The striking variation in damage tolerance among refractory complex concentrated alloys is examined through the analysis of atomistic fracture simulations,contrasting behavior in elemental Nb with that in brittle NbMo...The striking variation in damage tolerance among refractory complex concentrated alloys is examined through the analysis of atomistic fracture simulations,contrasting behavior in elemental Nb with that in brittle NbMoTaW and ductile Nb_(45)Ta_(25)Ti_(15)Hf_(15).We employ machine-learning interatomic potentials(MLIPs),including a new MLIP developed for NbTaTiHf,in atomistic simulations of crack tip extension mechanisms based on analyses of atomistic fracture resistance curves.While the initial behavior of sharp cracks shows good correspondence with the Rice theory,fracture resistance curves reveal marked changes in fracture modes for the complex alloys as crack extension proceeds.In NbMoTaW,compositional complexity appears to promote dislocation nucleation relative to pure Nb,despite theoretical predictions that the alloy should be relatively more brittle.In Nb_(45)Ta_(25)Ti_(15)Hf_(15),alloying alters the fracture mode compared to elemental Nb,promoting crack tip blunting and enhancing resistance to crack propagation.展开更多
A close study of Heisenberg uncertainty principles reveals many significant facts,and all four major physical quantities,energy,time,momentum and length,have both lower and upper limits.Now,many questions come up.What...A close study of Heisenberg uncertainty principles reveals many significant facts,and all four major physical quantities,energy,time,momentum and length,have both lower and upper limits.Now,many questions come up.What are these limits?Some answers may lead to the understanding of the development of our universe.What is the shortest limit of time?At the beginning of big bang,there exists a tre-mendously short time,the Planck time.This may be just the shortest time limit in our universe.The longest time limit might be the lifetime of our universe.The longest length might be the final diameter of our expanding universe.All these lead to a finite universe.Two more coupling formulae are formed for the other two pairs of physical quantities,mass and speed,thermal energy and temperature.These four physical quantities must also have limits.We already knew that speed has upper limit and temperature has lower limit.By these two formulae,Planck and Einstein equations are derived directly.Since most other physical quantities are somewhat related to these major physical quantities,it seems that there exists a principle of limitation of physical quantities.A quantitative sketch of big bang is described.It also shows that our universe will contract back to another big bang.The principle of limitation opens up some fields of investigation.It may bring nature back to the harmony and determined world described by classical physics.展开更多
基金supported by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,Materials Sciences and Engineering Division,under Contract No.DE-AC02-05-CH11231 within the Damage Tolerance in Structural Materials(KC 13)programThe study made use of resources of the National Energy Research Scientific Computing Center(NERSC),a U.S.Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory,operated under the same contract number,using NERSC Award No.BES-ERCAP0027535This research used the Lawrencium computational cluster resource provided by the IT Division at the Lawrence Berkeley National Laboratory(Supported by the Director,Office of Science,Office of Basic Energy Sciences,of the U.S.Department of Energy under Contract No.DE-AC02-05CH11231).The Scientific Computing Group(also known as High-Performance Computing Services)under Science IT supports the mission of Lawrence Berkeley National Laboratory by providing technology and consulting support for science and technical programs,in the areas of data management,HPC cluster computing,and Cloud services.
文摘The striking variation in damage tolerance among refractory complex concentrated alloys is examined through the analysis of atomistic fracture simulations,contrasting behavior in elemental Nb with that in brittle NbMoTaW and ductile Nb_(45)Ta_(25)Ti_(15)Hf_(15).We employ machine-learning interatomic potentials(MLIPs),including a new MLIP developed for NbTaTiHf,in atomistic simulations of crack tip extension mechanisms based on analyses of atomistic fracture resistance curves.While the initial behavior of sharp cracks shows good correspondence with the Rice theory,fracture resistance curves reveal marked changes in fracture modes for the complex alloys as crack extension proceeds.In NbMoTaW,compositional complexity appears to promote dislocation nucleation relative to pure Nb,despite theoretical predictions that the alloy should be relatively more brittle.In Nb_(45)Ta_(25)Ti_(15)Hf_(15),alloying alters the fracture mode compared to elemental Nb,promoting crack tip blunting and enhancing resistance to crack propagation.
文摘A close study of Heisenberg uncertainty principles reveals many significant facts,and all four major physical quantities,energy,time,momentum and length,have both lower and upper limits.Now,many questions come up.What are these limits?Some answers may lead to the understanding of the development of our universe.What is the shortest limit of time?At the beginning of big bang,there exists a tre-mendously short time,the Planck time.This may be just the shortest time limit in our universe.The longest time limit might be the lifetime of our universe.The longest length might be the final diameter of our expanding universe.All these lead to a finite universe.Two more coupling formulae are formed for the other two pairs of physical quantities,mass and speed,thermal energy and temperature.These four physical quantities must also have limits.We already knew that speed has upper limit and temperature has lower limit.By these two formulae,Planck and Einstein equations are derived directly.Since most other physical quantities are somewhat related to these major physical quantities,it seems that there exists a principle of limitation of physical quantities.A quantitative sketch of big bang is described.It also shows that our universe will contract back to another big bang.The principle of limitation opens up some fields of investigation.It may bring nature back to the harmony and determined world described by classical physics.
