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

29. Measurement of the loss coefficient with respect to strain of vibration-damping alloys

When measuring the loss coefficient of vibration-damping alloys, amplitude dependence occurs due to the damping mechanism. This is a characteristic not found in viscoelastic materials that are independent of vibration amplitude. For this measurement, when the center is excited, a strain gauge or similar device must be attached to the center position, and a graph must be created with the strain amplitude as a parameter. However, since attaching strain gauges to all samples is cumbersome and due to the signal-to-noise ratio, it is also advisable to take advantage of the fact that the strain amplitude at the center position and the tip position are proportional in the case of small amplitudes, and replace the tip position amplitude (measured with a laser vibrometer, etc.) with the strain amplitude at the center position for measurement.

The measurement block diagram is shown below.

Damping alloy loss coefficient strain-dependent measurement system

  • Figure 1

The graph below experimentally demonstrates that, for shapes with identical dimensions, thickness, etc., the tip amplitude-center strain amplitude is the same regardless of the Young's modulus of the material (data from seven different materials with different Young's moduli).

  • Figure 2

The measurement of the loss factor is:

  1. The amplitude is gradually changed, and the spread of the excitation velocity versus force (mechanical impedance) is determined using the half-width method (amplitude ratio is approximately 100:1).

  2. The device is excited with an impulse or a tone burst wave at the resonant frequency, and the loss coefficient is calculated from the time-domain decay rate via the logarithmic decay rate.

Two types are possible.

The following two figures were obtained using method 2 described above.

  • Figure 3

In addition to amplitude dependence, it also appears to depend on the thickness of the material. The following is a comparison of materials.

  • Figure 4

The figure below is a graph in which the horizontal axis is replaced with distortion amplitude (using different data than the previous figure).

  • Figure 5

Furthermore, it is easier to understand if you draw a contour plot as shown below, with the horizontal axis representing amplitude distortion, the vertical axis representing frequency, and the direction perpendicular to the plane of the paper (Z direction) representing the loss coefficient.

  • Figure 6