18.104.22.168 Axial Lead Parts in Lateral Vibration
22.214.171.124 Axial Lead Parts In Lateral Vibration
Lateral motion occurs when an axial lead part is vibrated in a direction
perpendicular to its body and parallel with the PWB surface. The parts move
back and forth in an arc. This movement tends to fatigue the metal leads at
the lead bends and ends. In order to prevent this fatigue, a vibration level
must be calculated that will sufficiently vibrate the parts and the leads
without causing fatigue damage. In order to accomplish this, the deflection of
the part, due to a 1 G (static) load, is determined using the parameters in
Figure 5-5 and Equation 5-23.
weight of the part
Using the deflection due to self weight, the natural frequency of the part
can be calculated using Equation 5-24.
Next, calculate the bending and shear stresses for the 1 G (static) load.
The two stresses are calculated such that the overall stress on the lead wires
can be determined. The bending stress is calculated by using Equation 5-25 and
the shear stress by Equation 5-26.
Figure 5-5. Axial Lead Parts
Using the principles of Mohrís circle and the values calculated for bending
and shear stresses, the principal stress due to a static load can be
calculated using Equation 5-27. Equation 5-28 represents the principal stress
accounting for a typical radius of the lead bend.
Using Crandallís equation, a value for Q equal to 62.5, and o equal to .04, the Gout level can be
calculated as shown in Equation 5-29.
This G level is used in Equation 5-30 to determine the stress on the lead
The Gmax of the part is calculated using the endurance limit of
the lead material (max) from Appendix B and the calculated stress level
on the lead wire as shown in Equation 5-31. The Maximum Allowable PSD level is
obtained from Equation 5-32.