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Lighter, cheaper and environmentally friendlier flying thanks to 'Structural Health Monitoring'10.06.2009 - (idw) Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF
At the 48th Paris Air Show, which is being held from 15 to 21 June at Le Bourget Airport, the Fraunhofer Institute for Structural Durability and System Reliability LBF is presenting a spectacular, four-metre-long exhibit - a mock-up of a light aircraft wing equipped with the latest structural health systems. This structural health monitoring (SHM) system is being developed within the Clean Sky Joint Technology Initiative, which aims to make flying environmentally friendlier.
Because of their great potential for lightweight construction, fibre-reinforced composites offer particular advantages in the aviation sector. However, their more complex damage behaviour relative to metallic materials means that this lightness cannot always be fully exploited. In aviation, for example, impact damage on reinforced composite structures represents a particular danger, limiting their potential uses and frequently causing greater safety risks. However, sensors, e. g. applied in the wings, can identify at an early stage structural damage that would otherwise not be externally visible, and thus reduce inspection time and costs. The operating safety of the structure is ensured by the design on one hand and by manual inspections held at regular intervals on the other hand. In the future, it will be possible to reduce costs and weight thanks to supplementary, automatic monitoring with structure-integrated sensors.
Clean Sky JTI: Environmentally friendly technology for the aviation industry
The Clean Sky Joint Technology Initiative aims to considerably reduce the environmental impact caused by aviation travel while simultaneously increasing the competitiveness of the European aviation industry. With a budget of 1.6 billion euros, it is the largest European research programme focussing on this topic. Beside renowned industrial companies, the Fraunhofer Society is one of the partners in this initiative, with the Fraunhofer LBF in Darmstadt coordinating all activities conducted by the Fraunhofer Institutes.
SHM - A component's nervous system
The basic idea: Structural Health Monitoring acts like the nervous system for a component. Sensors and evaluation electronics register external impacts and detect any damage. In particular, hail or bird strikes present a considerable danger to aircraft. Aircraft can also be chipped by grit from the runway or damaged by tools dropped during maintenance work. With fibre-reinforced sandwich structures, such damage is very rarely visible on the outside. As yet, the operating safety is therefore ensured by extensive inspections and the corresponding design of the components.
New SHM systems allow costs, weight and maintenance to be reduced, thus enabling lightweight structures to fully exploit their potential. Self-diagnosis reduces downtimes and the reduction in weight cuts fuel consumption. Continuous monitoring of the aircraft fuselage, even in areas difficult to access, reduces operating inspection expenses. Electrical and optical strain gauges as well as piezoelectric fibre modules and accelerometers are used to record measurements.
The exhibit's upper and lower frames are furnished with fibre-optic sensors in order to obtain information about the expansion of the structure by measuring the wavelength distortion of reflected waves. In addition to expansion, impacts can also be registered. Piezoelectric fibres convert mechanical expansion into electrical voltage. This makes it possible to measure the high-frequency acoustic waves within the structure that are caused by the impact of foreign particles, allowing the location and extent of any damage to be determined.
About the Fraunhofer LBF
With its comprehensive expertise in the fields of structural durability, adaptronics and system reliability, the Fraunhofer LBF develops, evaluates and implements customised solutions for all safety components - ranging from the materials to whole systems and from the first idea to the product. It works in conjunction with the associated System Reliability and Machine Acoustics department (SzM) of the Technical University Darmstadt and benefits from the experience of a team of around 290 staff. Cooperation projects with renowned partners exemplify its particular closeness to the industry. Automotive and commercial vehicle engineering, rail transportation technology, shipbuilding, machine and plant engineering, aviation, energy technology and other sectors utilise the proven expertise and cutting edge technology provided in the laboratory and testing areas that extend across more than 17,000 m2.
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