The controlling plastic deformation mechanisms(i.e.slip or twinning)and the structural crash performance of Mg alloys are strongly influenced by loading mode,texture and microstructure.This paper summarizes the main r...The controlling plastic deformation mechanisms(i.e.slip or twinning)and the structural crash performance of Mg alloys are strongly influenced by loading mode,texture and microstructure.This paper summarizes the main results from an experimental program to assess these effects for commercial Mg alloy extrusions(AM30 and AZ31),sheet(AZ31),and high pressure die castings(HPDC,AM50 and AM60).Uniaxial tensile and compressive tests were performed over a wide range of strain rate and temperature(i.e.0.00075–2800 s^(−1) and 100℃ to−150℃)using conventional servo-hydraulic and high-strain-rate universal test machines and a split-Hopkinson-bar(SHB)apparatus.In primarily-slip-dominant deformation,the true stress–strain curves showed approximate power-law behavior,and the effects of strain rate and temperature on yield strength could be approximately described by constitutive equations linearly dependent on the rate parameter,Tln(5.3×10^(7)/ɛ˙)where T is test temperature in Kelvin andɛ˙is strain rate in s^(−1).In primarily-twin-dominant deformation,the effects of strain rate and temperature on yield and initial flow stress were negligible or small from quasi-static to 2800 s^(−1) owing to the athermal characteristics of mechanical twinning;the effects may become more pronounced with exhaustion of twinning and increasing proportion of slip.展开更多
A coarse-grained AM50 alloy was used as a model alloy for investigation of constitutive behaviour,Charpy toughness and effect of stress state on deformation and failure of cast Mg alloys.The results provide critical m...A coarse-grained AM50 alloy was used as a model alloy for investigation of constitutive behaviour,Charpy toughness and effect of stress state on deformation and failure of cast Mg alloys.The results provide critical mechanical properties of a cast AM50 alloy for crashworthiness assessment and development of finite element simulation techniques.For cast Mg alloys,the effect of strain rate and temperature is larger on tensile strength than on compressive strength because twinning is more extensive in compression than in tension.The effect of strain rate on compressive strength is negligible because twinning activity of the cast Mg alloy is dominant.The load vs.deflection of Charpy specimens were measured for modelling,and the effect of loading rate and temperature on load of Charpy specimens is very small because part of the specimen is in compression.The equivalent strain to fracture of the cylindrical round notched tension specimen decreases with increasing stress triaxiality;though for the flat-grooved plane strain specimen,the equivalent fracture strain remains constant over the range of stress triaxiality investigated.Because the two different specimen geometries give rise to different Lode angle values,the test results show that the Lode angle parameter is an important parameter for deformation and fracture of Mg alloys.Finite element simulations of loading of the cylindrical notched-tension and Charpy specimens were carried out using a Lode-angle dependent von Mises model,and were found to provide a reasonable description of the load-displacement curves measured in the tests.For the flat-grooved plane strain specimens,the computations under-predicted the force-displacement response measured.展开更多
A new algorithm to compute continuous wavelet transforms at dyadic scales is proposed here. Our approach has a similar implementation with the standard algorithme a trous and can coincide with it in the one dimensiona...A new algorithm to compute continuous wavelet transforms at dyadic scales is proposed here. Our approach has a similar implementation with the standard algorithme a trous and can coincide with it in the one dimensional lower order spline case.Our algorithm can have arbitrary order of approximation and is applicable to the multidimensional case.We present this algorithm in a general case with emphasis on splines anti quast in terpolations.Numerical examples are included to justify our theorerical discussion.展开更多
Precipitation strengthening provides one of the most widely-used mechanisms for strengthen-ing multi-principal-element alloys(MPEAs).Here,we report dual-morphology B2 precipitates in Co_(36)Cr_(15)Fe_(18)Ni_(18)Al_(8)...Precipitation strengthening provides one of the most widely-used mechanisms for strengthen-ing multi-principal-element alloys(MPEAs).Here,we report dual-morphology B2 precipitates in Co_(36)Cr_(15)Fe_(18)Ni_(18)Al_(8)Ti_(4)Mo_(1)MPEA obtained by thermo-mechanical processing.Electron microscopy charac-terization reveals that the dual-morphology B2 precipitates are either recrystallized B2 particles formed at the grain boundaries or triple junctions with recrystallization process,or rod-like within the non-recrystallized FCC matrix.The dual-morphology B2 precipitates enhance the yield strength and ultimate tensile strength up to 1120 MPa and 1480 MPa,respectively.This work suggests the mechanical proper-ties of the alloy can be optimized by B2 precipitation strengthening to meet the needs of engineering applications.展开更多
基金This work is part of the crashworthiness R&D task of an on-going Canada-China-US Magnesium Front-End Research and Development(MFERD)project.The Canadian task is funded by the CCT&I and ASM-NGV programs,Govemment of Canada.
