Research On Three-dimensional Thermal Response Of Carbon Fiber Epoxy Resin Laminates Based On UMATHT

With the rapid development of composite materials and their widespread application in the civil aviation industry,the threats from fire have attracted more and more attention.Due to the influence of high temperature,the fire will cause the matrix to pyrolyze and reduce the structural strength,so the structural integrity will be influenced,and at the same time,heat as well as toxic and harmful gases will be released.This paper mainly studies the thermal response law of carbon fiber epoxy resin composite materials under high temperature environment.This paper considered a series of physical and chemical changes that occur during the single-sided heating of composite materials,and establishes a three-dimensional thermal response model for composite materials.Based on the secondary development of the program UMATHT and USDFLD,the composite thermal response subroutine was written,and the finite element model of the thermal response of the composite was established.By conducting finite element modeling and analysis of different material systems,this paper studied various composite materials in time and thermal response law in space.Through the research in this paper,an effective material thermal damage analysis tool for composite materials can be provided.The main contents of this paper were as follows:In this paper,the three-dimensional thermal response control equations of composite materials was established,including: heat transfer equation(energy conservation equation),decomposition rate equation and continuity equation(mass conservation equation).Based on the secondary development of user subprograms UMATH and USDFLD,through writing FORTRAN program to define and update the variables,a finite element model of the thermal response of the composite material which can consider the pyrolysis gas convection and matrix decomposition in the thickness direction of the material was obtained.Through the establishment of finite element models of different material systems,the simulation analysis of the thermal response at different positions inside the material during the pyrolysis process was realized.The thermal response laws of various composite material systems such as carbon fiber epoxy resin composite materials were analyzed,and the changes of temperature,density,carbonization rate and carbonation rate with time and space under the action of unilateral radiant heat flow were predicted,as well as the carbonation rate and the relationshipbetween the carbonization rate and temperature.The calculation results of carbon fiber epoxy resin composite materials show that: at the initial stage of heating,the temperature at different depths in the thickness direction of the carbon fiber epoxy resin composite material gradually increases with the increase of heating time.With the increase of heating time,the temperature rise rate of each depth position decreases;at the same time,the material density of different depth positions was different,the farther away from the heated surface,the lower the degree of material pyrolysis was,the greater the material density was.The materials at different depths have different carbonization rates when they reach the same temperature,and the closer they were to the heated surface,the lower the carbonization rate was.The materials have different temperatures when they reach the same carbonization rate,and the farther they were from the heated surface,the lower the temperature was.The materials at different depths have different temperatures when they reached the peak of carbonization rate,and the farther they were from the heated surface,the lower the temperature was when they reached the peak of carbonization rate.The calculation results of glass fiber phenolic composite materials and other material systems show that: in the initial period of heating,the material in the thickness direction of the material near the heated surface area firstly reached the critical pyrolysis temperature,and the resin pyrolysis reaction occurs quickly.With the increase of heating time,the pyrolysis zone gradually moved toward the back of the material in the thickness direction,the degree of carbonization of the heated surface gradually increased,and different degrees of carbonization occurred at different depths in the thickness direction of the material.When the heating was completed,the material thickness can be divided into a carbonized layer,a pyrolysis zone,and a raw material zone according to the degree of pyrolysis of the material.