Overview

The peculiarities of the mechanical behavior of ceramics did not go unnoticed, even as far back as 800,000 years ago, by flint makers or, more than 14,000 years ago, by makers of knives in obsidian a natural glass found on volcanic slopes. These primeval artisans knew that if on the one hand the materials that they were working with were brittle, they resulted on the other hand in efficient and durable tools: the edges of obsidian knives compete with the best present day steel edges. Later, they made use of the brittle nature of the stone for creating blocks with definite geometry and dimensions. In the 1 ^st century BC, King Herod constructed a fortress on the rocks of Massada; the rocks were wedged out to create large tanks by introducing wooden pegs in the surface cracks of rocks and then swelling these by soaking. The stress intensity factor was not invented yet: its effects were already known!

Yet, the mechanics of brittle materials is still a young and living science. Even now, the making of ceramic pieces for use in mechanical design, that are subjected to dimensional tolerances similar to those used for steel, or of complex geometry, gives rise to difficult problems, which hinder the large scale development of these materials, despite their extraordinary intrinsic properties. Hardness and brittleness: two fundamental characteristics sufficient to describe a ceramic, contribute to its originality and its specificity, but are also the root cause of all their...