Dear Rashiga Walallawita

The attached research paper may be helpful in resolving the singularity issues. In the research paper, the author has proposed some methods for ANSYS.

Thanks and regards

Vijay Kumar

Hi Rashiga Walallawita

The explanation of Claudio Pedrazzi was complete. Maybe your question would rather change to the distance from (the replacement of) the singularity after which the effect of singularity is negligible. It seems to me the distance would also depend on the singularity and the notion of "negligible".

Dear Claudio Pedrazzi

This is a continuation of a question I previously had,below I have attached the link https://www.researchgate.net/post/How_to_overcome_stress_singularities_due_to_interference_fit

https://www.researchgate.net/post/How_can_stress_concentration_occur_on_flat_contact_surfaces

Thank you for your valuable input on the previous questions.

The reason why I'm bringing this up again I still have some issues with this.

My objective is to do fatigue simulation of few components which are in contact. And the assembly is under two stress states. At each stress state where there is geometric discontinuity very high stress concentration can be observed. When the element size is reduced the maximum stress keeps increasing. Because of this I had to switch to axisymmetric analysis because the element count would be to high to do 3d simulation.

Below I have attached the maximum stress of a single component and the corresponding element size. As you can see at both stress states one can say both stress concentration will reach singularity. Whats more difficult is position of this singularity change at each stress state.

But if the stress is checked at a particular distance from the stress singularity point(ex. 0.2 mm away) the stress converges when the element size is reduced. So as Aram Soroushian Sir, mentioned can this area of stress concentration be concerned negligible according to the explanation done by you.

Since this point load is only concerned for simulation and not concerned for reporting the final stress of a particular component.

Further more in terms of fatigue life I think these kind of point concentrations world give wrong estimation of fatigue life since the nominal stress is much lower than the stress concentration. Even though this act similar to a stress raiser the issue is stress does not converge.

Also sir according to the guidelines you have posted. I think neglecting this area(ex. 0.2 mm) would give similar results or bit lower results concerning the stress gradient to the interpolation method in the guideline.

One more question sir, does strain life method be used to tackle with similar stress concentrations?

Dear Vijay Kumar Polimeru ,

Thank you very much for the paper. I'm still going through this, hope I will be able to use this as a reference.

I concur with all of the above. De Saint Venant Principle is more about "should the stress from structural discontinuity *here* be significant to conditions *there*." As an example of how it is applied, the procedures in ASME Boiler and Pressure Vessel Code checks penetrators (holes) in pressure vessels to ensure there are no overlapping stress fields based on DSV's Principle; ie, if an opening is 500mm in diameter, there should be no fixture or opening 500mm from the center of the opening. (Section VIII, Div1, Sect UG-42). I've attached an article where this is addressed.

As it was stated above, welds and other discontinuities as well as changes in material properties are also considerations. This is where the engineer has to use judgement. DSV's Principle is a good guideline, but detailed engineering will resolve whether the interacting stress fields are structurally sufficient or not.

There is a method called biological growth method to reduce the localised stress.

Dear Claudio Pedrazzi

Thank you for clearing out my confusion on St. venant's thoery. I went through the standard which you had posted which had lot of valuable information and I found an another method which can be used for general cases.

This theory is called "theory of critical distance", in this theory stress is not evaluated at the hot spot but at a given distance(L/2) of it without taking account of local yielding.

This distance can be found by the following equation

L/2 = [1/(2*pi)]*[Kc/UTS]^2

Kc = fracture toughness

UTS = ultimate tensile strength

More information can be found in following book which the author has included this method of several test cases.

https://www.sciencedirect.com/book/9780080444789/the-theory-of-critical-distances

Also one of the research paper which the same author has being part of

Article Implementation of the Theory of Critical Distances Using Mesh Control

shows where by using mesh size relative to the critical distance to determine the stress at the hot spot without further refining the mesh.

Since I'm facing similar situation I'm planning to use the above mentioned method.

I hope you will find this method interesting and would like to hear your opinion regarding this.

Thank you.

Best Regards,

Rashiga

Pranesh Sb Sir,

Thank you for your suggestion. I will read more about biological growth method!

Best Regards,

Rashiga