Ceramics Fail In Tension

They thus fail by breaking of the bonds between atoms which usually requires a tensile stress along the bond.

Ceramics fail in tension.

Crazing happens when the glaze is under extreme tension. The flexural compression failure begins by crushing of concrete at compression side followed by yielding of steel at tension side of the beam. It occurs when the beam is over reinforced which means the beam reinforcement ratio is greater than balanced reinforcement ratio as per aci 318 14. One category of failure with time in glasses and ceramics known as static fatigue is actually stress corrosion cracking promoted by moisture.

Specimens from the yz ft group showed 70 of partial failure in which the porcelain under compression failed before fracture of the framework material under tension resulting in delamination of the porcelain layer. Lateral cracks were observed in the porcelain layer subjected to compression. For a metal the compressive strength is near that of the tensile strength while for a ceramic the compressive strength may be 10 times the tensile strength. Tensile forces encourage crack formation and propagation.

Click a pore can exist in anything but let s consider a non crystalline phase for the time being. Ceramics are weak in tension and strong in compression. Thus sudden and catastrophic. Correspondingly crazing glaze under tension is ten times more prevalent as a glaze defect as compared to shivering.

Recognizing and understanding a problem are the first steps in solving any glaze defect. Alumina for example has a tensile strength of 20 000 psi 1138 mpa while the compressive strength is 350 000 psi 2400 mpa. Ceramics tend to be weak in tension but strong in compression. Applied stresses causing fatigue may be axial tension or compression flextural bending or torsional twisting.

Fatigue failure is brittle like relatively little plastic deformation even in normally ductile materials. Interestingly ceramic materials fail ten times faster under tension than compression. Recent results from a tension compression cycling study of alumina indicate that fatigue crack extension may occur. Micromechanically the breaking of the bonds is aided by presence of cracks which cause stress concentration.

Let s look at a simple pore.