To investigate the dynamic response problem of the double medium formed by the adherence of sprayed concrete and surrounding rock in the tunnel,a split Hopkinson pressure bar of 75 mm in diameter was adopted at the ag...To investigate the dynamic response problem of the double medium formed by the adherence of sprayed concrete and surrounding rock in the tunnel,a split Hopkinson pressure bar of 75 mm in diameter was adopted at the ages of 3,7 and 10 d.Experimental results showed that dynamic compressive strength and dynamic increase factors(DIF)of the combined bodies increase with the strain rate.With the growth of strain rate,the critical strain of the combined bodies first increases,then deceases.Furthermore,the combined bodies of 3 d reveal the plastic property and brittle property for 7 d and 10 d when the strain rate is over 80/s.The failure characteristic of the sprayed concrete changes from tearing strain damage to crushing damage as the growth of strain rate,and the failure characteristic of rock presents the tensile failure mode as demonstrated by the scanning electron microscope(SEM).展开更多
The bonded-particle model(BPM)is commonly used in the numerical analysis of ore samples.To improve the accuracy of simulating the mechanical process of ore process of ore crushing in a crusher,the parameters of the BP...The bonded-particle model(BPM)is commonly used in the numerical analysis of ore samples.To improve the accuracy of simulating the mechanical process of ore process of ore crushing in a crusher,the parameters of the BPM for the ore must be calibrated.In this study,a calibration method was proposed for the scientific determination of the parameters of the BPM for ore undergoing uniaxial compression.First,physical tests and simulations were conducted to determine the mechanical response(uniaxial compressive strength and macroscopic stiffness)of ore during uniaxial compression.Then,the sensitivity of the mechanical response to the values of microscopic parameters was tested using a Plackett-Burman design.Next,the microscopic parameters with the greatest impact on the response were identified,and the range of parameters that met the target response was determined using a steepest ascent design;Second,a second-order model of the mechanical response was established using the sensitive parameters by combining a Box-Behnken design with response surface methodology to obtain the optimal BPM parameters.Simulation tests showed that the normal stiffness per unit area,critical shear stress,and bonded disk radius had significant effects on the uniaxial compressive strength(UCS)and macroscopic stiffness(MS).To verify the validity of the proposed calibration method,laboratory tests were conducted.The consistency of the simulation results with experimental results indicated that response surface methodology with the Plackett-Burman design,steepest ascent design,and Box-Behnken design can be an effective method for calibrating the BPM of ores.展开更多
To change the situation of shape memory polymers(SMPs)that can only remember very few shapes and enable discretional morphing for practical application,the authors report a reversible stepless multiple SMP derived fro...To change the situation of shape memory polymers(SMPs)that can only remember very few shapes and enable discretional morphing for practical application,the authors report a reversible stepless multiple SMP derived from ultrahigh molecular weight polyethylene(UHMWPE).As the crystals of semicrystalline polymers are assembled by those with slightly different melting temperatures,and each type of crystal can remember a single shape,the crystalline region of UHMWPE is allowed to remember plenty of temporary shapes after programming.Changing the temperature of the programmed polymer within the melting/crystallization temperature ranges would lead to releasing/recovery of the memorized temporary shapes.Accordingly,multiple shape memory effects can be easily realized without an elaborate design of material structure and training process in advance as before.The temperaturedependent adjustability of the analog capacitor and soft lens with embedded programmed UHMWPE as actuators,characterized by the continuous/random/proportional responsivity,further reveals the utilization prospects of the controllable reversible stepless discretionary morphing effect.Moreover,the maximum work density of the programmed UHMWPE is found to be 210 kJ/m_(3),which is more than 10 times of piezoelectric ceramics,so that it can serve as a proof-of-concept mechanical driver for reversibly pumping of ethanediol-droplet upon heating/cooling.展开更多
基金Supported by the National Key Research Program(2017YFC0804200)the National Key Basic Research Program(2016YFC0600903)the National Natural Science Foundation of China(51274204)
文摘To investigate the dynamic response problem of the double medium formed by the adherence of sprayed concrete and surrounding rock in the tunnel,a split Hopkinson pressure bar of 75 mm in diameter was adopted at the ages of 3,7 and 10 d.Experimental results showed that dynamic compressive strength and dynamic increase factors(DIF)of the combined bodies increase with the strain rate.With the growth of strain rate,the critical strain of the combined bodies first increases,then deceases.Furthermore,the combined bodies of 3 d reveal the plastic property and brittle property for 7 d and 10 d when the strain rate is over 80/s.The failure characteristic of the sprayed concrete changes from tearing strain damage to crushing damage as the growth of strain rate,and the failure characteristic of rock presents the tensile failure mode as demonstrated by the scanning electron microscope(SEM).
