Kbru or the bearing efficiency factor determines what the allowable load of the lug will be with respect to bearing stress. This value is determined by figure 9-2 in AFFDL-TR-69-42. The required unitless geometric ratio is e/D, please see calculated geometry for a description of e/D. LugCalc™ automatically queries the chart to determine the value of Kbru that coincides with the supplied e/D ratio. Range for e/D is from 0.4 to 2.4. Any value for e/D outside this range will be assigned the last chart value before exceeding the documented range.

Lug Bearing Failure Zone

Sometimes it may desirable to adjust the automatic output if the engineer or designer wishes to use a lower or higher value for experimentation or to match an existing value that was calculated manually. To do this, the user uses the K Offset % feature to manually adjust the automatic value up or down linearly by the desired percentage. When set to 0.0, no adjustments are made.

Kbr Function Screenshot

LugCalc will automatically calculate Fbru (allowable stress) and Pbru (allowable load) for the user displaying the equation used. The equations for Fbru and Pbru change depending on the nature of the material properties. LugCalc™ will automatically select the correct equation for you. See AFFDL-TR-69-42 for further detail.

AFFDL-TR-69-42, Kbru Chart