A numerical and experimental methodology to investigate morphological changes in wood exposed to fire temperatures

In the last decade, there was an increasing interest in developing hygro-thermal models including also pyrolysis but the topic is still challenging above the charring temperatures.
In the present paper, the responses of 0.5×0.5×1cm spruce samples heated in a furnace under helium flow are investigated. To understand the effects of different charring temperatures on the material microstructure of wood, SEM pictures are taken from cuts made by a razorblade on perpendicular to grain wood sections. The morphological variations of vessels and wood cell layers are observed and discussed in relation to the corresponding increments of temperature and mass losses. These increments are evaluated by means of a multiphase hygro-thermal model including pyrolysis. Most relevant morphological changes are found for temperatures above 300 ⁰C. In addition, to observe morphological changes for temperatures below 300 ⁰C, microstructural finite element analyses (μFEM) [3] are carried out by taking into account thermal expansion and mass loss of cell walls.