Research On Time-Temperature-Stress Superposition Principle Of PMMA's Crazing Damage

Polymers are typical viscoelastic materials, and their mechanical properties depend on temperature, loading time, loading speed and strain etc, among which the loading time and the temperature are the main influence factors. In practice, more and more polymer is used in engineering structures. Its nonlinear viscoelastic behavior is needed in most. On the base of time-temperature-stress superposition principle, long-time nonlinear viscoelastic behavior in common temperature and low stress level can be evaluated in short time by enlarging the stress level and temperature to study.In this paper, we take high molecule physics and the damage theory of rheologic material with lacuna as the basic ,make the experiment as a mostly measure, take the PMMA as a research object, to study the time-temperature-stress superposition principle behavior of PMMA's crazing damage . The author presents the model of crazing damage in micro-mechanics, research the rule of craze initiation and evolvement by theory and experiment, get the commonly model of PMMA's craze initiation and evolvement. Williams-Landel-Ferry equation on time- temperature-stress-damage superposition principle is available which based the theory of time-temperature superposition principle. After analyzing the experiment data, we get the parameter of the equation and validate them with the result of experiment.Concretely,1 , Observe the PMMA's craze initiation in different temperature and discuss its temperature-dependence, research the craze initiation depend on stress level and time in certain temperature, and provide well base on researching the damage and life-span of polymer.2, Advance the theory of craze fibril's bearing weight and rupture from micro-view. Analyze the experiment data and get the PMMA's crazing damage evolvement equation in different temperature and stress level.3, Base on time-temperature superposition principle, discuss the behave of PMMA's crazing damage time-temperature-damage superposition, get Williams-Landel-Ferry equation on temperature-dependence and the parameter of the equationwith experiment result.4, Base on time-stress superposition principle, discuss the behave of PMMA's craze damage time-stress-damage superposition, get Williams-Landel-Ferry equation on stress-dependence and the parameter of the equation with experiment result.5 , Base on time-temperature-stress superposition principle, discuss the feasibility of time-temperature-stress-damage combined shift factor in Williams-Landel-Ferry equation. Get Williams-Landel-Ferry equation on time -temperature-stress superposition and the parameter of the equation with experiment result. Then use the equation simulate PMMA's crazing damage evolvement and compare with experiment data, which is proved to be true.