Introduction to FKM Assessments

FKM assessments enable you to simulate the strength and useful life of welds.

You can perform FKM assessments and other durability simulations only when you have the appropriate role. The app bases its FKM assessments on the FKM Guideline Analytical Strength Assessment of Components, 6th edition, chapters 3 and 4.

This page discusses:

Prerequisites and Conditions for FKM Assessments

  • The FKM Guideline used in this app applies to fatigue assessments where the required number of cycles is greater than 10000.
  • In the structural analysis that precedes the FKM assessment, the strains in the weld material and the plates near the welds must be relatively small. The simulation can include geometric and contact nonlinearity, and you can have nonlinear material behavior in components of the model that you do not plan to include in the FKM assessment. However, any nonlinearity in the structural behavior indicates that you should not scale the stresses used in the FKM assessments, directly or indirectly using superposition or spectrum events.
  • Toe failure is the only supported weld failure mode.
  • You must model the welds and plates as solids, not shells.
  • You must model the weld fillet, and the interface between the weld fillet and plates must have a compatible mesh.

FKM Assessment Workflow

You can assess the strength or fatigue life of welds using the FKM guideline by performing the following steps:

  1. Apply materials to your model that are suitable for FKM assessment.

    Dassault Systèmes provides a briefcase of materials that you can use for an FKM assessment; for more information about importing its contents into the database, see About the Material Briefcases Available for Import. You can also define your own material; materials suitable for FKM assessment must have the following options defined:

    • FKM material
    • Elongation
    • Proof (yield) stress
    • Ultimate strength

    The solver ignores the fatigue algorithm setting in the material in FKM assessments because the guideline fixes the algorithm. The mean stress choice is made as part of the fatigue assessment itself rather than in the material because it depends partly on the loading conditions.

    The material should also include linear isotopic elasticity for a structural analysis that precedes the FKM assessment.

  2. Mesh the model, creating the mesh for the weld fillets first. The mesh at the interface between the weld fillets and the plates must be compatible with nodal condensation. For more information, see Capturing Mesh Faces.
    • If you want to compute the structural stresses using surface stress extrapolation, define the elements on the plate near the weld toe line so that they are approximately one quarter of the plate thickness when using second order elements.
    • If you want to compute the structural stresses using through-thickness stress linearization, define the elements on the plate and on the weld fillet so that they are smaller than one tenth of the plate thickness when using second order elements.
    You can also perform mesh refinement studies to confirm that your mesh has a suitable level of refinement.
  3. Define a structural analysis case. For more information, see Overview of Durability Simulations.
  4. Define an FKM analysis case. For more information, see Creating FKM Analysis Cases.
  5. With the FKM analysis case selected, create a static FKM assessment, a fatigue FKM assessment, or a sequence of these assessment types. For more information, see Defining Static FKM Assessments and Defining Fatigue FKM Assessments
  6. For static FKM assessments, select a step or load case from a structural analysis case.
  7. For fatigue FKM assessments, define the fatigue loading using one or more superposition events, sequence of frames events, or spectrum events. Each fatigue assessment has its own fatigue loading history.
  8. Add one or more welds or fillets to capture the FKM-specific aspects of a weld. For me information, see Defining Weld Fillet Sets in FKM Analysis Cases.
  9. Optional: Customize the weld fillet for some of the FKM assessments. When you define a weld fillet, it takes its default values from the assessment.
  10. Run the simulation, selecting both the structural and FKM durability analysis cases. For more information, see Running a Simulation from an App.
  11. View the results. You can plot the contours for the output variables Static FKM Utilization and Fatigue FKM Utilization.
  12. If you want to see the detailed FKM calculation steps for the nodes with the highest utilization for each weld line, open the Simulation Status dialog box, click the Diagnostics tab and the Message file subtab for the FKM durability case.