Testing in Tension and Compression

Tensile testing is not widely used for ceramics for the following reasons  

Machining needed to make the sample may introduce surface flaws. Fracture of the samples normally takes place by the cracks nucleated at the surface flaws. Perfecf alignment is necessary because ceramics fail after about 0.1% strain. Because of fhese difficulties, ceramics are more commonly tested in bending rather than in tension. 

Tensile strength of a ceramic is important in certain situations. For example, in the growth of single crysfals by the Czochralski method, the maximum weight of the crystal that can be produced is determined by the tensile strength of fhe maferial. 

In tension, the fracture results from the critical flaw size. In the case of failure under compressive sfress, it is the average stress value that determines the failure. 

Unstable crack growth under tension and compression in a brittle material. 

---