<title>Design requirements and system payoffs for an on-board structural health monitoring system (SHMS)</title>

Abstract

To optimize military fleet readiness, life cycle lracking of aircraft is required under the Air Force Aircraft Structural Integrity Program (ASIP). However, cuffent methods for monitoring the life history of an aircraft are often costly and inefficient1. Improvements in aircraft inspection and maintenance procedures are essential in today s climate of increasingly complex aircraft and decreasing defense outlays, forcing life extension programs for current aircraft. Automated structural health monitoring incorporating remote damage detection, load/environment tracking, and structural integrity assessment could provide significant cost savings over the life of an airframe. A structural health monitoring system (SFIMS) would lead to a maintenance as necessary repair philosophy through the use of multiple sensor arrays, integrated signal processing, data acquisition hardware, and analysis algorithms to assess structural integrity.This paper presents the design requirements for development of an aircraft SliMS. Design of a SHMS requires careful analysis of structural geometry, operational environment, expected damage modes, etc., to determine sensor categories and locations. Additionally, the task of integrating data collection, processing, and storage hardware into the airframe must be addressed. Sensors and sensing technologies are discussed along with specific requirements for monitoring system hardware and software. Anticipated life cycle savings versus implementation costs are also presented for the ideal SHMS. INTRODUCTIONMilitary aircraft experience a wide range of flight and load environments. To ensure flight safety and airworthiness, it is necessary to track both aircraft usage and damage growth in the structure. This damage includes fatigue in metallic structure, delaminations and disbonds in composite structure, and large scale battle damage. ASIP and the equivalent Navy program (NASIP) currently guide life cycle tracking of aircraft structure. ASIP can be defmed as the design and implementation of engineering, test, and logistics tasks to minimize the possibility of catastrophic structural failure resulting from unanticipated or undetected structural or material degradation2. Of the five interrelated functional tasks defined by ASIP3, force management (FM) is most relevant to health monitoring implementation (defmed by NASIP as Service Life Monitoring -SLM). The elements which comprise FM include an individual aircraft tracking program (TAT), a loads/environment spectra survey (JJESS), and a force structural maintenance plan (FSMP).ASIP requires that aircraft structures, both metallic and composite, be capable of withstanding assumed damage initiations and subsequent growth to an equivalent of two design lifetimes of service usage3. A health monitoring system must be capable of detecting such damage, as well as large scale battle damage, and other structural flaws not directly mandated by ASIP requirements (e.g., metallic corrosion). The system must also perform the ASIP functions of LfESS and TAT monitor...

Damage detection and assessment in fibre-reinforced composite structures with embedded fibre optic sensors-review

“…Inverse models formulated on the basis of either modal response [139] or the finite element method [149] for postulated damage/deformed states are used to generate strain responses through a matching optimization. The locations of the impact sites and load levels can then be recovered through data comparison.…”

“…Moreover, the focus of the review is further restricted to applications in which fibre optic sensors are used to measure load-induced mechanical strains rather than to detect impact-induced acoustic stress waves, although the latter will be mentioned in discussing the determination of impact location. However, peripheral issues regarding the system integration of acquisition software, hardware and ingress/egress connections are beyond the scope of the present review; the interested reader can refer to [1,8,102,148,149] for a detailed discussion of the topics. An earlier review of research up to 1993 for detection and assessment of damage, especially by using the fracture approach of embedded optical fibres, is available in [103,104].…”