Nanostructured high-strength high-modulus film polymer materials: statistical elastic and fracture mechanical properties

The statistical distributions of the mechanical properties (strength σ, strain at break ε_b, and Young’s modulus Е) of the high-strength high-modulus oriented thin films and fibers of polyamide-6 (PА-6) have been investigated. For this purpose, two types of the PA-6 samples have been selected: single thin threads and multifilament fibers consisting of some hundreds of individual fibers. The statistical analysis has been carried out on a large number of mechanical tests of identical samples (50 testing samples for each of the two sample types) using the Gaussian and Weibull’s models. Beside the ‘traditional’ mechanical properties (σ, ε_b, and Е) commonly used for materials characterization, two additional viscoelastic and fracture characteristics have been estimated and introduced when analyzing the stress-strain curve by taking its first derivative. These are the tangent to the linear viscoelastic portion of the stress-strain curve at relatively large strains (6–14%) and the deformation interval between εb and the strain value received by extrapolation of this curve portion to σ = 0, referred to as the apparent viscoelastic modulus (Е₂) and apparent strain at break (ε_b-2), respectively. The similarities and differences of the statistical distribution behaviors of σ, ε_b, Е, Е₂, and ε_b-2 for two PA-6 sample types investigated, including the applicability of the Gaussian and Weibull’s models, have been discussed.