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Bolted connections play an overriding role in ensuring functionality and are often subject to great stresses. Up to now, visual inspections or the regular replacement of components have been common practice. This makes it all the more necessary to consider optimal monitoring as early as the planning phase so that the inspection effort and scope can be minimized. Such concepts are particularly in demand for monitoring fastening systems in the wind power industry, railroad systems, aircraft or pipelines.

A bolt connects at least two components in a force-fit manner. Durability and strength are affected by environmental influences and interdependent forces such as pretensioning force and operating force. Based on a MEMS technology platform, a sensor module was developed that determines the preload force and the operating force as well as their change over time. The sensor consists of miniaturized strain gauges. These are arranged via a mounting bracket as a Wheatstone measuring bridge and mounted on a bolt head. The electronics for power supply, measured value recording and processing, as well as the interfaces for the output of the measured signal are coupled via the sensor module. Optimum packaging guarantees hermetically sealed encapsulation. Universal interfaces ensure that the measurement signal processing or output can be integrated into the user's measurement system.
This allows the user to flexibly design the measurement cycle depending on the general conditions on site, such as energy self-sufficiency, accessibility by qualified personnel, thus achieving longer maintenance intervals as well as the possibility of remote diagnosis.

The research and development work described was funded by the German Federal Ministry of Economic Affairs and Climate Action (BMWK) in the research project "Determination of the Operating Force of Fasteners" (BAVI).
Funding code: 49MF180163