Thermomechanics of Composites under High Temperatures

The thermomechanical properties of composites on polymer matrix at high tem peratures are essentially different from those at normal temperatures. The main distinctions briefly consist in the following: - at high temperatures there occurs an irreversible variation (degradation) of all mechanical and thermal properties of a material that usually has a complex non-linear character depending on time exposure under high temperature; - there are complicated internal physico-chemical processes in a matrix and fibres under high temperatures called by the general notion of ablation; the internal physico-chemical and mechanical processes run differently in the matrix and fibres, and this leads to the appearance of considerable internal thermal stresses. Generally speaking, a composite under high temperatures can be considered as a multiphase system consisting of solid, gaseous and fluid phases interact.ing mechanically and chemically with each ot.her. There are t.hree levels of temperature: normal, elevated and high. Normal, or room temperatures are 10 - 30°C; elevated temperatures are 30 200°C; hzgh temperatures are those above 200°C. However, the dividing line between elevated and high temperat.ures depends on the material involved; a temperature is called high for a particular composite material if, at this temperature, irreversible internal physico-chemical transformations occur in the matrix and/ or fibres of the material.

1. High-Temperature Environment and Composite Materials.- 2. General Equations of Multiphase Continuum Mechanics for Ablative Composites.- 3. Mathematical Model of Ablative Composites.- 4. Behaviour of Matrices at High Temperatures.- 5. Reinforcing Fibres under High Temperatures.- 6. Unidirectional Composites under High Temperatures.- 7. Textile Ablative Composites Materials.- 8. Composites Reinforced by Dispersed Particles.- 9. Phenomena in Composite Materials Caused by Gradient Heating.- 10. Linear Ablation of Composites.- 11. Thermal Stresses in Composite Structures under High Temperatures.- 12. Mechanics of Composite Thin-Walled Shells under High Temperatures.- Appendix. Methods of Experimental Investigation of High-Temperature Properties of Composite Materials.- A1. Determination of Density under Heating.- A2. Determination of Thermal Characteristics under Heating.- A3. Determination of Gas Permeability.- A4. Determination of Heat Deformations under Heating.- A5. Determination of Strength and Elastic Modulus of Composites under High Temperatures.- A6. Gas-Dynamical Testing of Composites.- References.