Micro-mechanical interpretation of the non-linear tensile response of structured rods. Experiments on prototyped Gedankenmodelle with wavy sub-rods and application to Carbon NanoTube fibers

In order to demonstrate the wide range of inelastic non-linear tensile responses observed in structured fibers of various types, an ideal phenomenological model (Gedankenmodell) is theoretically analyzed, prototyped and tested. This consists in a rod made of a regular ensemble of sticks in a brickwork -like three-dimensional grid, hooped by elastic bands. The stick lateral faces are wavy surfaces in cohesive -frictional contact; their relative sliding induces a transversal expansion opposed by the bands, providing shear -slip constitutive laws that mimic the complex interaction forces in fibers composed of adherent fibrils. The macroscopic response of the rod to uniaxial loading is theoretically modeled in the framework of generalized standard materials. Experiments conducted on 3D -printed prototypes confirm the theoretical approach. As an example, the Gedankenmodell is applied to the tensile response of Carbon NanoTube (CNT) fibers, composed of CNTs laterally bonded via a spinning process. The model phenomenologically reproduces the tensile response of dry -spun, aerogel-spun and wet -spun CNT fibers, specifically the onset of a yield point, elastic unloading-reloading and inelastic aftereffects. This approach interprets the adhesion of the CNTs within the broad paradigm of cohesive -frictional adherence, combined with conservative forces of attraction.