Quantitative calculation of rock strain concentration and corresponding damage evolution analysis

Understanding the critical strain and damage evolution process of sandstone can help engineers more accurately predict the failure modes and critical states of sandstone in actual engineering structures. Therefore, this article quantitatively analyzes the strain field data obtained through digital image correlation (DIC), and for the first time establishes a strain concentration calculation model (SCCM) to analyze the critical strain, compaction, and damage evolution process of sandstone under uniaxial compression conditions. The experimental results show that both elastic and plastic strain zones exist on the specimen surface. The proportion curve of strain concentration calculated by SCCM indicates that the strain field e1 generally undergoes two stages: the elastic strain fluctuation stage and the plastic strain development stage. In contrast, the strain field e2 exhibits roughly three stages: a rapid change phase, a slow change phase, and a stability phase. Microscopic strain analysis reveals an overlap between the compaction and damage processes of the specimen, and the critical strain value emd for micro-damage in the specimen is significantly smaller than values obtained by traditional discrimination methods. Specifically, when the defect width of the specimen is 15 mm and 40 mm, the mean emd vaules are approximately 0.006016 and 0.00539, respectively. In contrast, the mean critical strain values determined by traditional discrimination methods are 0.0180 and 0.0178, respectively. The above research results provide a new method for analyzing the strain field data of geotechnical materials, serving the optimization of engineering structure design.