StickSlip

The dynamical rupture instability studied in this project is the so-called stick-slip instability i. e. the intermittent growth of a crack. Stick-slip rupture instabilities are observed in many different systems, for instance in heterogeneous rubbers used in the automotive tire industry and during the high speed peeling of adhesives in automatic labeling industrial processes, gluing of automotive parts or sealing of electronic housings. Overall, adhesive stick-slip reduces industrial productivity and its hard-to-predict nature hinders the development of new technical applications. From a fundamental perspective, the non-monotonous dependence of fracture energy on crack velocity that triggers stick-slip is still difficult to understand quantitatively due to the complex interplay between the fracture geometry, the strongly non-linear mechanical response of materials in large strain conditions and the existence of heterogeneities either in the material’s microstructure or induced by the rupture mechanism. Furthermore, the various physical parameters influencing the stick-slip instability have rarely been correlated to the actual characteristics of the stick-slip motion (stick and slip velocities, durations and amplitudes). The StickSlip project will develop and/or use various original and custom-designed experimental tools that are able to resolve in time and space the motion of the crack front during stick-slip in two situations: (i) the rupture of an adhesive at the interface between a backing tape and a substrate; (ii) the bulk rupture of an elastomer. The experiments that we propose will shed a new light on stick-slip instabilities in fracture. Measurements of the detailed characteristics of the stick-slip motion will allow us to clarify the key physical parameters controlling the instability (geometry, adhesive or elastomer rheology). The proposed experiments will also be used to test new ideas related to the effect of interfacial or bulk heterogeneities on stick-slip. The collective intermittent motion of the crack front that occurs during adhesive stick-slip might be disturbed by the presence of heterogeneities. A major goal of the project will be to understand whether heterogeneities might, in certain conditions, suppress the stick-slip instability at the macroscopic scale by destroying large scale correlations, and confine the stick-slip dynamics to smaller scales that would be less harmful for industrial applications. Being able to properly control the heterogeneities will be an important challenge of our project. On the one hand, the studies we propose are important for basic science since they will deepen our knowledge of the dependence of the fracture energy on crack velocity and even extend it to the widely unexplored case of materials with interfacial or bulk heterogeneities. Comparisons between adhesive peeling and elastomer tearing will allow us to validate the generality of our analysis. On the other hand, new solutions for controlling the instability (control of rupture geometry, control of polymer rheology, control of heterogeneities) would represent a significant breakthrough for industrial applications. In this context, the technical help offered by Bluestar Silicones is a significant added value to our project.