Frequently Asked Questions

Basically, a sample is mechanically excited with a small hammer. By hitting the sample, a vibration is induced in the sample which will be detected with a microphone (=listen to the “ping”) or laser vibrometer (in vacuum) and the software package uses this information to determine the resonant frequency and internal friction of the sample. Afterwards, the resonant frequency together with the dimensions and the weight of the sample is used to calculate the elastic properties (Young’s modulus, shear modulus and Poisson’s ratio) of the sample according to the ASTM E1876-15 standard.

In our high temperature systems, the impulse excitation measurements are performed inside a special furnace during predefined time intervals during the heating and cooling cycle. In this case, we can examine the changing elastic properties of samples vs. temperature continuously. Today, the complete temperature range between -50 °C and 1700 °C can be covered dependent on the specifications of each high/low temperature system. We produce systems that can perform measurements in air or in controlled atmospheres (inert, reducing, vacuum, …).

Generally, we prefer rectangular bars to obtain the Young’s modulus, shear modulus and Poisson’s ratio of the materials. However, also cylindrical rods (only Young’s modulus) and discs can be measured. In the case of discs, it’s possible that specific vibration modes can’t be excited and therefore the elastic properties can’t be calculated. This can only be verified experimentally and is dependent on the disc material properties.

Below you can find a reference document, which gives some guidelines to prepare a sample, which can be measured using the impulse excitation technique (IET) at room temperature and at elevated temperatures. In general, rectangular bars are preferred.

Recommended sample dimensions

If these sample dimensions are not feasible for your applications, contact us to discuss other opportunities!

The most important parameters to define the measurement uncertainty are the mass and dimensions of the sample. Therefore, each parameter has to be measured (and prepared) to a level of accuracy of 0.1 %. Especially, the sample thickness is most critical (third power in the equitation for Young’s modulus). In that case, an overall accuracy of 1 % can be obtained practically in most applications. Nevertheless, the accuracy of the calculation equations can also play an important role. However, these are consistent to a level better than 1 % if the sample sizes are in agreement with our recommendations.

Yes, according to the ASTM E1876-15 standard because the Poisson’s ratio is calculated by Hooke’s law which in only valid for isotropic materials. Special attention has to be taken for refractory materials or composites where the smallest dimension of the sample should be at least 4 times the largest grain or particle size. Nevertheless, for anisotropic materials, the Young’s modulus can be calculated along the length direction of the sample.

Considering the importance of elastic properties for design and engineering applications, a number of experimental techniques are developed and these can be classified into 2 groups; static and dynamic methods. Statics methods (like the four-point bending test and nanoindentation) are based on direct measurements of stresses and strains during mechanical tests. Dynamic methods (like ultrasound spectroscopy and impulse excitation technique) provide an advantage over static methods because the measurements are relatively quick and simple and involve small elastic strains. Therefore, IET is very suitable for porous and brittle materials like ceramics, refractories,… The technique can also be easily modified for high temperature experiments and only a small amount of material needs to be available.

For predefined shapes like rectangular bars, cylindrical rods and discs, we can calculate the elastic properties from the measured resonant frequencies. However, we can also analyze the obtained vibration signal from the damping/internal friction point of view. This gives information about the energy dissipation processes in a material due to the movement of microstructural features. For example, the interaction of point defects with dislocations in metals, phase transformations, brittle-to-ductile transition temperatures,… can be studied.

On the publications page, an extended list of recent publications with the IMCE RFDA systems can be found. They are grouped with respect to the different materials or applications.

Below you can find a table to compare the specifications of the different RFDA high temperature systems.

Comparison RFDA high temperature systems

If you still have questions regarding the RFDA high temperature systems, do not hesitate to contact us!

Yes, IMCE offers a reliable impulse excitation measurement service to determine the Young’s modulus, shear modulus and Poisson’s ratio, resonant frequency and internal friction at room temperature and/or at elevated temperatures up to 1700 °C according to the ASTM E1876-15 standard.
After the samples are received at IMCE, they will be analyzed with a short turnaround time and the results will be presented in a clear measurement report.

Contact us to discuss an optimal sample preparation!

It’s possible to measure coatings using the impulse excitation technique. Normally, the elastic properties of the substrate have to be measured first. Afterwards, the coated sample has to be characterized. From the difference in resonant frequency, it’s possible to calculate the Young’s modulus of the coating. However, an accurate thickness measurement of the coating is very important in the calculations and for very thin coatings, the impact on the resonant frequency of the substrate can be small.
If you are interested, contact us to discuss the possibilities in detail!