Mesoscopic damage quantification research of the deformation and failure of granite under circulatory load with different frequencies

Abstract

The failure damages of granite under cyclic fatigue load were caused by the propagation and coalescent of cracks at mesoscale, so it was helpful to understand the mechanical behaviours of rock by quantitatively investigating on meso-damage of granite. The uniaxial cyclic fatigue tests on granite coming from the ChangJiang of Hainan nuclear power first-stage construction conventional island were done on the RMT-150B multi-function automatic rigid rock servo material testing machine. Stress amplitude of 10 MPa and sine wave cyclic loads with five different frequencies of 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1 Hz were adopted as dynamic disturbance. The law between cyclic frequency and dynamic stress-dynamic strain hysteretic curve, dynamic elastic modulus and damping ratio are researched. Then, the microtest (SEM) is carried out to study its fractography morphology and the meso-structural images of marble were processed by regional growing theory based on image processing technique. The meso-damage information of granite microcracks was obtained from SEM images. Quantitative analysis of meso-damage characteristics under cyclic fatigue load wase made from angle, length, width and area. The results showed that the curves of strain and stress for loading and unloading are not superposition under cyclic loading, but hysteretic loops. When cyclic frequency changes between 0.01 and 1.0 Hz, the granite hysteretic loop area, dynamic elastic modulus and damping ratio are increased with frequency increasing; with the frequency of cyclic load increasing, the dispersion of microcrack growth azimuth value increased and the average of microcrack growth azimuth value fluctuated in the range. The development of microcrack length was fast, but only when the frequency was 1 Hz, the microcrack width began to develope and the method of energy dissipation changed. The research result offers great reference value to seismic response analysis and site safety evaluation of the nuclear power factory in ChangJiang.

Keywords:

• frequency conversion
• cyclic loading
• damping ratio
• microcrack
• quantification

Acknowledgements

Foundation item: Project (41272329) supported by the National Natural Science Foundation of China, Project (2011CBO13504) supported by the National key basic research and development programme (973). Project (LQ12E08004) supported by the National Natural Science Foundation of Zhejiang. Project (Y201226024) supported by the Scientific Research Foundation of Zhejiang province education department.