FEM: cslculix writer, fix if young's modulus is smaller than 500 kPa

src/Mod/Fem/femsolver/calculix/write_femelement_material.py

@@ -88,7 +88,12 @@ def write_femelement_material(f, ccxwriter):
         f.write("*MATERIAL, NAME=" + mat_name + "\n")
         if mat_obj.Category == "Solid":
             f.write("*ELASTIC\n")
-            f.write("{0:.0f}, {1:.3f}\n".format(YM_in_MPa, PR))
+            if YM_in_MPa >= 1000:
+                f.write("{0:.0f}, {1:.3f}\n".format(YM_in_MPa, PR))
+            else:
+                # may be not suited for structural engineerings but such soft materials exist ;-)
+                # https://forum.freecadweb.org/viewtopic.php?f=18&t=60066
+                f.write("{0:.3e}, {1:.3f}\n".format(YM_in_MPa, PR))
 
         if is_density_needed() is True:
             f.write("*DENSITY\n")