As can be seen in the figure, the axial modulus reduction rate of the material is very sensitive to the load level and number of cycles.
As void content increases, the axial modulus decreases more rapidly until reaching the fracture modulus, thus leading to a shorter fatigue life.
In addition, the nanoindentation predominantly measures transverse modulus along the radial direction in the fibers while the tensile tests are a measure of the axial modulus
Typically, as shown in the figure, for uniaxial tension the axial modulus
increases and the transverse modulus decreases with the increase of plastic strain.
0] for [alpha] = 150; [alpha] = 150 accounted better for the data for the fibers at low MMT contents, consistent with the significant increase in [alpha] on fiber drawing implied by morphological data, although it should be borne in mind that the MMT particles, and in particular the sheared stacks are not equivalent to monolithic particles with an axial modulus
equal to that of an individual platelet.
Continuous fiber composite micromechanics for axial modulus
is known to follow the rule of mixtures  derived from the assumption of constant strain in the constituents.
With this range of draw ratio for PET, the axial modulus
determined by ultrasonics increases almost linearly from 4 to 16 GPa while the transverse modulus is almost constant near 4 GPa.