Experimental investigation on fatigue mechanical behavior and energy evolution characteristic of fine-grained marble under multilevel constant-amplitude cyclic loading

This study systematically investigates the mechanical behavior and energy evolution mechanisms of marble under multilevel constant-amplitude cyclic loading through triaxial tests conducted at various confining pressures (0–30MPa). Using the MTS815 electro-hydraulic servo-controlled rock mechanics testing system, pure white calcite marble specimens from Hezhou, Guangxi, China, were subjected to cyclic loading. The results demonstrate that the stress-strain curves of marble exhibit five distinct stages, with increasing confining pressure significantly prolonging fatigue life and enhancing plastic deformation characteristics. The evolution of peak strain and secant modulus reveals a transition from brittle to ductile behavior under higher confining pressures. Energy analysis indicates that both total input energy and elastic strain energy increase stepwise with rising stress levels, while cumulative energy density follows a parabolic relationship with the stress ratio ( φ ), and dissipated energy grows approximately linearly. The energy distribution ratios (elastic strain energy ratio η e , dissipated energy ratio η d , and energy consumption coefficient η ) highlight the critical influence of confining pressure on energy conversion mechanisms, particularly showing a notable shift in energy partitioning behavior near 25 MPa. These findings provide a theoretical foundation for assessing the long-term stability of rocks in deep underground engineering applications. • Mechanical behavior and energy evolution of marble under various σ 3 were explore. • Brittle-ductile transition in marble at high confining pressures. • Energy conversion shifts critically at 25 MPa confining pressure. • Volumetric strain peaks at 10 MPa before declining.