General Mechanical

General Mechanical

FEA convergence problem

    • Sumit Paul

      Hello, I was trying to run a simulation in ANSYS static structural, in which I want converged results. However, it is quite challenging for me to get the converged results. The details of my simulation and issues are explained below.

      Material Properties

      Isotropic elasticity data was obtained from literature. Uniaxial tensile test data obtained from tensile testing 3D-printed PLA and PETG dogbone samples.  


      Fig 1: Non-linear material properties of PLA and PETG

      2.       Force and Boundary conditions

      Fig 2: 500 N tensile force applied on the bottom face and the top face is fixed


      3.       Contact

      Bonded contact was used for the simulation.

      Fig 3: Bonded contact between two parts. The red part is 50% relative density Octahedral cellular structure (material: PLA) and the blue part is the negative volume of the 50% relative density Octahedral cellular structure (material: PETG)




      4.       Meshing

      Mesh size- 1 mm

      Mesh method- automatic

      5.       Solution Settings




      6.       Convergence Study Results

      For convergence study of total deformation, equvalent stress and strain energy 5% change between two consecutive iterations was selected as the convergence criteria. Total deformation converged but equivalent stress and strain energy did not converge.


      Could anyone please help me with this convergence problem?






    • peteroznewman


      Did you convert the Engineering Stress and Engineering Strain data from the Tensile Test into True Stress and True Strain for use in a plasticity material model?

      Which plasticity material model did you use?

      Were the dogbone samples printed as solid or with Octahedral cellular structure? Did you print dog bone samples in mulitple directions?  The samples will have different properties in the three axes of the printer: the longitudinal axis, the lateral step axis and the vertical layer axis.

      I recommend you take this free course on Multilinear Hardening Plasticity Model

      The negative slope in a tensile test occurs when necking begins in the sample and the values of stress and strain are no longer accurate because the cross-sectional area is no longer accurate.

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