Structural health monitoring for CFRP bolted joints under tension/bending by embedded PZT transducers

Previous studies have demonstrated that health monitoring of carbon fiber-reinforced polymer (CFRP) laminates in service can be achieved using embedded piezoelectric (PZT) sensors. To extend this method to jointed structures, this study proposes a structural health monitoring approach for CFRP-bolted joints under tensile and bending load conditions using pre-embedded PZT sensors. CFRP specimens with embedded PZT sensors were fabricated, exhibiting ultimate tensile strengths of 47.92 kN (without PZT) and 49.84 kN (with PZT) under static loading. The sensor embedding positions were determined based on the numerical simulation results of the stress distribution around the embedded PZT sensor during tensile and bending loads. PZT sensor voltage signals, Acoustic Emission (AE) data, and Digital Image Correlation (DIC) images were collected during the experiments to establish correlations among different measurement methods. The results show that, in tensile tests, broad PZT signal pulses correspond to combined shear-out and tear-out failure modes, while narrow pulses indicate shear-out failures. In bending tests, low-frequency fluctuations in the PZT signal fitting curve indicate micro-damage, whereas rapid fluctuations signal catastrophic structural failure.