THE MORPHOLOGY, CHAIN STRUCTURE AND FRACTURE-BEHAVIOR OF HIGH-DENSITY POLYETHYLENE .2. STATIC FATIGUE FRACTURE TESTING

High-density polyethylene (HDPE) is being used more and more in critical long-term applications. For this reason it is important to have a strong understanding of those parameters which control the fracture behaviour of HDPE. In Part I of this work, fracture results were presented for eleven HDPE samples tested using a tensile testing machine. Such short-term tests do not accurately reflect the in-service loads on HDPE components, which tend to be low and static. It is, therefore, important to perform fracture tests under long-term static loads. The results of such testing are presented in this paper. The resistance to static fatigue was found to be most strongly dependent on molecular weight. Short branch concentration and short branch length were also found to exert an influence on the resistance to static fatigue. This result is similar to the findings presented in Part I of this work. However, there is some evidence that molecular weight influences fracture behaviour to a greater extent in the long-term tests. Notwithstanding, the similarity between the short-term and long-term results is important. It means that an early indication of the long-term performance of HDPE resins can be obtained from rapid comparative tests conducted using a tensile testing machine.