Perspectives on Structural Health Monitoring of Composite Civil Aircraft

Safe and cost effective operation are the highest priorities for civil aircraft. Considering that many events that can occur during normal aircraft operation which cause a reduction in the residual strength of the structure, a rigid adherence to inspection and maintenance schedules and timely repair of damage is required. Since Structural Health Monitoring (SHM) has the capability to investigate critical areas of the aircraft structure, it is potentially applicable to a wide range of current civil aircraft, including general aviation, business jets and large passenger aircraft. Although SHM could be extended to the complete aircraft structure in the future, in the shorter term it is more practical to consider the most critical structural elements/assemblies, both for reasons of cost and the time, especially in certification, leading to more standardised procedures in future. On a technical level SHM should be addressed by identifying critical structural elements/assemblies such as: blade stiffened skin panels, sandwich panels, hat stiffened skin panels, multi-rib and multi-spar structures, welded , mechanically-fastened and co-cured joints. For each of these, expected failure modes are assessed and used to determine the expected damage types. Damage sizes which post a risk to the structural integrity of the aircraft are then matched with SHM technologies which have suitable damage detection capability. This paper proposes the use of metrics to quantify the effectiveness and efficiency of the SHM system according to the six most important elements of SHM: Damage event detection, Damage event localization, Damage type detection, Damage extent detection, Damage effect estimation, and Damage prognosis. SHM Technologies are a combination of non-destructive testing techniques, developed further for in-situ monitoring, and new technologies. The techniques considered to have the most potential for SHM of composite aircraft are Acoustic emission, Guided Lamb wave sensing and Fibre optic sensing. SHM comprises part of the Smart Materials and Structures Concept that will be the basis for future Smart and Efficient Aircraft with lightweight structures, on-board monitoring, health diagnosis and adaptive structures. In this concept, optimal sensor positioning, distributed communication networks and algorithms, miniaturisation and energy harvesting are also considered.