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ASTM C158 | Glass | Modulus of Rupture and Flexural Properties

ASTM C158 describes two test methods to calculate the tensile strength of glass and ceramics, used in commercial and residential construction projects. Both test methods measure the modulus of rupture to determine the highest load level a specimen can tolerate before it breaks. Test Method A assesses the modulus of rupture of flat glass, while Test Method B compares the modulus of rupture in specimens with rectangular or elliptical cross sections.

Before conducting ASTM C158, it is important to read the entire specification in the relevant ASTM publication.

ASTM C158 | Glass | Modulus of Rupture and Flexural Properties

Test Method A Procedure

  1. Refer to the standard for the proper way to cut, size, count and prepare the specimen.
  2. Position the specimen in the bend fixture.
  3. Apply load to the specimen, as specified for annealed glass and prestressed glass, at a constant rate until the specimen breaks.
  4. Follow the directions to identify where the point of failure occurred.

Test Method B Procedure

  1. Refer to the standard for the proper preparation of the specimen.
  2. Measure the specimen as described in the test procedure. 
  3. Secure the specimen in the bend fixture.
  4. Constantly apply the load at the specified speed until the specimen fractures. 

Calculations:

  • Modulus of Rupture
  • Maximum Stress due to initial load if present
  • Rate of Increase of Maximum Stress

ASTM C158 | Glass | Modulus of Rupture and Flexural Properties

ASTM C158 Recommended Equipment
Testing System
Fixturing
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