ABSTRACT
There is currently a large demand for aluminum components to measure the mechanical and thermal loads to which they are subjected. With structural health monitoring, components in planes, vehicles, or bridges can monitor critical loads and potentially prevent an impending fatigue failure. Externally attached sensors need a structural model to obtain knowledge of the mechanical load at the point of interest, whereas embedded sensors can be used for direct measurement at the point of interest. To produce an embedded sensor, which is automatically encapsulated against environmental influence, the sensor must be able to withstand the boundary conditions of the host component's manufacturing process. This embedding process is particularly demanding in the case of casting. Previous work showed that silicon-based sensors have a high failure rate when embedded in cast aluminum parts and that using aluminum as a substrate is preferable under these circumstances. In the present paper, we present the fabrication process for the combination of a thick-film insulation and a thin-film strain gauge sensor, on such an aluminum substrate. The sensor is capable of withstanding high temperatures of at least 600 °C for over 20 min and a subsequent embedding in a gravity die casting process.
ABSTRACT
Moisture diffusion in carbon fiber composites changes the mechanical properties of the composite. Therefore, a monitoring method of the actual content of moisture in the composite is important. However, at the moment there are no online methods established. A common method is the measurement of the mass changes due to water uptake. This method is not suitable for online monitoring of a real composite part in service. We demonstrate that miniaturized flexible interdigital sensors are suitable for moisture measurement inside the carbon fiber composite. These sensors are directly integrated inside the composite. It was already demonstrated that these can be successfully used for resin-curing monitoring as a primary application. Here we demonstrate that the same sensors are also suitable for moisture measurement inside the material. In order to do so, we expose samples with and without integrated sensors to hot-wet conditions and measure the dielectric changes with the sensors and the mass gain. The moisture concentration and the measured admittance can be directly correlated to each other. This demonstrates that the sensors can be used for moisture measurement as a secondary application. In addition, it is shown that the sensors have the potential to measure the moisture locally inside the material.
