Abstract
The multi-relaxation (MR) test was developed based on the concept that stress relaxation behavior can be used to reflect the material state of polyethylene (PE) under tension. On the basis of this concept, critical stroke for the onset of plastic deformation in the crystalline phase, named the first critical stroke, was determined using the MR test. Results from wide angle X-ray scattering suggest that phase transformation occurred in the crystalline phase of PE after the specimen was stretched beyond the first critical stroke. In this work, the MR test was applied to six PEs of different mass densities to determine their first critical strokes and the corresponding total and quasi-static (QS) stress values. The results show that the first critical stroke had very similar values among the six PEs. More interestingly, the ratio of the QS stress at the first critical stroke to the yield stress from the standard tensile test showed little dependence on PE density. Therefore, it was possible to use the popular short-term tensile test to characterize the critical QS component of the applied stress to initiate plastic deformation in the crystalline phase, which is expected to play a significant role on the long-term, load-carrying applications of PE.
Highlights
Polyethylene (PE) is a family of commodity polymers with excellent durability, light weight [1,2,3], and relatively low cost
In view that σst-1st represents the critical QS stress to initiate local plastic deformation in the of σst at the first critical point to the yield strength listed in Table 1, plotted as crystalline phase of PE, its value could play a significant role on the long-term performance of PE, a function of PE density
Conclusions crystalline phase of PE, its value could play a significant role on the long-term performance of PE, especially formulti-relaxation load-carrying applications
Summary
Polyethylene (PE) is a family of commodity polymers with excellent durability, light weight [1,2,3], and relatively low cost. For PE used in load-bearing applications, the main concern is around PE’s time-, temperature-, and strain-rate-dependent mechanical properties [4,5,6]. This issue is further complicated by the semi-crystalline nature of PE’s microstructure, which has crystalline and amorphous phases mingled in a lamellar arrangement. Both phases are involved from the beginning of the deformation process, their role of involvement varies with the applied stress level [5]. Necking occurs after the yielding, which from the microstructural viewpoint is a process that transforms lamellae into fibril clusters
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