Evaluation of the GrindoSonic Analyzer for Characterisation of Chemical Products

Authors: Atul C. Sarma, Ph.D., Whip Mix Corporation (1997)

Conclusion

On the basis of the above evidences, it can be concluded that the test method for determining Dynamic Young’s Modulus by the use of impulse excitation of sonic vibration could be as good as the determination of crushing strength, ifnot a superior test for characterization of our different products lines. However, ifwe incorporate this test method as a routine one, fbrther work and possible correlative studies may lead us to establish better criteria for achieving quality and dependable consistency in conformance and performance. The technique would definitely be a valuable tool for R. & D. . It can also be useful for quality control after necessary calibration and standardization for comparison with our existing test methods. Even if the Grindosonic test itself takes shorter time, the time required to prepare test specimen may not be reduced unless some modification could be incorporated. The most important advantage should be the elimination or minimization of the personal and operational errors from our test procedure.

ASTM standards(ln list a number of technical merits and demerits of the test method as follows:

1. The relationships between resonant frequency and dynamic modulus are specially applicable best to homogenous, elastic, and isotropic materials. Other materials need careful consideration due to the effect of inhomogeneities and an isotropy.

2. The procedure involves measuring transient elastic vibrations. Materials with very high damping capacity may be diicult to measure with this technique if the vibration damps out before the frequency counter can measure the signal.

3. The specific surface treatments (coating, machining, grinding, etching etc.) change the elastic properties of the specimen, and there will be accentuated effects on the properties measured by this flexural method, as compared to static/bulk measurements by tensile or compression testing.

4. The test method is not satisfactory for specimens that have major discontinuities, such as large cracks or extreme voids extensive throughout the specimen.

5. This test method for determining modulii is limited to specimens with regular geometries (rectangular, parrallelepiped, cylinders, and discs) for which analytical equations are available to relate geometry, mass, and modulus to the resonant vibration frequencies. The method cannot be used for testing materials that cannot be fabricated into such geometries.

6. The test method assumes that the specimens are vibrating freely, with no significant restrain or impediment.

7. For accurate measurement, the locations of the impulse point and transducer should not be changed in multiple readings.

8. If the frequency reading are not repeatable for a specific set of impulse and transducer locations on a specimen, it may be because several different modes of vibration are being developed and detected in the test. The geometry of the test specimen and desired vibration mode should be evaluated. If the impulse point and transducer locations are shifted to create and measure the single desired mode of vibration, more consistent measurement would be obtained.

However, the acquisition of the Grindosonic instrument will surely expand our testing capability in both R.& D. and QC areas.

More info can be found here: http://www.matertest.com/mt/GS0087-MT73.pdf