I have a question about the nodal values stored in the FRD file when using the *EL FILE command. The manual for ccx2.18 says “This option is used to save selected element variables averaged at the nodal points in a frd file”. How are the averaged values calculated? What method is used to interpolate or extrapolate the values from integration points to the nodes?
This is done based on standard FEM procedures described in literature. You can check the book “The Finite Element Method for Three-Dimensional Thermomechanical Applications” by G. Dhondt (chapter 2.4. Extrapolation of Integration Point Values to the Nodes) which is considered a theory manual for CalculiX or just a generic book about FEM.