Dynamic self-strengthening of a bio-nanostructured armor — conch shell

Bio-nanowire structured armors — conch shells, which are often collected as art pieces, possess a special function — an unusual resilience against high speed predatory attacks. Under high-strain-rate compression (strain rate ~10³ s⁻¹) conch shells highlight significantly high fracture strength vis-à-vis under quasi-static loading (strain rate ≤ 10⁻²/s). The dynamic fracture strength reaches a strikingly high value of 600 MPa, 67% enhancement with reference to that of quasi-static loading with the fracture strength 360 MPa. Upon dynamic impact loading, conch shells ingeniously activated a new defense mechanism – intra-lamella fracture, which differs from the inter-lamella fracture damage under quasi-static loading. The lengthy third-order lamellae with a length of hundreds of micrometers were pulverized into rods with the length ranging from 0.4 μm and 2.5 μm upon dynamic loading, whereas the third-order lamellae in the quasi-statically fractured segments maintained the length of hundreds of micrometers. Multiple energy-dissipating mechanisms - intra-lamella fracture, nanoparticle rotation and dislocation enabled nanoparticle deformation in a synergistical fashion contribute to the high strain rate fracture strength of conch shells. This dynamic self-strengthening strategy provides a new guideline for designing dynamically robust materials.