How is the FLD obtained in LSPOST? What is the limitation of using this FLD?

The FLD in LSPOST is based on an experience data; it is only good for one specific material under linear strain path deformation.

If you want to use FLD for your own material, it is always better for you to supply you own FLD.

When the strain path is far away from linear, it is strongly that the effect of strain path be considered.