General Theory Of Hygrothermal Viscoelasticity Of Composite Materials And Simulation Of Nanoscale Matters Flow At Solid Surfaces

Composite materials exhibit obvious viscoelastic behavior under temperature, particularly those containing polymers and viscoelastic matrix. When composite materials are under temperature changes, the thermal stress will result from the expansion of components of composite materials. The wide applications of composite materials in advanced industries make the research of the composite material's viscoelastic and thermal properties more and more important. On one hand, the designs of ultralight, multifunction and intelligentizing require the research of composite materials in micromechanics and multi-scale analysis. On the other hand, it is very difficult that the thermal mechanics properties of viscoelastic composite materials are obtained by experiment, particularly when the properties of components of composite materials are related with temperature. Thus the research of the thermal viscoelastic theory of composite materials is an important task. As the polymer is hydrophilic, it will absorb the moisture in high humid environment. Recently, the failure caused by moisture and heat is often observed in package solder reflow and composite materials which absorb moisture. Thus the analysis of hydrophilic behavior of composite materials is very important.Nanoscience and nanotechnology is one of the most important researches in the 21st century. There exist in nano-scale matters many special effects, such as quantum effect, micro-scale effect and so on. These special effects would result in related special properties and behaviors of matters. The research emphases are mainly placed on behavior and variation of matters in nano-scale, the nano-engineering based on the behavior of matters in nano-scale and the effects of these behaviors and variation on the macro-properties of matters.In this thesis, the multi-scale methods for analysis of the thermal and moisture viscoelastic properties of composite materials are presented, and on the basis of the research, the general theory and multi-scale methods for analysis of thermal and moisture properties of composite materials under temperature changes are also presented. Some new concepts are defined in the above research. The molecular dynamics study of the alkyl matters in threedifferent states(gas, fluid, solid) which flow between two solid surfaces is presented and some conclusions are obtained. The contents and the conclusions in this paper include:1. Based on the homogenization theory, the multi-scale analysis methods of the viscoelasticity of the composite materials, and the effective thermal stress relaxation laws are studied in this paper. By defining the concepts, the effective thermal stress relaxation modulus (ETSRM) and the effective time-dependent coefficients of thermal expansion (ETCTE), the thermal viscoelastic constitutive equation is expressed in the same form as that of conventional materials. The multi-scale numeric methods for analysis of the thermal viscoelastic properties of composite materials are presented. The finite element processes for predicting the effective viscoelastic relaxation modulus, ETSRM and ETCET are given. The deformation analysis of one-dimensional structure of unidirectional fiber reinforced composites shows that the thermal strain depends on time.2. The general theory and multi-scale methods for analysis of composite materials, the components' mechanical properties of which are related with temperature, are also presented. By defining the concepts, the effective thermal stress relaxation modulus at final temperature (ETSRM-FT) and the effective time-dependent coefficients of thermal expansion at final temperature (ETCTE-FT), the thermal viscoelastic constitutive equation is obtained under continuous temperature changes.3. Based on the general theory and multi-scale methods for analysis of composite materials under temperature, the numerical analysis of thermal viscoelastic constitutive equation of the composite materials with the fiber reinforced thermorheological matrix is presented. ETSRM-FT and ETCET-FT of uni...