The increased use of fiber composites and the systematic optimization of components presuppose a precise knowledge of the load situation. In many applications, sensor integration is the only way to meet the demand for modern lightweight structures with regard to production control, load monitoring, damage analysis and generating control signal.
The HBM LI66 strain gauge is embedded directly in the structure during the fiber composite production process. This allows for measurements in places that are no longer accessible after production.
Practical connection of the strain gauge after production
The most striking feature of the LI66 SG is the two vertically attached contact pins for contacting the strain gauge embedded in the material. The measuring leads are only connected to the gold-plated pins after manufacture, outside the structure, which makes all the handling easier.
The SG is designed so that depending on the requirement the contacting of pins can be on the inside or outside of the structure. Thus, for example, with sandwich structures, the measuring leads or customized electronics can be introduced into the foam core.
The special layout of the SG is designed in such a way that the measuring grid is outside the fibers running round the pin. Furthermore, special strain relief of the solder terminals prevents the forces working on the pin from being transferred to the measuring grid.
When the strain gauge is Integrated, it is cemented to the material by the matrix resin. The point of the pin concept is that it eliminates the need to embed the measuring leads in the fiber composite as well.
Functionality and measurement accuracy confirmed in investigations
The measurement performance of the integrated LI66 strain gauge has been verified in countless investigations. Results show that the high level of measurement accuracy provided by strain gauges is retained in full by this integration concept. Secondary investigations related to damage analysis indicate that the strain gauge is sufficiently sensitive to determine when there are cracks in the resin and delamination in the fiber composite component.
Further information on using the LI66 may be found in our technical article "Structural Integration of Strain Gauges".