A fracture mechanics approach for the development of refractory materials with reduced brittleness

Ordinary ceramic refractories are used as lining material for industrial pyre-processes. A high resistance to mechanical failure from an imposed strain or thermal shock is usually termed ''flexibility''. A scientific approach to enhance this property is hindered by the fact that there is a lack of understanding, definition and measurement of this parameter in relation to its physical basis. Wedge splitting tests were performed on a variety of typically shaped refractories together with standard procedures. This type of test enables stable crack propagation even for relatively large specimen dimensions that are necessary due to the size effect. High ''flexibility'' proved to be achievable in low brittleness materials and can be characterised by a brittleness number, the characteristic length or the thermal shock fracture resistance parameter according to Hasselman. A sufficient decrease of brittleness can be successfully achieved by the formation of precracks during the burning process which enhance the development of a fracture process zone. For a magnesia refractory (with additions of magnesia-alumina spinel) a friction bridging mechanism plays an important role in reducing brittleness.