Study On Hyperelasto-viscoplastic Constitutive Models Of Thermal-induced Shape Memory Polyurethane At Deformation

Thermo-induced shape memory polyurethane(TSMPU)is a new kind of functional polymers,it owns many advantages,such as low density,low cost,good process ability,large deformation,glass transition temperature and adjustable capacity,and thus is widely used in the fields of aerospace,biomedical,textile industry and so on.In order to improve the practical application,studies on experiment and theory of TSMPU attracts more attention.However,experimental observations on the uniaxial tension at different temperatures and loading rate,the shape memory effect at different rates and loading amplitudes are necessary to be addressed further.In the meantime,existing models are fail in predicting the uniaxial tension at different temperatures and loading rates,the shape memory effect at different loading rates and loading amplitudes.Therefore,it is very necessary to carried out experimental investigations and establish the reasonable constitutive modeling,which is very important for the analysis of deformation mechanism and engineering application.Main work in this thesis are summarized as below:(1)The uniaxial tensile tests of TSMPU at different temperatures and loading rates were carried out,and results show that the yield stress decreases with the increase of temperature and increases with the increase of loading rate,the TSMPU has an obvious yield peak in the range of 308~313K and the yield peak disappears in the range of 323~343K.The shape memory tests of TSMPU at different loading rates and loading amplitudes were investigated,results show that the start recovery temperature increases with the increase of loading rate and decreases with the increase of loading amplitude,the recovery rate decreases with the increase of loading rate and increases with the increase of loading amplitude.(2)The typical hyper-elastic models of rubbery phase,visco-plastic models of glass phase and shape memory models were numerically implemented and evaluated by comparing with the corresponding experiments.Results show that the Mooney-Rivlin can provide good prediction in the hyper-elasticity of rubbery phase,the eight chains model proposed by Arruda and Boyce provide a poor prediction in the hyper-elasticity of TSMPU;the rheological model proposed by Boyce simulate the yield peak of TSMPU well,but fail in simulation of strain-hardening after yielding;the Qi's model provide poor predictions in strain hardening at low temperature and tensile behaviors at high temperature.(3)Base on the existing elasto-visco-plastic constitutive model and logarithmic stress rate,a hyper-elasto-visco-plastic constitutive model of TSMPU is established to reasonably simulate the uniaxial tests at different temperatures and loading rates,shape memory effects at different loading rates and loading amplitudes.