Issue34

D. Scorza et alii, Frattura ed Integrità Strutturale, 34 (2015) 70-73; DOI: 10.3221/IGF-ESIS.34.06 71 E XPERIMENTAL RESULTS rom the analyses of the fracture surfaces of the as-received as well as the thermally pre-treated specimens, we can observe two different types of specimen: (a) The first type, named A-type and related to the as-received specimens (C0-2, C0-4, C0-5, C0-6) and the thermally pre-treated ones (C32-3, C32-4, C32-6), shows wide portion of Fe-hydroxides (represented by black crust coating the bioclasts or by refilling of stylolites) embedded in the matrix with allochemical grains on such failure surfaces; (a) The second type, named B-type and related to the as-received specimens (C0-1, C0-3, C0-7) and the thermal pre- treated ones (C32-1 and C32-7), shows wide portion of matrix with a packstone texture, with compacted thin-shelled bivalves and interstitial micritic matrix on such failure surfaces. Such types have different fracture behaviours, as can be observed from the graphs reported in the figures below, resulting from a statistical analysis of the data of each specimen type. The experimental results regarding the specimens C32-2 and C32-5 are not plotted in the following graphs, since their failure is reached when the material behaves again elastically and, consequently, we are not able to determine the correct value of the peak load and of the corresponding critical Stress Intensity Factor (SIF). From Fig. 2a, referred to the case of as-received specimens, we can observe that: (i) For small values of the relative crack extension (lower than 10%), the peak load values are greater. This happens for the B-type: the mean value of the peak load is equal to 567.77 N, and its variation is about 3.38%; (ii) For high values of the relative crack extension (greater than 10%), the peak loads obtained from the tests are smaller than the previous ones. This happens for the A-type: the peak load mean value is equal to 310.63 N and its variation is about 24.38%. We can observe that the reduction of the peak load mean value with respect to the first type is about 83%. Also the experimental data related to the case of thermally pre-treated specimens are plotted in Fig. 2b: in this case, the difference between A-type and B-type is less significant, with a peak load mean value equal to 311.31 N and a variation of about 18.20%. In the case of as-received specimens, Fig. 3a shows that: (i) For B-type, the variation of the initial compliance is very small and, therefore, the mean value of the Young Modulus is equal to 50.02 GPa with ±7.55%; (ii) For A-type, instead, the variation of the initial compliance is more significant and, therefore, the mean value of the Young Modulus is equal to 46.18 GPa with ±29.44%. In Fig. 3b, analogous results are reported for the thermally pre-treated specimens. We can observe that, also in this case, the difference between the two types is less significant than that for the as-received specimens. Fig. 3b also shows a sensible variation of the initial compliance and, consequently, the mean value of the Young Modulus is equal to 34.07 GPa with ±44%. 0 10 20 30 40 Relative Crack Length Increment, % 0 200 400 600 800 Peak Load, P max [N] A-type B-type As-received 567.77 N 310.63 N (a) 0 15 30 45 60 Relative Crack Length Increment, % Ther. treatment 323.25 N 303.35 N (b) A-type B-type Figure 2 : Peak load against relative crack length increment for: (a) the as-received and (b) the thermal pre-treated specimens. F (a) (b)