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Inspection of monolithic carbon composite spars is largely restricted to visual and destructive methods, using whatever experience happens to be available at the time and place. This is the case both for new build and in-service. This can raise significant technical inadequacies and the quality standards fall far below what would be expected in industries which require good standards. NDT Solutions have developed a state-of-the-art ultrasonic inspection technology for the rapid inspection of aerospace composites. The research prototype for this technology was delivered through a previous DTI link project (UWASI YAF 8/2/3203). The novel use of ultrasonic medical imaging technology housed in a scanning wheel probe has lead to the possibility of delivering true “structural imaging” of composites rather than simple point testing which is the current practice. Recent preliminary investigations in support of this proposal have shown that there is considerable potential for the application of this technology for the assessment of marine and wind turbine composite structures. |
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The high quality imaging and data acquisition speed delivered by the RapidScan system supports the aims of this proposal by offering the potential for a fully documented assessment of the composite structures. The system is capable of detecting, imaging and characterising a wide range of defect types and manufacturing problems including impact damage, disbonds and delaminations, fibre misalignment, fibre wetting and porosity. Structural Health Monitoring (SHM) is a highly emerging field of technology and there is a variety of advanced sensing technology available for monitoring the structural integrity of composite structures. This sensing can be related to load/strain monitoring where the relationship between load and damage is known or is a flag to trigger inspections. Structural health can also be monitored by directly monitoring damage in the structure, thus making non-destructive testing an integral part of the structure itself. In the yacht and wind turbine industries, there is a move to an inspection-free philosophy through the use of SHM. Thus, Insensys have developed and installed a fibre-optic composite mat for SHM currently used in both industries. The use of high rate data scanning and a composite mat to protect the fibre-optic has offered much more reliability and usefulness for this method. Wireless data transfer has additionally facilitated communication between the sensing device and a data processing unit. This has allowed design and realisation of structural health monitoring systems, which can be adapted onto or integrated into a structural component. However, these outputs are only useful once they have been calibrated to identify what the measured change in strain actually means for the remaining structural integrity. Despite the perceived concerns of impact damage, lack of design tools, lack of standards, composite material structures have been successfully used in primary structure for decades. The Aerospace industry is a risk adverse industry yet composite structures are dominant in current commercial aircraft including the Boeing 777 (tail section) and the Airbus A380 (wing box and fuselage). These aircraft are successful, because of the damage tolerance and no-growth approaches developed and used by the aircraft industry. Here, damage threats are identified with potential damage scenarios. Structures are designed and tested in a building block approach where coupons and structures are tested containing worst case damage. This approach is understood by the constructors and the aviation authorities and is successful. The structures are designed to be able to still operate with damage, or be able to be repaired or replaced when the damage is too severe. MERL has been at the forefront of developing no-growth methods to assess the effect of defects for the aerospace industry. No such approach exists for the highly loaded carbon fibre spars in the yachting and wind turbine industries. Hence, the work proposed in the MSI SPAR project. The processes must be developed for these industries, such that damage threats and the corresponding damage are incorporated into finite element analysis models utilising damage mechanics to determine the effect of the damage, and building block testing such that the limit of damage acceptance can be identified. As a result, a new building block design and inspection philosophy will be developed. This work will integrate the above state of the art activities together and apply it within a guide focussed on typical damage threats that carbon fibre spars are likely to experience. This can only be achieved from a consortium project such as proposed here bringing together the prime R&D providers with NDT, composites failure and market application knowledge. Click here to view the project work packages. |
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