关键词: Kapton薄膜, 粘弹性力学, 蠕变性能, 初始应力, 蠕变本构模型

Abstract:

As a kind of aerospace membrane material, polyimide film’s (Kapton film) creep effect is very important to its structure. In order to study its creep mechanical properties, firstly the study selected Kapton film with a thickness of 25 μm, and carried out the uniaxial creep tensile test under the four stress levels of 35%, 50%, 65% and 80% of the ultimate tensile strength. Secondly, according to the creep mechanics curves obtained, the creep characteristics of the film under different initial stresses were analyzed, and the intrinsic mechanism was discussed by combining the creep elongation. Five creep constitutive models of classical Kelvin, classical Maxwell, four-element Burgers, three-parameter generalized Kelvin and five-parameter generalized Kelvin were used to fit the experimental data, and the fitting effects of each model were compared and analyzed. The results show that Kapton film has obvious viscoelastic properties, which should be considered in the design. The initial stress has a significant effect on the creep properties of Kapton film. The greater the initial stress, the higher the strain at the initial creep stage, the higher the strain retention value at the steady creep stage, and the more obvious the viscoelasticity is. The tensile fracture stress levels in different directions lead to the differences of creep properties, and the total strain of TD (Transverse Direction) is greater than that of MD (Machine Direction) under each stress state. With the increase of the initial stress, the creep elongation of the film first increases and then decreases. This is because the influence of the initial stress on the stress state and dislocation motion inside the film is complex, and there is an equilibrium point. The five-parameter generalized Kelvin model adopted in this paper can well predict the creep properties of Kapton film, and the coefficient of determination of the fitting results is more than 0.99, followed by the Burgers model. The fitting coefficients of classical Kelvin, three-parameter generalized Kelvin and classical Maxwell model are between 0.71 and 0.86, and the fitting results meet the needs of practical engineering.

Key words: Kapton film, viscoelastic mechanics, creep properties, initial stress, creep constitutive model