What is a Superbolt?
Superbolt is a product offered by the Nord-Lock Group. It is a Multi-Jack bolt Tensioner that offers a simple and cost effective method to tighten large bolts. You can learn more about how Superbolts work in the video linked below:
Applying Pretension in Ansys Mechanical
Before attempting to model a Superbolt in Ansys, the user must understand how bolt preloads work in general with Ansys Mechanical. The following article goes over the basics which should be understood :
A guide to applying bolt pretension in Ansys Mechanical
As the article describes, in order to apply pretension, Ansys splits the bolt’s free length in half and pulls the two halves together – This pushes the mating components together and generates the expected compressive force.
Note that, the elongation of the fastener that takes place in real life is not captured with this approach. However, upon tightening the jackboots cause the nut to move away from the washer (instead of being pushed together), as shown in the video below:
Modeling this jacking mechanism can be tricky in Ansys.
How to model a superbolt in Ansys Mechanical
Consider the model shown below. Six Jacking bolts are modeled using rigid beams and a pretension of 5,000 N applied to each.
By this “default” approach we would expect the blue nut to push against the red washer. This can be seen in the video shown below (the deformation has been magnified X1500).
The trick to modeling a superbolt is to apply a negative bolt pretension. A negative pretension mimics the effect of bolt elongation, and in this case, will simulate the jacking mechanism.
Instead of 5,000 N preload we can apply -5,000 N and get the result shown in the video below:
As you can see in the video above, a gap develops between the nut and the washer as stresses are induced on the center shaft.