Standards Development

Scope

This document specifies methods for the determination of the elastic moduli, specifically Young's modulus, shear modulus and Poisson's ratio, of advanced monolithic technical ceramics at temperatures above room temperature. The document specifies three alternative methods for determining some or all of these three parameters:

a) Method A - the determination of Young’s modulus by static flexure of a thin beam in three- or four-point bending;

b) Method B - the determination of Young's modulus by forced longitudinal resonance, or Young's modulus, shear modulus and Poisson's ratio by forced flexural and torsional resonance, of a thin beam;

c) Method C - the determination of Young's modulus from the fundamental natural frequency of a struck bar (impulse excitation method).

This part of EN 820 extends the above-defined room-temperature methods described in EN 843‑2 to elevated temperatures. All the test methods assume the use of homogeneous test pieces of linear elastic materials. The test assumes that the test piece has isotropic elastic properties. At high porosity levels all of the methods can become inappropriate. The maximum grain size measured in accordance with EN ISO 13383‑1, excluding deliberately added whiskers, is less than 10 % of the minimum dimension of the test piece.

NOTE 1 Method C in EN 843‑2 based on ultrasonic time of flight measurement has not been incorporated into this part of EN 820. Although the method is feasible to apply, it is specialized, and outside the capabilities of most laboratories. There are also severe restrictions on test piece geometries and methods of achieving pulse transmission. For these reasons this method has not been included in EN 820‑5.

NOTE 2 The upper temperature limit for this test depends on the properties of the test pieces, and can be limited by softening within the timescale of the test. In addition, for method A there can be limits defined by the choice of test jig construction materials.

NOTE 3 It is possible that Methods B and Method C are not appropriate for materials with significant levels of porosity (i.e. > 15 %) which cause damping and an inability to detect resonances or natural frequencies, respectively.

NOTE 4 This method does not provide for the effects of thermal expansion, i.e. the measurements are based on room temperature dimensions. Depending upon the use to which the data are put, it can be necessary to make a further correction by multiplying each dimensional factor in the relevant formulae by a factor (1 + ΔT) where is the mean linear expansion coefficient over the temperature interval ΔT from room temperature.