Stick-slip substructure in rapid tape peeling

The peeling of adhesive tape is known to proceed with a stick-slip mechanism and produces a characteristic ripping sound. The peeling also produces light and when peeled in a vacuum, even X-rays have been observed, whose emissions are correlated with the slip events. Here we present direct imaging of the detachment zone when Scotch tape is peeled off at high speed from a solid surface, revealing a highly regular substructure, during the slip phase. The typical 4-mm-long slip region has a regular substructure of transverse $220\mu \text{m}$ wide slip bands, which fracture sideways at speeds over 300 m/s. The fracture tip emits waves into the detached section of the tape at $\sim 100\text{m}/\text{s}$, which promotes the sound, so characteristic of this phenomenon.

Figure 1

(Color) Experimental setup and overall view of the peeling tape. (a) Sketch of the imaging setup. (b) Typical stick-slip pattern formed during the rapid peeling of Scotch Tape, with the detachment front, i.e., where the tape separates from the substrate, having moved from top to bottom in the image. The thick dark bands (white arrows) are the primary stick locations, whereas the dark arrows point to the thin fracture bands, which appear during the slip phase. The thin white line indicates a wave-crest traveling in the detached tape. The dark bands dissipate after the tape detaches. The detached section also moves out of focus. The tape and image is here 12 mm wide. See also online video [23].

Figure 2

Typical fracture bands. (a) Fracture front is moving to the left. The vertical arrow points at its tip. (b) The thick dark band is an earlier stick location, whereas the arrows point to thin lines which appear between the fractures during the slip phase. The region above the thick dark band did contain thin dark fracture bands which have dissipated during the stuck phase, which here lasted for about 1 ms. (c) Two fractures traveling along the front. Scale bars are 1 mm. The overall motions of the fronts are from top to bottom, with the lower parts still in contact with the glass plate. See also the online videos [23].

Figure 3

Images of the progression of the fracture tip. (a) Frames taken from a 1 Mfps video sequence and the panels are separated by $1\mu \text{s}$. The left panels show the raw images, with the arrows pointing to the tip of the crack which is traveling to the left at about 325 m/s, for $\alpha \sim 2°$. The overall motion of the front is downwards. The scale bar is $500\mu \text{m}$ long. (b) The difference in image intensity between the individual frames in (a) and the frame immediately preceding the sequence. See also video clip online [23].

Figure 4

Characteristics of the fracture bands. (a, b) The width and speed of the fracture bands, as a function of the angle of the front. Data exclude the first fracture bands, at start of slip phase. (c) Fracture velocity vs the number of the band from onset of slip. The symbols indicate two separate realizations. (d) The strain zone vs distance ahead of the detachment front. The differences in image intensity between a frame showing the undisturbed tape and the slowly moving front, at 3.5 m/s during a long stick-phase. The averaging was performed both transverse over a 1.5 mm section from each frame, as well as over a sequence of 90 video frames. Compression of minute air pockets shows up as slight brightening in the image, highlighting the strain region in the adhesive which is responding to the applied pulling force.

Figure 5

Waves traveling in the detached tape. (a) Three wave crests (black arrows) traveling at 85 m/s away from the front (dark region in the bottom right), in the direction of the white arrow. The scale bar is 1 mm and the exposure is $2\mu \text{s}$. (b) Image difference showing an isolated wave, traveling upwards in the detached tape, which is generated by a fracture front traveling to the left. See also online video [23].