ISBN 9783843924993

978-3-8439-2499-3, Reihe Mikrosystemtechnik

Timo Schotzko
Sensor Integration in Silicone and Rubber Gaskets for Structural Health Monitoring (SHM)

185 Seiten, Dissertation Universität Bremen (2016), Softcover, A5

Zusammenfassung / Abstract

The research work presented in this dissertation shows the integration process and characterization of a miniaturized strain gauge sensor in silicone and rubber O-rings for structural health monitoring (SHM).

First, a theoretical consideration of the stress-strain properties of a compressed O-ring was put forth to study the effect of the compression on the gasket material and on embedded sensors.

As suitable sensors for sensor integration, strain gauges were selected, designed and fabricated. The advantages of these sensors are that this sensor type is simply processed, sturdy, and can easily be miniaturized. With all of this taken into consideration, a reliable sensor signal can still be achieved. These properties are important for the integration into rubber materials. The strain gauges are fabricated on 5 µm polyimide. Additional substrate materials based on NBR (nitrile butadiene rubber) were used as well. The material properties are more similar to the host material so that better sensor performance is achieved.

The focus of the integration processes were laid on the embedding of sensors into silicone via casting liquid silicone into a mold, as well as through compression molding of a viscous rubbery material. This allowed to non-destructively integrate the sensors during the fabrication of the O-rings. Uniaxial tensile tests of dumbbell specimens containing the sensors were also performed.

The embedded sensors measure the horizontal strain inside the gasket while compression force is applied on the O-ring. The evaluation of the sensor signal reveals a direct dependency on the compression force that is applied on the O-ring. The strain gauges resistance is found to correlate nearly linearly with the contact pressure. Thereby, the NBR sensors reflect the elastic properties of the rubber material more closely. Artificial aging tests, where the rubber material was artificially aged at 70°C for 72 h, exhibit an exponential decline in the resistance, caused by relaxation processes and degradation of the compressed rubber O-rings that can be detected. This can be exploited for lifetime predictions. In this context, improved sensors that are able to compensate temperature effects have been demonstrated as well. The results obtained have been shown to be a very promising first approach for the potential use of sensory gaskets for SHM.