ASTM C848

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

Description:

Significance and Use

3.1 This test system has advantages in certain respects over the use of static loading systems in the measurement of ceramic whitewares.

3.1.1 Only minute stresses are applied to the specimen, thus minimizing the possibility of fracture.

3.1.2 The period of time during which stress is applied and removed is of the order of hundreds of microseconds, making it feasible to perform measurements at temperatures where delayed elastic and creep effects proceed on a much-shortened time scale.

3.2 This test method is suitable for detecting whether a material meets specifications, if cognizance is given to one important fact: ceramic whiteware materials are sensitive to thermal history. Therefore, the thermal history of a test specimen must be known before the moduli can be considered in terms of specified values. Material specifications should include a specific thermal treatment for all test specimens.

Scope

1.1 This test method covers the determination of the elastic properties of ceramic whiteware materials. Specimens of these materials possess specific mechanical resonance frequencies which are defined by the elastic moduli, density, and geometry of the test specimen. Therefore the elastic properties of a material can be computed if the geometry, density, and mechanical resonance frequencies of a suitable test specimen of that material can be measured. Young’s modulus is determined using the resonance frequency in the flexural mode of vibration. The shear modulus, or modulus of rigidity, is found using torsional resonance vibrations. Young’s modulus and shear modulus are used to compute Poisson’s ratio, the factor of lateral contraction.

1.2 All ceramic whiteware materials that are elastic, homogeneous, and isotropic may be tested by this test method.2 This test method is not satisfactory for specimens that have cracks or voids that represent inhomogeneities in the material; neither is it satisfactory when these materials cannot be prepared in a suitable geometry.

NOTE 1: Elastic here means that an application of stress within the elastic limit of that material making up the body being stressed will cause an instantaneous and uniform deformation, which will cease upon removal of the stress, with the body returning instantly to its original size and shape without an energy loss. Many ceramic whiteware materials conform to this definition well enough that this test is meaningful.

NOTE 2: Isotropic means that the elastic properties are the same in all directions in the material.

1.3 A cryogenic cabinet and high-temperature furnace are described for measuring the elastic moduli as a function of temperature from −195 to 1200 °C.

1.4 Modification of the test for use in quality control is possible. A range of acceptable resonance frequencies is determined for a piece with a particular geometry and density. Any specimen with a frequency response falling outside this frequency range is rejected. The actual modulus of each piece need not be determined as long as the limits of the selected frequency range are known to include the resonance frequency that the piece must possess if its geometry and density are within specified tolerances.