PSI - Issue 44

Andrea Meoni et al. / Procedia Structural Integrity 44 (2023) 1632–1639 Andrea Meoni et al. / Structural Integrity Procedia 00 (2022) 000–000

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Fig. 3. Reference system of the DIC monitoring during bending test and fracture at failure

4. Results

This Section collects the results obtained in the performed experimental tests. 4.1. Mechanical tests on beam and cube samples

Table 1 collects the results obtained by testing beam samples under bending. In this circumstance, doped beam samples showed slightly lower mechanical performance than plain beam samples. Likely, such a result can be attributable to a lower homogeneity of the composite material, due to the presence of the filler, compared to that of the plain matrix. Results obtained by carrying out compression tests on cube samples are collected in Table 2. A higher maximum compressive strength, also characterized by a lower value of the standard deviation, was determined by testing doped cubes. Accordingly, the conductive filler added to the plain matrices improved the mechanical behavior of the composite material under compressive stress states. 4.2. Sensing tests on beam samples Time histories of the total electrical resistance and applied strain obtained by testing beam samples under compression loads are reported in Fig. 4. Results confirm that both the tested samples were able to sense the applied load history, yet in general, the doped sample demonstrated a greater sensitivity with respect to the plain beam sample. All the instrumented sections of the doped beam sample were able to detect the load application by outputting, consistently, lower variations in their electrical outputs as the distance of the monitored section from the load application point increased. Similar behavior was less developed in the plain beam sample, given the poor sensitivity to the applied loads demonstrated by its outer section. Fig. 5 shows the cracking patterns obtained by carrying out three-point bending tests on the beam samples. Cracks formed in sections 1 and 2 of the plain sample, while they interested sections 2 and 3 of the doped beam sample. Fig. 6 illustrates the time histories of the total electrical resistance and applied load obtained by subjecting the beam samples to three-point bending tests. Both the tested samples detected crack formation by outputting variations in the trends of the relative resistance, yet only the outputs from the doped sample clearly localized the crack formed in the proximity of section 2 by means of a greater change in the electrical signal acquired from that section with respect to the others. 4.3. DIC The fracture opening plot defined in Section 3.3 are reported in Fig. 7. In detail, Fig. 7(a) shows the fracture opening plot associated with plain beam sample while Fig. 7(b) the fracture opening of the doped beam sample. Both fracture opening plots show that fractures arise in the neighborhood of the middle span of the beam samples involving the region 75 ≤ x ≤ 95. The time at which the crack starts are similar and consistent with the results shown in Fig. 6. Indeed, near to t = 40 sec, both samples display the growth of the fracture. It is observed that the ratio between the final values of the fracture opening of doped beam and plain beam sample is 0.8. Although a lower flexural strength of the doped beam samples than the plain sample (see Table 1), the best behavior is observed referred to the fracture evolution.