Issue 50

A. Marinelli et alii, Frattura ed Integrità Strutturale, 50 (2019) 438-450; DOI: 10.3221/IGF-ESIS.50.37 447 0 0 lig     F W mg G A where δ ο is the deformation when the force has fallen to zero and A lig is the projection of the fracture area on a plane perpendicular to the beam axis (ligament area). The summary of average results for parameters as outlined above is presented in Table 3: Span/ Depth Ratio Span (mm) Fracture Energy (Nm/m²) Flexural Strength (MPa) Deflection at Peak Load (mm) CMOD at Peak Load (mm) 5/2 200 67.46 1.89 0.042 0.039 400 95.30 1.76 0.103 0.066 800 284.33 1.08 0.750 0.104 4 200 36.45 2.37 0.076 0.043 400 40.12 1.84 0.076 0.043 800 152.45 1.48 0.446 0.085 6 200 37.78 3.18 0.028 0.021 400 49.27 1.82 0.089 0.029 800 83.88 1.35 0.274 0.074 Table 3 : Summary of three-point bending tests results for Portland limestone. Completing the testing program as detailed in the section presenting the experimental protocol, led to observations on average results regarding the influence of the specimens’ geometry on key properties such as the deflection at mid-span and the CMOD at peak load, the flexural strength, the fracture energy and potential failure modes. For all three sets of span/depth ratios, there is a steep increase in deflections when the specimen span length increases to 800 mm. The magnitude of this increased rate of deflection at mid-span increases as the test specimen’s span/depth ratio decreases (Fig. 15a). In terms of CMOD, apart from the case of a span/depth ratio equal to 4 with span lengths of 200 mm and 400 mm, where values remained constant, in general it was observed that CMOD values increase at an almost uniform rate as their span length increased (Fig.15b). Larger values of CMOD were recorded as the span/depth ratio decreased. In terms of flexural strength, the span/depth ratio, which appears to be most sensitive to changes in size, is the largest, 6. The test specimens with span/depth ratios of 5/2 and 4 present very similar outcomes to each other, which is the case also for the span/depth being 6, with span lengths 400 mm and 800 mm (Fig.16a). The values of fracture energy obtained from test specimens with span/depth ratios of 4 and 6 are very similar for spans 200 mm and 400 mm while those for span/depth ratio of 5/2 are significantly larger (Fig.16b). Values of fracture energy for all span/depth ratios increase as test specimen size increases but particularly those of 5/2 and 4 appear to increase at a higher rate for spans above 400 mm. These findings are in good agreement with data existing in the literature, stating that fracture energy is directly influenced by the configuration of the test specimens [22]. Figure 15: Average values ± STDEV for (a) Deflection at mid-span vs. span length for all span/depth ratios; (b) CMOD vs. span length for all span/depth ratios. (a) (b)