Fractography of shear failure surface of softwood decayed by brown-rot fungus

Abstract

In order to investigate shear failure surface of decayed wood, wood pieces of ezomatsu (Picea jezoensis) were exposed to brown-rot fungus (Fomitopsis palustris), and standard shear test in radial plane was conducted. The failure surfaces were examined by scanning electron microscopy and surface roughness measurements were also conducted. Transwall failure that the crack elongated parallel to the tracheid axis was observed in the earlywood region through all phases of decay. Intrawall failure principally occurred in the latewood region on the early phase of decay. When decay progressed considerably, transwall failure that the crack elongated perpendicularly to the tracheid axis occurred. And transwall failure was also dominant failure morphology in the latewood region. Fragments of tracheids which were partly peeled out from S-2 layers were observed in some specimens. Size and appearance frequency of fragments of tracheid were smaller and lower when decay progressed. Arithmetic average roughness, which was the index of fragment size and appearance frequency, had positive correlation to shear strength ratio. Especially, line surface roughness of radial direction, which was measured across the radial files of tracheid, had the highest correlation to the shear strength ratio. The surface roughness would be a good indicator to evaluate the decay degree

Lateral strength of nailed timber connections with decay

“…et Curt. ; a brown rot fungus) on a mycelium mat, and the nutrient solution consisted of tap water, including 4% d-glucose, 0.3% peptone, and 1.5% malt extract [7,16]. The main and side members were assembled with paper strings and the lead hole of the main member was aligned with that of the side member.…”

“…There has been a great deal of research on the strengths of wood exposed to a wood-decaying fungus [1]. The effects of decay on wood strength have been investigated for compressive strength [2,3], tensile strength [4], bending strength [2,5,6], shear strength [2,7], and hardness [2]. Although few studies have been conducted on timber connections with decay, reports have recently been increasing.…”