ASTM C848 Test for Young’s Modulus, Shear Modulus, and Poisson’s Ratio For Ceramic Whitewares by Resonance

Scope:

Specimens of ceramic whitewares possess specific mechanical resonant frequencies. Resonance frequencies depend upon the mass, elastic moduli, and geometry of the test specimen, and knowledge about these parameters helps to calculate the resonance frequency of a material. Resonance frequency values can be used to calculate elastic properties. Dynamic Young’s modulus is determined using the resonance frequency in the flexural mode of vibration. The dynamic shear modulus, or modulus of rigidity, is determined using torsional resonance vibrations. Young’s modulus and shear modulus are used to compute Poisson’s ratio. This test method is used in quality control and for determining whether a material meets specifications.

Ceramic whitewares that are elastic, isotropic, and homogeneous can be tested in ASTM C848. Cracks or voids represent inhomogeneities in the material; therefore, such materials cannot be tested with this method. Materials that cannot be prepared in a suitable geometry cannot be tested as well. 

This ASTM C848 test is nondestructive. Only minute stresses are applied to the specimen. The time during which stress is applied and removed is of the order of hundreds of microseconds. A range of acceptable resonant frequencies is determined for a specimen with a particular geometry and mass. Any specimen whose frequency falls outside this range is rejected.

Test Procedure:

This ASTM C848 test method determines the elastic properties of ceramics by calculating the resonance frequency of test bars. Resonance frequencies of test specimens are determined by exciting the specimens at different frequencies to find a particular frequency that matches the specimen’s natural resonance frequency. It is a hit-and-trial method. Specimens are excited by a transducer; a transducer transforms a set electric signal into a mechanical vibration which causes a vibration in the specimen. Another transducer converts the vibration in the specimen into an electric signal that is displayed on the screen of an oscilloscope to measure resonance. The dimensions of the specimen, its resonance frequency, and its mass are used to calculate Young’s modulus and shear modulus.

Video 01: What is resonance in physics?

Specimen size:

In ASTM C848, the specimens should be either rectangular or circular in cross-section. They should have a minimum mass of 5 g to avoid coupling effects. Their surfaces should be flat, and opposite surfaces should be parallel within 0.02 mm. Recommended dimensions of the specimen are 125 by 15 by 6 mm for bars of rectangular cross-section and 125 by 10 to 12 mm for the circular cross-section.

Data:

In ASTM C848, Young modulus, shear modulus, and Poisson’s ratio of ceramic whitewares are calculated and reported. 

Conclusion:

Ceramic whitewares that are elastic, isotropic, and homogeneous can be tested in ASTM C848. Cracks or voids represent inhomogeneities in the material; therefore, such materials cannot be tested with this method. Materials that cannot be prepared in a suitable geometry cannot be tested as well.