| Composite materials are currently evolving rapidly in the design and manufacture of civil aircraft,but one of the safety challenges they face is the fire hazard.When exposed to fire,the composite will undergo pyrolysis,resulting in loss of structural strength,failure to ensure structural integrity,and release heat,gas and fumes at the same time.In order to study the thermal response of composite materials in fire environment,the thermogravimetric experiments of carbon fiber/epoxy resin and glass fiber/epoxy materials were carried out,and the thermal response mechanism was summarized.The finite difference method was used to numerically calculate the equations,and the thermal response and carbonization process at different locations inside the material during the pyrolysis process were predicted,and the thermal response test of carbon fiber/epoxy composites was carried out.This paper provides an effective analysis tool for thermal damage analysis and structural fire protection design of common aerospace composite structures such as carbon fiber/epoxy resin and glass fiber/epoxy resin.The main research contents were as follows.Firstly,the thermogravimetric analysis experiment of carbon fiber/epoxy resin and glass fiber/epoxy materials were carried out.The thermogravimetric curves and differential thermogravimetric curves were used to study the pyrolysis characteristics of carbon fiber/epoxy composites and glass fiber composites under different temperature rise rates and different atmospheres.The Kissinger method and the Flynn-Wall-Ozawa method were used to numerically calculate the pyrolysis kinetic parameters of the materials.The applicability of the pyrolysis model established by the two thermal analysis methods were discussed,it was proposed that the pyrolysis model considering the reaction mechanism function should be established.The summary of the thermal response mechanism of the composite material.Secondly,one-dimensional thermal response equations for composites considering pyrolysis kinetics were given.The finite difference schemes of thermal analysis model,pyrolysis model and mass conservation model were derived.The finite difference method was used to calculate the thermal response at different locations inside the material during pyrolysis.The thermal response characteristics of glass fiber/phenolic composite,glass fiber/epoxy composite,and carbon fiber/epoxy composite were analyzed.The temperature-time progress,temperature-thickness distribution,density-time progress,density-thickness distribution and residual mass fraction as a function of temperature under unilateral radiant heat flow were predicted.The numerical results show that the nonlinear thermal response equations and calculation method established in this paper can predict the thermal response of different composite systems.The theoretical results were validated against experimental data and a good agreement was observed.The prediction of carbonization process of different material systems under high temperature conditions was given,and the dynamic process of carbonization of materials at high temperature was clarified.With the increment of the depth,composite materials reaching the pyrolysis temperature increased,the rate of material density decreased and the carbonization process slowed down.The residual mass fraction of materials at different depth in the pyrolysis reaction zone was slightly different at the same temperature,the residual mass fraction decreased and the degree of carbonization increased as the deeper the position rose.Finally,the thermal response of carbon fiber/epoxy composite laminates was carried out by cone calorimeter.It can be seen that at 20 kW/m~2 and 25 kW/m~2 heat flux,the mass loss of the smooth surface was greater than 1%and 6%of the rough surface,respectively.Due to the different boundary conditions,the exposed surface temperature was lower than the insulation surface by 73°C at a heat flux of 20 kW/m~2. |
