Unidirectional Fatigue Tab

If the material being created is to be used in a fatigue analysis, fatigue data must be entered in the Fatigue tab.

N - Fatigue Data

This field contains experimental lamina fatigue data which are S-N data points. An S-N data point contains the following information:

• S - maximum lamina stress reached in a load cycle (the units of stress must be consistent with the unit set chosen)
• N - the number of load cycles to failure
• f - the frequency of the loading in Hertz (cycles per second)
• R - ratio of the minimum stress to the maximum stress
• Angle of Loading - the angle of loading off from the axis of the fiber, in degrees

This data is used to optimize material fatigue constants used in a Helius PFA fatigue analysis.

At least two data points at a 0-2o load angle and two data points at a 2-90o load angle are required to perform the optimization.

Suppose the data below is provided as experimentally measured fatigue data. The data would be entered into the GUI as shown below.

A Note on Material Strengths

You must provide the out of plane shear strength (S23) when creating a material for use with Helius PFA. A good approximate value if no experimental value exists is 5.0E+7 Pascals. The equation below can also be used as an estimate for S23:

where S22Tension is the transverse tensile strength and S22Compression is the transverse compressive strength.