The effect of cyclic loading parameters on the physical, mechanical, and microcracking behavior of granite

Abstract

Rocks endure diverse cyclic loadings from natural and anthropogenic sources, exhibiting varied magnitudes, frequencies, and amplitudes. Understanding microcracking behavior is essential for insights into rock damage and failure. This study investigate the impact of cyclic loading parameters—frequency, amplitude, waveform (sinusoidal, square, and linear), and loading cycles—on the physical, mechanical, and microcrack properties of granite rock and its constituent minerals by fluorescent microscopy method. Results reveal that loading frequency and square waveform significantly influence the physical properties, with a notable sensitivity to this parameters. At lower stress levels, variations in cyclic loading parameters minimally affect Linear Microcrack Density (LMD). As stress levels increase, higher loading amplitude and lower loading frequency create fewer but larger microcracks, reducing physical properties and fatigue life. Compared to the other loading waveforms, the square waveform yielded the highest LMD in transgranular microcracks, accelerating degradation in the elastic modulus, fatigue life, and overall properties. Microcracking in fatigue stages aligns with changes in axial residual strain. Stage 1 sees a rapid increase in LMD across minerals, Stage 2 shows a gradual rise, directing energy towards microcrack length growth. Stage 3 witnesses a substantial increase in LMD, particularly in transgranular and intergranular microcracks, leading to sample failure. Minerals with pre-existing microcracks, like feldspars presenting higher LMD and are more sensitive to variations in cyclic loading parameters. Conversely, quartz (due to high elastic modulus) and biotite (due to its plastic behavior and high surface energy) are more resistant to microcracking when cyclic loading parameters are changed.