Why Cracks in Ceramic Wear Protection liners are more important than you think.
Cracks in brittle materials have a lot of energy stored at their tip. In 1921 the British physicist A.A. Griffith worked out that every crack has enough energy at its tip to extend itself. He also worked out that once a crack reaches a critical length it will extend whatever the load on the material. The only question then is what will stop it.
That was the foundational insight for designing ceramic wear liners, a century ago. Since then, the practice of Ceramic Wear Protection has evolved in various ways, but the core concept has remained the same: the designers of such components do not design them to prevent cracking. They design them so that cracks do not cause any damage.
Ceramics are very different from steel. The biggest difference between the two is how they fail. Steel will slowly start to bend and eventually deform until it reaches its ultimate failure point. However, a ceramic tile will continue to be as rigid as ever until the point at which a crack front suddenly propagates throughout the material in a matter of milliseconds. The designer of a Ceramic Wear Protection system cannot hope to prevent every single crack in the material from growing to this size, but what they can do is to try to ensure that the crack is not allowed to propagate to such an extent before it is intercepted by some other feature of the design.
Designing for cracks within ceramic wear liners is a matter of controlling the crack’s path to cause the minimum amount of damage. The three main variables that are used are the joint geometry between tiles, the size of the individual tiles and the use of a backing layer. By making the individual tiles as small as possible the crack will reach a free edge before it has a chance to store too much energy. The joints between the individual tiles are designed to be staggered to prevent a single crack running between tiles. The backing layer is designed to be as resilient as possible in order to absorb the micro-shocks that cause the initial nucleation of a crack in the ceramic tile. These tools all work to allow a single tile to ‘chip’ rather than the whole liner to ‘break’. Further information on the failure of brittle materials if required can be obtained from the National Physical Laboratory (how fracture mechanics measures crack resistance).
For Ceramic Wear Protection, visit kingfisher-industrial.com/wear-protection/ceramics/.
In this sense the crack is not the enemy. It is the adversary that you cannot remove from the playing field. Thus your efforts are concentrated on arranging the furniture in the room so that the adversary cannot travel very far.
