Molecular based temperature and strain rate dependent yield criterion for anisotropic elastomeric thin films

Abstract

A molecular formulation of the onset of plasticity is proposed to assess temperature and strain rate effects in anisotropic semicrystalline rubbery films. The presented plane stress criterion is based on the strain rate-temperature superposition principle and the cooperative theory of yielding, where some parameters are assumed to be material constants, while others are considered to depend on specific modes of deformation. An orthotropic yield function is developed for a linear low density polyethylene thin film. Uniaxial and biaxial inflation experiments were carried out to determine the yield stress of the membrane via a strain recovery method. It is shown that the 3% offset method predicts the uniaxial elastoplastic transition with good accuracy. Both the tensile yield points along the two principal directions of the film and the biaxial yield stresses are found to obey the superposition principle. The proposed yield criterion is compared against experimental measurements, showing excellent agreement over a wide range of deformation rates and temperatures.

Quantification of the Young's modulus for polypropylene: Influence of initial crystallinity and service temperature

“…Many researchers have explored the correlation between mechanical properties and the service temperature of semicrystalline polymers . An exponential formal function was further proposed to evaluate the dependence of the elastic modulus of semicrystalline, crosslinked, low‐density PE (XLPE) on the test temperature .…”

Identification of the LLDPE Constitutive Material Model for Energy Absorption in Impact Applications

“…The structure of LLDPE leads to its heterogeneous non-linear behavior. LLDPE is very flexible, elongates under stress, absorbs a high level of impact energy, and thus, is suitable for making thin and ultra-thin films [5][6][7][8]. The mechanical properties of polyethylene depend on its complex structure [9], which leads to non-linear heterogeneous behavior during mechanical and numerical tests.…”

“…The double yield point is also mentioned in the literature [16]. The relation between yield stress, temperature, and strain rate can be described by constitutive laws [5,6,9,17], and the temperature-dependent mechanical properties of thin-layered materials have been addressed [18]. Upon comparing LDPE, LLDPE, and HDPE, LLDPE showed greater rate sensitivity than the other two materials under both static and dynamic regions of a compression test [9].…”

“…The main mechanical characteristics of polyethylene are the yield stress and the yield strain, corresponding to the point where plastic non-recoverable deformation due to permanent changes in the polymer chains starts. The yield stress and the yield strain of LLDPE depend on the temperature and the strain rate [ 5 , 6 , 15 ]. The yield stress increases while the yield strain decreases with rising strain rate [ 9 ].…”

“…The local preferential orientation of chains in LLDPE affects the tensile strength in the MD and TD [ 11 ]. In the direction of the main chain orientation, mostly the MD, LLDPE is stiffer than in the perpendicular direction, mostly the TD [ 3 , 5 , 6 , 15 ]. The tensile stress-strain relations in the MD and TD play an important role during the biaxial deformation of the impact test [ 3 ].…”