ASTM C158

Standard Test Methods for Strength of Glass by Flexure (Determination of Modulus of Rupture)

Theory:

ASTM C158 covers two test methods for examining the flexural strength of glass and ceramics. Glass samples are brittle and therefore are highly elastic. The almost perfect elasticity of the material causes the glass to shatter due to the tensile forces at the surface of the sample. These tensile forces increase as the sample bends. Therefore the modulus of rupture is a good indication of the tensile strength of a glass or ceramic material. 

Geometry:

Glass and Ceramic bend testing is usually performed on a square specimen. The specimens can be larger, such as 10x10 inches or more. For information on the exact size of the samples, please read the ASTM publication and refer to test method A or B. 

Solution:

Universal Grip offers a fully articulating 4 point bend fixture for performing this test. The contact spans are also extra wide so that they can contact a large area on the sample. UGC can offer contact spans of 8 inches or higher, depending on the exact application needs.

A dual column material testing system must be used for this test because of the size of the samples. Also, the test must be performed at very slow rates of speed. Galdabini's premium testing machines are able to run at 0.0005mm/min which is the slowest in the industry. Slow and highly controlled movement is ideal for Ceramics and Glass material testing.

Analysis:

The modulus of rupture (MOR) is also commonly known as the bending strength. MOR is taken as the highest load seen before rupture.