Influence of moisture on the time and temperature dependent properties of polymer systems

摘要

The use of temperature and time dependent material parameters is state-of-the-art in mechanical engineering. An advanced measurement method for the determination of moisture dependent parameters for micro and nano scale samples was developed. In combination with FE-analysis, this tool (involving time, temperature, and humidity) ensures a sure deployability. The present paper deals with the influence of the moisture absorption on the time and temperature dependent properties of epoxy systems. These thermosetting polymers have strong time and temperature dependent mechanical properties. It is an excellent material for understanding moisture induced thermo mechanical behaviour. The influence of humidity on the materials behaviour shows that the humidity diffusion does not only effect a shift in the glass transition temperature and a reduction in the modulus, but also influences the visco elastic properties significantly. The moisture-dependent properties are analyzed by novel experimental procedures. It was found that for a lifetime model the relaxation behaviour as a function of temperature over time and moisture has a significant influence, which increases not only with temperature but also with moisture concentration. The cause of variant properties is the free volume and/or polarity of the structure. The combination of several such factors of different materials parameters (moisture concentration, hygroscopic swelling, and diffusion coefficient) and their interrelated influences makes an important contribution to mechanical reliability analysis.