The experimental caustics method is a useful technique to determine the stress intensity factor K. In this study, we applied a surface-reflection- type caustics method to a dried Japanese cypress material, and carried out a basic examination for the experimental determination of stress intensity factor KI under mode I loading. Furthermore, we analyzed the stress-displacement field near the crack tip of a wood specimen using 2D and 3D FEM(finite element method).
Wood is a natural resource that has a wide range of uses, such as in housing, furniture and personal items. When wood is used as structural members, the junction or connection between two members often takes the form of a beam-column joint or other joint, and many cracks are sometimes present; failure of the wood often develops from this stress-concentration point. In general, the tissues and cells which comprise wood have a constant directionality and exhibit mechanical anisotropy. Therefore, wood can be treated as an orthotropic material in which the transverse direction (axial direction, L), tangential direction (T) and direction of radius (radial direction, R) are mutually orthogonal(Sawada, 1983). A caustics method is an effective optical method for the experimental determination of stress intensity factor K, which is an important parameter in the field of fracture mechanics. When a caustics method is used, accurate values of K can be determined by a fairly simple measurement system; therefore, this method has been applied to various problems by many researchers(Baik, 1995; Rossmanith, 1995; Rosakis, 1986). However, in past studies employing the caustics method, analyses and experiments were mainly performed on isotropic materials, and there have only been a few studies on anisotropic materials. Soh et al.(1993) proposed a measurement method for the stress intensity factor of orthotropic materials and reported the experimental results.
