Elastic and electromagnetic monitoring of TRC sandwich panels in fracture under four-point bending

Textile-reinforced cementitious (TRC) sandwich panels with insulation core are mechanical- and material-efficient composites, however, under service loads might develop complex fracture that is still inadequately detected. Among damage mechanisms, the weak core-facing interfacial bond can substantially reduce its load-bearing capacity and lead to premature failure; therefore, early detection of damage is crucial to guarantee optimal long-term structural performance. Periodic inspection is necessary during the service life, however, there is neither a standardized methodology nor monitoring protocol that detects and characterizes premature interfacial debonding. In this study, a novel multi-modal monitoring is developed for the first time, based on acoustic emission (AE), digital image correlation (DIC), and millimeter wave (MMW) spectrometry, to characterize the response to bending of TRC sandwich beams. The core-facing interlaminar bond is artificially weakened during casting to simulate manufacturing defects. The proposed methodology showed high sensitivity to damage and complementarity of the techniques, where, AE allowed to characterize and locate damage, MMW showed high sensitivity to progressive failure, and DIC provided the strain data to validate and interpret AE, and MMW results.