The Subtropolis room-and-pillar mine extracts the Vanport Limestone(Allegheny Formation,Pennsylvanian System)near Petersburg,Ohio.Strata instability problems associated with excessive concentrations of lateral stress ...The Subtropolis room-and-pillar mine extracts the Vanport Limestone(Allegheny Formation,Pennsylvanian System)near Petersburg,Ohio.Strata instability problems associated with excessive concentrations of lateral stress caused the mine operator to implement a change in layout design.This mining method has been identified as a stress control layout and has been used by other underground stone mines in the past with varying degrees of success.Practical experience has shown that entry headings advance in the direction of the principal lateral stress,producing lower stress concentrations with better mining conditions.It is important to minimize stress concentrations along the mining front,so an arrowshaped advance is recommended.This technique advances more developments(headings)in a"good"direction and reduces developments(crosscuts)in the"bad direction."As is expected,the stress control layout enhances the potential for shear failures in crosscuts.It is,therefore,important to focus crosscut engineering interventions that either:(a)lower stress concentrations(for example,an arched roof)or(b)enhance strength of the strata containing the shears(for example,rock reinforcement).This study focuses on observing strata conditions on a regular basis and monitoring the response of these strata to changing geologic and mining conditions through 3D Dynamic LiDAR scans.展开更多
Uniaxial ratcheting behaviour and low cycle fatigue(LCF)failure mechanism of nickel-based single crystal superalloy DD6 with[001]orientation are investigated through the stresscontrolled LCF tests with stress ratio of...Uniaxial ratcheting behaviour and low cycle fatigue(LCF)failure mechanism of nickel-based single crystal superalloy DD6 with[001]orientation are investigated through the stresscontrolled LCF tests with stress ratio of-1.Then the deformation behaviour during the wholelifetime from the beginning of the experiment to the fracture of the specimen,as well as the fractographic/metallographic morphology,are compared with the strain-controlled LCF experimental results.Through the scanning electron microscope(SEM)observations,it is shown that the failure characteristics under stress-controlled LCF loading are similar with those under strain-controlled loading.Nevertheless,unlike strain-controlled LCF loading,even under fully reversed cycle loading for stress-controlled LCF,DD6 shows significant ratcheting behaviour due to the tensioncompression asymmetry.In addition,the LCF lifetimes under stress control are significantly shorter than the LCF lifetimes under strain control,and the culprit might be the detrimental effect of ratcheting strain on LCF lifetime.Based on these phenomena,an improved crystal plasticity constitutive model on the basis of slip-based Walker constitutive model is developed through modifying the kinematic hardening rule in order to overcome the inaccurate prediction of decelerating stageand stable stage of ratcheting behaviour.Furthermore,combining the continuum damage mechanics,a damage-coupled crystal plasticity constitutive model is proposed to reflect the damage behaviour of DD6 and the accelerating stage of ratcheting behaviour.The simulation results for the stress-controlled LCF deformation behaviour including the whole-lifetime ratcheting behaviour show good agreement with the experimental data.展开更多
文摘The Subtropolis room-and-pillar mine extracts the Vanport Limestone(Allegheny Formation,Pennsylvanian System)near Petersburg,Ohio.Strata instability problems associated with excessive concentrations of lateral stress caused the mine operator to implement a change in layout design.This mining method has been identified as a stress control layout and has been used by other underground stone mines in the past with varying degrees of success.Practical experience has shown that entry headings advance in the direction of the principal lateral stress,producing lower stress concentrations with better mining conditions.It is important to minimize stress concentrations along the mining front,so an arrowshaped advance is recommended.This technique advances more developments(headings)in a"good"direction and reduces developments(crosscuts)in the"bad direction."As is expected,the stress control layout enhances the potential for shear failures in crosscuts.It is,therefore,important to focus crosscut engineering interventions that either:(a)lower stress concentrations(for example,an arched roof)or(b)enhance strength of the strata containing the shears(for example,rock reinforcement).This study focuses on observing strata conditions on a regular basis and monitoring the response of these strata to changing geologic and mining conditions through 3D Dynamic LiDAR scans.
基金financial support from National Natural Science Foundation of China(Nos.51875020,51675024 and 51811540406)National Science and Technology Major Project(No.2017-IV-0004-0041)+1 种基金Aviation Science Foundation of China(No.6141B090314)Academic Excellence Foundation of BUAA。
文摘Uniaxial ratcheting behaviour and low cycle fatigue(LCF)failure mechanism of nickel-based single crystal superalloy DD6 with[001]orientation are investigated through the stresscontrolled LCF tests with stress ratio of-1.Then the deformation behaviour during the wholelifetime from the beginning of the experiment to the fracture of the specimen,as well as the fractographic/metallographic morphology,are compared with the strain-controlled LCF experimental results.Through the scanning electron microscope(SEM)observations,it is shown that the failure characteristics under stress-controlled LCF loading are similar with those under strain-controlled loading.Nevertheless,unlike strain-controlled LCF loading,even under fully reversed cycle loading for stress-controlled LCF,DD6 shows significant ratcheting behaviour due to the tensioncompression asymmetry.In addition,the LCF lifetimes under stress control are significantly shorter than the LCF lifetimes under strain control,and the culprit might be the detrimental effect of ratcheting strain on LCF lifetime.Based on these phenomena,an improved crystal plasticity constitutive model on the basis of slip-based Walker constitutive model is developed through modifying the kinematic hardening rule in order to overcome the inaccurate prediction of decelerating stageand stable stage of ratcheting behaviour.Furthermore,combining the continuum damage mechanics,a damage-coupled crystal plasticity constitutive model is proposed to reflect the damage behaviour of DD6 and the accelerating stage of ratcheting behaviour.The simulation results for the stress-controlled LCF deformation behaviour including the whole-lifetime ratcheting behaviour show good agreement with the experimental data.
