PSI - Issue 42

Sabrina Vantadori et al. / Procedia Structural Integrity 42 (2022) 133–138 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 3 shows front sides and back sides of the fractured zones of the shot-earth specimens being analysed. It can be observed that cracks, starting from the notch tip, usually deflect due to the inhomogeneities embedded in the material and, consequently, such cracks grow under mixed mode even in presence of a Mode I remote loading. From Fig. 3, the crack kinking angle  for a given specimen is computed by averaging the angles measured on the front side and back side of the such a specimen. Moreover, when  is not constant along the crack path, the MTPM assumes that the crack at max P is composed by two branches, and the following procedure is employed: - if the length of the first crack branch is greater than the second one,  is equal to the orientation of the first branch; - if the length of the first crack branch is smaller than the second one,  is equal to the orientation of the second branch.

Fig. 3. Front side and back side of the fractured zone in each shot-earth 772 specimen analysed.

For each analysed specimen, the experimental values of max P and  are listed in Tab. 1 together with the computed values of E and ( ) S I II C K + according to the MTPM. Moreover, the values of the fracture toughness, S IC K , obtained through the original formulation of the TPM, are also reported in such a Table.

Table 1. Fracture test results: peak load, crack kinking angle, elastic modulus and fracture toughness.

S IC K [MPa·m 0.5 ]

( S I II C K + [MPa·m 0.5 ] )

max P [kN] 0.334 0.454 0.442 0.372 0.382

 [°]

E [MPa]

SPECIMEN

T1 T2 T3 T4 T5

0.210 0.378 0.336 0.272 0.275

26.50 17.50 34.50 38.00 30.00

6730.78 6881.41 7164.49 6703.77 7115.65

0.183 0.367 0.300 0.200 0.252

The fracture toughness average value determined by applying the MTPM is equal to about 0.261 MPa·m 1/2 , which is 11% lower than that computed through the TPM (0.294 MPa·m 1/2 ). Moreover, for the specimen T4, it can be observed a decrease of 26% of the fracture toughness value related to the MTPM with respect to that related to the TPM. Consequently, it can be stated that the use of the MTPM formulation prevents the overestimation of the