Thermal Response For Carbon Fiber Epoxy Resin Composites Based On Uncertainty Analysis

Carbon fiber epoxy composites have developed rapidly in aviation field due to their light weight and superior performance.However,the softening and pyrolysis of the material under heating will make it difficult to withstand external loads,which will further deform and eventually fail.Due to the existence of uncertain parameters,the thermal response analysis of composites based on the deterministic framework system is often difficult to reasonably evaluate the true safety performance of the material.Thus,it’s important to consider the impact of parameter uncertainty of composite thermal response model.In this paper,the pyrolysis mechanism of carbon fiber epoxy resin composites was studied and thermal physical properties and the reaction kinetics model was established.Based on the uncertainty analysis method,the thermal response analysis of carbon fiber epoxy composites was carried out to support the fire protection design analysis and airworthiness verification of the composite airframe.In this paper,the thermophysical properties were tested,the TG experiment was carried out,and the kinetic parameters of Arrhenius reaction were calculated by the Kissinger method,Friedman method,and Ozawa method,so the parameter model was established.The change trend of activation energy with conversion obtained by Ozawa method is close to that obtained by Friedman method,which verifies the accuracy of the results.After improving the one-dimensional thermal response model,the correctness and validity of the thermal response mathematical model was verified through experiments on a carbon fiber epoxy composite laminate with one-sided heating.Local and global sensitivities of thermophysical parameters and reaction equation constants were analyzed,and uncertainties of output responses were analyzed by Sobol sampling and Latin hypercube sampling.It is found that the thermal degradation of the composite is carried out in three steps under inert atmosphere.The first step is mainly moisture drying and carbon dioxide escaping.The second step is the decomposition of the epoxy resin matrix,and the third step is the further pyrolysis of the polymer.In the air,it will add the last step of oxidative decomposition of carbon fiber.The kinetic analysis confirmed that the thermal decomposition reaction of carbon fiber epoxy resin composites under inert gas is multi-step,and the thermal degradation reaction mechanism of carbon fiber epoxy resin composites obeyed the F₄ model showed by the Coats-Redfern method.From the sensitivity analysis,it is found that the influence of the pre-exponential factor and the heat of decomposition on the temperature-time history can be ignored,while the influence of the activation energy,the reaction order,the specific heat capacity of the original material and the thermal conductivity of the original material are more significant.Regarding the density,the activation energy has the greatest influence,accounting for 67.09%.Sobol sampling is more dispersive than Latin hypercube sampling,and the latter sampling results are more uniform;this difference is more obvious at the heated surface,while at the cold surface,the cumulative probability distribution curve of Sobol sampling and Latin hypercube sampling in the main confidence interval is basically the same.