Studying the Characteristics of Chaos and Fractals of Construction Rocks under Different Loading Velocities

HIGHLIGHTS: Rock materials exhibit obvious strain rate effects at different loading velocities. The damage evolution process of rock materials contains chaotic features. Logical mapping is used to analyze rock material damage–strain information sequences. The fractal dimension of rock sample crack is positively correlated with load velocity. ABSTRACT: Rock is a widely used construction material; its mechanical properties change due to the influence of different load speed. In this study, the split Hopkinson pressure bar (SHPB) was used to test the dynamic properties of rock samples by loading four different pressures (0.05, 0.08, 0.14, and 0.23 MPa). The peak stress of the sample increases from 82.19 to 284.16 MPa, and the particle size of the sample debris decreases from 46.57 to 18.34 mm as the impact pressure increases from 0.05 to 0.23 MPa. As a chaos method in nonlinear dynamics, it is introduced into the quantitative evaluation of the sample at four loading pressures, which is then calculated. The damage evolution process of the sample under four loading pressures is calculated, and the chaotic characteristics contained in the process are analyzed. Based on the logistic mapping, the increase in the load velocity can delay the entry of the damage variable into the period-doubling bifurcation and chaotic states. Finally, the fractal dimension of the rock crack at the corresponding time under different load speeds is calculated, and the results showed that the increase in the load velocity can increase the uniformity of the crack distribution.