Determination of Critical J‐Integral for Wood

The determination of the critical J‐integral value for wood is considered. The methods are based on the American Society for Testing and Materials standard “$J_{\mathrm{IC}}\text{,}$ a measure of fracture toughness.” A significant revision of the method proposed in the J‐integral standard is needed. Three possibilities for analyzing of the results are developed. The graphical method presupposes no knowledge of the material properties and relies on the recorded Jhyphen;integral versus crack growth curve. The compliance method uses the compliance data recorded during each loading and unloading cycle and the maximum load. The measured maximum load can also be inserted in an equation based on the finite element method. Another method based on the standard “plane strain fracture toughness of metallic materials” is used to study the dependence between the critical J‐integral and the experimental and material parameters. The determined critical J‐integral values are independent of the analysis method. The effect of time is observed: The slower J‐integral tests give a lower value than the more rapid fracture toughness $\left(K_{\mathrm{IC}}\right)$ tests. The effects of moisture and the fracture system reflect the behavior of the modulus of elasticity.