Conversion from FreeCAD to Nastran is not supported yet :(

FreeCAD is a customizable, open-source paramentic 3D CAD and BIM software with FEM support, built on the Opencascade geometric kernel. It was created primarily for product design and mechanical engineering, but it can be used in a wide range of industries, such as electrical engineering, or architecture. It runs on Windows, Mac OS, and Linux.

FreeCAD is made to craft real-life objects of different sizes and is perfect for a home user/amateur, programmer, experienced CAD software user, or educator. This software provides tools similar to those of SolidWorks, Catia or Autodesk Revit.

MSC Nastran is a multidisciplinary structural analysis application used by engineers to perform static, dynamic, and thermal analysis across the linear and nonlinear domains, complemented with automated structural optimization and award winning embedded fatigue analysis technologies, all enabled by high performance computing.

Engineers use MSC Nastran to ensure structural systems have the necessary strength, stiffness, and life to preclude failure (excess stresses, resonance, buckling, or detrimental deformations) that may compromise structural function and safety. MSC Nastran is also used to improve the economy and passenger comfort of structural designs.