Learning Forum

[Rania]

Hi, 

Model discription: 

I have modelled two cylinders connected by screw elements, as shown in the figure attached.  

frictional contact were created between the internal two surfaces and bonded contact between the screw shaft and the holes. the screws were modeled as 3D model,

in the experment, te screws are failed by shear because it si the weakest part in the geometry. 

my question:

how can I let the screws to fail by shear in ANSYS? OR IS THERE ANOTHER WAY TO MODEL THE SCREWS TO BE FAILED BY SHEAR? 

 

[peteroznewman]

Below is your image. ANSYS staff are not permitted to open attachments, so to have their input, please use the Insert Image button in future posts.

Please reply with annotations and arrows pointing to the screw that you want to evaluate for shear failure.

[Rania]

[Rania]

thanks for reply I have inserted the picture, due to the applied load the screws will failed first by shear, but in ANSYS is not showing that. 

while the max shear force for each bolt is around 12 kN and after that the results should drop down because of shear failure, which is not accounted in ANSYS as shown in the figure attached, the load is kept increasing. 

[peteroznewman]

Please read this post.

[Rania]

Thanks, I have read this post before, I tried to use the EKILL approch. but it didnot work because I have contact element surface to surface created. the results is not improved. 

[peteroznewman]

Don't plot any results after the bolt reaches a shear force of 12 kN if that is the failure point. Take that data into Excel and manually add a point at zero force if you want to see a vertical line.

Why do you need to simulate the system after failure?

[Rania]

I need to validate the FEM results with experiement, and because the results is not showing where the fail point, I know this from the experiment but ANSYS is not showing that, as the load vs. displacemnt is kept increasing. 

[peteroznewman]

What is the grade of material of that screw?  In other words, what is the Yield Strength and Ultimate Tensile Strength of the screw material? Is the screw shaft smooth or is it threaded at the point where the shear failure occurs? What is the minimum diameter of the shaft? With all that information, you can calculate the shear force required to single shear that shaft.

In Mechanical, suppress the screw. Under the Connections folder, Insert a Joint, type is Fixed. On the Reference side, select the face of the hole in the inner tube, on the Mobile side, select the face of the hole in the outer tube. It would be simpler to replace the applied displacement of 20 mm with an applied force of 12 kN to match the known failure load. That way, the last solved substep is the known point of failure.

Under Solution, insert a Probe > Joint > Force. Now you have a result for the shear force being applied by those two holes to a screw shaft, if one was present.

Compare the force going through the Fixed Joint with the shear force calculated in the first paragraph above. That is your validation of the FEM model to the experimental result.