Research On Rheological Fracture And Damage Of Polymethyl Methacrylate

The extensive applications of the polymer materials necessitate people paying more and more attention to their strength and fracture properties. Polymers are a kind of typical viscoelastic materials, whose deformation not only is related with time, temperature, but also strain rate on loading. Nonlinear deformation and localized deformation usually occur, that is to say, they display crazing, shear zone and neck deformation which often are the foreboding of macro-failure of materials. Therefore it is important for theoretical meaning and practical value to study mechanic behaviors related with time, temperature and strain rate in the processing of deformation and fracture, and the development law of craze and the mechanism of material fracture. Since Sauer and Hsiao etc. studied the phenomenon of polymeric craze in 1950,based on their different knowledge backgrounds and by the different technica and methods, the researchers have carried out the extensive research on craze from different viewpoints and put forward each standpoint and established some relative models, such as the construction models and mechanic ones of craze, mechanic criterions and microscopic mechanisms on the initiation and shape of craze and models of stress distribution of craze damage at the tip of crack etc.. The paper has still gotten the strain-rate-dependent stress-time function of PMMA material, by the uniaxial tension test. At the same time, the craze distribution law and the strain-rate-dependence of the craze density by microscope test of craze. The paper has proposed a concept of median stress from the standpoint of energy. It has resulted the critical median stress of PMMA has nothing to do with strain rate at the range of the given strain rate, so it is represented as a parameter to scale the break of PMMA.