Prediction of Fracture Toughness of Conifers

Equations were developed to use in the prediction of the fracture toughness values of coniferous species based on the variation of specific gravity and moisture content. Equation parameters were determined for clear wood in opening mode fracture when the crack is located in a plane normal to the tangential direction and it propagates in the longitudinal direction, (KIcTL). The prediction equations developed are based on test results of ten coniferous species representing wide ranges of specific gravities and moisture conditions.Analysis of the data revealed that the relationship between fracture toughness and specific gravity is similar for all species tested and a single equation may be used for all species. However, the effect of moisture content was significantly affected by extractive content, and separate relationships are required for low and high extractive content species below the fiber saturation point.Tensile strengths and moduli of elasticity were determined both in the L and T directions. A highly significant relationship between ultimate tangential tensile stress and fracture toughness was found, indicating that flaws present in wood are likely the controlling mechanism of failure for this system