Knu or the net tensile efficiency factor determines what the allowable load of the lug will be with respect to tensile stress. This value is determined by figure 9-4 (b-d) in AFFDL-TR-69-42. The required unitless geometric ratio is D/W, please see calculated geometry for a description of D/W. LugCalc™ automatically queries the charts to determine the value of Knu that coincides with the supplied D/W ratio. Range for D/W is from 0.0 to 1.0. Any value for D/W outside this range will be assigned the last chart value before exceeding the documented range. Because Knu is also a function of Fty/Ftu and Ftu/E*e, multiple curves on multiple charts are required. LugCalc™ queries all the required charts and interpolates the value of Knu both between curves on a single chart and between curves of different charts.

Tensile Failure Mode

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.

Knu Screenshot

LugCalc will automatically calculate Fnu (allowable tensile stress) and Pnu (allowable tensile load) for the user displaying the equation used. The equations for Fnu and Pnu 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.

Tensile Efficiency Factor Curve, AFFDL-TR-69-42