The fracture toughness (KQ) 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 KQ in Zr-based bulk glassy alloys (BGAs). The plane strain fracture toughness KIC of the BMG of Zr50Cu40Ni10 at.% prepared by an arc tilt casting method showed a large value of 53 MPa m1/2 under the conditions satisfying ASTM E399. With over(K, ̇) of about 0.1 MPa m1/2 s-1, there were cases that the KQ exhibited more than 100 MPa m1/2. The KQ increased with increasing R even for smaller R of 30 μm, and KQ exhibited more than 120 MPa m1/2 with R of more than 90 μm. KQ 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.
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