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Technical Report on Vibration-Damping Materials and Their Performance Measurement 11-2

29. Measurement of the loss coefficient for the strain of damping alloys.

When measuring the loss coefficient of damping alloys, amplitude dependence occurs due to the damping generation mechanism. This is a characteristic not found in viscoelastic materials, which do not depend on vibration amplitude. For this measurement, it is necessary to attach strain gauges at the central position during central excitation and create a graph with the strain amplitude as a parameter. Additionally, due to the complexity of applying strain gauges to all measurement samples and the issue of signal-to-noise ratio, it is also advisable to utilize the proportionality between the central strain amplitude and the tip amplitude in the case of small amplitudes, replacing the tip amplitude (measured with a laser vibrometer, etc.) with the central strain amplitude for measurement.

Below is the measurement block diagram.

Damping Alloy Loss Coefficient Strain Dependence Measurement System

  • Figure 1

The graph below shows the results of an experiment demonstrating that if the dimensions and thickness are the same, the tip amplitude and central strain amplitude will be the same regardless of the Young's modulus of the material (data from seven types of materials with different Young's moduli).

  • Figure 2

The measurement of the loss coefficient is;

  1. Gradually change the amplitude and determine the mechanical impedance from the spread of the excitation speed against force using the half-value width method (the amplitude ratio is about 100:1).

  2. Calculate the loss coefficient by exciting with an impulse or resonant frequency tone burst wave, and deriving it from the time-domain decay through the logarithmic decay rate.

Two types can be considered.

The following two types of diagrams were obtained by the method mentioned above.

  • Figure 3

In addition to being dependent on amplitude, it seems to also depend on the thickness of the material. Below is a comparison of materials.

  • Figure 4

The following figure is a graph where the horizontal axis has been replaced with strain amplitude (using different data than the previous figure).

  • Figure 5

Additionally, it is easier to visualize by creating a contour plot where the horizontal axis represents amplitude distortion, the vertical axis represents frequency, and the contour lines represent the loss coefficient in the direction perpendicular to the paper (Z direction).

  • Figure 6