Intermittency-driven subcritical fiber breakage in turbulence

Turbulence fragments slender fibers in oceans, process industries, and the atmosphere, shaping size spectra, transport, and impact. Mean-field estimates compare typical turbulent bending with a material failure threshold and predict a critical span below which fibers should be effectively unbreakable. We show that this conclusion changes when turbulent intermittency is included. In the quasistatic inertial-range regime, the fiber relaxes elastically faster than the turbulent load changes, so its curvature is set by the velocity increment across the fiber; refined similarity relates the amplitude of that increment to the coarse-grained dissipation at the fiber scale. Rare fluctuations of the velocity increment across the fiber therefore generate rare curvature bursts, opening a subcritical breakage channel for fibers whose mean-field curvature lies far below threshold. In a log-normal cascade model, the resulting hazard decays algebraically with span, rather than with the much stronger Gaussian suppression obtained from a nonintermittent model. The same rare-event statistics can be mapped onto an effective mean dissipation: the mean dissipation that an equivalent nonintermittent model would need to reproduce the intermittent exceedance probability. Under realistic conditions, this effective dissipation can exceed the bare mean by orders of magnitude. Intermittency can therefore control fiber fragmentation in nominally subcritical regimes.