Calculation of the macroscopic mechanical properties of polyamide 6.6 underwater influence using molecular dynamics simulations, hyperelastic material modeling of the amorphous fraction, and homogenization schemes

Abstract

The macroscopic mechanical properties of water-influenced polyamide 6.6 is analyzed by combining molecular dynamics simulation and experimental measurements of the media concentration and the degree of crystallization. The mechanical properties of α-crystalline and amorphous polyamide 6.6 are analyzed separately by using molecular dynamics simulations. The anisotropic linear-elastic stiffness tensor of the crystalline material is determined by unidirectional tensile and shear stress simulations. The deformations of amorphous simulation cells with different water concentrations are fitted in a compressible hyperelastic Yeoh material model. The media concentration of tensile specimens conditioned in air with 50% relative humidity at 23°C and in water is determined after different conditioning times. The degree of crystallization of the material is determined using Differential Scanning Calorimetry. Both parameters are used to estimate the macroscopic mechanical properties of polyamide 6.6. The homogenization schemes by Reuss and Ahzi are compared to calculate the resulting macroscopic properties. Tensile tests are used to validate the calculated properties: The weakening of the material due to water molecules in the amorphous phase can be shown, but it is underestimated in the methods used.