A fighter aircraft has been instrumented with piezo sensors on a carbon fibre reinforced plastic main landing gear door. During ground handling and standard test flights, the piezo sensor output was recorded on a flight test instrumentation tape recorder with a frequency range from 30 kHz to 250 kHz. Parallel to the flight test, a number of laboratory impact tests have been performed on a separate CFRP main undercarriage door with the same sensor suite. The measured background noise level has been compared to the impact spectra from the laboratory tests. The comparison shows at least a difference of 30 dB between the impact and the background noise.
For some structural components conventional methods of loads and usage monitoring, supplemented by on ground NDT measurements to detect damages can be unsatisfying due to various reasons: low reliability of sensing technique or low accessibility and sometimes high cost of dismantling for regular NDT. Sensor methodologies having evolved form conventional ultrasonic inspection in principle have the potential to detect damages in various types of structures: 2D, 3D, metal, composite - provided significant interaction of ultrasonic waves with local damage is given. SWISS (Smart Wide-area Imaging Sensor System) requires a physical interaction model of ultrasonic excitation with structure and its potential damage and merges sensor data to determine spatial distribution of impedance by imaging which performs localization and sizing of damage in one. Second: use of signal and image processing techniques to alert when damage becomes critical. SWISS has been designed by EADS to image various types of damage from considerate distance by means of permanently installed piezo-elements. SWISS features a sensor minimization to achieve low weight and still high reliability and the use of cheap electronics but clever testing and analyzing to achieve low cost for in-service application. SIEMENS NDT has been able to demonstrate SWISS functionality on complex components by appropriate use of Phased Arrays.
Piezoelectric sensor arrays and sensor networks have been suggested as a means to monitor the integrity of composite structures throughout the service life for instance of an aircraft. Complex sensor systems will require significant additional expenditures with respect to cabling and electronics, with the added weight and effort possibly outweighing any benefits. Sensor positions in remote locations of an aircraft will often necessitate accessibility to these locations for maintenance purposes. For these reasons wireless, integrated sensors have recently become an object of increasing interest. Within the framework of a feasibility study various aspects of integrated wireless sensor system were investigated in detail. Particular emphasis was thereby laid on issues that are essential form a practical point of view, but that have not been discussed in the literature extensively. As a starting point a trade-off study between different sensor network configurations was conducted, form passive, remotely queried senors without power supply to fully functional active sensor pads with integrated power supply and electronics. Various concepts for the on-board energy supply of remotely queried sensor pads were studied and a comparison between rechargeable, and single-use batteries was performed. The suitability of different electronic components for integration into carbon fiber composites was investigated with particular emphasis on their survivability under typical temperature cycles experienced in autoclave runs. Finally, a crackwire sensor as an example of a passive remotely queried sensor system was pursued further in order to show the feasibility of such a wireless system for composite health monitoring purposes.
One of the most innovative concepts for active fin-buffet alleviation in vertical tail aircraft is the use of piezoelectric patch actuators distributed across the tail surface to actively induce a counter-strain into the structure. This concept involves the development of a novel material compound structure consisting of a fiber-composite aircraft skin, a ceramic patch actuator and the bonding layer between both components. This actively controllable structure has to provide enough authority to dampen the fin- buffet vibrations. It also has to function reliably during long-term aircraft operation under severe mechanical and environmental load conditions.
Requirements of future military aircraft structures are constantly increasing with advancing technological progress. While performance is still the main focus, costs have become a major issue in military aircraft procurement.In order to efficiently support its technological base oriented on the future demands of the market Daimler Chrysler Aerospace/Military Aircraft Division has inaugurated the Advanced Aircraft Structures Program, a collaborative research effort together with the German Aerospace Center and Daimler Chrysler Research and Technology, the corporate research division of Daimler Benz. The two key technologies to be pursued within the framework of this program are cost- effective composite structures and smart materials. This paper will give an overview of the Advanced Aircraft Structures Program with particular emphasis on smart structures technology as applied to active vibration damping, vibration isolation of equipment and composite health monitoring.
When lasers were introduced to general surgery in the late sixties great expectations were
cherished and abundant optimism developed. A great amount ofbasic research and clinical
trials were peformed and indications for the new surgical device gradually defined. Only
detailed evaluation and comparison with established forms oftreatment was able to describe
the place oflaser application in surgery (1,2).
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