The Uniaxial Rate Sensitivity Characteristics of Polymers at Uniaxial Tension Process under Loading Control Mode

Uniaxial stretching is a commonly method for testing the mechanical properties of materials. The polymer materials are rate-sensitive due to their viscoelastoplastic behavior during loading. It is vital to consider the time-dependent characteristics of polymer mechanical behavior. The paper conducted creep and uniaxial tensile tests with different loading rates using Nylon 12 (PA12) as a typical polymer material, and the corresponding viscoelastic parameters were obtained through creep experiments. For the loading control mode condition, we can define a linear loading process in a stretching experiment with a certain stress rate. The loading process is divided into n equal segments, and the result is approximated as the sum of n step loading processes with a constant equivalent load. Based on these, a rate sensitivity model was constructed based on the generalized Kelvin model and superposition principle for uniaxial tension under the loading control mode. The results show that the model can match the experiential results well in the viscoelastic section of the tensile stress-strain curve. The model can effectively reflect the rate sensitivity characteristics of the viscoelastic section under loading control mode. However, a significant deviation begins to appear before entering the viscoelastic-plastic stage due to the small deformation assumption and the change of physical properties in the viscoplastic deformation stage of the material.