  Considering the time-varying of the poriness of the materials in the loading
process, a dynamic classifying method for the materials is proposed based on
the strain factor defined from the strain relationship in three orthogonal
directions. Comparing with the current classifying approach based on the
Poisson's ratio, the method presented in this work is a dynamic approach that
can reflect the real-time strain relationship in three orthogonal directions as
well as the varying specific molecular structures partly in the loading process
of the materials.
