Abaqus Standard or Explicit? 1

[jball1]

Hello,

I will be doing an analysis of the torque-tension test of a multi-fastener bolted joint. I plan on varying multiple factors in order to determine their effect on the nut factor (which I expect to vary from bolt to bolt). This will be a very large model (fastener threads will be modeled, etc). I plan on applying the torque to the heads of the fasteners one by one to simulate the assembly sequence. I have two questions - first of all, would this be considered a "dynamic analysis"? The response of the model will vary over time, as the fasteners are sequentially torqued, which makes me think it would be considered dynamic? Also, would Abaqus Standard or Abaqus Explicit be better for this analysis? All of my experience has been in Abaqus Standard, and from what I understand, Abaqus Standard can do Low-Speed nonlinear dynamic analyses.

Thank you so much for your input!

 

[StefCon]

Hi,
Are you going to make a full 3D M-thread interface? If so, elements would have to be quite small which makes explicit not very good (stable time increment). On the other hand, the contact would be complex (and sliding) and might cause convergence issues in implicit.

There is something called implicit dynamics (step module). Check that out (manual).

Did I understand you correctly?

Best regards,

 

[PeteTranc]

I am still quite new to Abaqus and FEM in general so take my advice with a pinch of salt.

If you are simulating a sequence of applied loads try a static/general step for each applied load. In that way you include the loading history of each applied torque.

 

[jball1]

Thanks both of you for your responses. StefCon, you did understand me correctly. I am modeling the full thread interface (ASME, not metric though). I was actually able to get a model of a single fastener torque-tension test to run today in Abaqus Standard, so I will probably use Standard for now. I may need Implicit for the multi-fastener model though. PeteTranc, I will use a separate step for each applied torque, as you suggest.

Separate question. I am trying to extract torque vs. tension data from my results. For the tension data, I thought I could simply extract nodal forces from a plane of nodes (cutting through the fastener shank) and sum them. However, I forgot to specify the variable in my Field Data. Is NFORC the correct variable for this? Is there a better way to determine the tension in the fastener?

 

[StefCon]

Hello,
I have gotten the most exact results using NFORC. The viewer can estimate forces using the section tool without NFORC but it usually gives a noticeable error (plus minus x%).

If you define a cut on element faces, the viewer will sum the results for you and (if the section is flat) will give you the option to view axial force and radial forces (force components). This also goes for torque.

Good luck!

 

[jball1]

Thanks. I was able to do exactly what you described. I appreciate the help.