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Message 1 of 3

Anonymous

450 Views, 2 Replies

06-22-2012
05:31 PM

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Simple Beam Problem

Not applicable

06-22-2012
05:31 PM

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Hi,

I am a student having a play with FEA software and I have an error using Simulation software to model a pipe under a transverse load. The pipe has an OD of 20mm and an ID of 10mm and 150mm long. I have applied a force of 500N at one end, and the pipe is fixed at the other end. When I run the analysis I get a bending stress of 118 N/mm^2 using an mesh size of 2.5mm. However I calculate this stress, using Stress=M*Y/I, to be 101.8 N/mm^2. Can some please inform why this could be happing/what I am doing wrong as I dont have access to someone that could help

Thankyou

Reply

Reply

06-22-2012
05:31 PM

Simple Beam Problem

Hi,

I am a student having a play with FEA software and I have an error using Simulation software to model a pipe under a transverse load. The pipe has an OD of 20mm and an ID of 10mm and 150mm long. I have applied a force of 500N at one end, and the pipe is fixed at the other end. When I run the analysis I get a bending stress of 118 N/mm^2 using an mesh size of 2.5mm. However I calculate this stress, using Stress=M*Y/I, to be 101.8 N/mm^2. Can some please inform why this could be happing/what I am doing wrong as I dont have access to someone that could help

Thankyou

2 REPLIES 2

Message 2 of 3

Anonymous

in reply to:
Anonymous

06-25-2012
05:33 AM

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Not applicable

06-25-2012
05:33 AM

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you can try again reducing the mesh size.....and you know the solution is always the approximation.....

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06-25-2012
05:33 AM

Message 3 of 3

07-02-2012
02:59 PM

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Hi two_out_of_two,

I can think of a number of possibilities.

What type of element are you using? If you are using brick or plate elements, your hand calculations probably do not take the 3D effects into account. That is, Poissons ratio, distortion of the cross section (which would not be a problem in linear stress). If you are using beam elements, the stresses should match.

Another related effect occurs in brick elements if the end is fully fixed: no translations allowed. The stress right at the fixed end can be abnormally high. Select some of the nodes along the length leading up to the fixed end, right-click, and choose to create a path plot. If you visually extrapolate the stress to the fixed end, does it match your hand calculation?

What type of result are you viewing? Chances are your hand calculation is not taking the shear stresses and all of the other bending components into account. So stress results such as von Mises and the principal stresses will not match the hand calculation. If this is the case, then you can only view the "Results Contours > Stresses > Tensor > NN Component", where N is the axis parallel to the length of your pipe.

Otherwise, please provide your hand calculations and an archive of your model. (See "Create, Post, or Provide an Archive of your model".)

Global Product Support

Autodesk, Inc.

If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius 😉

Reply

Reply

07-02-2012
02:59 PM

Hi two_out_of_two,

I can think of a number of possibilities.

What type of element are you using? If you are using brick or plate elements, your hand calculations probably do not take the 3D effects into account. That is, Poissons ratio, distortion of the cross section (which would not be a problem in linear stress). If you are using beam elements, the stresses should match.

Another related effect occurs in brick elements if the end is fully fixed: no translations allowed. The stress right at the fixed end can be abnormally high. Select some of the nodes along the length leading up to the fixed end, right-click, and choose to create a path plot. If you visually extrapolate the stress to the fixed end, does it match your hand calculation?

What type of result are you viewing? Chances are your hand calculation is not taking the shear stresses and all of the other bending components into account. So stress results such as von Mises and the principal stresses will not match the hand calculation. If this is the case, then you can only view the "Results Contours > Stresses > Tensor > NN Component", where N is the axis parallel to the length of your pipe.

Otherwise, please provide your hand calculations and an archive of your model. (See "Create, Post, or Provide an Archive of your model".)

Global Product Support

Autodesk, Inc.

If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius 😉

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