Book Description

Composite materials have excellent mechanical and thermal properties and are the materials of choice for many applications. Even so, the low inter-laminar mechanical properties and poor impact resistance of fiber reinforced composite materials has limited their use. Broader use of composites would be possible if, there was a continuous structural monitoring that could ensure the safe operation and economical maintenance of composites. The monitoring system can be made reliable and economical if the sensors could be embedded within the material. This thesis proposes a new approach to monitor the state of strain and delamination in composite materials. The method is to use carbon nanotube thread as a continuous sensor that can be placed wherever desired inside or onto the composite material. This thesis indicates the approach is new, simple and reliable. The significance of this continuous sensor is that it opens up development of the next generation of composite materials and structures that continuously monitor their state of strain and damage. This will provide a better prediction of their life span and allow the possibility of applying corrective action if neededThis thesis investigates structural health monitoring of simple composites based on monitoring the electrical resistance of fine threads used as embedded sensors. The threads are spun from Carbon Nanotube arrays. The threads exhibit a tailorable piezo-resistive property, which is the basis of the sensor operation. It is shown that the presence of CNT threads in simple specimens does not cause any significant voids or areas of stress concentrations, which might affect the overall mechanical properties of the material. Two types of sensor configurations were evaluated; a straight sensor and a stitched sensor. The behavior of these sensors was compared under tensile and bending loads in composite materials. These sensors are tested both for damage detection and strain sensing and successfully detected when the damage reached the thread. The continuous thread sensor may be an important component in the design of future aerospace composite structures that operate safely and economically.