Fracture properties of softwood under mode I loading perpendicular to the grain are studied
in this paper. The stress intensity factor KIC in the R and L directions is measured by the compact
tension test using small several specimens. The shape and size of plastic zone in crack tip is
determined by numerical simulations based on von Hill yield criterion. The results show that
anisotropic material constants do not affect the length of plastic zone along crack direction and it only
operates on the plastic zone with θcr≠ 0. Strength ratios α1, α2 and toughness ratios r1, r2, influencing
on the plastic zone, are discussed. Comparative analysis shows that r1 and r2 work markedly on the
shape and size of plastic zone, whereas α1, α2 do less.