文摘The controlling plastic deformation mechanisms(i.e.slip or twinning)and the structural crash performance of Mg alloys are strongly influenced by loading mode,texture and microstructure.This paper summarizes the main results from an experimental program to assess these effects for commercial Mg alloy extrusions(AM30 and AZ31),sheet(AZ31),and high pressure die castings(HPDC,AM50 and AM60).Uniaxial tensile and compressive tests were performed over a wide range of strain rate and temperature(i.e.0.00075–2800 s^(−1) and 100℃ to−150℃)using conventional servo-hydraulic and high-strain-rate universal test machines and a split-Hopkinson-bar(SHB)apparatus.In primarily-slip-dominant deformation,the true stress–strain curves showed approximate power-law behavior,and the effects of strain rate and temperature on yield strength could be approximately described by constitutive equations linearly dependent on the rate parameter,Tln(5.3×10^(7)/ɛ˙)where T is test temperature in Kelvin andɛ˙is strain rate in s^(−1).In primarily-twin-dominant deformation,the effects of strain rate and temperature on yield and initial flow stress were negligible or small from quasi-static to 2800 s^(−1) owing to the athermal characteristics of mechanical twinning;the effects may become more pronounced with exhaustion of twinning and increasing proportion of slip.
基金This study is part of CanmetMATERIALS(CMAT)projects funded by the Magnesium Front End R&D(MFERD)program provided by Natural Resources Canada through the Program of Energy Research and Development and Transport Canada.
文摘A coarse-grained AM50 alloy was used as a model alloy for investigation of constitutive behaviour,Charpy toughness and effect of stress state on deformation and failure of cast Mg alloys.The results provide critical mechanical properties of a cast AM50 alloy for crashworthiness assessment and development of finite element simulation techniques.For cast Mg alloys,the effect of strain rate and temperature is larger on tensile strength than on compressive strength because twinning is more extensive in compression than in tension.The effect of strain rate on compressive strength is negligible because twinning activity of the cast Mg alloy is dominant.The load vs.deflection of Charpy specimens were measured for modelling,and the effect of loading rate and temperature on load of Charpy specimens is very small because part of the specimen is in compression.The equivalent strain to fracture of the cylindrical round notched tension specimen decreases with increasing stress triaxiality;though for the flat-grooved plane strain specimen,the equivalent fracture strain remains constant over the range of stress triaxiality investigated.Because the two different specimen geometries give rise to different Lode angle values,the test results show that the Lode angle parameter is an important parameter for deformation and fracture of Mg alloys.Finite element simulations of loading of the cylindrical notched-tension and Charpy specimens were carried out using a Lode-angle dependent von Mises model,and were found to provide a reasonable description of the load-displacement curves measured in the tests.For the flat-grooved plane strain specimens,the computations under-predicted the force-displacement response measured.
文摘A new algorithm to compute continuous wavelet transforms at dyadic scales is proposed here. Our approach has a similar implementation with the standard algorithme a trous and can coincide with it in the one dimensional lower order spline case.Our algorithm can have arbitrary order of approximation and is applicable to the multidimensional case.We present this algorithm in a general case with emphasis on splines anti quast in terpolations.Numerical examples are included to justify our theorerical discussion.
基金supported by the Central Guidance on Local Science and Technology Development Fund of Hebei Province(No.216Z1012G)the National Natural Science Foundation of China(No.12174274).
文摘Precipitation strengthening provides one of the most widely-used mechanisms for strengthen-ing multi-principal-element alloys(MPEAs).Here,we report dual-morphology B2 precipitates in Co_(36)Cr_(15)Fe_(18)Ni_(18)Al_(8)Ti_(4)Mo_(1)MPEA obtained by thermo-mechanical processing.Electron microscopy charac-terization reveals that the dual-morphology B2 precipitates are either recrystallized B2 particles formed at the grain boundaries or triple junctions with recrystallization process,or rod-like within the non-recrystallized FCC matrix.The dual-morphology B2 precipitates enhance the yield strength and ultimate tensile strength up to 1120 MPa and 1480 MPa,respectively.This work suggests the mechanical proper-ties of the alloy can be optimized by B2 precipitation strengthening to meet the needs of engineering applications.
