The Thermomechanical Behaviour of Wood Subject to Fungal Decay

Abstract

Summary Specimens of Pinus sylvestris have been subject to decay by the brown rot fungus Coniophora puteana, the white rot fungus Phanerochaete chrysosporium, and to doses of γ irradiation sufficiently high to cause significant molecular damage. Specimens of Picea abies have been subject to decay by the brown rot fungus Postia placenta. The dynamic mechanical properties of the decayed and degraded materials have been assessed between −100 °C and 120 °C using in some cases a natural frequency instrument and in other cases a driven frequency instrument. The results obtained have allowed calculation of the temperature coefficients of modulus for the materials at various stages of decay or degradation, and these are relatively constant regardless of the history of the specimen. Such changes as do occur can be explained by modulus dependent frequency effects. The static mechanical properties of some specimens were also assessed by three point bending at 20 °C. Measured changes in dynamic stiffness and flexural modulus have been compared with the weight changes and the proportionality constant relating strength and stiffness loss to weight loss obtained for each situation. These show that in the case of fungal attack the dynamic stiffness falls more quickly than flexural strength, and that, as would be expected, the brown rot fungi are the more effective at reducing mechanical properties.