Video-controlled tensile deformation experiments giving true stress-strain
curves were carried out on samples of s-PP. Dividing the total tensile defo
rmation into elastic and plastic parts shows three critical strains (A, B,
C) for which the differential compliance and the recovery properties change
. It was found that all critical strains remain constant on varying the cry
stallite thickness or the testing temperature. Point A marks the end of the
linear-elastic range. The yield point, as given by the maximum on the engi
neering stress-strain curve for a necking sample, essentially corresponds t
o the second critical point, although the yield point is shifted relative t
o B to higher strains and varies with temperature. It is associated with th
e collective onset of inter- and intralamellar slip processes. At the third
critical strain (C), the lamellae become destroyed, and fibrils are formed
. The texture changes accompanying the drawing determined by a simultaneous
measurement of wide-angle X-ray scattering (WAXS) patterns indicate a comm
on activity of intra- and interlamellar slip processes setting in at A and
a dominance of intralamellar block slips at moderate deformations above B.
The Young's modulus and the yield stress show a large decrease with tempera
ture, whereas there are only minor changes in the crystallinity. We underst
and it as resulting from a change of coupling, both between the crystalline
lamellae and of the blocks within the lamellae.