The resulting cracks evolve and form patterns whose characteristics are described.
Cracks are found to generally originate at the surface in response to heating, but occasionally they form in the bulk, away from ever-changing material boundaries. When the principal stress exceeds a prescribed threshold value, the material forms a local crack. Stresses develop in response to the thermal degradation of the material by means of a shrinkage strain caused by local mass loss during pyrolysis.
The pyrolysis mechanism is described by a one-step overall reaction that is dependent nonlinearly on the temperature (Arrhenius form). In this work the sample is heated uniformly over its entire top surface by a hypothetical flame (a heat source). A model is developed for the formation and propagation of cracks in a material sample that is heated at its top surface, pyrolyses, and then thermally degrades to form char.
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