Towards an understanding of the mechanical response of aramid fibers at the filament scale

Technical fibers, and especially aromatic polyamide fibers, known as aramid fibers, are used as reinforcements in high performance composites. Mechanical characterization at the single fiber scale is challenging, especially when the diameter is as small as 12 µm, but essential to optimize performances at the product scale. In this work, we developed multiaxial characterization techniques at the filament scale.
Fibers mechanical properties are linked to their highly oriented structure resulting in a strongly anisotropic behavior: both longitudinal tensile tests and single fiber transverse compression tests (SFTCT) were used. The fiber showed remarkable properties in the longitudinal direction: a modulus of 87 GPa and a failure stress around 3 GPa. In the transverse direction, the fiber showed dissipative mechanisms and plastic deformation above 0,25N/mm, the experimental elastic limit. Using Finite Element Simulations, we showed that the transverse mechanical response of the fiber is closely linked to the fiber skin/core structure and is not strongly influenced by the geometry of the transverse section. We determined transverse modulus: E(skin)= 0,3 GPa et E(core)= 5 GPa. These results highlight microstructure/mechanical properties relationships of aramid fiber at filament scale.