Abstract: As a fibrous bio-composite material with quasi-brittle fracture property, bamboo fiber composites represented by bamboo scrimber has the size effect problem in its material strength, which would influence the design theory of its components. In order to solve the size effect problem of bamboo scrimber in its material strength, especially the longitudinal tensile strength, the three-point-bending test and direct tensile test were carried out to measure the size effect behavior. Meanwhile, the calculating methods of material defect and size effect were analysed by the tensile strength models on the basis of fracture theory. The test results show that the tensile strength of bamboo scrimber has obvious size effect phenomenon. However, by the tensile strength model on the basis of fracture theory, the theoretical plastic tensile strength of bamboo scrimber in its fiber direction, which considered the influence of material surface defect, was independent from size effect. Therefore, the influence of size effect can be determined by the theoretical plastic tensile strength and the defect size.

Key words: bamboo scrimber, quasi-brittle fracture, size effect, tensile strength, defect size, composites