Prediction For Hygro-and-Temperature-Dependent Viscoelastic Properties Of Composite Materials

Researches have physically shown that composite materials can exhibit obviousviscoelastic behavior under hydrothermal environments, particularly those containingpolymers and viscoelasticity matrix. Their obvious disadvantage is sensitive about the changeof the hydrothermal environments that results in the decreasing of the strength of the materials.Polymers and composites with polymer matrix have been widely used in advanced industriesfor their inherent advantages, such as designable character, high specific strength and specificstiffness. However, the moisture and temperature are always changing. At present, most ofstudies focused on this work for the properties at some moment. So it is very necessary andimportant to study micro-mechanical methods predicting numerically or analytically thetime-dependent viscoelastic properties of composite materials based on the heterogeneousmicrostructural details of composite materials. Therefore, this paper focuses on this researchwork, including:1. Based on homogenization method, the property of time-temperature-dependentviscoelastic behavior of unidirectional fiber reinforced composites withthermorheological simple matrix is studied. The character of the viscoelastic relaxationlaw subject to variation in temperature is investigated, and the global effectiveviscoelastic relaxation modulus considering the temperature-dependency of properties isgiven. And numerical examples for unidirectional fiber reinforced composites withthermorheological simple matrix is presented.2. By inducing the history of temperature, the analysis of the thermal strain of the plate isexpressed. It is found that the time effect of the relaxation is small, so the coefficient ofthermal expansion may be given by the instantaneous thermal deformation.3. Focused on particle-reinforced composites, the relaxation rules at constant temperature ofvarious fractions and those at different history of temperature are expressed.4. Based on homogenization theory, the moisture viscoelastic theory is expressed. It issimilar to that for thermal viscoelastic. Through the numerical analysis of unidirectionalfiber reinforced composites, the rules of the effect relaxation modulus, the effectmoisture stress relaxation modulus and the effect moisture expansion coefficient aregiven. This research was supported by the National Natural Science Foundation (No.10332010,10421202), the National Basic Research Plan (No. 2006CB601205) and by the program fornew century excellent talents in university of china (2004). The financial supports aregratefully acknowledged.