循环加载条件下岩石单轴抗压强度的经验公式反演法

Inverse Deriving Method of Empirical Formula for the Uniaxial Compressive Strength of Rock Under Cyclic Loading

S-lnN曲线是岩石疲劳分析的基础,而岩样之间的个体差异较大,导致S与lnN之间定量关系难以确立,因此,估算岩样的实际抗压强度至关重要。首先,针对静态加载峰前段以及循环加载中静态加载段的应力应变曲线,以二次函数和线性函数拟合微裂纹闭合段和弹性段试验数据,分析了拟合参数的物理意义以及拟合参数之间的定量关系。其次,基于岩石极限破坏规律及静态加载全应力应变曲线,提出一种估算循环加载试样单轴抗压强度的方法——经验公式法。结果表明,以经验公式法估算的单轴抗压强度非常接近真实值,试验条件完全相同的4个试样的估算单轴抗压强度各不相同,单轴抗压强度越大,则上限应力比越小,疲劳寿命也就越高,修正应力水平下S与lnN之间具有明确的线性规律。

The S-lnN curve was the foundation of rock fatigue analysis.Due to the large individual differences between rock samples,it was difficult to establish the quantitative relationship between S and lnN.Thus,it was very urgent and important to estimate the actual Uniaxial Compressive Strength(UCS)of rock.Firstly,according to the stressstrain curves during the pre-peak period of static loading and static loading period of cyclic loading,quadratic and linear functions were respectively used to fit the experimental data in crack closure and elastic deformation stages.The physical meaning of fitting parameters and the quantitative relationship between fitting parameters were studied.Secondly,based on the ultimate deformation law and the complete stress-strain curve of static loading,a new method,namely empirical formula method,was put forward to evaluate the UCS of rock sample in cyclic loading.Calculation results showed that the UCS evaluated with empirical formula method was very close to the true value.Besides,the UCS of four rock samples under the same test condition was different.With the increase of UCS,the upper stress ratio was reduced and the fatigue life was enhanced.There was obvious linear law between S and lnN when the upper stress ratio was modified.