Xiufeng (2008)made fatigue test researches on grayish yellow sandstone, and concluded the S-N relationship of grayish yellow sandstone fatigue strength under cyclic loading:
Figure 4 and Figure 5 showed both grayish yellow sandstone and red sandstone were called as sandstone; however, due to different internal mineral composition, content and strength of rocks, the slopes of fatigue life S-N curves were different.
(2) S-N fitted curves had clear concept, simple form and convenient measurement; under the constant amplitude loading condition, the interpolation method was applied in the S-N curves to estimate the fatigue life of rock.
(4) The slope of fatigue life S-N curves reflected the sensitive relationship between the fatigue life of specimens and upper limit stress ratio.
Fatigue Life S-N Curve Table of Rocklike Specimens Fractured Dip Curve Parameters S-N Curve a b Complete 0.75798 0.09615 lg S = 0.75798 - 0.096151g N 0[degrees] 0.73887 0.09489 lg S = 0.73887 - 0.094891g N 30[degrees] 0.63917 0.07931 lg S = 0.63917 - 0.079311g N 45[degrees] 0.55511 0.06348 lg S = 0.55511 - 0.063481g N 60[degrees] 0.62014 0.07422 lg S = 0.62014 - 0.074221g N 90[degrees] 0.76277 0.10267 lg S = 0.76277 - 0.102671g N Fractured Dip Correlation Coefficient [R.sup.2] Complete 0.90071 0[degrees] 0.91066 30[degrees] 0.85416 45[degrees] 0.90898 60[degrees] 0.85370 90[degrees] 0.91967 Table 2.
If the S-N curve at R = 10 is available, it can be used to replace the S-N curve at R = [+ or -] [infinity].
When the S-N curve at R = 0 is taken into account, the [A.sub.II], [A.sub.III], [B.sub.II], and [B.sub.III] in the above equation can be defined as follows:
Similarly, if the S-N curve at R = 0.1 is available, it can be used to replace the S-N curve at R = 0, and the boundary conditions of the above model will be adjusted accordingly.
The model can be used directly based on a power S-N curve or an exponential S-N curve.
The mode can be applied when the given fatigue data are random data that are not necessarily required to belong to an S-N curve.
Based on the existing fatigue data of various laminate materials, the study shows that the slopes of the S-N lines under different mean stresses are variable.
The parameter [m.sub.0] is defined as the S-N curve slope on the log-log scale when [S.sub.m] = 0, and the parameter D is the skewness parameter depended on m.