合板とMDFを用いたTwo-Rail Shear 法における応力集中・ひずみ分布に関する検討

抄録

Two-rail shear method is popularly adopted in Japan as in-plane shear test for wood-based structural panels. We studied analytically and experimentally on the stress concentration and the distribution of strain when two-rail shear method was verificated. Parameters were materials (MDF and plywood), thickness (9, 15, 24mm) and shape of the specimen. Two kinds of the shape were conducted. One was conformed to ASTM standard (N type), and the other was the specimen which had fillets at the corner in order to suppress failure caused by the stress concentration (F type). In FEM analysis, stress concentrations at the corner were observed. We classified the stress concentration areas into the two types. One was named as T area, which was loaded the tear force from the rails, and the other was named as C area, which was loaded compressive stress at the diagonal cut area. Furthermore, in order to study the effect by the yield and the failure of T and C area, the FEM model containing slits in these areas was analyzed. As a result, the strain in the y axis, positive strain was increased by the yield of C area and negative one was increased by the yield of T area. It suggested that strain in the y axis could be utilized as a barometer of the local yield and failure. In the experimental result, N and F type of MDF were different in the failure area and in the apparent shear strength. On the other hand, no difference was observed about plywood. The load-strain curves in the y axis measured experimentally were observed in various types. These curves were classified based on their shape. As a result, curves convex into positive were observed about N type of MDF and the reverse was about F type of MDF. It suggested the validity of fillets. On the other hand, no trend was observed on the plywood. It suggested that the failure areas of plywood would be different by specimens and that the stress concentration rarely affected on the plywood under the ultimate condition.