Learning Forum

[Jack Cool]

I have watched the video on youtube to avoid artificial stresses but it does not solve contact related problems. I am solving rivet joint problem and with each mesh refinement the stress is continously increasing. Any help how to avoid it and do grid independence.

[Sampat Kumar]

Hi jack,
Will you please upload the screenshot of the model here? 

Regards,
Sampat

[Jack Cool]

[Jack Cool]

THE SECOND LAST PICTURE IS WITH MESH SIZE IN THE CONTACT REGION OF RIVET TO BE 0.8mm WHILE LAST IS ON 0.4mm the stress simply doubles. what i yhink it should converge to a same value it means there is disontinuity

[peteroznewman]

Jack,

To avoid artificial stress, replace Bonded Contact with Frictional Contact. Below are brief comments on riveting.

Deforming the Rivet: To create a permanent joint, the rivet needs to be deformed or “set.” This is typically done by applying a large force to the protruding end of the rivet. The force can be applied using various methods, such as manual rivet guns, pneumatic or hydraulic tools, or even automated machinery. As the force is applied, the tail end of the rivet is deformed, which causes the shaft of the rivet to expand and fill the hole, creating a secure and tight connection between the plates.

Residual Compression: During the process of deforming the rivet, a significant amount of force is applied. This force causes the rivet to plastically deform and create a tight joint. Additionally, some residual compression is locked into the structure as a result of the deformation. This residual compression helps to maintain the integrity and strength of the joint over time, even under loads and vibrations.

Are you interested in simulating the residual compression?  If you have a rivet shaft that is the same diameter as the holes and the length of the rivet shaft is the same as the thickness of the two plates, there will be no residual compression. This may result in a larger deformation of the tip of the plate due to a tip force than you might get from the real parts.

You can make a rivet shaft diameter that is slightly larger than the hole diameter and a rivet shaft length that is slightly shorter than the two plate thickness dimension. As the frictional contact resolves the interference, a compression stress will be developed. This may result in a smaller deformation of the tip of the plate with a tip force compared with the non-interfering geometry.

[Jack Cool]

no i am not interested in residual compression. I am just validating my result with analytical formulas. I want to check what is the max shear stress in the rivet. 

Is there any need of bolt pretension necessary to be applied in these rivets.

[peteroznewman]

Jack,

Please reply with the analytical formula you are using for the max shear stress in the rivet.

Many analytical formulas calculate the average stress in the cross-section of the rivet. Ansys calculates element stress which changes from one side to the other. You can add Construction Geometry to your model and put a Surface at the plane between the plates. You can plot the stress in the rivet on that surface and look at the average stress.

The problem with bolt pretension is that it splits the cylinder in the middle to pull each side together to apply the load which will interfere with extracting stress on the construction surface.

[Jack Cool]

i am using shear stress=F/A , F=1000 and A=pi*(10)^2