Development of sensor technology to facilitate in-situ measurement of damage in composite materials for spacecraft applications

• Main Author: Mowlem, Matthew Charles
• Format: Dissertation
• Language: English
• Published: University of Southampton 2002
• Subjects: satellites; Unmanned spacecraft

The work presented in this thesis, which details the development and evaluation of an optical fibre damage sensor, was supported by The European Space Administration and by a DTI-NERC LINK grant under the SEASENSE programme. The sensing system developed as part of this programme uses fibre Bragg gratings as sensing elements. The translation of the output of these sensors into strain information is achieved using a novel interrogation system described in this work. The work presented in this thesis is believed to be the first evaluation of this technology for the detection / characterisation of hypervelocity impacts and impact damage. In order to evaluate the suitability of this system for spacecraft impact damage assessment, this work explores the response of aerospace composites to impact by reviewing previous work in composite modelling, acoustics and experimental evaluation. This knowledge is extended by the use of the system in both high and low velocity impact experiments with sensors embedded in carbon fibre reinforced plastic. Alternative optical techniques and conventional sensing methods are compared to the observed performance. The system has also proved to be of sufficient resolution and close to sufficient accuracy for use in monitoring an array of Bragg grating based temperature and pressure sensors for oceanographic applications. This work enabled a detailed examination of the system's accuracy, and stability, which was required for structural sensing studies, and illustrates the breadth of possible applications for this technology. The work concludes that this system would be capable of measuring impacts large enough to cause damage that would threaten the integrity of the composite component. Very few of the large number of small impacts expected would occur close enough to a Bragg grating sensor to register a reading. However, with further development, an interrogation system could be created that was capable of monitoring the impact induced flexural wave in the composite. An array of sensors would allow triangulation of the location of impact, and measurement of the impact: momentum.