Stepped Isothermal Method for CreepRupture Studies of Aramid Fibres

Abstract

Synopsis: Aramid fibres have been used in rope construction and for prestressing tendons, but when subjected to a constant static load the fibres creep with time and may rupture, leading to a catastrophic failure of the rope. To understand this behaviour many life-time models have been suggested but they suffer from the lack of long term creep rupture data to make firm conclusions on rupture times and load levels. Such data is expensive to obtain using conventional creep testing as it takes a long time before failure of a specimen. To overcome this problem, and to obtain the creeprupture data at low stress levels within a reasonably short time scale (hours), accelerated testing methods, the Stepped Isothermal Method (SIM) and Time Temperature Superposition (TTSP), have been investigated. In SIM testing a single yarn specimen is tested at a specific stress level under a series of increasing temperature steps from which a single response curve, known as the master curve, is obtained which predicts the long-term behaviour. Some manipulation of the data is required, but the technique has many advantages over the TTSP and conventional creep testing and it can be automated to obtain the long-term creep-rupture data points relatively easily.