The resonant frequency of a sample is determined by it’s shape, dimensions, weight and elastic properties. So, by measuring the resonant frequency, dimensions and weight of a sample with a specific shape, we can calculate the elastic properties (ASTM E 1876).
In the impulse excitation technique the resonant frequency is determined by tapping the sample with a small hammer, recording the induced vibration signal with a microphone and analysing the vibration signal. This type of measurement is non-destructive, can be carried out in a matter of minutes and achieves overall accuracies of up to 1% if done correctly.
The impulse excitation technique calculates Young’s modulus, Shear modulus, Poisson ratio, internal friction and resonant frequency directly. By doing high temperature measurements, it’s also possible to determine relaxation, creep, brittle to ductile transition temperature, Debye temperature, …
Example 1: comparison with tensile testing
To compare the modulus data generated from tensile and resonant frequency and damping analysis, an inter comparison test was carried out using the BCR Nimonic 75 tensile reference material. This test was organized by National Physical Laboratory, Teddington, UK. The test showed tensile data has a greater scatter and uncertainties than the dynamic test methods .
Example 2: brittle-to-ductile transition temperature (BDTT)
The internal friction data has been successfully used to determine the brittle-to-ductile transition temperature (BDTT) of ceramic. Technically, BDTT can be defined as the temperature at where the exponential increase of damping is initiated. There are several possible explanations that contribute to the exponential increase of damping: grain boundary sliding, dislocation slipping at GB and dislocation activation inside grains .
- R. Morrell, D.A. Ford, K. Harris. NPL Measurement Note DEPC(MN)004 (2004) ISSN 1744-3911 (2006)
- Zhilin Tiana, Luchao Suna, Liya Zhenga, Jingyang Wanga, Junning Lib, Zijun Hub. In situ hot pressing/reaction synthesis, mechanical and thermal propertiesof Lu2SiO5. Journal of the European Ceramic Society 34 (2014) 4403–4409