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Cyclic loading–unloading creep behavior of composite layered specimens

100%

Hu B. , Yang S. Q. , Xu P. , Cheng J. L.

tom Vol. 67, no. 2

449--464

Soft and hard interbedded rocks show obvious time-dependent deformation after deep tunnel excavations, and it is therefore necessary to research the mechanical behavior of the layered rock. However, it is hard to obtain ideal transversely isotropic rocks in fields, so rock-like specimens were poured by using artificial materials. Cyclic loading–unloading creep experiments were performed on the artificial layered cemented specimens with various layer angles (0°, 30°, 60° and 90°) at a 20 MPa confinement. Time-independent deformations and time-dependent deformations of the rock-like specimens were distinguished to investigate the visco-elasto-plastic deformation characteristics. Instantaneous elastic strain and instantaneous plastic strain had linear correlations with stress ratio, whereas creep strain, including visco-elastic strain and visco-plastic strain, increased nonlinearly with an increasing stress ratio. The specimens with a small layer angle had more noticeable time-independent and time-dependent deformations and larger steady-state creep rates than those of the specimens with a large layer angle. Attenuation creep and secondary creep could be observed at relative low stress levels, whereas accelerating creep until failure occurred at the creep failure stress level. The time for creep failure can be predicated according to the axial steady-state creep rate or volumetric creep curve. Damage in the rock-like specimens showed linear correlation with the stress ratio. Dip angle has a significant effect on the creep failure mode under cyclic loading–unloading conditions.

Microstructure and texture of PM2000 tubes - correlation with multiaxial creep and failure behaviour.

70%

Wasilkowska A. , Ratuszek W. , Penkalla H. J. , Kędzierski Z. , Czyrska-Filemonowicz A.

tom R. XIX, nr 4

1187-1190

A relationship between the microstructure and multiaxial creep properties of PM2000 tubes is discussed. The microstructure was investigated by X-ray diffraction, optical metallography, scanning- and transmission electron microscopy (TEM). Creep properties were established at 1000 degrees centigrade under multiaxial loading. The results show a low creep ductility and intergranular failure of tubes at high temperatures, related to the microstructural and mechanical anisotropy. The development of a special pancake grain structure is seen as a factor for increasing the life time of tubes subjected to multiaxial creep.