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Abstract The nonlinear elastic hysteresis behaviour of granite is studied based on experimental results under constant amplitude cyclic loading. It is found that the strain phase is lagging behind the stress phase in unloading while lagging，coincident or leading in loading. The results of further analysis show that the difference of damping effect during loading and unloading can result in the malformation of the strain-time curve. It becomes a nonstandard sine curve wide at the top and narrow at the bottom. And the accumulation of plastic deformation leads to the average strain level rising gradually and the strain phase being leading of stress phase. Then，according to the relation between strain phase and stress phase，the potentially existing shapes of hysteresis loop are explored. The hysteresis loop is oval-shape if the strain phase is always lag behind the stress phase，crescent-shape if the strain phase is leading of the stress phase during loading and long eggplant-shape if the strain phase is lagging，coincident and leading of the stress phase in one cycle. While the rock is treated as a visco-elastoplastic material，the calculating method of dynamic elastic modulus and damping ratio is discussed；and the improved formulae are proposed. Based on the experimental data，the evolution of dynamic elastic modulus and damping ratio is analyzed. It is shown that the development of dynamic elastic modulus is closely related with the stress level and the developing curve may be linear or inverted-S shape. The shape of evolution curve of damping ratio，which can be U shape or L shape，greatly depends on the dynamic elastic modulus as well as the area of the hysteresis loop.
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Received: 30 March 2010
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