A novel analytical model to predict fracture resistance of a quasi-brittle material, like wood, is presented. The model is based on a scaling parameter introduced into the non-local fracture theory to take into account the specimen size effect on the development of the damage zone. An expression for length of the critical process zone, which can be used in damage tolerant design of wooden structures is derived from this theory. The model is validated with mixedmode bending tests. A numerical analysis using cohesive elements is performed to understand the role of specimen size in the development of the damage zone. The analytical predictions of the fracture resistance and the critical process zone length for wood are compared with numerical results and experimental data available in the literature.
A new micromechanical model for predicting the failure locus of long fiber composites under combined axial compression and in-plane shear is proposed. The model is based on a periodic unit cell with centrally located imperfections. Predictions of the compressive behavior for various biaxial loading ratios are made. The role of distribution of fiber imperfections in predicting the biaxial strength is discussed. The failure locus calculated from the new model is found to be in good agreement with experimental data available in the literature and less conservative than that from the periodic model with uniform imperfections.
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