Thermomechanical surface instability at the origin of surface fissure patterns on heated circular MDF samples

Research output: Contribution to journalArticleScientificpeer-review

Researchers

Research units

  • Tallinn University of Technology
  • VTT Technical Research Centre of Finland
  • Wuhan University of Technology

Abstract

When a flat sample of medium density fibreboard (MDF) is exposed to radiant heat in an inert atmosphere, primary crack patterns suddenly start to appear over the entire surface before pyrolysis and any charring occurs. Contrary to common belief that crack formation is due to drying and shrinkage, it was demonstrated for square samples that this results from thermomechanical instability. In the present paper, new experimental data are presented for circular samples of the same MDF material. The sample was exposed to radiant heating at 20 or 50 kW/m2, and completely different crack patterns with independent eigenmodes were observed at the two heat fluxes. We show that the two patterns can be reproduced with a full 3-D thermomechanical surface instability model of a hot layer adhered to an elastic colder foundation in an axisymmetric domain. Analytical and numerical solutions of a simplified 2-D formulation of the same problem provide excellent qualitative agreement between observed and calculated patterns. Previous data for square samples, together with the results reported in the present paper for circular samples, confirm the validity of the model for qualitative predictions and indicate that further refinements can be made to improve its quantitative predictive capability.

Details

Original languageEnglish
Pages (from-to)707-716
Number of pages10
JournalFire and Materials
Volume43
Issue number6
Early online date20 Jun 2019
Publication statusPublished - 1 Oct 2019
MoE publication typeA1 Journal article-refereed

    Research areas

  • analytical models, heat transfer, MDF cracking, thermal effects, thermomechanical buckling

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