Determination of Modulus of Rupture of Glass ASTM C158-02

Determination of Modulus of Rupture of Glass ASTM C158-02

ASTM C158-02 measures the modulus of rupture, also known as the transverse flexural strength or flexural strength of glass and glass-ceramics, which is the maximum load capacity material can hold before it breaks. The center point loading test apparatus is used to measure the modulus of rupture and is expressed in the units of pounds per square inch (psi) and pascals or megapascals.


    ASTM C158-02 provides a parameter for the development of structural materials and includes information about the durability and resistance of the glass. The test is pertinent to prestress and annealed glass-ceramics. The flexural strength of glass is affected by certain variables linked to the test procedure like test environment, rate of stress, and the area under pressure.

    Test Procedure:

    In ASTM C158-02, load force F is applied to the glass. The glass is slightly elevated from the ground, and load force F is applied on the center of the beam of the glass. Using the experimental setup of the center point loading test, the flexural strength of glass is observed and analyzed for assessing all the parameters.

    Specimen Size : 

    The specimen length should be 0.5 inches or 12.7 mm (minimum length). The width of the glass should be at least 9.5 mm. The recommended value for width to thickness ratio is in the range of 2:1 to 10:1.


    The modulus of rupture σr is calculated by using the following equation


    where F denotes the load force (pounds/newton) or while x, y, and z are the size dimensions in three directions taken in inches or millimeters.


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