文摘The bonded-particle model(BPM)is commonly used in the numerical analysis of ore samples.To improve the accuracy of simulating the mechanical process of ore process of ore crushing in a crusher,the parameters of the BPM for the ore must be calibrated.In this study,a calibration method was proposed for the scientific determination of the parameters of the BPM for ore undergoing uniaxial compression.First,physical tests and simulations were conducted to determine the mechanical response(uniaxial compressive strength and macroscopic stiffness)of ore during uniaxial compression.Then,the sensitivity of the mechanical response to the values of microscopic parameters was tested using a Plackett-Burman design.Next,the microscopic parameters with the greatest impact on the response were identified,and the range of parameters that met the target response was determined using a steepest ascent design;Second,a second-order model of the mechanical response was established using the sensitive parameters by combining a Box-Behnken design with response surface methodology to obtain the optimal BPM parameters.Simulation tests showed that the normal stiffness per unit area,critical shear stress,and bonded disk radius had significant effects on the uniaxial compressive strength(UCS)and macroscopic stiffness(MS).To verify the validity of the proposed calibration method,laboratory tests were conducted.The consistency of the simulation results with experimental results indicated that response surface methodology with the Plackett-Burman design,steepest ascent design,and Box-Behnken design can be an effective method for calibrating the BPM of ores.
基金Guangdong Basic and Applied Basic Research Foundation,Grant/Award Number:2019A1515110327Science Foundation for Young Teachers of Wuyi University,Grant/Award Number:2018AL017+4 种基金Innovation and Entrepreneurship Foundation of Students of Wuyi University,Grant/Award Number:2020CX16National Natural Science Foundation of China,Grant/Award Numbers:52003201,52033011Guangdong Science and Technology Major Special Fund,Grant/Award Number:2019-252Science Foundation for Young Research Group of Wuyi University,Grant/Award Number:2019td08Joint Research Fund for Wuyi University,Hong Kong and Macao Young Scholars,Grant/Award Number:2019WGALH05。
文摘To change the situation of shape memory polymers(SMPs)that can only remember very few shapes and enable discretional morphing for practical application,the authors report a reversible stepless multiple SMP derived from ultrahigh molecular weight polyethylene(UHMWPE).As the crystals of semicrystalline polymers are assembled by those with slightly different melting temperatures,and each type of crystal can remember a single shape,the crystalline region of UHMWPE is allowed to remember plenty of temporary shapes after programming.Changing the temperature of the programmed polymer within the melting/crystallization temperature ranges would lead to releasing/recovery of the memorized temporary shapes.Accordingly,multiple shape memory effects can be easily realized without an elaborate design of material structure and training process in advance as before.The temperaturedependent adjustability of the analog capacitor and soft lens with embedded programmed UHMWPE as actuators,characterized by the continuous/random/proportional responsivity,further reveals the utilization prospects of the controllable reversible stepless discretionary morphing effect.Moreover,the maximum work density of the programmed UHMWPE is found to be 210 kJ/m_(3),which is more than 10 times of piezoelectric ceramics,so that it can serve as a proof-of-concept mechanical driver for reversibly pumping of ethanediol-droplet upon heating/cooling.
