Micrometer cantilever experiments are frequently used to evaluate the fracture toughness of brittle and ductile materials and interfaces. For brittle materials the fracture toughness evaluation depends on the experimentally determined critical force and analytical models which account for the geometry. Although the models require an isotropic material and perfect geometries, these models are often used for non-ideal materials and geometries, e.g. FIB production induced rounded edges, non-parallel sides. In addition, the ductile fracture toughness depends on the fracture energy and the hence the cantilever deflection, which enters in more elaborate analytical models.
This contribution compares the analytical models for brittle failure and investigates the influence of anisotropy, pre-crack production shape and cantilever geometry. In addition, the influence of the testing equipment on the reported fracture toughness is discussed based on hundreds of FEM simulations. The fracture toughness of ductile materials is investigated fundamentally and the influence of pre-crack length and cantilever height are elaborated. Moreover, the effect of sample compliance and the origin of the analytical models is evaluated. I will close with an outlook on future fracture toughness experiments at the microscale.