PSI - Issue 11

Mario Fagone et al. / Procedia Structural Integrity 11 (2018) 250–257 Author name / Structural Integrity Procedia 00 (2018) 000–000

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fiber fabric using a wet lay-up procedure, as suggested by the producer: the lateral faces were sanded and cleaned and the primer was spread of the surface portion to be reinforced; within 24 hours, a first hand of epoxy resin was spread, the carbon fiber fabric was laid on the epoxy resin and a second hand of epoxy resin was spread as to form a composite having a final thickness of about 1 mm. All the specimens were reinforced at the two opposite lateral faces. 3.2. Test setup and procedure The test fixture and the test instrumentation are schematized in Figure 1 and Figure 3. The specimens, subjected to a four-point bending test scheme, were positioned vertically so that the self weight did not affect the test results. In order to align the end hinges to the specimen axes, two steel plates were glued to the end surfaces. The load was applied to the lateral surface of the specimens by means of two steel cylinders soldered to a steel plate, connected to a screw jack. Since the loading cylinders were directly in touch with the CFRP sheet, it was verified at the end of each test that they did not damage the reinforcement. The length of the middle constant bending moment region was 118 mm while the total length of the specimens was 935 mm.

Load

lvdt 3

lvdt 4

lvdt 2

lvdt 1

935 118

51

Figure 3. Test setup and instrumentation.

The load, applied by a screw jack as schematized in Figure 3, was measured using a 50 kN load cell. Two transducers (namely “lvdt 1” and “lvdt 2” in Figure 3) measured the displacement of the loading plate and two other transducers (“lvdt 3” and “lvdt 4”) measured the displacement of the steel plates glued to the end surfaces of the specimens, in order to determine the neat deflection of the beam. The load was applied with a constant displacement rate of 0.015 mm/s. 4. Experimental results 4.1. Monotonic tests The load-deflection diagrams obtained from monotonic four-point bending tests are reported in Figure 4a (continuous line). In order to make more easy the comparison among the global behavior of the specimens of 1T.0.M series, the load-displacement diagrams have been interpolated by trilinear diagrams (dashed lines in Figure 4) starting from the origin and defined by points P1, P2 and P3, being respectively the intersection point between the first and the second branches, the intersection point between the second and the third branches and the final point of the third linear interpolation branch, having abscissa equal to the deflection recorded during the test at failure. Note that, according to their definition, P1, P2 and P3 do not necessarily belong to the equilibrium path. The characteristic load values F1 and F2, corresponding respectively to points P1 and P2, the maximum load Fmax and the average slope of the first (K1) and second (K2) branches of the load-displacement diagrams are reported in Table 2, as well as the corresponding mean values and coefficients of variation. The experimental results