Fracture and tensile strength of aggregates of frictional flexible fibers

Flexible frictional fibers aggregates show significant cohesive behavior without the need of glue between particles. In nature, this effective cohesion provides mechanical stability of natural structures such as birds’ nests or beaver dams. Here, we aim to rationalize the cohesive strength of a disordered assembly of flexible frictional fibers. We design a non-destructive experimental protocol that allows us to access the tensile strength of the aggregate through force-displacement measurements. The results show that the tensile strength is highly dependent on the initial packing fraction set by the pre-compression. X-ray microtomography gives us access to relevant quantities such as the number of contacts, average fibers curvature, and fiber reorientation throughout the tensile process. We construct a simple mechanical model taking into account the number of fibers participating in the fracture process that well captures the effective cohesion of the assembly.