Line element - pipe

[Anonymous]

I'm trying to to prepare my self for a pipe analyse and therefore I do some models that I can verify (analytical).

I have a created a simple pipe, supported by two pinn-support (the right one can translate in the direction of the pipe).

I hava a internal pressure of 0,15 MPa, the pipe is loaded by gravity and I also have a NSM (that simulates the mass of the water in pipe).

It is easy to calculate the hoop and longitudinal stress the sigmahoop=pR/t and the sigmalong=pR/(2t) (analytical).

If I have both ends closed.

The total longitudinal stress become the sum of maximum bending stress and the longitudinal stress (from internal pressure). Verified!!!!

The problem is that the hoop stress i always zero in my model, and I don't understand way. Can ju give me hint?

I also wounder way the octahedral is given and there the equivalent stress comes from? Way not a von Mises stress?

/Madeleine

[John_Holtz · Accepted solution]

Hi Madeleine.

Same question as always: What version of Inventor Nastran are you using?

The only question that I have a possible answer is this question: "Why is the hoop stress always zero in my model". And the answer is: Is it zero? Or is the result not shown because you are using an older version? (The hoop stress should be equal throughout the entire model. Prior to version 2020, uniform results were not shown on a contour plot, so it is easy to think the result is "0" when it is actually some unknown value.)

I do not know who decided to output the other types of results (Octahedral, equivalent, but not von Mises), but the answer is probably "because that's what was done 500 years ago when the pipe element was released".

[Anonymous]

Thanks for your answer.

I use version 2019. Put a version-reminder in the "new post"-form 🙂

Okey. Using the probe I found the correct value for the hoop stress.

Do you have a link to the formulation used for the equivalent stress ...and hopefully document is not 500 yrs old?

Best regards Madeleine