Hot pressing is mainly used to fabricate hard and brittle materials.
It is assumed that the brittle material has no tensile strength.
In the table is the computed brittle material stress.
Naturally brittle materials, such as glass, are not difficult to toughen effectively.
This makes homogeneous brittle materials much too dangerous to use in practice when there is any serious stress on them.
It is a brittle material that cannot be scratched with a knife.
But actually concrete differs from ideal brittle materials in many aspects.
Mother of pearl is a brittle material and can exhibit cracks after some use.
Consider strength measurements made on many small samples of a brittle ceramic material.
This is especially bad for brittle materials, because it will dramatically skew the results.