage of the fighters deployed by the Swiss Air Force, further full scale fatigue tests were undertaken on the Venom, the Mirage III, and the F/A-18. As the complexity of the materials used in modern aircraft design increases, more and more analysis is being taken over by highly sophisticated software and test procedures. Structural integrity is still an important means to ensure safe operations in aviation for all types of airplanes.

Abstract: Aircraft full-scale fatigue tests are expensive to conduct and they are a critical item on the certification path of any aircraft design or modification. Two aspects that contribute to the cost of a test are its duration and the loads spectrum development process. This paper provides a summary of a proposed supplemental pseudo full-scale fatigue test (FSFT) aimed at rapid certification. In this instance the method was developed with the aid of extant FSFTs that were found to be deficient. The proposed process involves the development of proof loads, damage size estimates, a loads application rig, insertion of the target damage or modifications and conducting proof testing. As all locations with a propensity to crack are known, the process is considered to be the equivalent of having conducted a representative fatigue test for the required service life target and then demonstrating adequate residual strength (i.e. proof testing the damage state at the end of a FSFT).

Abstract: 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.

Abstract: The RAAF found significant corrosion on the C-130H fleet Centre Wing Lower Surface (CWLS) panels at the tangs adjacent to the rainbow fittings. Repair of this corrosion involves blends and spot facing, and often requires the addition of a doubler to reinforce the region. All RAAF C-130H aircraft had various combinations of spot faces, blends and in some cases doublers at this location. Due to the number and combination of repairs, providing fleet wide management advice is problematic. The fleet condition was assessed from damage maps, repairs and previous analyses. From this a number of worst case configurations were determined. A Finite Element Model was developed and used to determine the bearing and by-pass loads in each fastener row of the panel tangs. Stress intensity correction factors were developed for cracks growing from or to a spot face using Stress Check. These correction factors were applied on top of geometry factors for the baseline configuration. A Damage Tolerance Assessment (DTA) was performed to assess the impact of spot face and blend repairs on the centre wing lower surface panel tangs, in order to develop a fleet wide management strategy. Based on the results for the repair cases, it was shown that the repairs identified in the damage maps could be managed within the existing safety by inspection program.

Abstract: QinetiQ has been the primary engineering support contractor to the RAAF airworthiness section (ASI-DGTA) since 1996. Over that 16 year time period many airworthiness investigations and assessments of structural integrity have been performed on a wide variety of RAAF aircraft types and Army rotary wing aircraft. A complete capability has been developed to manage structural fatigue in accordance with airworthiness standards, and indeed to transition the management of an aircraft from a design standard to a preferred RAAF management standard in response to capability requirements. Many important lessons have been learnt and have reinforced the capability. This paper describes some of the major programs that QinetiQ has undertaken for the RAAF, and the lessons learnt from them.

Abstract: This paper describes techniques for affordable teardowns on aircraft to extract condition data for assessment of system integrity durability and damage tolerance. Studies of fleet accidents show a significant proportion are due to failures in systems other than structures and engines but knowledge of their degradation with usage and age are less well understood. Forensic results from a full teardown provide robust data that supplement design and service data to support safety assessments. Fleet retirement is a golden opportunity to carry out a full system teardown if it is cost-effective. This permits a condition assessment of all critical systems after decades of Australianspecific configuration, roles and environment. Rapid dismantling techniques that do not destroy key information are being refined. Performance measurements are being compared with original design specifications and forensic data can be compared with non-destructive inspection data.

Abstract: The aim of the present work is to develop a statistical approach for the correlation between the quality of metallic materials with respect to the size and arrangement of inclusions and fatigue life in the VHCF regime by using the example of an austenitic stainless steel AISI 304. For this purpose, the size and location of about 60000 inclusions on cross sections of AISI 304 sheet in both longitudinal and transversal directions were measured and subsequently modeled using conventional statistical functions. In this way a statistical model of inclusion population in AISI 304 was created. The model forms a database for the subsequent statistical prediction of inclusion distribution in fatigue specimens and the corresponding fatigue lives. By applying the extreme value theory the biggest measured inclusions were used in order to predict the maximum inclusion size in the highest stressed volume of fatigue specimens and the results were compared with the failure-relevant inclusions. The location of the crack initiating inclusions was defined based on the modeled inclusion population and the stress distribution in the fatigue specimen, using the probabilistic Monte Carlo framework. Reasonable agreement was obtained between modeling and experimental results.