Preload Bolt 1

[drasticxxx]

Hello,

Actually i know how to model pre load in the bolt using ABAQUS, but my question is related to the results actually:

my questions:

I have bolt only

1. when i model the bolt and apply the pre load the model run if i constrain the top and the bottom head,so my question why it is not working if i constrain the bottom only,since in the real case we only prevent motion in one direction

please explain this to me ,i need to understand,since i am afraid the results will be different in the two cases.


Sorry if my question is basic, but i cant find proper explanation

 

[portliner]

You can not apply a force if only one end is fixed , no stiffness

 

[drasticxxx]

I read the manual carefully and found the following statement which definitely is my problem,but i cant understand i t well
{{{{Controlling the pre-tension node during the analysis
You can maintain the initial adjustment of the pre-tension section by using a boundary condition fixing the degrees of freedom at their current values at the start of the step once an initial pre-tension is applied in the fastener; this technique enables the load across the pre-tension section to change according to the externally applied loads to maintain equilibrium. If the initial adjustment of a section is not maintained, the force in the fastener will remain constant.

When a pre-tension node is not controlled by a boundary condition, make sure that the components of the structure are kinematically constrained; otherwise, the structure could fall apart due to the presence of rigid body modes. Abaqus/Standard will issue a warning message if it does not find any boundary condition or load on a pre-tension node during the first step of the analysis.}}}}}

Actually i defined 3 steps

step 1 i defined the preload force
step 2 i fix the length through modifying step one
step 3 i applied the load

but according to the above statemnt it seems i missed to fix something,
so according to what i understand i have to fix what exactly
imagine that i have bolt head and nut and shank
please explain it to me since i read it 10 times,and was not able to fully undedtand

 

[drasticxxx]

Also, i found this in the manual examples
{{The “prescribed assembly load” capability is used to define pre-tension loads in each of the bolts. For each of the two bolts we define a “cut” or pre-tension section and subject the section to a specified load. As a result, the length of the bolt at the pre-tension section changes by the amount necessary to carry the prescribed load, while accounting for the compliance of the rest of the joint. Once a bolt has been pre-tensioned, the applied concentrated bolt load is replaced with a “fixed” boundary condition, which specifies that the length change of the bolt at the “cut” remains fixed, while the remainder of the bolt is free to deform}}

So this what i did i have the bolt apply pretension in the first step in in the second step i apply fixed boundary condition at the cutting section(in the fix length step)<< but i still receive singularity problem
The only way to make model work is to fix the top and bottom for bolt for the whole duration for analysis
which is not convenient to me at all

I am certain there is something missing in my understating , so please any comment could be useful

 

[portliner]

The pre-tension section divides the bolt into two parts. The force or distance between the two surfaces, created when defining the "cut" is governed by either a prescribed force or a prescribed distance. If a prescribed force is to be applied, the both parts of the bolt are NOT allowed to be free.

 

[drasticxxx]

Fabulous,
So if i fixed the head and bottom of the bolt, i prevent the the plates from separation ,since i apply constrain ,since the tension load has no effect on the bolt(the bolt is constrained).
Could u please just once full description about how to fix and when

What i want to know if i keep fixing the top and bottom part of the bolt, so how can i apply the real tension force on the preloaded bolt,since it will have no effect, the bolt is constarined

 

[portliner]

1. I suppose you have a predefined mounting force to be applied on the bolt.
2. Then you I suppose you have an EXTERNAL load to be applied on the structure, not on the bolt nessescarly.

The model consist, as I believe of the bolt and at least one other structure, stretching between the bolt-head and its thread.

*Contact or *Tie must be defined between the contact surfaces between the bolt-head and its mating structure
The same must be defined for the thread-connection.

The pre-tension procedure requires two *Step
Step 1: apply the given axial force on the bolt.
Step 2: fix the now existing small offset between the two surfaces of the pre-tension cut.
This step ensures the axial load in the bolt to varies accordin to external loading, temperatues, etc applied in the next Step.


Step 3: Apply the external load, whatever it is, temperatues, pressures , or....

 

[drasticxxx]

Thank you very much
I really appreciate
Please help me(once i find my problem, i will be very happy)

In order to fully understand ,i create simple model to implement your advice and i get this error(seer video)
My main point fixing the plate only is not enough(why),since the bolt should be stable and clamp the plate!!!
the only way to make the model to work is to fix the head and bottom of the palte(thus the plate will never separate since its constrained,no logical)

http://www.youtube.com/watch?v=sRA-JoduhbA&feature=youtu.be

 

[drasticxxx]

it does work perfectly

Thank you very much

I really appreciate,you effort

I a have simple question, about meshing,I know from finite element the it always better to have node on node of the mesh for two different parts.But if i have node of mesh of on part intersect with line of mesh on the other part(line nit exactly the node,,how does this effect the analysis and results


Thank you again