Questions about stresses in cantilever beam with CBEAM elements & PBEAML property

ECor
ECor Altair Community Member
edited December 2022 in Community Q&A

Hello, 

I hope you are doing well.

I am doing a dummy model to validate shear stresses on a beam (actually it is a fastener in a larger model). 

The model is really simple, a cantilever beam, fixed at left and a 100 [N] vertical force on the other end. It has a length of 100 [mm] and thus, 100 elements. The beam has a circular section of r = 5 [mm]. The solver is Nastran MSC.

image

Questions/Problems :

1) I found one thing that I do not understand. The force is applied in the vertical Y direction, and the bar follows the X direction. Then, I should have the whole shear in the plane normal to the bar axis, i.e., the YZ plane. However, I found the shear decomposed in two planes (named 1 & 2). The so-called Web Shear Plane1 is 32.444 and the Web Shear Plane2 is 94.591. In the modulus I found the 100 [N] in Shear, but I do not understand why it is split in two planes. The same happens with the bending moment, which should only be present in the Z direction given the loading. 

image

2) The problem that I found is that by no means I can get neither VM stresses nor shear stresses output for the CBEAM elements.

I've tried with the global output request STRESS(VM), STRESS(SHEAR) but I do not have these results later in HyperView. 

For 1D Stress the results available are : CBEAM Long Stress at Point C1/D1/E1/F1, CBEAM Maximum Stress1 & CBEAM Minimum Stress1 and some others like these.

For CBEAM Maximum Stress1, I found 96.349 [MPa] which I imagine is a normal stress given by Sigma= M * y / I, being M = 10000 [N.mm], y = r & I = 490.87385, which manually calculated gives 101.85 [MPa].

 

Thank you in advance !

 

Sincerely, 

                 EC

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Answers

  • Adriano A. Koga
    Adriano A. Koga
    Altair Employee
    edited December 2022

    Beam elements have an orientation vector, which defines what is the Y direction of your local coordinate system. The X-axis is always aligned with the beam elmenet. The Y axis is given perpendicular to X, and dfeined by this orientation vector, and the Z direction is defined by the right-hand rule.

     

    Shear1 is the Y component, and Shear2 is the Z.

    Probably your beam elements have some weird orientation, wrt the global coordinate system.

     

    Concerning stress values, have you tried requesting results in PUNCH format? These are ASCII format text files, that usually are easier to check, for smaller models such yours.

    I'm not so familiar with Nastran outputs.

    I know that OptiStruct writes these Shear1 and Shear2.

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