PSI - Issue 67

Oscar Aurelio Mendoza Reales et al. / Procedia Structural Integrity 67 (2025) 8–16 Mendoza Reales et. al./ Structural Integrity Procedia 00 (2024) 000 – 000

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2.2.2. Effect of temperature in transient regime To assess the electrical resistance of the SSCC, the four-probe method was employed. In this method, a direct current (DC) voltage is applied to the samples through the external electrodes and the voltage between the internal electrodes is measured and recorded by a data acquisition system. The power source provided a constant voltage of 4.0 V to the SSCC. Testing began only after 20 minutes of voltage application to minimize polarization effects on the electrical response. A 27 kΩ shunt resistor was connec ted in series with the electrodes to determine the electric current, which was subsequently calculated utilizing Ohm's first law. Two samples of SSCC were placed in a Controls 10-D1429/A environmental chamber, as presented in Fig. 2, to monitor their electrical resistivity simultaneously with a temperature increase from 25 to 60 °C in 120 minutes. Deformations of the SSCC due to thermal expansion were measured using the two strain gauges installed in opposite faces of the SSCC. The deformation measured by the strain gauges was orthogonal to the direction in which the copper plates were inserted. The temperature (T) versus strains (ε) curves were used to obtain the thermal expansion coefficient (α) for each sample by fitting equation 1. ∆ = (1)

(a) (b) Fig. 2. (a) Heating ramp and (b) SSCC samples in environmental chamber connected to the data acquisition system

2.2.3. Effect of temperature in steady regime

The SSCC were initially tested through the application of monotonic compressive loading up to 2.0 MPa. This process was carried out using a Shimadzu EH-F EM300K1-070-0A testing machine with a 300kN load cell, simultaneously monitoring the changes in its electrical resistivity using the same measurement circuit and experimental conditions described in the previous section. The obtained results were then normalized as Fractional Resistivity Change (FCR), using the initial resistivity (Ro) and the resistivity at a given time (Ri), as presented in equation 2. = − 0 0 100% (2 ) Subsequently, SSCC samples were enclosed in a heating furnace, as presented in Fig. 3, to determine the effects of temperature on the piezo-resistive properties of the composites. The SSCC were tested at room temperature (approximately 25 °C), 50 °C, and 75 °C. Samples were heated to the target temperature using a heating rate of