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Damage deterioration mechanism and damage constitutive modelling of red sandstone under cyclic thermal-cooling treatments

Cao Ri-hong, Fang Lei, Qiu Xianyang, Lin Hang, Li Xilong, Li Wenxin

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 4

art. no. e188, 2022

In the process of exploiting mineral and geothermal energy resources, the influence of the cyclic heat effect on the mechanical properties of the surrounding rock becomes increasingly prominent. To further study the damage deterioration mechanism, deformation and failure characteristics of cyclic heating–cooling (H–C) of the rock, cyclic H–C treatment tests and uniaxial compression tests were conducted, acoustic emission (AE) events were monitored, and the mesoscale characteristics of the fracture surface were imaged and analysed. The results show that the number of H–C cycles played an important role in the evolutions of the strength, cumulative damage variables and deformation modulus of the red sandstone. The peak strength of the specimens decreased with the increase in the number of H–C cycles, and the damage variables increased with the number of H–C cycles. The cyclic H–C treatments promoted the development of microcracks and the growth of the stress–strain curve crack closure stage. Both the crack closure stress and crack closure strain increased with the number of H–C cycles. Furthermore, both the number of transgranular microcracks and the microcrack spacing increased during cyclic H–C treatment, which also led to the failure mode of the specimens gradually changing from shear failure to splitting failure. In addition, based on the principle of strain equivalence, a damage constitutive model under the coupling action of cyclic H–C treatment and loading was deduced. The crack closure deformation of specimens treated with different numbers of H–C cycles was well reflected by the proposed model, and the prediction of other mechanical parameters, such as the peak stress, peak strain and tangent modulus of the theoretical curves, was also verified by test data.

Cu-doped TiO2 brookite photocatalyst with enhanced visible light photocatalytic activity

Zou Yunling, Huang Xianshou, Yu Tao, Tong Xiaoqiang, Li Yan, Lian Xiaoxue, Xie Yao, Huang Jiaming, He Wei, Li Wenxin

Materials Science Poland

2020

Vol. 38, No. 4

644--653

Cu-doped TiO2 having a brookite phase and showing enhanced visible light photocatalytic activity was synthesized using a mild solvothermal method. The as-prepared samples were characterized by various techniques, such as X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectroscopy. Photocatalytic activity of Cu-doped brookite TiO2 nanoparticles was evaluated by photodegradation of methylene blue under visible light irradiation. The X-ray diffraction analysis showed that the crystallite size of Cu-doped brookite TiO2 samples decreased with the increase of Cu concentration in the samples. The UV-Vis diffuse reflectance spectroscopy analysis of the Cu-doped TiO2 samples showed a shift to lower energy levels in the band gap compared with that of bare phase brookite TiO2. Cu doped brookite TiO2 can obviously improve its visible light photocatalytic activity because of Cu ions acting as electron acceptors and inhibiting electron-hole recombination. The brookite TiO2 sample with 7.0 wt.% Cu showed the highest photocatalytic activity and the corresponding degradation rate of MB (10 mg/L) reached to 87 % after visible light illumination for 120 min, much higher than that of bare brookite TiO2 prepared under the same conditions (78 %).