岩石非线性黏弹性蠕变特性的时温等效效应

Nonlinear viscoelastic creep property of rock with time-temperature equivalence effect

岩石的时温等效效应是指岩石在低温、长时间尺度下与在高温、短时间尺度下的流变力学特性等效的效应。利用岩石的时温等效效应,可以通过提高试验温度方法得到岩石在相对低温下的长期流变力学特性。为研究岩石在非线性黏弹性条件下的时温等效效应,基于Schapery单积分型的非线性本构方程,得到了岩石非线性黏弹性蠕变力学特性时温等效效应的数学表示。根据不同应力及温度下花岗岩的蠕变试验结果,设定20℃为参考温度,考虑温度改变对岩石瞬时蠕变柔量的影响,得到了垂直移位因子随温度的变化规律及修正后的蠕变柔量的时间对数曲线;对修正后的曲线进行水平移位使得相邻温度曲线之间相交于一点,得到不同应力下蠕变柔量的主曲线及水平移位因子的变化规律;主曲线中相邻温度曲线之间的一致性较好,进一步验证了花岗岩时温等效效应的存在性。通过对不同应力下的垂直移位因子和水平移位因子的变化规律分析,发现应力为40～60 MPa之间的非线性并不明显,但到87 MPa,非线性特性明显增强。

The rheological behavior of rock at low temperature in a long time scale equal to that at high temperature in a short time scale is called time-temperature equivalence effect （TTEE）. It is convenient to obtain the rheological data in a long time scale through increasing temperature. In order know about the TTEE of rock in nonlinear viscoelastic field, based on the single-integral nonlinear constitutive equation presented by Schapery, the equivalence equation of TTEE on the nonlinear viscoelastic creep property is put forward. According to the creep test data of granite at different stresses and temperatures, setting 20~C as the reference temperature, the variation of the vertical shift factor with temperature and the modified compliance curves are obtained through considering the temperature influence on instantaneous creep compliance. The master curves at different pressures and the variation of the horizontal shift factor with temperature are o^ained by shifting the modified curves horizontally to make the adjacent curves cross to a point. The coincidence of the master curves is good, which further confirm the existence of TTEE of granite. It is found that the nonlinear property of granite from 40 MPa to 64 MPa is not evident but reaching to 87MPa is distinct.