Modelling Behaviour of a Carbon Epoxy Composite Exposed to Fire: Part II-Comparison with Experimental Results

A Coupled Thermochemical Model for Predicting Fire-Induced Thermal Responses and Decomposition Behavior

Composite materials are increasingly used in aerospace applications due to their high strength-to-weight ratio, but their fire safety remains a critical concern. This study develops a coupled thermochemical model to predict the thermal response and decomposition behavior of composite materials under high-temperature fire conditions. The framework integrates heat transfer, resin pyrolysis kinetics, and gas generation dynamics, employing the Rule of Mixtures to dynamically update temperature-dependent thermophysical properties (thermal conductivity, specific heat capacity, and density). Decomposition kinetics are governed by an n-th-order Arrhenius equation, explicitly resolving the gas convection effects on energy transport. The governing equations are solved numerically using a hybrid explicit/implicit finite element scheme, ensuring stability under severe thermal gradients. Experimental validation compliant with the 14 CFR Part 25 and ISO 2685 standards demonstrates high predictive accuracy. The model successfully captures key phenomena, including the char layer insulation effects, transient heat flux attenuation, and decomposition-induced property transition. This work establishes a computational foundation for optimizing fire-resistant composites in aerospace applications, addressing critical gaps in the existing models through coupled multiphysics representation.

A Fast Thermal 1D Model to Study Aerospace Material Response Behaviors in Uncontrolled Atmospheric Entries

A preliminary thermal 1D numerical model for studying the demise behavior of stainless steel 316L, silicon carbide (SiC) and carbon fiber reinforced polymer (CFRP) during uncontrolled atmospheric entry is proposed. Test case modeling results are compared to experimental data obtained in the framework of ESA Clean Space initiative: material samples were exposed to different heat flux conditions using the Plasma Wind Tunnel (PWT) facilities at the Institute of Space Systems (IRS) of the University of Stuttgart. This numerical model approximates the heating history of the selected materials by simulating their thermal response and temperature profiles, which have trends similar to the experimental curves that are found. Moreover, when high heat flux conditions are considered, the model simulates the materials’ mass loss due to the ablation process: at the end of the simulation, the difference between the experimental and the modeled results is about 17% for CFRP and 35% for stainless steel. To reduce the model’s uncertainties, the following analysis suggests the need to consider the influence of adequate material thermophysical properties and the physical-chemical processes that affect the samples’ temperature profile and mass loss.

Mechanism Identification and Kinetics Analysis of Thermal Degradation for Carbon Fiber/Epoxy Resin

For carbon fiber epoxy resin used in aerostructure, thermal degradation mechanism and kinetics play an important role in the evaluation of thermal response and combustion characteristics. However, the thermal decomposition process and mechanism are difficult to unify strictly due to the complexity of the components from different suppliers. In the present study, a product of carbon fiber epoxy resin made by AVIC (Aviation Industry Corporation of China) composite corporation is examined to identify its thermal degradation mechanism and pyrolysis products by measurements, including simultaneous thermal analysis, Fourier transform infrared spectroscopy and mass spectrometry, establish the kinetic model by Kissinger/Friedman/Ozawa/Coats-Redfern methods. The results show thermal degradation occurs in three steps under the inert atmosphere, but in four steps under air atmosphere, respectively. The first two steps in both environments are almost the same, including drying, carbon dioxide escape and decomposition of the epoxy resin. In the third step of inert atmosphere, phenol is formed, methane decreases, carbon monoxide basically disappears and carbon dioxide production increases. However, in air, thermal oxidation of the carbonaceous residues and intermolecular carbonization are observed. Furthermore, thermal degradation reaction mechanism submits to the F₄ model. These results provide fundamental and comprehensive support for the application of carbon fiber epoxy resin in aircraft industry.

Simulation of Thermal Behavior of Glass Fiber/Phenolic Composites Exposed to Heat Flux on One Side

A 3D thermal response model is developed to evaluate the thermal behavior of glass fiber/phenolic composite exposed to heat flux on one side. The model is built upon heat transfer and energy conservation equations in which the heat transfer is in the form of anisotropic heat conduction, absorption by matrix decomposition, and diffusion of gas. Arrhenius equation is used to characterize the pyrolysis reaction of the materials. The diffusion equation for the decomposition gas is included for mass conservation. The temperature, density, decomposition degree, and rate are extracted to analyze the process of material decomposition, which is implemented by using the UMATHT (User subroutine to define a material’s thermal behavior) and USDFLD (User subroutine to redefine field variables) subroutines via ABAQUS code. By comparing the analysis results with experimental data, it is found that the model is valid to simulate the evolution of a glass fiber/phenolic composite exposed to heat flux from one side. The comparison also shows that longer time is taken to complete the pyrolysis reaction with increasing depth for materials from the numerical simulation, and the char region and the pyrolysis reaction region enlarge further with increasing time. Furthermore, the decomposition degree and temperature are correlated with depths, as well as the peak value of decomposition rate and the time to reach the peak value.

The Effect of Multilevel Carbon Reinforcements on the Fire Performance, Conductivity, and Mechanical Properties of Epoxy Composites

We studied the effect of a multilevel presence of carbon-based reinforcements-a combination of conventional load-bearing unidirectional carbon fiber (CF) with multiwalled carbon nanotubes (CNT) and conductive CNT-containing nonwoven carbon nanofabric (CNF(CNT))-on the fire performance, thermal conductivity, and mechanical properties of reference and flame-retarded epoxy resin (EP) composites. The inclusion of carbon fibers and flame retardant reduced the peak heat release rate (pHRR) of the epoxy resins. The extent to which the nanoreinforcements reduced the pHRR depended on their influence on thermal conductivity. Specifically, high thermal conductivity is advantageous at the early stages of degradation, but after ignition it may lead to more intensive degradation and a higher pHRR; especially in the reference samples without flame retardant. The lowest pHRR (130 kW/m²) and self-extinguishing V-0 UL-94 rating was achieved in the flame-retarded composite containing all three levels of carbon reinforcement (EP + CNF(CNT) + CNT + CF FR). The plasticizing effect of the liquid flame retardant impaired both the tensile and flexural properties; however, it significantly enhanced the impact resistance of the epoxy resin and its composites.