Fracture Mechanics. Influences of Various Factors on Fracture Toughness of Wood.

In this study, the influences of loading rate, crack length, notch acuity, moisture content of specimen, heat-treatment, and polyethylene glycol (PEG) treatment on the fracture toughness of wood were examined experimentally at room temperature. The materials used for the experiment were douglas fir, spruce, western hemlock, Alaska cedar, castor aralia, Japanese beech, ramin, ash, false arbor-vitae and red lauan.The results were summarized as follows:(1) The fracture toughness was independent of the loading rate in the range of the present experiment.(2) The fracture toughness decreased with increasing crack length (a/W) of specimen.(3) The fracture toughness increased with inceasing notch root radius (ρ).(4) Above moisture content of 15%, the fracture toughness decreased with increasing moisture content.(5) The fracture toughness of wood heat-treated at 120°C was larger than that of solid wood, but the fracture toughness decreased with increase of treatment temperature over 120°C.(6) The fracture toughness of the PEG impregnated wood was larger than that of the solid wood.