Comparative assessment of CPC and PZT sensor embedding strategies via FFF for structural health monitoring

Structural Health Monitoring (SHM) systems can rely on surface-mounted or embedded sensors; the latter approach protects against environmental exposure and enables placement within the host component, but is inherently constrained by manufacturing process compatibility. Fused Filament Fabrication (FFF) has emerged as a viable platform for embedded SHM, primarily through two strategies: Multi-Material Additive Manufacturing (MMAM) and Hybrid Additive Manufacturing (HAM). Despite growing interest, the effect of each embedding strategy on the structural integrity of the host component remains poorly quantified. This study addresses this gap through displacement transmissibility measurements on three FFF cantilever beam configurations: a Reference Beam (RB), a MMAM beam integrating a sensor based on Conductive Polymer Composite (MMAM-CPC), and a HAM beam with an embedded PZT piezoelectric sensor (HAM-PZT). Both MMAM-CPC and HAM-PZT sensors produce negligible stiffness changes. Resonance frequency shifts are driven primarily by mass addition, significant only for the heavier PZT (+6.04%, −2.6% frequency reduction). Nonlinear dynamic behavior is evidenced by a decrease in resonance frequency and an increase in damping with excitation amplitude, a trend observed independently of the sensor used and attributed to the viscoelastic properties of the PLA matrix. The PZT sensor demonstrates superior sensing performance, with consistent sensitivity of 0.147 ± 0.001 V/g-pk and reliable broadband response (R2 > 0.980). The CPC sensor, which sensitivity of 5.201 ± 3.012 × 103 g-pk−1, suffers from amplitude-dependency and irreversible resistance drift, raising concerns about its long-term operational reliability.