Abstract
ABSTRACTThis study focuses on the prediction of long‐term failure of glassy polymers under static or cyclic loading conditions, including the role of stress‐accelerated progressive aging. Progressive physical aging plays a dominant role in a polymer's performance under prolonged loading conditions, and to obtain accurate predictions of failure, its effect has to be considered. First, the aging kinetics, as influenced by temperature and stress history, are studied extensively. Similar to an elevated temperature, the application of a stress (below the yield stress) activates the aging process, and as a result, the yield stress will evolve faster in time. The activation by stress appears to be limited; at some stress level, the activation stagnates and is followed by rejuvenation. This evolution is captured in a model by introducing a state parameter, which describes the thermodynamic state of the material and is directly linked to the yield stress. With the aging kinetics included in the model, an accurate prediction of the failure time for cyclic loading conditions is obtained. For static loading conditions, however, the effect of physical aging is overestimated because of the stagnation of the activation by stress. It appears that there are marked differences in the stress level where stagnation and subsequent rejuvenation occur for a cyclic or static load. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1300–1314
Highlights
Polymers are increasingly used in demanding load bearing applications, with service life-time requirements typically in the order of decades
Stress-Accelerated Aging To illustrate the effect of stress on physical aging and rejuvenation, results of the thermo-mechanical treatments on PPSU are shown in Figure 4(a and b), for a temperature of 125C
Note that the range of stresses that can be applied successfully is limited, because too low stresses do not lead to any observable acceleration of physical aging within an experimentally acceptable time, whereas too high stresses result in strain softening and subsequent failure already before the sample can be unloaded and a yield stress can be measured
Summary
Polymers are increasingly used in demanding load bearing applications, with service life-time requirements typically in the order of decades. Experimental as well as numerical methods are preferred that predict this performance based on short-term tests only, such that premature failure under long-term loading can be accurately predicted. Such methods potentially support the process of designing new materials with improved long-term properties. Note that the deformations during this process are small, indicating that contribution of strain hardening is negligible Both types of data, namely aging accelerated by temperature or by a combination of temperature and stress, can be shifted toward a smooth master curve as shown, using reduced time approaches: aging time–temperature superposition (TTS)[33,34] and aging time–stress superposition (TSS).[35] Namely aging accelerated by temperature or by a combination of temperature and stress, can be shifted toward a smooth master curve as shown in Figure 2(b), using reduced time approaches: aging time–temperature superposition (TTS)[33,34] and aging time–stress superposition (TSS).[35]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call