Experiment And Theory Research On Craze Damage Depending On Stress And Time

The capability of polymer is highly demanded to meet the needs of constantly developed economic. Strength and toughness are two significant parameters for polymer and must meet the needs of structure. The deformation and failure theory of polymers and their composites attract many researchers' attention.Polymers are viscoelastic material in nature. During deformation they are usually time and stress-dependent. When loads are high, their deformation may be nonlinear. In order to describe the mechanical behavior of nonlinear viscoelastic material accurately, the effect of damage must be considered in the constitutive equation. Craze is an important form of polymer damage. Therefore, it's essential to study the time and stress pertinent mechanical behavior and the interrelated processes such as craze initiation, craze growth and craze breakdown in polymers. The research is of vital importance in both industrial applications and theoretical complications.PMMA (polymethyl methacrylate) , a sort of significant and widely used polymer, is selected as the main research object. The achievements are listed as follows.(1) An optical technique is presented to quantify the creep crazing damage in stressed transparent glassy polymeric sheet of PMMA. Craze area density in this article is defined by ratio of crazing area and the overall area of the region selected. The specimens were loaded for a defined period of time under creep condition with room temperature, by optical microscope the evolvement of craze density varying with stress and time is obtained.(2) Using craze density Dcraze(σ,) to illustrate the damage degreeof material, considering strain equivalent hypothesis, Non-linear visco-elastic constitutive equation of PMMA taken into consideration of the operation of craze damage is arrived. The PMMA sheet is loaded under different forces to validate the Non-linear visco-elastic constitutive equation with damage. The result shows that the theory curves obtained by the nonlinear viscoelasticity constitutive relation agrees with experimental data considerably well.