Dynamic failure characteristics of high-strength concrete and high-strength rock based on fractal theory

To quantitatively reveal the damage mechanism of high-strength concrete (HSC) and high-strength rock (HSR), an analysis method based on macro-meso fractal theory is proposed. Based on the SHPB test device, the dynamic impact compression test of HSC and HSR was carried out. The stress–strain curve characteristics and macroscopic damage of the two materials were obtained. The fracture morphology of the specimen was obtained by SEM test equipment, and the meso-damage characteristics of the material were analyzed. On this basis, the macro-meso damage behavior of the two types of materials is quantitatively described based on fractal theory, and the correlation between macro-meso fractal dimension, dynamic compressive strength, and strain energy is constructed. The results show that the dynamic compressive strength of HSC and HSR increases with the increase in strain rate. Due to the high density of HSR and fewer internal defects, its DIF and energy absorption effect are higher. After the impact of HSC, the fragments are long strips, and the particle size is not uniform. The surface of the meso-fracture is rough, and the crack passes through the micro-holes and aggregates and bifurcates at the end. After the impact of HSR, a large amount of white powder debris is produced. The fragments are spindle-shaped, and the particle size is uniform. The meso-fracture shows obvious transgranular fracture and cleavage fracture characteristics. The cracks are mainly transgranular, and a porous fracture zone appears around the cracks. In addition, the macro fractal dimension D_b and meso fractal dimension D_c of HSC and HSR show an increasing trend with the increased strain rate. The macro and meso-fractal dimensions of HSR are larger, and the fractal dimension is less sensitive to strain rate. The expressions of strain energy U and D_b of the two kinds of materials were obtained by fitting, and the relationship between macro and micro fractal dimensions was discussed. The microscopic fracture characteristics of the specimen can reflect the macroscopic crushing situation.