Condition monitoring in polymer composites and structures based on continuous carbon fibers show overwhelming advantages over other potentially competitive sensing technologies in long-gauge measurements due to their great electromechanical behavior and excellent reinforcement property. Although carbon fibers have been developed as strain- or stress-sensing agents in composite structures through electrical resistance measurements, the electromechanical behavior under flexural loads in terms of different loading positions still lacks adequate research, which is the most common situation in practical applications. This study establishes the relationship between the fractional change in electrical resistance of carbon fibers and the external loads at different loading positions along the fibers’ longitudinal direction. An approach for real-time monitoring of flexural loads at different loading positions was presented simultaneously based on this relationship. The effectiveness and feasibility of the approach were verified by experiments on carbon fiber-embedded three-dimensional (3D) printed thermoplastic polymer beam. The error in using the provided approach to monitor the external loads at different loading positions was less than 1.28%. The study fully taps the potential of continuous carbon fibers as long-gauge sensory agents and reinforcement in the 3D-printed polymer structures.

Surface acoustic wave sensors offer overwhelming advantages over other potentially competitive sensing technologies in rotating mechanical structures for their wireless and passive capability. Nevertheless, the challenges of using these sensors have not been adequately addressed. Radio frequency signal of surface acoustic wave sensors acts as not only the role of data transmission but also the role of energy supply during the sensing system working process. Thus, the performance of surface acoustic wave sensors when they are used to monitor rotating spindles should be investigated due to the harsh metallic environments for radio propagation in machine tool. This article aims to experimentally study the performance of surface acoustic wave sensors on both rotating spindle with Computer Numerical Control machine tool and self-developed spindle apparatus. The measurement study is performed using a temperature surface acoustic wave sensor working in the Industrial Scientific and Medical (ISM) band (433.05–434.79 MHz). Experimental results have shown that transmission and measurement characteristics were closely depended on the surface acoustic wave sensor installation location and rotation speeds. The conclusions will directly guide the sensor location optimization, power setting, errors avoidance, or correction in the future work.