Pressure over-closure values appropiate for axially loaded lugs

[Stress_Eng]

This is the first time I’ve posted a question on this website. Out of personal interest, I’ve generated an analysis template that calculates lug stresses for an axially loaded pin in a lug and clevis joint, both of which have parallel sides with a radius (not square ended). I want to compare the template results to those obtained from a finite element analysis. I’m using PrePoMax to construct and run the FE model and FreeCad to generate the model. The models constructed are for Aluminum Alloy lugs and clevis joints with steel and titanium pins, at pin diameter to lug width ratios of 0.25, 0.50 and 0.75. My question is, what are the pressure over-closure values (surface spring stiffness) considered appropriate for the combination of materials being used? In some instances, the lug wall thickness may be considered relevant [(lug width – hole diameter)/2]. In situations where a small hole diameter is used (d/W = 0.25), would the full wall thickness be relevant? Any suggestions would be much appreciated.

 

[FEA way]

You can find some general recommendations regarding contact element stiffness in the CalculiX User's Manual (since you are using CalculiX for your analyses). There you will see that 5-50 times Young's modulus of adjacent materials usually makes sense. But it's really case-dependent and requires some testing. You may also find some general tips on the CalculiX forum ("Contact stiffness setting" thread).

 

[Stress_Eng]

Thanks for your feedback. I’ve done some investigating, as suggested. As two different materials are used, I’m currently using the equivalent single modulus equation given in Roark, for contact analysis. In addition, one of the forum post’s suggested viewing the output from COPEN, which gives the gap and penetration values. It was suggested that a value no larger than 0.001mm would be acceptable. My FE analysis is currently giving a max penetration of -0.000734mm. Seems reasonable. Thanks again!