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 (over(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 Zr₅₀Cu₄₀Ni₁₀ 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 over(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.