Research On Hygro-Thermo-Stress Coupling Response And Damage Of Composites

Fiber reinforced composite materials have many advantages and they are widely used in aviation, aerospace and other engineering fields. However, they will inevitably bear the temperature changes, humidity changes and the coupling effect of external loads when they are in the course of using, result in generating damage inside the structure, seriously affect the mechanical properties of the overall structure of composites. Researches on the subject at home and abroad at present are mainly about experimental analysis and less about theoretical research. It has not formed a set of analysis and evaluation methods which are mature, easy to accept and can be widely used in engineering. Carrying out the elastic response research on hygro-thermo-stress coupling of composites with damage has important engineering significance for the structure design, manufacture, application, maintenance and life prediction of composites and the development and research of new materials.For the elastic response research on hygro-thermo-stress coupling of composites, this paper analysed the computational process of ultimate failure load and ultimate failure strength of symmetric composite laminates using the classical lamination theory, and taking carbon fiber reinforced epoxy composite laminates CCF300/5228 as an example, using Hoffman strength theories and partial damage assumptions, respectively performed the strength analysis of two kinds of different layer schemes under hygro-thermo-stress coupling, compared the initial layer failure load, initial layer failure strength, ultimate failure load and ultimate failure strength of two kinds of laying programs and gave a specific theoretical solution.For all of the current structural analysis softwares can not performe response analysis with"humidity", this paper programmed using MATLAB software and gave the complete humid response analysis program of fiber reinforced resin matrix composites laminates structure, analyzed and calculated the theoretical solution problem which has been given above using program, and proved that the program was accurate and reliable.For the elastic response research on hygro-thermo-stress coupling of composites with damage, using the basic theory of classical thermodynamics, avoiding the common assumptions of classical damage theory and using the relevant theory of tensor analysis, this paper established general theory of hygrothermal elastic anisotropic damage of composites, derived all of the constitutive equations of composites with damage under hygro-thermo-stress coupling, including specific free energy constitutive equation, stress-strain constitutive equation, entropy density constitutive equation, damage strain energy release rate constitutive equation, hygroscopic dual force constitutive equation, hygro-thermo-stress-damage coupled heat conduction constitutive equation and damage evolution constitutive equation, thus a complete theoretical description was established of hygrothermal elastic damage problems of composites. Finally, from two aspects of mesomechanics and experimental observations, the determination methods were illustrated of damage effect tensor functions and coefficient tensors in every constitutive equation of hygrothermal elastic damage of composites in three common forms of damage.This paper considered the coupling factors of the change of environmental temperature and humidity, external load and internal damage comprehensively and provided important theoretical basis for analyzing the damage problems of composites in practical projects under the change of temperature and humidity and other complex and severe environment.