When designing a vibration isolation solution, modulus and shape
factor are among the first variables described by shock and
vibration engineers. In Part
1 of a 3-part video series, E-A-R™ Application Engineer Chirag
Patel walks us through how to determine these attributes.

Inputs

The first step in the process requires knowledge of two inputs:
frequency and operating temperature. These inputs represent the
vibration issue that needs solved - what is the problem frequency
or frequencies being produced, and at what temperature(s) will the
device or component be operating. With these numbers in-hand, they
can then be applied to a material nomogram to derive shear modulus
and loss factor.

When examining a nomogram you will first want to notice the axis
on the right, Frequency, and top, Temperature. These correlate with
the two inputs described above. The two curved lines on the chart
represent the shear modulus (the "S"-shaped curve, shear stress to
shear strain) and the loss factor (the bell-shaped curve, energy
dissipated to energy stored). Using the inputs, find:

1) The point of intersection of
the diagonal temperature line and horizontal frequency line

2) At that point, draw a vertical
line

3) Where the drawn vertical line
intersects the "S"-shaped curve is the material modulus. The scale
for this is on the left (note: compressive modulus is approximated
3x shear modulus)

4) Where the drawn vertical line
intersects the bell-shaped curve is the loss factor. The scale on
the left is generally 10x loss factor (values to scale are
sometimes annotated in parenthesis)

In general, a higher loss factor is more desirable in most
applications. Many ISODAMP™ materials contain peak damping above 1,
which is considered highly damped, and some ISOLOSS™ SL materials
even reach 2! Material nomograms are available for all E-A-R™
Precision Electronics materials.

Shape Factor

While the modulus of the material displays its rigidity, shape
factor is also used in geometric design to add or remove stiffness.
This is calculated by dividing the area under load by the area free
to bulge. A rule of thumb is to use a shape factor of 0.5 - 1.0,
depending on the application and load. Features such as ribs are
often utilized to modify this value.

The next video, Part 2 of Designing a Vibration Isolation
Solution, will highlight stiffness and natural frequency.

For more than 40 years, Aearo Technologies LLC has led the way
in energy-control technology. We've pioneered new treatment
techniques and developed proprietary, high performance materials
that control unwanted energy.

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