The double yield in the tensile deformation of the polyethylenes

Abstract

Double yields, as well as other complex yielding behavior, that are observed during the tensile deformation of the polyethylenes have been studied in a systematic manner. The conditions under which such yielding is observed were established by studying a set of linear polyethylenes and well‐characterized ethylene copolymers of narrow molecular weight and composition distributions. A wide range in crystallinity levels were developed and the rate of deformation and the deformation temperature were varied. These experimental results make clear why such complex yielding processes are not always observed. A qualitative explanation, based on the postulate of a partial melting‐recrystallization process during deformation, is given that encompasses all of the experimental data.

The effect of molecular weight and crystallite structure on yielding in ethylene copolymers

“…enes, display a complex yield behavior. [1][2][3][4][5][6][7] This In the present work we continue this effort and phenomenon has been particularly manifest in direct our attention to some of the other important random copolymers. In such systems diffuse variables that define the crystalline state, namely yields and multiple yield points are commonly obthe molecular weight, and the crystallite and suserved.…”

“…This behavior was postulated to be a consequence of a partial melting-recrystallization process. 7 Other works 2, 3 have made clear that for the polyethylenes that have been studied the yield stress is directly proportional to the degree of core crystallinity. The series of samples listed in Table I were chosen for their uniqueness in maintaining a constancy in the degree of crystallinity for a given copolymer under different crystallization conditions.…”

“…Complex yield behavior, depending on the crystallization method, has been reported. [1][2][3][4][5][6][7] In a detailed previous report the systematic changes in the nature of the yield process, from single to double to diffuse yields, was attributed to the differences in the crystallinity levels. This behavior was postulated to be a consequence of a partial melting-recrystallization process.…”

“…To accomplish this purpose shape of the force-elongation curve in the yield we have studied the stress-strain behavior of a region. 7 It was found that there was a systematic set of random ethylene-hexene copolymers that change in the form of the yield with crystallinity have most probable molecular weight distribulevel. The main experimental observations, intions as well as very narrow composition distributions.…”

Plasticity of semi-crystalline polymers: crystal slip versus melting-recrystallization

“…Mandelkern et al [85,86] have discussed the occurrence of double yield points in PE and ethylene copolymers in relation to two populations of crystalline lamellae having different size distributions. The smaller and less perfect crystals undergo straininduced melting, and then the fraction of recrystallized material can undergo yielding again at higher strain level.…”