How does a bend test help estimate the tensile strength of brittle materials such as glass and ceramics?

Direct tensile testing is often difficult to perform on brittle materials like glass and ceramics. To estimate their tensile strength, a bend test is used instead.

During a bend test, the material is subjected to bending forces that create tensile (stretching) stresses on one side of the member and corresponding compressive stresses on the opposite side. Because these materials are typically much stronger in compression than in tension, the material will fail on the tensile side. By identifying the point of failure, researchers can determine the material's tensile strength.

However, this method is only applicable to a restricted class of materials and conditions, as it requires knowing the exact magnitude of the tensile stress at the moment of failure to accurately establish the material's strength.1