## How to explain this singularity?

## How to explain this singularity?

(OP)

I have a wall that is subjected to water pressure, and in the corner of the structure I get this singularity. My coworker told me it wont be a problem in real life. I was wondering how could I explain to someone that even though its red (forces above the limit in the red area), its okay?

Edit: Its a 2-D shell element model.

Edit: Its a 2-D shell element model.

## RE: How to explain this singularity?

## RE: How to explain this singularity?

A better explanation is to replace that corner with a few elements that conform to a small, but realistic radius, and present that analysis to them as well. This would show that the stress concentration is much lower than the sharp corner predicts and gives a cost of doing that additional modeling and analysis time vs the amount of information gained. It small for one case, but if multiplied by 10,000 cases that time and cost increase.

It may also be valuable to do that a few times to see just how sensitive the design is - perhaps the material is so notch-sensitive that it requires a radius in that area to prevent crack initiation. Gain enough experience doing this and you will begin to recognize when the extra effort will pay off.

## RE: How to explain this singularity?

valuesof stress at point. (Its different from stress at point to find out stress tensor components.) As the area approaches zero (consider point as nearly zero area) stress values tend to infinity. At the sharp corner, the resistance to the stress is concentrated at a corner point and hence the stress values are higher than adjoining area.In reality, we cannot make perfect corner or anything that is perfectly round, square, flat etc. Some finite radius will always be present at corner and finite area resist the stresses at corner and hence the stress will be finite in real structures. Discretization/meshing introduces singular points in our FEA model (which is nothing but approx. mathematical model of real structure) which mathematically produces infinite or higher stress values.

## RE: How to explain this singularity?

(as others have posted) is there not a radius in the real world ?

another day in paradise, or is paradise one day closer ?

## RE: How to explain this singularity?

Thomas

## RE: How to explain this singularity?

People use the phrase "singularity, you can forget it", but is very important to put attention to peak stresses, not simply forgeting, very dangerous!!.

Others say "

".in ductile materials the local stress concentrations can be ignored, and then it is permissible for the stress to exceed the material yield stressWell, we have do demostrate it: the way I run always is to perform nonlinear analysis and prove by calculation that the areas of local plastic deformation associated with stress concentrations are sufficiently small so as not to cause any significant permanent deformation when the load is removed.

But please note "

". So the above depends of the material type and the load type, with alternate loading the only way to prevent failure is to design using a Factor of Safety (FoS) well bellow of yield stress of the material, a FoS=1.1 is useless, probably you will need values of 4 & 5 minimum.give me a point, and I will broke the part by fatigueAlso other important point: "The Finite Element mesh should be fine enough & with the best quality to accurately predict the actual peak stress at the features". Coarse mesh is not valid at all.

In summary, you have the answer in your hands: run nonlinear analysis.

Best regards,

Blas.

~~~~~~~~~~~~~~~~~~~~~~

Blas Molero Hidalgo

Ingeniero Industrial

Director

IBERISA

48004 BILBAO (SPAIN)

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