Sensitive washer detects clamping force of bolted joints


Influencing factors such as surface properties of the contact surfaces, friction, tightening methods or operating loads determine the function and safety of bolted connections. Particularly in difficult-to-access locations on oil and gas platforms, wind turbines or underwater pipelines, tests of bolted connections are only possible with great effort and expense. Usually, the load cannot be predicted exactly. Bolts that had sufficient safety reserves at the time of construction can reach load limits and fail due to the extreme operating conditions. In order to be able to retrofit special bolt connections, the CiS Research Institute developed a sensitive washer together with an industrial joint partner in a ZIM project (Screw Fixing Monitoring).

The measuring system is based on silicon strain sensors, which were integrated into the spring body designed as a washer. To ensure that the measuring system does not represent a weak point for the connection, the mechanical properties of the spring body correspond to those of a solid washer for high-strength screw connections. In particular, the clamping forces with which the assembled plates are held together can be measured. For verification and testing, a measurement method was developed that experimentally verifies the theoretical assumptions and simulations. Following the development of a sensor for measuring the preload force on a bolt head, this sensitive washer expands the possibilities for measuring forces on safety-relevant bolted joints.

The research and development work in the "Screw Fixing Monitoring" project was funded by the German Federal Ministry for Economic Affairs and Energy.
FKZ: ZF4001703HBB