The pyrolysis kinetics of charring materials plays an important role in understanding material combustions especially for constructions materials with complex degradation chemistry. Thermogravimetric analysis (TGA) is frequently used to study the heterogeneous kinetics of solid fuels, however, there is no agreed method to determine the pyrolysis scheme and kinetic parameters for charring polymers with multiple components and competing reaction pathways. This study develops a new technique to estimate the possible numbers of species and sub-reactions in pyrolysis by analysing the second derivatives of TG (DDTG) curves.The pyrolysis of a medium density fibreboard (MDF) in nitrogen is studied in detail, and the DDTG curves are used to locate the temperature of peak mass-loss rate for each sub-reactions. Then, based on the TG data under multiple heating rates, the Kissinger's method is used to quickly find the possible range of values of the kinetic parameters (A and E). These ranges are used to accelerate the optimization of the inverse problem using genetic algorithm (GA) for the kinetic and stoichiometric parameters. The proposed method and the kinetic scheme found are shown to match the experimental data and are able to predict accurately results at different heating rate better than the Kissinger's method. Moreover, the search method (K-K method) is highly efficient, faster than the regular GA search alone. Modelling results show that as the TG data available increases, the interdependence among kinetic parameters becomes weak and the accuracy of first-order model declines. Furthermore, conducting TG experiment under multiple heating rates is found to be crucial in obtaining good kinetic parameters.

This work is part of a wider scope of research on developing comprehensive pyrolysis model for medium density fibreboard (MDF) in fires. A simplified model is developed to predict the vertical density profile of virgin MDF. The model shows that vertical density profile can be reproduced using a second order conic curve. Several sets of experimental data are used to validate the model with promising results that are presented. Further investigation shows that the density difference between surface and core densities tends to maintain constant within a range of 300 to 450 kg/m3. Moreover, the model can predict the mean density with an error less than 30 kg/m3. Typical MDF panels were experimentally charred using thermogravimetric analysis and cone calorimetry to investigate the shrinkage and density of char. The actual char density is measured as 330 kg/m3 with a uniform density distribution along the char layer thickness. A model is developed to predict the shrinkage ratios. The restraining effect caused by surface deformation will lead to different vertical and horizontal shrinkage ratios. The volume reductions at vertical and horizontal directions are experimentally measured as 40% and 20% for the two tested MDF panels, which is comparable with the model predictions. Copyright © 2013 John Wiley & Sons, Ltd.

Coal-based carbon foam (CCF) has been widely used in the hypersonic vehicles’ thermal protection system (TPS) due to its good thermal insulation and mechanical properties. In addition, CCF can absorb large quantities of energy when crushed so that the CCF sandwich structure can effectively improve the impact resistance of the TPS. However, there are few studies on the impact performance of CCF sandwich structures, even the mechanical constitutive model (MCM) of CCF. This research work built the CCF MCM and studied the low-velocity impact properties. A large number of experiments were implemented to establish an effective and comprehensive CCF MCM which has three parts: basic mechanical properties, multiaxial loading failure criteria, and hardening rules. A series of tests on the low-velocity impact performance of two CCF sandwich structures were carried out, and finite element models (FEMs) were established according to the CCF MCM to simulate these tests. The experimental and simulation results were in good agreement. The impact damage mechanism was revealed by the tests and the FEMs. The MCM can be used not only for the simulation of low-velocity impact process but also for failure analysis of other CCF structures, which will help to design CCF structures at a low cost.