Stress-strain Behaviors Of Semicrystalline Polymeric Materials And Their Relationship With Morphologies

On the basis of a brief introduction of the deformation behavior and yielding characteristics including the unusual double yielding phenomenon of polymers, especially semicrystalline polymers, this thesis reviewed the influencing factors of deformation behavior of polymers from the temperature activated molecular mobility, stress activated molecular mobility, effect of heating history and dependence of stress strain behavior of polymers, polymer blends and polymer composites on the structures and morphology and forward the purpose and arrangement of this study.Firstly the dependence of stress strain behavior of polyolefin on the test conditions was investigated. The results showed that at room temperature high density polyethylene (HDPE), isotactic polypropylene (iPP) and copolypropylene (cPP) presented the typical stress strain behavior of semicrystalline polymers in a wide range of tensile velocities, no yielding point was shown for low density polyethylene (LDPE), and the unusual double yielding behavior and distinct strain hardening phenomenon was observed for linear low density polyethylene (LLDPE). With the tensile velocity increasing, the basic characteristics of these stress stain behavior were unchanged while the overall stress strain curves were raised and elongation at break (ε_b) depressed. In a certain range of tensile velocities, the double yielding behavior of LLDPE was more notable with lower tensile velocity. In a certain range of tensile temperature, the stress strain behavior of polyolefins studied showed good similarity. With the tensile temperature increasing, the tensile strength decreased and elongation at break increased greatly. In a certain tensile temperature range, all these polyolefins showed marked stress oscillation phenomenon and unstable, uneven deformation behavior. Under the coupling effect of temperature field and tensile force field, the tensile yield stress (σ_y) showed a linear relationship...