Effects of loading rates, notch root radius and specimen thickness on fracture toughness in bulk metallic glasses

The fracture toughness ( K Q) tests were carried out in order to study the effect of loading rate ( K ˙ ), notch root radius ( R) and specimen thickness ( B) on the K Q in Zr-based bulk glassy alloys (BGAs). The plane strain fracture toughness K IC of the BMG of Zr 50Cu 40Ni 10 at.% prepared by an arc tilt casting method showed a large value of 53 MPa m 1/2 under the conditions satisfying ASTM E399. With K ˙ of about 0.1 MPa m 1/2 s −1, there were cases that the K Q exhibited more than 100 MPa m 1/2. The K Q increased with increasing R even for smaller R of 30 μm, and K Q exhibited more than 120 MPa m 1/2 with R of more than 90 μm. K Q decreases a little with decreasing the B from 2.3 to 0.12 mm was shown. In these cases, the estimated plane stress plastic zone sizes agreed well with the length of shear bands near the fatigue crack tips or notch roots on specimen surfaces.