Issue 47

L. Marsavina et al., Frattura ed Integrità Strutturale, 47 (2019) 266-276; DOI: 10.3221/IGF-ESIS.47.20 269   max 1/2 / IC F K f a W B W  (1) with W specimen width, B = W/2 specimen thickness and f(a/W) is dimensionless SIF for SENB specimens, calculated with the following [42]:   2 3/2 1.99 ( / )(1 / ) 2.15 3.93( / ) 2.7( / ) / 6 / (1 2 / )(1 / ) a W a W a W a W f a W a W a W a W            . (2) Specimen Thickness B [mm] Width W [mm] Crack Length a [mm] Maximum load F max [N] Fracture toughness K IC [MPa·m 1/2 ] Mean Fracture toughness K IC [MPa·m 1/2 ] I.1 23.8 50.1 24.6 466 0.868 0.841 I.2 23.6 50.1 24.5 465 0.868 I.3 23.6 50.1 24.5 454 0.847 I.4 23.6 50.1 24.5 417 0.778 I.5 23.6 50.1 24.5 452 0.843 I.6 16.3 32 17.8 178 0.784 0.736 I.7 16.1 32 16.8 154 0.618 I.8 16.2 32 18.8 149 0.740 I.9 16.1 32 17.8 153 0.682 I.10 16.1 32 17.5 198 0.855 Table 1 : Mode I fracture toughness results The specimen dimensions, maximum load and mode I fracture toughness are summarized in Tab. 1. It could be observed that the maximum value of K IC = 0.841 MPa·m 1/2 was obtained for the 25 mm PB thickness. On contrary, the mode I fracture toughness for 16 mm thickness was 0.736 MPa·m 1/2 . Mode II fracture toughness tests Compact Shear (CS) specimens [43], Fig. 4b, were used for mode II fracture toughness determination. Tests were performed on a 100 kN A009 (TC100) universal testing machine, at room temperature and using 10 mm/min displacement control. Maximum load was used to estimate the mode I and mode II stress intensity factors. The SIFs solutions could be expressed on the form:   max , , iC i F K a f a W i I II H B   (3) with B as the specimen thickness, a as crack length and H as specimen width. A numerical calibration of the specimen was performed earlier by Petrova et. al. [44] using finite element analysis in order to determine the non-dimensional SIFs f i (a/W) , resulting:     4 3 2 4 3 2 / 2.472( / ) 1.784( / ) 1.135( / ) 0.213( / ) 0.295 / 6.416( / ) 11.154( / ) 8.992( / ) 3.667( / ) 1.01 I II f a W a W a W a W a W f a W a W a W a W a W           (4) It should be noted that even if the applied load produce shear in front of the crack, a small amount of mode I still exist at the crack tip [44], so the fracture thoughness could be expressed using an effective SIF value: