Study on the Mechanical Properties of Stay Cable HDPE Sheathing Fatigue in Dynamic Bridge Environments
As the main force-bearing component of a cable-stayed bridge, a durable stay cable is paramount to the safety and durability of the entire bridge. High-density polyethylene (HDPE) sheathing is the main protective component of a stay cable and is the key to insuring cable durability. To address the issue of HDPE sheathing fracture on service, strain level data for in-service, HDPE bridge cable sheathing was used in this study as the basis for HDPE material aging and fatigue testing. A fatigue yield phenomenon with a yield platform on the hysteresis curve of the fatigue cycles is observed by the fatigue test. The parameters to describe this phenomenon are proposed and defined in this paper. A preliminary examination of the relationship between these parameters and the factors, such as the number of cycles, the strain amplitude, and strain rate, are presented. Based on the results obtained, it is suggested that the condition of fatigue yield of HDPE sheathing be defined as the fatigue durability limit state for the purposes of durability design, assessment, and protection of cable-stayed bridges.
Compression and tension fatigue resistance of medical grade ultra high molecular weight polyethylene: the effect of morphology, sterilization, aging and temperature
Abstract It is shown in this study that polymer morphology, sterilization with or without accelerated aging, and temperature affect the fatigue crack propagation behavior of ultra high molecular weight polyethylene (UHMWPE). Changes in UHMWPE orthopedic implants due to sterilization and shelf aging are of great clinical interest and importance. In recent years, accelerated aging has been used to simulate shelf aging and post-sterilization oxidation in UHMWPE orthopedic components. In order to understand the role of sterilization and post-sterilization aging, two commercially available polymers (GUR4150HP and Hylamer®-M) with distinct morphologies were subjected to one of four sterilization techniques (gamma radiation in air, gamma radiation in vacuum, ethylene oxide gas, and gas plasma). Non-sterile samples were used as controls for all studies. Half the groups were tested in the unaged condition. The remaining samples were aged under accelerated conditions via elevated temperature (70°C) and oxygen pressure (5 atm) for 14 days to simulate five years of shelf aging. Subsequent to sterilization and aging treatments, specimens were subjected to cyclic compression loading followed by cyclic tensile loading in order to characterize the fatigue resistance. Scanning electron microscopy was used to provide an understanding of fatigue fracture mechanisms. Fourier transform infrared spectroscopy and density gradient column methods were used to determine the structural changes brought about by sterilization and aging. It is found in this work that accelerated aging causes a decrease in fatigue resistance regardless of sterilization method. Fatigue degradation is most severe for gamma radiation in air coupled with accelerated aging conditions. The results of this study have important implications for the design of fatigue resistant polymers used in medical applications.
Nietzsche: Philosopher, Psychologist, Antichrist
This classic is the benchmark against which all modern books about Nietzsche are measured. When Walter Kaufmann wrote it in the immediate aftermath of World War II, most scholars outside Germany viewed Nietzsche as part madman, part proto-Nazi, and almost wholly unphilosophical. Kaufmann rehabilitated Nietzsche nearly single-handedly, presenting his works as one of the great achievements of Western philosophy. Responding to the powerful myths and countermyths that had sprung up around Nietzsche, Kaufmann offered a patient, evenhanded account of his life and works, and of the uses and abuses to which subsequent generations had put his ideas.Without ignoring or downplaying the ugliness of many of Nietzsche's proclamations, he set them in the context of his work as a whole and of the counterexamples yielded by a responsible reading of his books. More positively, he presented Nietzsche's ideas about power as one of the great accomplishments of modern philosophy, arguing that his conception of the "will to power" was not a crude apology for ruthless self-assertion but must be linked to Nietzsche's equally profound ideas about sublimation.He also presented Nietzsche as a pioneer of modern psychology and argued that a key to understanding his overall philosophy is to see it as a reaction against Christianity. Many scholars in the past half century have taken issue with some of Kaufmann's interpretations, but the book ranks as one of the most influential accounts ever written of any major Western thinker.