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Rigid Bolt with Spring and Pretension

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I have a question that comes from the user guide. (Radioss 2019 User's Guide p.239)



'To describe pretension with this method another two spring elements (/PROP/SPR_PRE and /PROP/ SPR_BEAM) need to be added.'


I have an example.


When the bolt joint with preloading (bolt joint stiffness 10000N/m, preload 10kN) is replaced by RBODY+SPRING element,  


1) Distance between node1,2,3 is 10mm?

2) In PROP/SPR_BEAM, K1 is 20000N/m? (due to series spring??)


3) In PROP/SPR_PRE, Stif0 is 10000N/m? (same as bolt joint stiffness)




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If you are using 2019 and modeling the bolts with solid elements then you can use the option /PRELOAD.   See the /PRELOAD reference guide and the

User's guide, Explicit Structural Finite Element Analysis, Loads, Preload


Unfortunately the /PRELOAD option, setup is not supported by HyperMesh but it is supported in HyperCrash 2019. 


If you are not modeling your bolts with solid elements but instead with springs, then you need to use the method you mentioned in your post.  The SPR_PRE spring only has stiffness in 1 degree of freedom (tension / compression between the two nodes.)  The SPR_BEAM spring has 6 degrees of freedom (DOF).  Since SPR_PRE is in parallel with SPR_BEAM, you set for SPR_BEAM, k1=0 and Stif0=10000 N/m.  Then for DOF k2-k6 in the SPR_BEAM you must calculate the correct stiffness for the other directions for your bolt. 



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Thank you for your answer.


In your answer, for x-direction DOF, Stif0 in the SPR_PRE replace k1 in the SPR_BEAM

and for other direction DOF, k2-k6 in the SPR_BEAM is used.


I have a question. 


Why should another SPR_BEAM be added?



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