Multiscale characterisation of strains in semicrystalline polymers

A nondestructive probe for mapping elastic strains within polymers would be an asset for materials engineering: for validation of mechanical models and for understanding damage nucleation. As a step towards this aim we demonstrate an X-ray wide angle diffraction methodology probing strain tensor components on mesoscopic length scales, in the range 3-50 Å. We demonstrate its use on a 50 % semi-crystalline polyethylene sample subjected to tensile straining up to 8.8 % . The mesoscopic strains derived for the crystalline phase scale linearly with the macroscopic strain, in contrast to the crystallised volume fraction and the texture evolution. In the crystalline phase, the material becomes softer and exhibit a larger degree of alignment with decreasing distance in direct space. The inherent strain sensitivity is 10 - 5 . The prospect of 3D mapping of local strain and stress tensors is discussed.