Learning Forum

[Barnaby Hawthorn]

Hi, I am analysing a static structural model in Ansys Mechanical and am interested in the "Average" equivalent stress value across 2 bodies in the model.

Could someone please enlighten me as to how this average is calculated? Is it an average across the total number of elements or total volume?

I am wondering because I do not have a uniform mesh, there are mesh refinements in areas where higher stress is seen. If the average is done across the number of elements, I imagine that this will skew the result as there are a higher number of elements in the high stress regions.

I have ran the model with a coarser, more uniform mesh and the average value decreased considerably (from 5.7 MPa to 4.6 MPa) but maintained relatively consistent max/min values. 

Any information will be appreciated, thank you.

Barn

[Giorgos Papa]

Hello Barnaby,

 

This value is simply an arithmetic average.  It is the arithmetic average of the equivalent stress values of all the nodes scoped in the result. Since you defined a finer mesh on the high stress area it is expected that you will have a larger number of nodes with higher stresses, therefore the average of all nodes is much higher in that case.

 

Hope this helps.

 

Regards,

Giorgos.

[Barnaby Hawthorn]

Is it possible to normalise by element volume somehow?

[Barnaby Hawthorn]

Hi Giorgos,

Thank you very much for your quick reply. Great, that has cleared up my question and helped a lot.

In this case, do you know of a way that I could calculate an average stress that is not skewed by number of elements?

I am modelling two different fracture fixation methods (titanium bone plates) and I am interested in comparing the average stress produced in the bone as a result. However, the two different plates use slightly different bone geometries (due to different number of screws required etc.). As such: they require different meshes, therefore I believe that this average stress value is not exactly comparable between the two models. (It could be skewed by different amounts in the different models).

I would like to be able to compare the average stress in the bone between these two different models. Do you know if it is possible to calculate a comparable average that would suit my needs?

Thanks again for your help.

 

Regards,

Barn