Determination of Modal Scale Factors

GageMap has the ability to determine the modal scale factors such that a node will reside at 100% of the material fatigue limit. This modal scale factor is determined using the following for each active node group:

  1. Determine the dynamic stress limit using each nodes static stress.
  2. Compute the ratio of the node dynamic stress to the vibratory limit.
  3. Identify the node with the highest ratio – this is the limiting node.
  4. The inverse of the ratio computed in #2 is the mode scale factor for the group.
  5. The minimum modal scale factor for each group is the modal scale factor,

For example if the vibratory limit for a particular node is 116 ksi and the nodal stress is 1,500 ksi the ratio is 1,500/116 = 12.931. If this is the node with the highest ratio the modal scale factor would be 1/12.931 = 0.077.


Application of Modal Scale Factors

The modal scale factors are then multiplied by the each gage nominal strain & stress values to arrive at strain & stress limits. In addition the modal scale factor is multiplied by the actual tip timing deflection to determine deflection limits.