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.

Klappentext

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.

Inhalt

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.