Effect of stabilization on creep crack growth in high‐density polyethylene

Abstract

Polyolefins, particularly polyethylene, are known to fail via crack initiation and crack propagation when exposed to multiaxial long-term static stresses at elevated temperatures. Using concepts of linear elastic fracture mechanics, this article describes and discusses the effects of stabilization on the kinetics of creep crack growth (CCG) in high-density polyethylene (PE-HD) and the failure micromechanisms involved. As for the influence of stabilization, six PE-HD formulations (two polymer types, each with three stabilizer systems) were investigated. CCG initiation times and CCG rates were determined at 60 and 80°C in distilled water as functions of the crack tip stress field characterized by the stress intensity factor. Although no influence of the stabilizer type was found in either polymer type for CCG initiation times and CCG rates at high crack speeds, significant effects of the added stabilizer type and concentration were detected for low CCG rates. The observed phenomena were explained in terms of local aging processes in the immediate vicinity of the crack tip, which were controlled by the presence and content of various stabilizers.

Influence of Hot Chlorinated Water and Stabilizer Package on the Fatigue Crack Growth Resistance of Glass Fiber Reinforced Polyamide

“…On the one hand, the presence of an environmental medium may cause “physical aging” such as plasticization effects, post- and rec-crystallization or free volume changes in amorphous regimes. On the other hand, the combined action of high-local stresses and an aggressive environment (i.e., elevated temperature and environmental medium) may result in “chemical aging” locally at the crack tip, which leads to enhanced stabilizer consumption and rupture of covalent bonds of the polymeric molecules and thus ultimately to material degradation in the crack tip region [53,54,55,56,57,58,59,60,61,62,63,64,65]. This mechanism is facilitated by free volume increase and plastic deformation mechanisms in the highly stressed crack tip region, where a larger materials surface to volume ratio allows for a better interaction with the environmental medium [15].…”

PE-HD fatigue damage accumulation under variable loading based on various damage models

“…Therefore, it is judicious to model the Wöhler curve by Basquin's equation [36]. This latter is commonly used to model the S-N curve of PE-HD material, see [21,23] and [37]. Thus, parameters of Basquin's equation are given in Equation (8): (8) where Basquin [36] proposed a power function between the stress level and the number of cycles as shown by Equation (9): (9) where A and b are material constants.…”

Comparing cracking time and structure changes of different high‐density polyethylenes during stress and photo‐oxidative aging

“…So many researchers studied about photo‐oxidative aging on HDPE and analyzed changes in mechanical properties and chemical structure . On the other hand, many works discussed about stress aging on HDPE with the crack growth and predicted the lifetime of material . Nevertheless, there are a few studies simulating materials aging under stress and photo‐oxidative conditions …”

“…[2][3][4][5] On the other hand, many works discussed about stress aging on HDPE with the crack growth and predicted the lifetime of material. [6][7][8][9] Nevertheless, there are a few studies simulating materials aging under stress and photo-oxidative conditions. 10,11 In this work, the materials were applied on an aging oven which with ultraviolet irradiation, stress, and humidity thermal conditions to simulate the HDPE materials accelerated aging process.…”