Papers by Keyword: Ageing Aircraft

Abstract: This paper reports on investigations on the residual fatigue resistance of a 2024 aluminium alloy of an A320 aircraft at the end of life. The fatigue data (S-N and da/dN curves) are compared with data obtained on a pristine alloy using a similar procedure. The results are analysed on the basis of fracture surfaces observations and of AFGROW fatigue life computations.

Abstract: Greatly reduced inspection intervals of skin damage repairs pose a significant financial problem for aging commercial aircraft fleets. Such intervals for visual inspections are the result of simplified conservative repair substantiation analyses, based on the same crack propagation scenarios and curves that were established in the initial project development. These neglect the structural role of external repair (“doubler”) and consider only the increase in hidden crack path. A more refined approach to reassessing inspection intervals after a repair may keep maintenance jobs in accordance with common C-check routines in most cases. This approach, based on new crack growth simulations for worst case scenarios that could occur at the region of repair, uses respective kinetic equation and new geometric stress intensity factor functions, obtained in additional FEM (Finite Element Method) analyses. In particular, for standard rectangular repairs, the number of possible geometric configurations is astonishing considering length, width, skin and “doubler” thickness, reinforced panel dimensions, and frame and stringer cross sections. This investigation deals mainly with defining a minimum sufficient number of intermediate crack length values for FEM analyses in each propagation scenario. A conservative but efficient definition of most relevant parameters for a new numerical analysis campaign is another important issue. The results obtained are helpful for the improvement of the operational efficiency and safety of an aging fleet.

Abstract: In recent years aircraft maintenance practices have been influenced by changes in aircraft design philosophy and improvements in engineering technology. Advances in manufacturing techniques and material specifications have made it less necessary to carry out frequent disassembly of aircraft and components to establish confidence. The need to be competitive and to reduce costs has meant that the aviation industry has sought to gain advantage from these improvements by moving from time consuming and cost extensive, invasive maintenance to a philosophy of on condition maintenance (OCM). The research is aimed at highlighting an OCM based maintenance methodology by carrying out an extensive study on structural integrity of various vintage Chinese fighter aircraft. The study finds that the structure of Chinese fighter aircraft is robust and is capable of flying for more hours/years than specified by OEM. The study will help air forces operating the ageing Chinese fighter aircraft in extending the lives of their respective fleets well beyond the OEM prescribed limits.

Abstract: This paper presents the perspective of the Structural Mechanics program of the Air Force Office of Scientific Research on the damage assessment of structures. It is found that damage assessment of structures plays a very important role in assuring the safety and operational readiness of Air Force fleet. The current fleet has many aging aircraft, which poses a considerable challenge for the operators and maintainers. The nondestructive evaluation technology is rather mature and able to detect damage with considerable reliability during the periodic maintenance inspections. The emerging structural health monitoring methodology has great potential, because it will use on-board damage detection sensors and systems, will be able to offer on-demand structural health bulletins. Considerable fundamental and applied research is still needed to enable the development, implementation, and dissemination of structural health monitoring technology.

Abstract: Widespread Fatigue Damage (WFD) is a technical expression used in the certification of aircraft. The paper presents a set of issues which may influence the probability that a structural item exhibits WFD. The paper mainly follows the line of a stochastic approach to these subjects, and includes the influence of realistic parameters - like manufacturing - and tries to assess what may be the impact of new technologies.