Sequence of loads and Step-by-step preloading of bolts
Hello,
Currently, i am trying to learn, how to use Sequence of loads. But I have a problem.
I have a bolt that I want to preload in steps.
For example, add 500N for the first step, 1000N for the second step, and so on.
Another situation is that there are multiple bolts, the No. 1 bolt is preloaded first, then No. 2 and No. 3. Each step needs to extract the preload of other bolts.
Thank you so much for your help
Best Answer
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Yes, the attached simple example has 4 pretensioned bolts, loaded sequentially in loadsteps 1-4, the 5th loadstep is pretensioning all 4 simultaneously for comparison, the difference is small, but it is there (compare disp stress and final tension in the 4 bolts) when you play the animation of loadstep 4 it still looks like they are all applied together, but that is due to it being a linear static analysis with only the start and end states in the results
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Altair EmployeeAnswers
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The first: (add load to an already loaded pretension) is not available I don't believe. You may add an 'adjustment' in a subsequent step, defined in terms of length, but not change the force directly.
The second: You may achieve by defining separate pretensions for bolts 1, 2 and 3, in loadstep one you have pretension 1, in loadstep 2 you have pretension 2 and statsub (pretens) loadstep 1, and in loadstep 3 you have pretension 3 and statsub (pretens) loadstep 2.
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Paul Sharp_21301 said:
The first: (add load to an already loaded pretension) is not available I don't believe. You may add an 'adjustment' in a subsequent step, defined in terms of length, but not change the force directly.
The second: You may achieve by defining separate pretensions for bolts 1, 2 and 3, in loadstep one you have pretension 1, in loadstep 2 you have pretension 2 and statsub (pretens) loadstep 1, and in loadstep 3 you have pretension 3 and statsub (pretens) loadstep 2.
First of all, thank you very much for your answer.
For the second case, I would like to ask, does statsub (pretens) realize that step1 is loaded first, and then step2 is loaded? rather than being loaded together at the same time.
I am sorry for not being able to reply you in time due to the time difference.0 -
Yes, the attached simple example has 4 pretensioned bolts, loaded sequentially in loadsteps 1-4, the 5th loadstep is pretensioning all 4 simultaneously for comparison, the difference is small, but it is there (compare disp stress and final tension in the 4 bolts) when you play the animation of loadstep 4 it still looks like they are all applied together, but that is due to it being a linear static analysis with only the start and end states in the results
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Thank you very much ,Paul Sharp.
WIll go with these suggestions.
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Hello,
Firstly, this is very usefull explanation, @Paul Sharp . Thank you.
- 1.Question: How can we do what you stated below? Could you please elaborate a little?
"You may add an 'adjustment' in a subsequent step, defined in terms of length, but not change the force directly."
- 2.Question: For example, there is a gasket between the two components and it is being compressed. For this case, I want to calculate the pressure on the compressed surfaces. What would you recommend me to examine in the analysis results? (contact pressure, gasket thickness- direction pressure, ..... )
- 3. Question : How can I use the "Gasket Sealing Status" that I see in hyperview? I think, I need to enter a scale for this.
Thank you.
Best Regards,
Ovunc
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Ovunc2 said:
Hello,
Firstly, this is very usefull explanation, @Paul Sharp . Thank you.
- 1.Question: How can we do what you stated below? Could you please elaborate a little?
"You may add an 'adjustment' in a subsequent step, defined in terms of length, but not change the force directly."
- 2.Question: For example, there is a gasket between the two components and it is being compressed. For this case, I want to calculate the pressure on the compressed surfaces. What would you recommend me to examine in the analysis results? (contact pressure, gasket thickness- direction pressure, ..... )
- 3. Question : How can I use the "Gasket Sealing Status" that I see in hyperview? I think, I need to enter a scale for this.
Thank you.
Best Regards,
Ovunc
1: Add a pretension load of type PTADJST (instead of PTFORCE), in attached, I added a 6th loadstep (with loadstep 4 as statsub (pretens) that shortens the 3rd bolt by 1e-2, if you are using the new interface you can manage it in bolt pretension manager (adjustment line) this creates the loadcol (PRETENSION) for you, you then need to create the loadstep with that pretension, with the preceding case as the statsub (pretens) case.
For 2 and 3, I've not used the gaskets, but there is an example for this in help, link: Gasket with Preload in Help
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Paul Sharp_21301 said:
1: Add a pretension load of type PTADJST (instead of PTFORCE), in attached, I added a 6th loadstep (with loadstep 4 as statsub (pretens) that shortens the 3rd bolt by 1e-2, if you are using the new interface you can manage it in bolt pretension manager (adjustment line) this creates the loadcol (PRETENSION) for you, you then need to create the loadstep with that pretension, with the preceding case as the statsub (pretens) case.
For 2 and 3, I've not used the gaskets, but there is an example for this in help, link: Gasket with Preload in Help
Hi @Paul Sharp,
Thank you for your answer.
As I understand it, the 3rd bolt is pre-tightening 0.01 units, right? (in units of length(milimeter, meter ets.))
Thank you.
Best Regards,
Ovunc
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Ovunc2 said:
Hi @Paul Sharp,
Thank you for your answer.
As I understand it, the 3rd bolt is pre-tightening 0.01 units, right? (in units of length(milimeter, meter ets.))
Thank you.
Best Regards,
Ovunc
Yes, but there is a caveat to be aware of, the PTADJST it is set to show the 'effect' of shortening the bolt by 0.01 units (in this case mm) but the stiffness of the bolt has an effect (the force required to achieve this shortening is calculated and applied to the bolt, but the bolt then stretches due to that force so the change in length will usually not match the requested PTADJST shortening value)
So for the model I shared, the 'actual' shortening of bolt 3 in loadstep 6 in the result is only 0.004 units, if you e.g. increased bolt material modulus by a factor of 100 then you would get the full 0.01mm length change as the stiffness of the bolt would be sufficient to make the 'restretching' negligible.
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Paul Sharp_21301 said:
Yes, but there is a caveat to be aware of, the PTADJST it is set to show the 'effect' of shortening the bolt by 0.01 units (in this case mm) but the stiffness of the bolt has an effect (the force required to achieve this shortening is calculated and applied to the bolt, but the bolt then stretches due to that force so the change in length will usually not match the requested PTADJST shortening value)
So for the model I shared, the 'actual' shortening of bolt 3 in loadstep 6 in the result is only 0.004 units, if you e.g. increased bolt material modulus by a factor of 100 then you would get the full 0.01mm length change as the stiffness of the bolt would be sufficient to make the 'restretching' negligible.
Hello Paul,
Thanks for the very useful information.
Best Regards,
Ovunc
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