Past exam of the materials science course of the University of Cambridge / 2017 / Paper 1 / 6 / a

Make the implicit fixed-crack-geometry assumption explicit by writing ${\sigma }_f=C\sqrt{E{G}_c}$, where $C$ is common to the compared specimens and includes the crack-size dependence needed for dimensional consistency. linear elasticity givesThe appropriate materials merit index is therefore $G_c/E$, or its monotonically equivalent square root. This comparison holds crack geometry and the brittle-failure model fixed; changing crack sizes or yielding before fracture changes the selection problem.