Deformation mechanisms and plastic resistance in single-crystal-textured high-density polyethylene

Abstract

Highly textured high-density polyethylene (HDPE) prepared by plane strain compression in a channel die was used as a macroscopic approximation to a single crystalline material to study the plastic deformation mechanisms. Samples cut out of the textured rectangular bars were subjected to tensile, compressive, and simple shear deformation in different crystallographic orientations, specifically chosen to probe the deformation resistances of specific crystallographic mechanisms of deformation. The degree of dominance of specific mechanisms in certain ranges of crystal orientation was ascertained by WAXS and S AXS measurements together with measurements of incremental shape changes of deformed samples. Through these studies it was determined that in deformation orientations requiring chain slip the most dominant mechanism was (100) [001] chain slip, with (010) [001] chain slip being a frequent alternative. Only scant evidence was found for the activity of (110) [001] chain slip. In deformation orientations requiring transverse slip evidence was found for the presence of (100) [010] transverse slip. In such orientations, however, very clear evidence was found also for deformation twinning on (110) planes. Martensitic transformations were not detected in any of the experiments. In compression experiments with the compression axis making a small angle with the chain axis and in tension experiments with the tensile axis making a large angle with the chain axis, chain slip often manifested itself in the formation of prominent kink bands. Shear resistances of the prominent slip systems and twinning systems together with their normal stress dependences at room temperature are reported together with considerably detailed descriptions of the observed kinematical modes of the specific deformation mechanisms.

Crystallographic texture evolution in high-density polyethylene during uniaxial tension

“…The results presented here pose new challenges to the modeling efforts reported in current literature [10][11][12][13][19][20][21][22][23][24][25]. As described earlier, previously reported models predict the formation of the (001) fiber component (with a slight misalignment in some cases); they do not predict the formation of either the near-(011) component or the weaker (010) component.…”

“…These can produce large unloading strains, especially in tensile loaded samples, and potentially cause significant changes in the underlying texture in the sample. Therefore, the textures reported in previous studies [10][11][12][13][14][15]19,[22][23][24] correspond to "deformed and relaxed" textures in the samples, and may not represent accurately the "deformation only" texture in the sample.…”

“…Bartczak and co-workers [11,12] produced a highly textured (quasi single-crystal) sample of HDPE by employing extremely large strains in the channel-die and studied its mechanical behavior. Samples were cut from the textured material and subjected to tensile, compressive, and simple shear deformation in different directions, which were chosen to probe the deformation resistances of specific potential slip mechanisms.…”

The degree of crystalline orientation as a function of draw ratio in semicrystalline polymers: a new model based on the geometry of the crystalline chain slip mechanism

“…The type of chain slip does not need to be specified either; but given that the easiest chain slip systems in PE are (100) [001] and (010)[001] [10], these are expected to dominate the orientation process.…”

Crystalline plasticity in isotactic polypropylene below and above the glass transition temperature

“…In this connection, two deformation mechanisms have been discussed, those are a) an approach based on adiabatic melting and recrystallization [3], and b) the deformation by crystallographic slip [4]. The major part of publications, favor the occurrence of the latter mechanism even for a wide range of strain [5][6][7]. Recently it could be shown that this mechanism is governed by nucleation and propagation of dislocations [8][9][10], although it was also reported [9] that in some polymer systems other deformation modes have to be considered in the crystalline phase.…”