Fatigue, Creep Properties and Long-term Strength of Granite under Uniaxial Compression.

Abstract

To predict the long-term strength of granite, fatigue and creep tests were conducted under uniaxial compression. Fatigue and creep properties of granite were investigated and compared . The results showed that the strength properties are different for fatigue and creep. For lower applied stresses , the time to failure in the fatigue becomes shorter than that in the creep. This indicates that it is important to evaluate both the fatigue and creep strengths for the prediction of long-term strength of granite . The behaviour of dilatant strain in fatigue is similar to that in creep. The volume of dilatant strain , giving an indication of the degree of damage in rock, is larger in the fatigue than in the creep at lower stress levels. This implies that the damage in rock is influenced strongly under cyclic loading than under constant stress.Effect of stress amplitude on fatigue failure time was investigated and the mechanism of fatigue failure was discussed based on the Costin's model. It is concluded that fatigue failure can be explained by the two mechanism .One is stress corrosion cracking ruled by the mean stress level and the other is fatigue cracking influenced by the stress amplitude. The relative contribution of the latter becomes more when maximum stress is small and/or stress amplitude is large.

Crack growth in Westerly granite during a cyclic loading test

“…The three stages are a primary stage in which the upper peak strain increases at a decelerating rate (stage I), a second stage with linearly slight increasing rate of strain following stage I (stage II), and the third and final stage in which the upper peak strain increases at an accelerating rate and culminates in specimen failure (stage III). A similar tendency for the strain behavior of granite during cyclic loading was reported, and the behavior observed in this study was similar to that in these studies (e.g., Haimson, 1978;Kodama et al, 1992). Consequently, the stage in the fatigue process was decided by the strain behavior, and microcrack development patterns at each stage were observed to examine the granite fatigue process.…”

“…In many geological engineering problems, granite is one of the most important materials to investigate. The fatigue characteristics of granite have also been studied (e.g., Scholz and Koczynski, 1979;Kodama et al, 1992;Heap and Faulkner, 2008). To examine crack development during granite fatigue tests, samples were monitored by the acoustic emission method, and it was revealed that crack development increased with increasing stress cycles (Haimson, 1978).…”

岩石の時間依存性挙動と周圧の影響に関する最近の研究

“…σ 1 and σ 3 , positive in compression, are the maximum and minimum principal stress, respectively. * Strength at loading rate C = 10 -4 /s 14,25) 。なお，これら は軸歪だけでなく周歪でも成り立つ 26,27) 。また，周圧の増加に 6 Schematic stress-strain curve for alternate switching of the strain rate from C' 1 to C ' 2 (C ' 1 < C ' 2 ) at each predetermined interval Δε 29) . Thick line indicates the experimentally obtained curve.…”

Estimation of the Fatigue Strength of Granite Subjected to Long-period Cyclic Loading.

“…The characteristics of fatigue deformation of granite can be divided into three stages just as creep deformation (for example, Kodama, 1992). In the primary stage, the rate of the strain increment at maximum applied stress decreases.…”