The static properties of a grinding wheel can be tested by compression, tensile or bending tests, in which the deformation of tool samples in the form of cylinders or rods is measured [QUIR80, p. 6]. Industrial practice is the three-point bending test, for example after DIN EN 993-7 [MERB03, p. 25, BOTS05, p. 88]. The bending strength is appropriate to assess the quality of brittle materials. Decneut et al. [DECN70] found a direct correlation between the Young’s modulus measured by bending tests and by grindo-sonic tests.
5.3.1.2 Elasticity Testing with the Grindo-Sonic Method
There is a direct correlation between Young’s modulus and hardness of the grinding wheel [DECN70, KLOC05a, RAMM74]. However, the Young’s modulus of the abrasive layer cannot be calculated from a given volumetric proportion and Young’s moduli of each component [RAMM74]. Therefore, the Grindo-Sonic method is used to determine the Young’s modulus of grinding wheels from the tool’s natural frequency (Eq. 5.8) [KLOC05a]. The Grindo-Sonic equipment measures the natural frequency of a wheel body that is positioned on three tips. The support defines the natural vibration mode. The Grindo-Sonic method can be also used for mounted points [KLOC05a].
(5.8)
F(a, ц) form coefficient depending on body dimensions, body form and ц ц Poisson’s ratio
Cj velocity of propagation of the longitudinal elasticity oscillation
p density
E Young’s modulus
Cracks change the natural frequency of grinding tools and can therefore be detected via Grindo-Sonic methods [RAMM74].