PSI - Issue 78

Paolino Cassese et al. / Procedia Structural Integrity 78 (2026) 607–614

610

The final mixture was leveled to the standard measures, and four copper mesh leaves, of size about 35 × 70 mm 2 , were gently inserted perpendicular to the largest dimension until almost 80% of the cross section was covered. The specimens were cured for 28 days in an environmental chamber under controlled temperature (T) and relative humidity (RH) conditions (T = 23 ± 2 °C; RH = 55 ± 5%). A cured specimen within the environmental chamber is shown in Fig. 2.

3

3

4

3

3

Fig. 2. Picture of a cured specimen.

2.2. Test setup and procedure The self-sensing response of the specimens was investigated through electromechanical tests. Each specimen was subjected to quasi-static cyclic uniaxial compression load while its electrical properties were continuously monitored. The compression load was applied using a universal testing machine model INSTRON 5500. The load time history was characterized by: (i) a first linear loading branch up to 4 kN; (ii) a constant load phase at 4 kN; (iii) seven compression cycles between 3 kN and 5 kN, with constant loading rate under displacement control. The compressive load levels were selected to obtain reversible elastic deformation. The electrical response was measured using a four-probe scheme. The electrical properties were read using an LCR meter and source unit based on programmable hardware and controlled by software developed in the LabVIEW programming environment. The AC technique was used to reduce the effect of polarization. The electrical signal was characterized by a frequency of 10 Hz and a voltage of 1 Volt. These values were selected after some previous trials. Since the main objective of the experimental program was to estimate the self-sensing properties of the tested SSCCs, the specimens were equipped with a couple of linear strain gauges with a length of 60 mm, pasted along the midline of the two opposite surfaces perpendicular to the copper electrodes, in the load direction. A schematic sketch of the test setup with the installed specimen is shown in Fig. 3. Before starting the loading protocol, the specimens were subjected to the selected AC signal for some minutes until a stable reading was obtained. The electrical properties (impedance, resistance, capacitance) were measured by the LCR meter and recorded by the acquisition system during the tests. Starting from the measured resistance ( R ), the self-sensing response can be expressed as the Fractional Change in Resistance, known as the FCR ratio, and defined in Eq. (1), where R and R 0 are the actual and the initial values of electrical resistance, respectively.

R R R

 − R R

FCR

= =

0

(1)

0

0