PHASE FIELD MODELING OF NEGATIVE STIFFNESS COMPOSITE MATERIALS

摘要

This research studies the effects of ferroelastic phase transition on the overall mechanical properties of the 2D materials by the phase field simulation (PFS) method Without directly using negative values in elastic moduli PFS enables the study of negative-stiffness effects due to the phase transformation Under simultaneous straining and temperature cycling enhancements on effective viscoelastic modulus and damping in the vicinity of phase transition are observed in consistence with classical composite theory with negative modulus and experiment Regardless of externally applied stress ferroelastic domains may be formed when constant temperature is set to T=0 5 since the system possessing two energy minimal points If the constant temperature is set to be T=1 7 no domains will be formed Under no external stresses domains will not re-form under temperature cycling The uniaxial deformation under the fast temperature rate may enhance effective stiffness due to the negative stiffness effects generated from phase transition by 15 folds Enhancements on effective stiffness are also observed in biaxial shear and 2D bulk deformation but their magnitudes are less than those in the uniaxial mode The cracked ferroelastic materials show less NS-induced enhancement than those intact ones and the domain evolution would start from crack tips Foamed ferroelastic materials auxetic or non-auxetic show similar behavior as continuum ferroelastic media but some oscillatory responses were observed in stress response of the foams which may be due to the responses of each rib in the foam

獎項日期	2017 8月 1
原文	English
監督員	Yun-Che Wang (Supervisor)