Assessment of fatigue behavior of Alvand monzogranite rocks

Comprehensive laboratory tests were performed to assess fatigue behavior of Alvand monzogranite rock subjected to uniaxial cyclic loading. Before cyclic tests، a series of static loading tests has been done to obtain required data for the fatigue tests. Three maximum load levels (85، 90، 95% uniaxial compressive strength (σc)) at amplitudes 70% were used with 1Hz cyclic loading frequency. The results indicated that maximum stress level has significantly influenced fatigue behavior of this rock. It was found that fatigue life decrease in a power function with increasing maximum stress level. Accumulative fatigue damage process shows three stages of behavior including crack initiation phase، uniform velocity phase and acceleration phase. Fatigue damage process were analyzed according to axial and lateral maximum and minimum strain، tangent and second modulus، toughness and hysteresis energy in both loading and unloading conditions. Among these parameters، lateral strain، axial strain and second modulus show the best three-stage fatigue damage behavior. It also should be noted that، most of the cracks generated in parallel to loading direction and lateral strain are affected more than axial strain.