Accurate quantification of damage in aircraft structures during their life cycle through an automated monitoring system could ensure airframe integrity and long term durability. Nonlinear Elastic Wave Spectroscopy is an innovative class of non-destructive techniques providing an extreme sensitivity in the diagnosis of manufacturing defects such as porosity, component assembly contact conditions, incipient damage in the form of micro cracks, delaminations, clapping areas, and adhesive bond weakening, which are superior to what can be obtained with traditional NDTs.
Following the automated monitoring, the next logical scientific step lies in the development of material with in-situ wound healing, that will move the intrinsic limiting material boundaries which are encountered by aerospace manufacturers. Classical healing and self-healing concepts are based on the embedding of hollow-fibres/microcapsules in the resin. A new potential class of self-healing materials can be introduced by adopting thermally reversible cross-linked polymers.
This new class of polymers is capable of healing internal cracks through thermo-reversible covalent bond formation. This new approach eliminates the need for additional ingredients such as catalyst or monomer. Moreover, these new healable resins have the built-in capability to restore mechanical properties several times through multiple cycles of healing. This allows multiple damages occurring, at the same location, to be repaired.
The goal of this project is to develop and build an autonomous modular system for monitoring and healing aircraft structures and to demonstrate its efficiency in a life-cycle simulated environment starting from the production to the in-service loading.
ALAMSA: the goal will be accomplished by combining integrated modular NEWS techniques and ad-hoc developed Nonlinear Imaging Methods (NIM) for a smart quality control system and maintenance of aircraft structures.
Detecting and fixing aircraft defects in situ
The return on investment for inspection and maintenance technologies for the aerospace sector is among the highest of any area of the economy. New inspection and self-healing technologies will have major impact on competitiveness and safety.
Typically, more than 30 % of an aircraft's average life-cycle cost is due to inspection and repair. This does not include lost profits during grounding for scheduled replacements of parts, with profit losses around EUR 250 000 per day for a grounded commercial plane.
Scientists are developing state-of-the-art non-destructive inspection technology and new self-healing materials with EU funding of the project http://www.bath.ac.uk/ris/about/rpms/projects/alamsa/index.html (ALAMSA) (A life-cycle autonomous modular system for aircraft material state evaluation and restoring system). Continuous monitoring of structural integrity in situ will enable self-repair at an early stage, minimising lost hours on the ground. The innovations support smart aircraft maintenance and an important step on the path toward maintenance-free planes.
The non-destructive monitoring exploits cutting-edge non-linear elastic wave spectroscopy techniques, an innovative class of vibro-acousto-ultrasound techniques. They have higher sensitivity and the ability to image internal areas not accessible with conventional methods. Further, they are able to detect a variety of defects in structural integrity, including microcracks, delaminations and adhesive bond weakening. Several different types of non-linear imaging methods (surface or subsurface imaging, tomography and time reversal) were developed, improved and tested on a variety of composite samples and components.
Self-healing capabilities focus on thermally activated materials and magnetically activated ones. The intrinsic self-healing (thermally activated) materials were obtained by inclusion of liquid healing agents in a compartmented thermoset polymer matrix. They promise the ability to restore mechanical properties more than once through reversible processes. The extrinsic self-healing materials consist of magnetic nano- and/or microparticles embedded in a thermoplastic polymer stabilised by ionic cross-linkages (ionomer).
Numerous models are supporting development of the innovative technologies. They will be a lasting legacy for future projects, providing important insight into non-linear interaction of waves with defects for aviation applications and composites in general. The project has been widely publicised via a strong presence at numerous international conferences and exhibitions as well as publications in peer-reviewed scientific journals.
Quality control, inspection and maintenance technologies under development within the ALAMSA project will increase the competitiveness of Europe's aerospace industry while enhancing the safety of its passengers.