Microstructure And Thermal Insulation Of Fiber Reinforced Resin Matrix Composites

In recent years,with the rapid development of shipping industry,space industry,large gas turbine and military industry,the demand for the research and development of high performance insulation material becomes more and more urgent.For high performance insulation materials,excellent heat insulation and heat protection performance is essential,at the same time,good mechanical properties and more lightweight properties are required to reduce the energy loss of equipment operation.In this experiment,the carbon fiber reinforced phenolic resin matrix composites were studied.The carbon fiber reinforced carbon fiber skeleton materials with small density,low thermal conductivity and strong mechanical properties were used as reinforcement and phenolic resin as the matrix to prepare high performance insulation materials.In the preparation process,the compression molding process of the skeleton is carried out,so the structure and performance parameters of the material are not the same in the parallel and perpendicular to the forming direction.It is anisotropic.The microstructure of two different directions can be seen by scanning electron microscope.The carbon fibers in the material are distributed randomly and parallel in two directions,and phenolic fibers are filled between the fibers.In this paper,the density of material is measured by two ways,and the apparent density and true density are obtained.Through two values,it can be seen that the internal pores of the material are more abundant.The isothermal desorption curve can be obtained from the data measured by nitrogen sorbent.According to the shape of hysteresis loop,it can be seen that it belongs to H3 type hysteresis loop,and the pore is uneven.The pore is a slit hole formed by sheet particle accumulation,and most of them are mesoporous.Through the electronic universal testing machine,the two directions of the material are compressed separately,and it can be analyzed that it is more compressibility in parallel to the forming direction than perpendicular to the forming direction.The materials were analyzed by differential scanning-thermogravimetric analysis(DSC-TG)and thermal conductivity.The materials were treated at a temperature of 200,300,400,600,800,1000.Then,the microscopic morphology(SEM),infrared absorption spectrum(FI-IR)and X ray diffraction(XRD)of the samples treated at various temperatures were analyzed.From the sample macroscopic view,the sample color changed from yellow green to brown to black with the increase of heating temperature,and the specimen remained intact,and there was no crack on the surface of the sample.From the microscopic appearance,after high temperature,the fiber structure in the composite material has not changed,and the material does not increase the defects such as obvious cracking and hole.The phenolic resin impregnated inside the carbon fiber skeleton has been pyrolyzed at high temperature,but it still maintains the uniform pore structure in structure.The thermal conductivity of the material is 0.2748 W/(m K),and the total weight loss of the material is 36.5% at 30~1200 C,and the rate of weightlessness is very low after 800.After the infrared spectrum analysis,it is found that after heating,the hydroxyl,carbon and carbon double bonds and ether bonds in the material are carbonized one after another and release small molecular gas until the carbon is completely carbonized,and the material composition will hardly change.According to the material performance data,it can be explained that the material is rigid lightweight insulation material.The thermal analysis of materials is simulated by ANSYS software.First,the simulation model of heat insulation material is set up.The preprocessing includes modeling,grid division,input parameters and so on.Then the simulation model is calculated and post processed.The thermal analysis and transient thermal analysis of the thermal insulation are completed.A stable temperature distribution cloud is obtained through the steady state thermal analysis,and the transient thermal analysis has obtained the temperature distribution clouds at different time before the stable state is reached.The temperature distribution in the steady state heat analysis shows that the final temperature of the upper surface is about half the temperature of the thermal load at a steady temperature analysis at a certain temperature.Because the specimen model is light and thin,it can be seen that the material still has good heat insulation performance at high temperature.The temperature of each part of the sample varies with time.It can be seen that in the process of transient thermal analysis,with the increase of the heating temperature,the time increase of the steady state is much smaller than that of the heating rate.The heat of the material reaches a shorter steady state time and no longer continues to heat up,and the material has better insulation performance.