Sensor-Integrating Bolt for Multiaxial Force Measurement

Standardized fasteners such as bolts are particularly suitable for structurally integrated force measurements, as they are located directly in the force flow and therefore allow the monitoring of the overall system status in situ via the multiaxis components of the acting forces. Available solutions are either tailored to specific applications or focus solely on measuring individual components such as the axial force. We present a sensor integrated bolt that is capable of measuring axial force and bending torques. Two cavities are designed within the bolt for the measurement and full integration of electronics, allowing for full encapsulation and autonomy of the sensor. Adjustments to the bolt, such as the cavity design, are optimized using a finite-element analysis (FEA) to minimize any weakening of its primary function. Losses in resilience correspond to the reduction of a strength class. The sensor incorporates three bending beams equipped with strain gauges benchmarked through a calibration setup, which demonstrates a low uncertainty of only 2.5% and the capability to decouple axial and bending loads from the sensor’s output signals. The sensor is integrated into a prototype M20 bolt by means of screwing and bonding connection. Measurements confirm a linear force transmission to the sensor with a linearity error of 1.0% for axial loading and a hysteresis error of 1.9%. Experimental validation confirms the bolt’s capability to detect bending moments under axial pretension, thus allowing for capturing all acting forces on such bolted connections.