Fig. 1.

Selected demonstration problem from a common sample to measure fracture toughness at small scales. A prenotched microcantilever with pentagonal cross-section, whose dimensions are $\left\{w,b,a,L_0,L_1\right\}$, is loaded at one end using a nanoindenter. The fracture toughness is directly correlated with the critical load at the onset of fracture as well as the specimen geometry. The relationship, ${\mathrm{\Gamma }}_{pent}$, that describes the stress intensity factor, $K_I$, at the crack tip for a given load, $P$, is required for a valid toughness measurement.