Recent experiments revealed many new phenomena of the macroscopic domain patterns in the stress-induced phase transformation of a superelastic polycrystalline NiTi tube during tensile loading. The new phenomena includ...Recent experiments revealed many new phenomena of the macroscopic domain patterns in the stress-induced phase transformation of a superelastic polycrystalline NiTi tube during tensile loading. The new phenomena include deformation instability with the formation of a helical domain, domain topology transition from helix to cylinder, domain-front branching and loading-path dependence of domain patterns. In this paper, we model the polycrystal as an elastic continuum with nonconvex strain energy and adopt the non-local strain gradient energy to account for the energy of the diffusive domain front. We simulate the equilibrium domain patterns and their evolution in the tubes under tensile loading by a non-local Finite Element Method （FEM）. It is revealed that the observed loading-path dependence and topology transition of do- main patterns are due to the thermodynamic metastability of the tube system. The computation also shows that the tube-wall thickness has a significant effect on the domain patterns： with fixed material properties and interfacial energy density, a large tube-wall thickness leads to a long and slim helical domain and a severe branching of the cylindrical-domain front.展开更多
A new non-uniform yield phenomenon is found during tension of austenite stainless steel at -190℃, which consists of elasto-plastic instability ξph and stress plateau ξL resulting from strain-induced martensite tran...A new non-uniform yield phenomenon is found during tension of austenite stainless steel at -190℃, which consists of elasto-plastic instability ξph and stress plateau ξL resulting from strain-induced martensite transformation. It is essentially different from non-uniform yield that is related to dislocation obstacles. The experimental results show that ξph and ξL increase with increaslng strain rate, and ξph, increases but ξL decreases with increasing prestmin.Tronsformation enengy of strain-induced martensite keeps a constant, 3.85×106J/m3, with increasing strain at the stages of both elasto-plastic instability and stress plateau.展开更多
文摘Recent experiments revealed many new phenomena of the macroscopic domain patterns in the stress-induced phase transformation of a superelastic polycrystalline NiTi tube during tensile loading. The new phenomena include deformation instability with the formation of a helical domain, domain topology transition from helix to cylinder, domain-front branching and loading-path dependence of domain patterns. In this paper, we model the polycrystal as an elastic continuum with nonconvex strain energy and adopt the non-local strain gradient energy to account for the energy of the diffusive domain front. We simulate the equilibrium domain patterns and their evolution in the tubes under tensile loading by a non-local Finite Element Method （FEM）. It is revealed that the observed loading-path dependence and topology transition of do- main patterns are due to the thermodynamic metastability of the tube system. The computation also shows that the tube-wall thickness has a significant effect on the domain patterns： with fixed material properties and interfacial energy density, a large tube-wall thickness leads to a long and slim helical domain and a severe branching of the cylindrical-domain front.
文摘A new non-uniform yield phenomenon is found during tension of austenite stainless steel at -190℃, which consists of elasto-plastic instability ξph and stress plateau ξL resulting from strain-induced martensite transformation. It is essentially different from non-uniform yield that is related to dislocation obstacles. The experimental results show that ξph and ξL increase with increaslng strain rate, and ξph, increases but ξL decreases with increasing prestmin.Tronsformation enengy of strain-induced martensite keeps a constant, 3.85×106J/m3, with increasing strain at the stages of both elasto-plastic instability and stress plateau.
