Research On Viscoelasticity And Life Prediction Of Spandex In Z-pinch

Spandex is newly developed as an important part of Z-pinch —— the adaptive fiber due to its high elasticity,corrosion resistance and oxidation resistance.The viscoelasticity properties of spandex under the small deformation(strain?10.0%,stress?0.0011N/tex)affect the safety and reliability of Z-pinch significantly.In order to improve the safety and reliability of Z-pinch,viscoelasticity experiments to simulate the actual service conditions of spandex in Z-pinch were designed;the effects of temperature,load and time on dynamic and static viscoelasticity of spandex were studied;and the service life of spandex was predicted.1)Firstly,the effects of temperature,dynamic load frequency f on microstructure and dynamic viscoelasticity of spandex were studied.The results show that:(1)When the temperature is above-26?,the rate of descent of loss factor tan? decreases because of some crystallization-melting soft-segments;when temperature is above 15 ?,all soft segments are loosened to high elastic state.(2)Storage modulus E' and loss modulus E' curves move toward high temperature as f increases,and the moving trend is not obvious when f is higher than 21.5Hz.The dynamic viscoelastic performance under wide range frequency(10-7Hz~1011Hz)was predicted by the principle of time-temperature superposition(TTS),it is found that E' increases as the f increases,and E' increases first and then decreases as the f increases and maximizes at 107 Hz.(3)In the temperature range of-70?~-26?,the activation energy of soft-segments decreases with the increase of temperature,and the relationship between relaxation time and temperature of soft-segments containing some crystallization-melting soft-segments doesn't conform to the WLF equation nor the Arrhenius equation.2)Secondly,the effects of strain(or stress)and temperature on microstructure and static viscoelastic properties of spandex were studied.The results show that:(1)At the temperature of 25?,under the effect of different constant strains for same time,structures of spandex's hard segment domains don't change,soft segments don't produce induced crystallization,stresses increase linearly as strains increase,and stress relaxation modulus are the same as strains increase;under the effect of different constant stresses for same time,strains increase linearly as stresses increase,creep compliances are the same as stresses increase.(2)But temperature has a significant effect on the microstructure and stress relaxation behavior of spandex.In the range of-30?~-20?,the higher the temperature,the lower the crystallinity of soft-segments,the lower the initial stresses,the greater the stress relaxation rate,the greater the difference of stress relaxation rates between two adjacent relaxation moments;In the range of-20?~45?,the higher the temperature,the same the initial stresses,the higher the orientation degree of soft segments,the more the short range order structures of hard-segments,the smaller the stress relaxation rates and its,the smaller the difference of stress relaxation rates between two adjacent relaxation moments,the stress relaxation rates tend to be constant when temperature is above 0?.3)Finally,the optimal stress relaxation constitutive models of spandex at different temperatures in the range of-30?~45? were established and it's service life were predicted.The results show that the service life of spandex at five temperatures of 0?,10?,25?,35? and 45? are much longer than 1 year and meet the project requirement,and the service life of spandex at five temperatures of-30?,-25?,-20?,-15? and-10 ? are 48 s,62s,108 s,312s and 1471 s respectively.At the temperature of 25?,stress relaxation constitutive models under arbitrary strains were predicted by the interpolation method,and creep constitutive models under arbitrary stresses were also predicted.