Hi,
I am new to Prepomax and to understand it I used a Square section 300x300x1500mm and fixed one end and applied load of 10000N on the bottom area of the other side at distance of 100mm from the edge, the results do not align with hand calculations too. Do I need to check on anything.
How did you apply the load ? As concentrated force or surface traction ?
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I think I need to add a warning when more than 5? nodes are selected for the concentrated force. I see a lot of problems with new users. Other suggestions?
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Maybe a warning when selecting a face on the geometry for concentrated force.
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Please check this: Don't apply concentrated force load to surfaces
Thank you for the reply. I read in the forum that there is no spring point to point connection as for now, any other way to get around this. I am trying work on assemblies, where in I bolt two parts with a spring connection.
Forgot to type, the issue is sorted now, applied the surface traction.
If you need to connect two holes you can create a rigid body connecting a reference point and both hoels.
rigid body does not take the spring constants/stiffness idealized for the bolt?
A rigid body has infinite stiffness. So, it increases the stiffness of your model.
what would be the alternate to rigid body to idealize bolts, I would have to enter bolt stiffness values. The model which I would practise has got many bolts and want to get away using spring constraints with stiffness to tie both the hole reference points
You could use 2 node spring elements or beams (both not currently supported in PrePoMax and thus require manual definition in Keyword Editor) and connect them with rigid body constraints to the rest of the model. It’s a common approach in other FEA software.
I would suggest looking into the EnterFea blog for different approaches for bolt modeling (I really like the blogs from Lucas).
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Or the “Practical Finite Element Analysis for Mechanical Engineers” book by D. Madier. He also covers this. Łukasz has a civil engineering point of view while Dominique is an aerospace engineer.
This paper is interesting too: http://wanderlodgegurus.com/database/Theory/FEA%20Bolt%20and%20Bolted%20Joint%20Modeling.pdf
Thank you guys for the reference, I normally use 2 node spring constraint this was useful doing modal and dynamic frequency analysis.
since CalculiX work best with solid element, so the bolt model also. Simplification can get complicated when trying to represent bolt by spring, it’s a nonlinear and work in tension or compression only. Three of force transmitted in bolt, only two in normal/axial and shear being considered using spring element. Another one in bending does not, but simplified solid model is complete one and most accurate.
regarding rigid body with reference nodes connect to spring element, as i far as i know is allowed for one node spring only in CalculiX, two node spring as usually in another FE codes did not.
*edited
may i corrected regarding rigid body and two node spring element, i check again later, i can be wrong and seems to be allowed. Did not know and remember why my previous test in old version’s failed.
also checked for beam element and rigid body reference nodes, it seems allowed and versatile in bolt materials nonlinearity, displaying internal force result and defining prestressed. Global response may represent, but local stress is not accurate, at least gap element being used instead of rigid body.
Tried to add SpringA, looks like it does not connect the reference points 13,26.
I used the below code, 13 and 26 are my reference points which connect the nodes.
Any suggesions
**ELEMENT,TYPE=SPRINGA,ELSET=SPRING *
*99999,13,26 *
***Element Number, first Node or reference Point, second node or reference point *SPRING,ELSET=SPRING *
*2000. *
***constant spring stiffness in N/mm*
maybe stiffness of spring element is too low, another spring in transversal/tangential direction also not defined.