Design of a sensor integrating bolt for multiaxial force measurement and development of a design methodology

Abstract Structurally integrated force measurements enable real-time monitoring of the overall system status. Existing sensor integration strategies in bolts often compromise mechanical integrity and deviate from standardized external dimensions, limiting their applicability. In this paper, a sensor is presented that is integrated into a M20 bolt to measure axial force and bending torques. The sensor is integrated directly into the bolt itself without altering its external dimensions. This integration method offers a more flexible solution compared to currently available solutions. Furthermore a method is presented that is extracted out of the development process. It includes the optimization of the design space for sensor and electronics as well as a general procedure based on the VDI 2206 and the methodology of testing. The sensor-integrating bolt retains 76.5% of the static load capacity of a standard bolt, which can be compensated by selecting a higher strength class. The sensor body consists of three vertical bending beams with applied strain gauges. The experimental findings have revealed a low linearity error of ±0.82% for axial load and ±0.11% for bending load. Linearity errors were measured at ±1.53% and ±0.52%, respectively. A flexible modular electronic platform has been developed, suited for complete integration into the bolt’s head. It allows experimentation with the sensors read-out electronics, and various modules for communication. The energy supply is evaluated using different energy harvesting and energy transmission concepts. The novel sensor integrating bolt can be used to measure all relevant loads on bolts and to indicate early failure like decrease of clamping force or opening joints. The method can be used to support future sensor integration projects.