Strength: Toughness Versus Hardness

This post is primarily intended as an educational one, to discuss some of the terminology and thought-processes involved in materials science, but it was inspired by world-building considerations. As you may recall, if you've been following along with what I've been reading (and my regular book reviews), I recently read a book called The Substance of Civilization, which detailed how the materials to which our species has had access have shaped the course of cultural evolution over the past ten thousand years. It prompted me to think in more detail about choice of materials and construction techniques in world-building.