Hierarchical scaling model for size effect on tensile strength of polycrystalline rock

•A hierarchical scaling model which can characterize the ascending then descending variation trend of rock tensile strength with the size increase is developed.•The Meso damage evolution in polycrystalline rock under tensile stress can be described by this model, which revels the mechanism of non-monotonic size effect trend.•The theoretical predictions are consistent well with the mechanical and AE data obtained from the direct tensile tests, proving the rationality of this model.