We report an extensive experimental study of a detachment front dynamics instability, appearing at microscopic scales during the peeling of adhesive tapes. The amplitude of this instability scales with its period as Amss ∝ T 1/3 mss , with a pre-factor evolving slightly with the peel angle θ, and increasing systematically with the bending modulus B of the tape backing. Establishing a local energy budget of the detachment process during one period of this micro-instability, our theoretical model shows that the elastic bending energy stored in the portion of tape to be peeled is converted into kinetic energy, providing a quantitative description of the experimental scaling law.The periodic velocity oscillations of the detachment front during the peeling of adhesive tapes constitute an archetypal example of a dynamical rupture instability. This stick-slip motion leads to a screechy sound that everyone has experienced, when peeling-off packing tape. However, despite a large number of studies [1][2][3][4][5][6][7][8][9][10][11][12], this instability is not fully understood and still causes industrial problems, with deafening noise levels, and damages to both adhesives and peel systems.The effective fracture energy of adhesivesubstrate joints can decrease over certain ranges of peel front velocity [2][3][4][5]. In such unstable condition, for which less energy is required for the crack front to grow faster, a transition from a quasi-static rupture mode to a dynamic one occurs, as for frictional interfaces [13][14][15]. During the rapid slip phases, the dynamical mode of failure is likely to give rise to small scale spatiotemporal front instabilities [16]. Indeed, ultrafast imaging could unveil that the peel front locally advances by steps in the main peel direction as a result of the propagation of a dynamic fracture kink in the transverse direction, at spatiotemporal scales much smaller than the macroscopic stick-slip [17][18][19]: the kink occurs periodically at ultrasonic frequencies with an amplitude of a few hundred microns, not only during the slip phase of the macro-instability, but also, for imposed peel velocities in a finite range beyond the macro-stick-slip domain where the peeling is regular at macroscopic scales [19].Interestingly, this micro-instability of the peel front characterized by the side-ways propagation of fracture kinks share similarities with other physical processes, as for instance the local con-tact lines dynamics on textured surfaces [20], or the dislocations motion in the yielding of crystalline materials [21]. While it was shown that those transverse cracks are accompanied by cycles of load and release of the elastic bending energy stored in the tape backing in the vicinity of the peel front [19], the physical origin of the micro-instability and its interaction with the macroscopic one remains an open issue.In this Letter, we provide a detailed experimental study of this micro-instability, varying systematically the peeled length L, the peel angle θ, the lineic mass µ and bending modulus...

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