The importance of toughness in manufacturing

Energy scaling poses the fascinating question of what do we really understand by the classifications of 'brittle' and 'ductile' as determined by the behaviour of laboratory-size testpieces since glass, for example, can be machined with continuous ribbons at micrometer depths of cut, and ductile metals will split at very large depths of cut. It all comes down to the toughness-to-strength (R/k) ratio.