University of Twente Student Theses


Detection of delaminations based on dynamic behavior : application of fibre bragg gratings for dynamic damage detection

Grouve, W.J.B. (2006) Detection of delaminations based on dynamic behavior : application of fibre bragg gratings for dynamic damage detection.

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Abstract:Nowadays, fibre reinforced plastics enjoy an increase in popularity. Their high specific strength and stiffness together with the high degree of design freedom have resulted in whole new variety of applications. However, due to their nature composites can suffer from complex damage types unknown to conventional materials. Common encountered examples include matrix cracking and delaminations. The detection of these damages can be a real challenge as it generally cannot be identified by visual inspection. The currently available non-destructive evaluation methods, such as ultrasonic evaluation, are time consuming and costly. In search for alternatives, part of the research concentrated on damage detection by monitoring changes in dynamic behaviour of structures. The first part of this thesis gives an overview of the existing literature on this subject. Various techniques and methods are discussed and compared. The second part will underline the possibilities of damage detection based on dynamic behaviour. A theoretical analysis will show that delamination detection based on shifts in flexural resonance frequencies can give very accurate results. Also it is shown that measured frequency shifts of multiple modes can be used to locate the delaminations. The theory is experimentally validated with delaminated composite beam shaped test specimens. Finally, an experimental programme is conducted to investigate the use of fibre bragg gratings for dynamic health monitoring. Fibre bragg grating have some advantages over conventional methods for capturing the response of a vibrating composite structure. The most notable is the fact that fibre bragg gratings can be embedded in composite structures, which protects them from environmental influences. More advantages can be found in the possibility of multiplexing, i.e. having multiple sensors on one fibre, and the strong resistance against fatigue. It is concluded that, despite the necessity of additional research, fibre bragg gratings will aid in the development of an applicable online health monitoring system.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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