PSI - Issue 68

M. Totaro et al. / Procedia Structural Integrity 68 (2025) 197–204

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M. Totaro et al. / Structural Integrity Procedia 00 (2025) 000–000

3.

Results

3.1. Static characterization Fig. 2 shows the stress versus strain curve, obtained from tensile tests. The curve does not increase continuously until failure; instead, there is an initial load loss due to the failure of some fibre segments on the lateral sides, followed by a more significant load drop corresponding to the first delamination at ! = 375 ± 8.55 MPa. In this work, Basalt failure is defined as the stress value that leads to the first delamination, where the outermost ply detaches. Earlier load losses are considered only as initial damage that does not lead to the collapse of the structure in which the material is applied. Both tests with crosshead speed of 2 mm·min -1 and 4 mm·min -1 were conducted, but only the 2 mm·min -1 velocity was found to ensure a low heat exchange between the specimen and the environment.

Fig. 2. Stress vs strain curve.

The delamination instant was chosen to synchronize the temperature and load data. The applied stress is plotted versus the filtered temperature signal in Fig. 3. In the initial part of the ΔT vs t curve, a linear trend is clearly visible (Phase 1). Then, the temperature deviates from linearity (Phase 2) showing variable slope between different cases. This is followed by a temperature increase until failure. It is possible to draw two linear regression lines, one for Phase 1 and the other for Phase 2, and to determine the equations of these lines. By solving the two equations system, the coordinates of the intersection point of the two lines can be determined. The value of limit stress evaluated with STM is "#$ = 100.97 ± 7.73 MPa. 3.2. Fatigue characterization To compare the value of the stress limit with the fatigue limit, stepwise fatigue tests were performed with RTM. In particular, RTM can be used to assist in better interpreting static results and support the correctness of the selected transition points between Phase 1 and 2 in Fig. 3. Fig. 4 shows the temperature trend vs the applied stress level. For each stress level, the corresponding value of the stabilization temperature has been estimated. As observed, the temperature does not stabilize when the stress level increases from 110 MPa to 120 MPa, continuing to rise until specimen fails. By plotting the stabilization temperature against the corresponding stress level (Fig. 5), a bilinear trend is evident. By performing the linear regression of the lowest and highest sets of points and finding their intersection, the fatigue limit at R= 0.1 using TM can be assessed,