The macroscopically localized deformation behaviors of Ni–Co-based superalloys with differentγ’precipitate content were investigated at 500?C and 1×10-4 s-1 via an in situ method namely,digital image correlati...The macroscopically localized deformation behaviors of Ni–Co-based superalloys with differentγ’precipitate content were investigated at 500?C and 1×10-4 s-1 via an in situ method namely,digital image correlation(DIC).The DIC results showed that the serrated flow of the stress–strain curves was accompanied by localized deformation of the specimens.The fracture morphology was characterized mainly by transgranular fracture with numerous dimples in the lowγ’content alloy,and intergranular fracture with large fracture section in the highγ’content alloy.The Portevin–Le Chatelier(PLC)effect occurred in the investigated Ni–Co-based superalloys.Furthermore,the localized deformation of the highγ’content alloy was more severe than that of the lowγ’content alloy,and the band width was slightly larger.Moreover,for the first-time ever,a special propagation feature,namely±60?zigzag bands characterized by head-to-tail connections,was observed in the highγ’content alloy.展开更多
The visco-elastoplastic mechanical behavior related to the applied strain rate and temperature around the glass transition temperature of Polymethylmethacrylate(PMMA)has been systematically investigated.The uniaxial t...The visco-elastoplastic mechanical behavior related to the applied strain rate and temperature around the glass transition temperature of Polymethylmethacrylate(PMMA)has been systematically investigated.The uniaxial tensile test was performed at strain rate and temperature rangs 1.0×10^(-4)-1.0×10^(-2)s^(-1)and 363-393 K,respectively,and the Dynamic Mechanical Analysis(DMA)test was carried out between 363 K and 413 K at various frequencies.Moreover,the robust complex constitutive model considering the temperature and strain rate effect is proposed.A nonlinear viscoelastic model is established to describe the viscoelastic response on the basis of the Zhu-Wang-Tang(ZWT)model and the time temperature equivalence principle,including the dependence of strain rate and temperature.Considering the yield stress,the cooperative model is adopted.The viscoplastic mechanical response is manifested as the competition performance of the softening deformation and hardening behavior.The predicted mechanical responses maintain good consistency with the experimental results,indicating that the visco-elastoplastic constitutive model proposed can accurately predict the mechanical behavior of PMMA materials within the imposed strain rate and near the glass transition temperature range.展开更多
A new medium-Mn steel was designed to achieve unprecedented tensile properties,with a yield strength beyond 1.1 GPa and a uniform elongation over 50%.The tensile behavior shows a heterogeneous deforma-tion feature,whi...A new medium-Mn steel was designed to achieve unprecedented tensile properties,with a yield strength beyond 1.1 GPa and a uniform elongation over 50%.The tensile behavior shows a heterogeneous deforma-tion feature,which displays a yield drop followed by a large Lüders band strain and several Portevin-Le Châtelier bands.Multiple strain hardening mechanisms for excellent tensile properties were revealed.Firstly,non-uniform martensite transformation occurs only within a localized deformation band,and ini-tiation and propagation of every localized deformation band need only a small amount of martensite transformation,which can provide a persistent and complete transformation-induced-plasticity effect dur-ing a large strain range.Secondly,geometrically necessary dislocations induced from macroscopic strain gradient at the front of localized deformation band and microscopic strain gradient among various phases provide strong heter-deformation-induced hardening.Lastly,martensite formed by displacive shear trans-formation can inherently generate a high density of mobile screw dislocations,and interstitial C atoms segregated at phase boundaries and enriched in austenite play a vital role in the dislocation multipli-cation due to the dynamic strain aging effect,and these two effects provide a high density of mobile dislocations for strong strain hardening.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.11335010,51271174,11802080 and 11627803)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB22040502)。
文摘The macroscopically localized deformation behaviors of Ni–Co-based superalloys with differentγ’precipitate content were investigated at 500?C and 1×10-4 s-1 via an in situ method namely,digital image correlation(DIC).The DIC results showed that the serrated flow of the stress–strain curves was accompanied by localized deformation of the specimens.The fracture morphology was characterized mainly by transgranular fracture with numerous dimples in the lowγ’content alloy,and intergranular fracture with large fracture section in the highγ’content alloy.The Portevin–Le Chatelier(PLC)effect occurred in the investigated Ni–Co-based superalloys.Furthermore,the localized deformation of the highγ’content alloy was more severe than that of the lowγ’content alloy,and the band width was slightly larger.Moreover,for the first-time ever,a special propagation feature,namely±60?zigzag bands characterized by head-to-tail connections,was observed in the highγ’content alloy.
文摘The visco-elastoplastic mechanical behavior related to the applied strain rate and temperature around the glass transition temperature of Polymethylmethacrylate(PMMA)has been systematically investigated.The uniaxial tensile test was performed at strain rate and temperature rangs 1.0×10^(-4)-1.0×10^(-2)s^(-1)and 363-393 K,respectively,and the Dynamic Mechanical Analysis(DMA)test was carried out between 363 K and 413 K at various frequencies.Moreover,the robust complex constitutive model considering the temperature and strain rate effect is proposed.A nonlinear viscoelastic model is established to describe the viscoelastic response on the basis of the Zhu-Wang-Tang(ZWT)model and the time temperature equivalence principle,including the dependence of strain rate and temperature.Considering the yield stress,the cooperative model is adopted.The viscoplastic mechanical response is manifested as the competition performance of the softening deformation and hardening behavior.The predicted mechanical responses maintain good consistency with the experimental results,indicating that the visco-elastoplastic constitutive model proposed can accurately predict the mechanical behavior of PMMA materials within the imposed strain rate and near the glass transition temperature range.
基金supported by the National Key R&D Pro-gram of China(No.2017YFA0204402)the NSFC Basic Science Cen-ter Program for“Multiscale Problems in Nonlinear Mechanics”(No.11988102)the National Natural Science Foundation of China(Nos.11790293 and 52192591).
文摘A new medium-Mn steel was designed to achieve unprecedented tensile properties,with a yield strength beyond 1.1 GPa and a uniform elongation over 50%.The tensile behavior shows a heterogeneous deforma-tion feature,which displays a yield drop followed by a large Lüders band strain and several Portevin-Le Châtelier bands.Multiple strain hardening mechanisms for excellent tensile properties were revealed.Firstly,non-uniform martensite transformation occurs only within a localized deformation band,and ini-tiation and propagation of every localized deformation band need only a small amount of martensite transformation,which can provide a persistent and complete transformation-induced-plasticity effect dur-ing a large strain range.Secondly,geometrically necessary dislocations induced from macroscopic strain gradient at the front of localized deformation band and microscopic strain gradient among various phases provide strong heter-deformation-induced hardening.Lastly,martensite formed by displacive shear trans-formation can inherently generate a high density of mobile screw dislocations,and interstitial C atoms segregated at phase boundaries and enriched in austenite play a vital role in the dislocation multipli-cation due to the dynamic strain aging effect,and these two effects provide a high density of mobile dislocations for strong strain hardening.
