On the fracture toughness of bulk metallic glasses under Berkovich nanoindentation

Measurements of fracture toughness from the crack tip opening displacement (CTOD) testing methods are complex and paramount important for a range of bulk metallic glasses (BMGs). In this work, we attempted to propose an indentation protocol to evaluate indentation fracture toughness based on two key considerations: First, the plastic deformation induced damage to the characteristic fracture initiation point calculated from integrating the indentation load-displacement curves is obtained and used to estimate indentation fracture toughness. Second, the continuum damage mechanics theory has been adopted to identify the characteristic fracture initiation point. To verify the applicability of the suggested approach, fracture toughness values of BMGs were estimated and compared with those from CTOD tests in the literature. The estimated fracture toughness values Kc obtained from the indentation tests agreed well with those K-Q from the CTOD tests within an approximately relative difference of 10%. We also found that K9 linearly correlates with K-C (K-Q = 1.1K(C) - 3.7). The value of K-Q in Al-based BMG is predicted to be similar to 35 MPa root m.