Why pin joint (truss element) collapsed?

[ccz90]

I use pin joint setting in my numerical model. But the solver program always shows lots of warning messages like:

*** Warning : Truss element collapsed!

                      Numerical exception may occur

                      Element number=51

                      Original element length =11.87

                      Current element length=NaN

 then the time step is reduced again and again, and the model seems difficult to converge.

Why and how to avoid the problems? Thanks!

                                                                                                     CCZ90

[AstroJohnPE]

It sounds like a numerical problem in the MES simulation, so I suggest trying a smaller time step just before this event occurs. (online wiki Help) I am hoping that a different calculation path will avoid the problem. (NaN stands for "Not a Number", so something is occurring mathematically.)

Otherwise,

1. What material model are you using for the trusses?
2. What is the stiffness of the trusses? (Cross-sectional area and modulus of elasticity)
3. What step does this occur on?
4. What is the force in the truss before it collapses? ("Results Contours > Other Results > Element Forces > Axial Force")
5. What element type is the truss connected to?

[ccz90]

• What material model are you using for the trusses?

      Linear

• What is the stiffness of the trusses? (Cross-sectional area and modulus of elasticity)

      Cross-sectional area from 7~300 mm^2 , E= the defacut material parameters from autodesk material library

• What step does this occur on?

      Changeful. It maybe at the bigining or the process of the calculation.

• What is the force in the truss before it collapses? ("Results Contours > Other Results > Element Forces > Axial Force")

     In some cases, the forcees are very small, 7 ~ -4.9N

• What element type is the truss connected to?

    Brick (isotropic elastic steel)

I have used a smaller time step with bigining of 1~0.1 ms, and the solver might reduce the time step more. The

warning messages still display  randomly.

                                                                                 Ccz90