VISCOELASTIC PROPERTIES OF SATURATED SANDSTONES UNDER FATIGUE LOADING
(1. School of Earth and Space Science，University of Science and Technology of China，Hefei，Anhui 230026，China；
2. School of Mechanical Engineering，Beijing Institute of Petrochemical Technology，Beijing 102671，China；
3. Geophysical Research Institute of Geophysical Prospecting，China National Petroleum Corporation，Zhuozhou，Hebei 072750，China；4. CAS Key Laboratory for Mechanical Behavior and Design of Materials，University of Science and Technology of China，Hefei，Anhui 230027，China)
Abstract：Experiments are performed by Metravib dynamic mechanical analyzer under sine wave loading as to imitate the seismic wave(travelling wave). The static load is fixed to 100 N，and the constant dynamic load of the sine wave is 60 N，so that the total loading force is controlled under yield stress. Temperature is controlled between －50 ℃—125 ℃，and the heating speed is 1 ℃/min. At frequency of 5—90 Hz，pump-oil saturated arkoses and Pengshan sandstones are tested under uniaxial cyclic loading. The variations of travelling wave energy attenuation，imaginary modulus，Young?s modulus and elastic wave velocity with temperature or frequency are obtained. The energy attenuation peak and the imaginary modulus peak shift to higher temperatures when the frequency increases；and the energy attenuation and imaginary peak values increase for the travelling wave. These phenomena are caused by thermal relaxation mechanism. The Young?s modulus and elastic wave velocity increase with frequency increase and decrease with temperature increase. These are obvious frequency dispersion，and the dispersion weakens when temperature decreases. The experimental results are similar to the low-frequency resonance standing wave experimental results. Thus the thermal relaxation regularities generally exist in saturated porous rocks. The results are the experimental and theoretical foundation for the study of time-temperature equivalence，and are very instructive for the study of theoretical rock physics model. This investigation is very helpful to the interpretation of seismic，acoustic wave，and seismic prospecting data.
2011, Vol. 30 
