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How can I explain high stress spot in bolt joint with femap/NX Nastran

Experimenter
Experimenter

I have a 3 pieces assembly jointed by bolt. I use RB2 in Femap/Nx Nastran to simulate the bolt. Two side parts are fixed. One part is under the upper right load from the two free hole. After run the analysis, I get results shown in attached picture.


I can see the bolt squeezing the side piece. so there is high stress area. This high stress is much high than the yield strength 36ksi.



The results show is the max value of nodal stress. if I use average stress of elements, the high stress is down to 48.4kis from 66.6.

it is still higher than yield strength. In real case. we know it could be safe. but not 100% sure. and we also want safety of 2. Could anybody help me the interpret this case? Is the result correct?
I would appreciate if somebody could help me out.

2 REPLIES

Re: How can I explain high stress spot in bolt joint with femap/NX Nastran

Legend
Legend

Looking at the model, this is the typical way of modeling the bolt joint to take into account the stiffness of the bolt joint. In this way to can analyze the overall behaviour of the system . But as, always for the stresses not enough,  as the stresses are very local phenomenon. To see the real stresses you should model the bolt joint(head, preload.etc....). You may have also  high stresses exceeding yield. Then you may have to run non linear with plastic material properties

 

With the approach you used you can say that the component is ok and you have localized stresses at this area. If the material is ductile the material can redistibute the stresses to the surrounding area (i see only high stresses on the outer surface)

 

Normally I usually leave free the RBE2 rotational dof  

 

Jon

Re: How can I explain high stress spot in bolt joint with femap/NX Nastran

Experimenter
Experimenter

Thank you so much, Jon.

 

Anderson