A generalized model for the yield behavior of epoxy networks in multiaxial stress states

✍ Scribed by Alan J. Lesser; Robert S. Kody

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 198 KB
• Volume: 35
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(19970730)35:10<1611::aid-polb13>3.0.co;2-d

✦ Synopsis

Several yield criteria for glassy polymers are reviewed, and their limitations in predicting the effects of stress state, strain rate, test temperature, and molecular architecture are noted. These criteria are then generalized, so that a working model can be developed for predicting the yield response of glassy networks subjected to a multiaxial state of stress. To form the model, we summarize the phenomenological yield and fracture response of amine cured epoxies. In stress states ranging from uniaxial compression to biaxial tension, the yield response of these glassy networks follows a modified von Mises criterion ( t oct y Å t oct yo 0 ms m ), when tested at a constant temperature and octahedral shear strain rate, g h oct . Furthermore, changes in g h oct and molecular weight between crosslinks, M c , affect t oct yo only, and m remains unchanged. This was shown to be true for a broad range of M c (380 to 1790 g/mol). Additional results are included to illustrate the effects of temperature and strain rate on yield response. These results show that the yield behavior of epoxy resins is best described by a thermally activated process, similar to an Eyring type process. Finally, we extend the model to include intrinsic properties of the resin (e.g., M c , f, and T g ) and compare the model's predictions with experimental results.