Temperature-dependent fracture mechanisms in ultra-high strength polyethylene fibers

Abstract

Abstract:The influence of the temperature on the mechanical properties of gel-spun hotdrawn ultra-high molecular weight polyethylene fibers has been investigated.From these experiments two different fracture mechanisms could be distinguished.The results indicate that above 20 ~ a stress-induced orthorhombic-hexagonal phase transition is responsible for fiber failure. In the hexagonal or rotator phase the chains can easily slip past one another and fiber fracture is initiated by creep. Below 20 ~ the phase transition cannot be introduced because the stress needed for the phase transition would exceed the covalent-bond strength in the polyethylene chain. The strength temperature data of the low temperature region was treated with Zhurkov's kinetic concept, leading to a bond-fracture activation energy of 160 kJ/mol and an activation volume of 0.01 nm 3. These values, together with the data from irradiation and shrinkage experiments, indicated that in the low temperature region fiber failure might be initiated by the fracture of trapped entanglements instead of that by overstressed, taut tie molecules.

Understanding the Thickness Effect on the Tensile Strength Property of Dyneema®HB26 Laminates

“…The volume fraction $v_f$ defines the amorphous material in the same unit volume as the irreversible damage. Based on existing nanoscale models [4], the total length of the representative volume would have crystalline regions with a length of ~70 nm separated by disordered regions with a length of ~4 nm thus a total length of ~74 nm. Hence, as a volume fraction the representative volume of amorphous material is defined as simply (4/74).…”

Annealing behavior of gel‐spun polyethylene fibers at temperatures lower than needed for significant shrinkage

“…In this article, we focus on the annealing behavior at 373 K, a temperature lower than needed for significant shrinkage and melting, but at this temperature the yield stress has already begun to decrease rapidly, and the stress–strain behavior has changed from brittle to ductile 38. A thermal analysis must consider the fact that the glass transition of the rigid amorphous fraction is completed at this temperature (it ranges up to 300 K), and the upturn of the apparent heat capacity beyond the vibrational heat capacity due to beginning fusion starts at about 375 K 7.…”

Chain Ends and the Ultimate Strength of Polyethylene Fibers

“…Mesoscale investigations have shown that atomic scale studies are needed to accurately quantify these weak van der Waals forces and determine if fibers yield primarily by chain slip, bond breaking, or some combination of the two. [14][15][16] In this letter we use large scale MD simulations to determine the tensile strength of crystalline PE, which is believed to provide an upper bound for PE fibers. We find that infinite chains fail through chain scission at ∼ 20GPa, which is consistent with previous estimates.…”