A thermo-mechanical damage constitutive model for deep rock considering brittleness-ductility transition characteristics

This paper developed a statistical damage constitutive model for deep rock by considering the effects of external load and thermal treatment temperature based on the distortion energy.The model parameters were determined through the extremum features of stress−strain curve.Subsequently,the model predictions were compared with experimental results of marble samples.It is found that when the treatment temperature rises,the coupling damage evolution curve shows an S-shape and the slope of ascending branch gradually decreases during the coupling damage evolution process.At a constant temperature,confining pressure can suppress the expansion of micro-fractures.As the confining pressure increases the rock exhibits ductility characteristics,and the shape of coupling damage curve changes from an S-shape into a quasi-parabolic shape.This model can well characterize the influence of high temperature on the mechanical properties of deep rock and its brittleness-ductility transition characteristics under confining pressure.Also,it is suitable for sandstone and granite,especially in predicting the pre-peak stage and peak stress of stress−strain curve under the coupling action of confining pressure and high temperature.The relevant results can provide a reference for further research on the constitutive relationship of rock-like materials and their engineering applications.

A nonlinear creep model for surrounding rocks of tunnels based on kinetic energy theorem

The initiating condition for the accelerated creep of rocks has caused difficulty in analyzing the whole creep process.Moreover,the existing Nishihara model has evident shortcomings in describing the accelerated creep characteristics of the viscoplastic stage from the perspective of internal energy to analyze the mechanism of rock creep failure and determine the threshold of accelerated creep initiation.Based on the kinetic energy theorem,Perzyna viscoplastic theory,and the Nishihara model,a unified creep constitutive model that can describe the whole process of decaying creep,stable creep,and accelerated creep is established.Results reveal that the energy consumption and creep damage in the process of creep loading mainly come from the internal energy changes of geotechnical materials.The established creep model can not only describe the viscoelasticeplastic creep characteristics of rock,but also reflect the relationship between rock energy and creep deformation change.In addition,the research results provide a new method for determining the critical point of creep deformation and a new idea for studying the creep model and creep mechanical properties.

Optical limiting performances of transitional metal dichalcogenides MX_(2)(M = V, Nb, Ta;X = S, Se) with ultralow initial threshold and optical limiting threshold

The optical limiting performances of few-layer transitional metal dichalcogenides (TMDs) nanosheets in the VB group(VS_(2),VSe_(2),NbS_(2),NbSe_(2),TaS_(2),and TaSe_(2)) were systematically investigated for the first time,to the best of our knowledge.It was found that these TMDs nanosheets showed a normalized transmittance in the range of 20%–40%at the input energy of 1.28 GW/cm^(2).Ultralow initial threshold F_(S)(0.05–0.10 J/cm^(2)) and optical limiting threshold F_(OL)(0.82–2.23 J/cm^(2)) were achieved in the TMDs nanosheets,which surpassed most of the optical limiting materials.This work showed the potential of TMDs beyond MoS_(2)in optical limiting field.