Abstract:

The current standards are difficult to measure the characteristics of silage polyethylene （PE） film under actual working conditions. In this study， uniaxial tensile tests at different tensile rates with a strain range within 200 % and stress relaxation tests at different initial elongations were conducted on the PE film specimens in the machine direction （MD） and transverse direction （TD）. The tensile test results indicated that there was a pronounced dependency on both stretching speed and direction in the stress⁃strain （σ⁃ε） profiles， and the films exhibited a secondary yielding phenomenon in both MD and TD orientations. With an increase in the tensile rate， there was a decrease observed in the elongation at the second yield. The first and second yield strengths in the MD direction showed a good linear mapping relationship with the logarithm of tensile rate （ln v）. An increase in the tensile rate could improve the yield strength of the PE film. However， the yield strength reduced the toughness of PE film after reaching a certain rate. Stress relaxation tests indicated that both the MD⁃ and TD⁃oriented films presented a rapid decrease followed by a gradual reduction in stress across a range from a low initial stretch level （10 %） to the high one （70 %）. The generalized seven⁃element Maxwell model could accurately describe the stress relaxation behavior of the PE film， which offered insights into its long⁃term stress relaxation characteristics. The quantity of stress relaxation and rate of stress decay decreased with an increase in the stretch level. This indicated a reduction in the relaxation modulus as well as a more stable modulus during the slow stress decline phase. These findings suggest that to realize the optimal silage sealing， the PE films should balance stiffness with resilience to relaxation with an ideal stretch range of 50~70 % during wrapping.

Key words: silage polyethylene film, mechanical characteristics, tensile rate, yield elongation, stress relaxation