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A Time-domain Reflectometry Method for Automated Measurement of Crack Propagation in Composites during Mode I DCB Testing

This article describes a new technique for automated measurement of crack initiation, growth, and propagation in composite materials during mode I double cantilever beam (DCB) testing. The proposed method uses time-domain reflectometry (TDR) to detect changes in geometry and electromagnetic properties (dielectric or magnetic) along a transmission line that can be embedded in or bonded to the surface of the specimen. Two types of transmission line TDR sensors are evaluated (IM7 carbon fiber and ARACON) during DCB tests. A P-SPICE transmission-line simulation model is used to verify the baseline signal response for the DCB sensor and the sensitivity for crack detection, with good agreement. Comparison with standard visual methods in DCB testing showed excellent correlation in crack location, crack propagation (LC), and the interlaminar fracture toughness (GIC) values. The TDR sensor design and model-based parametric studies are carried out to determine optimal sensor geometry and configuration. The results demonstrate that the TDR-based method can measure crack propagation parameters at high resolution and accuracy, in an automated manner using low-cost sensors.