Vibration based Structural Health Monitoring of Composite Structures
Start / End:
1st November 2009 to 1st November 2013
UNIVERSITY OF TWENTE.
Faculty of Engineering Technology
Chair of Production Technology
Address: Building Horst, Room N131
P.O. Box 217
7500 AE Enschede
Phone: +31 (0)534892569
This research is part of the Eco-Design ITD within the European Clean Sky project.
Damage identification in advanced composite structures based on dynamic behaviour by using an integrated sensor system.
One of the key issues in composite structures for aircraft applications is the early identification of (invisible) damage. Often service induced damage does not involve visible plastic deformation, but internal matrix related damage, like transverse cracks and delaminations. Their identification often imposes costly and time consuming maintenance procedures (figure 1). Structural health monitoring proposes a promising alternative.
Figure 1: Time consuming and costly maintenance inspections.
Structural Health Monitoring (SHM) is the multidisciplinary process of implementing a strategy for damage identification by Non-Destructive testing (NDT). This process (figure 2) involves the definition of potential damage scenarios for a structure, the observation of the structure over a period of time using periodically spaced measurements, the extraction of damage sensitive features from these measurements and the analysis of these features to determine the current state of health of the structure. The output of this process is periodically updated information regarding the ability of the structure to perform its intended function in consideration of the applied loadings, aging and degradation resulting from the operational environments.
Figure 2: A multidisciplinary Structural Health Monitoring process.
The number of successful practical applications of SHM on composite aircraft structures is limited compared to applications in civil industry. This is mainly due to the complexity of the components and the high demands on safety and reliability of the SHM system. A robust SHM system requires the unique characterization of the presence, location and severity of the damage by methodologies operating on measured field data from an integrated sensing system.
A wide range of technologies (figure 3), comprising global vibration and local wave propagation methods, is employed for health monitoring purposes. The selection of the best technology for a SHM system is often a matter of compromises. No method solves all problems in all structures. Defining damage sensitive parameters that are able to uniquely identify damage scenarios based on measured field data under real operational conditions is one of the key challenges for these technologies.
Figure 3: Technologies based on mechanical vibrations and roughly categorized according to their operational frequency range.
Current experimental and numerical research has been concentrated on the feasibility of a vibration based SHM approach to identify impact induced damage at skin-stiffener connections of advanced composite aircraft structures. These structures consists of carbon fibre reinforced thermoplastic skins with multiple stiffeners. A skin-stiffener structure is vulnerable for delamination damage at the skin-stiffener interfaces.