PSI - Issue 78

Antonella D’Alessandro et al. / Procedia Structural Integrity 78 (2026) 1887–1894

1890

1.2. Experimental procedure Electromechanical characterization was conducted using an Instron 68TM-50 Universal Testing Machine. This equipment was also used to assess the damage-sensing capabilities of prismatic 3D-printed specimens. A displacement-control test was performed up to a maximum displacement of 1.5 mm, with incremental loading applied in each cycle to track crack initiation and propagation. Electrical measurements were acquired using an NI PXIe-1071 system. A ±10 V square wave at 1 Hz was supplied to the samples via a RIGOL DG-1022 function generator connected to two electrodes. Voltage drops across a shunt resistor and the specimen were recorded using both channels of the NI PXIe-4313 module (Downey et al. (2017)). The electrical current ( I ) was determined using Ohm’s Law (Equation 1) from the voltage drop across the shunt resistor, and the sample resistance ( R ) was subsequently calculated. The fractional change in resistance ( FCR ) was then computed (Equation 2) and correlated with a damage metric to evaluate damage sensing effectiveness. = ( ) (1) = ∆ 0 (2) where V(t) is the voltage, R 0 is the initial resistance of the sample, immediately before the application of the load, and Δ R is the change in resistance. 1.3. Principle Conductivity (σ) of the specimens was estimated based on Equation 3, where L is the distance between electrodes and A is the cross-sectional area of the sample. = (3) A correlation between the electrical response and the estimated elastic parameter of the prismatic samples was also established to support damage detection. To this end, an electrical parameter, 0 was defined to represent the variation in conductivity during the displacement-controlled loading cycles. Here, σ 0 indicates the conductivity of the sample in the cycle immediately before cracking. A mechanical parameter, dt , computed for each displacement-controlled loading cycle (Meoni et al. (2025)), is defined in equation 4. =1 − 0 (4) where E represents the estimated elastic modulus for each cycle, and E 0 corresponds to the value obtained in the cycle immediately preceding crack initiation. This mechanical parameter can be seen as a metric measuring the damage state of the beam. In a three-point bending configuration, the maximum bending strain (ε) occurs at the outermost layers of the beam and is related to the mid-span deflection ( δ) a s follows: =6 ∗ ∗ ℎ 2 (5) where h denotes the height of the beam, and D represents the span length between the two supports. The bending moment ( M ) at the midpoint of a simply supported beam under a central point load was computed following Equation 6: