Issue 47

M.F. Funari et alii, Frattura ed Integrità Strutturale, 47 (2019) 277-293; DOI: 10.3221/IGF-ESIS.47.21 284 The SCB loading scheme consisted of a point load centered on the top edge of the half-disc, which was spanned at 120 mm   1 2 60 mm S S   . In the ASCB loading scheme the left supports was moved to a 5.5 mm   2 S distance from the specimen mid span, with the second supports remaining at a 60 mm   1 S distance from midspan. All tests were performed in displacement control, at 2 mm/min rate. Load and displacement data were continuously recorded using the testing machine built-in sensors and data acquisition system. Additionally, fixed focal lens camera shots were taken every 5 second to digitally monitor the specimen change of configuration under the applied loads. (a) (b) Figure 4 : Experimental Setup: (a) SCB specimen; (b) ASCB specimen. Results Fig 5(a) and (b) show the average force vs. mid-span vertical displacement relations, exhibited by the SCB and ASCB specimens, respectively, as well as the xx  strain maps retrieved by means of the DIC processing. The black curves refer to the specimen displacement measured at the top point A, using the machine built-in transducer. These values are affected by the loading-pin penetration, as evidenced by the heavy non-linear behavior of the curve. An additional measure of the experimental displacement at the crack mouth (point B) was retrieved from the correlation of the digital images collected, each corresponding to a known load step. The DIC processing was performed using the freeware Matlab script Ncorr, developed by Blaber et al. [31]. The red curve obtained in this manner is a more realistic representation of the flexural deflection of the specimen, being only affected by minor local compressions occurring at the specimen supporting pins. The average values of maximum forces detected in the experimental tests, as detailed in Tab. 1, were employed for the calculation of the Stress Intensity Factors (SIFs). The SIFs for mode I, 1 c K , and mode II 2 c K , were computed according to the following expression, proposed by Ayatollah et al. [27]:   max 1 2 , , , 1, 2 2 ic i i P K a Y a R S R S R i Rt    (12) where max P is the average value of the maximum load experimentally measured either on SCB or ASCB specimens, and the functions   1 2 , , i Y a R S R S R are given by Marsavina et al. [28, 29]:                     3 2 1 2 2 2 2 5 4 3 2 2 2 2 2 2 2 2 6.235 15.069 17.229 1.062 1.884 7.309 5.037 2.77 5.075 1.983 Y S R S R S R S R Y S R S R S R S R S R S R           (13) Computed values of SIFs with reference to the two set of tests are listed in Tab. 1.