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Pinning and structuration

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Lina Alzate (PhD 2009-2012) - Etienne Barthel - Davy Dalmas

Thin film multilayers deposited on glass are widely used for flat optical, photoelectric and electrochromic devices. In many applications, adhesion is a crucial issue. This is the case for instance when mechanical strength is required for further processing or for integration in complex systems. Thus, it becomes of great interest for those applications to increase the adhesion. Many mechanisms of toughening a brittle solid can be found in literature (local transformations, crack bridging, crack trapping, microcracking…); but few of them can be applied to thin film layer. One possible way to increase the adhesion of an interface between two brittle solids is to create a composite interface in order to modify the crack front morphology due to pinning on region of higher toughness. By a judicious choice of the heterogeneous interfacial toughness field, it becomes possible to have an adhesion which will be higher than the simple mean value of the local toughness. This toughness modification is the consequence of the existence of a strong pinning regime which is characterised by a rapid local change of the toughness in the direction of crack propagation. Crack pinning has been widely theoretically and experimentally studied since more than two decades, but few, if any, of these experimental studies have been done in the past in a manner which allows evaluating the front morphology modification due to pinning by a single defect.

We have already performed one of the first experimental validation of the pinning theory for simple toughness patterns. It opens a certain number of prospects such as: (i) studying pinning with more complex defects geometries in order to be in a strong pinning regime, (ii) developing structured interfaces in thin multilayers to increase their adhesion.

Collaboration

Daniel Bonamy: SPCSI, CEA Saclay Damien Vandembroucq : Laboratoire PMMH, ESPCI

Publication

  • Patinet S., Alzate L. Barthel E., Dalmas D., Vandembroucq D. and Lazarus V., Finite size effects on crack front pinning at heterogeneous planar interfaces: Experimental, finite elements and perturbation approaches, J. Mech. Phys. Solids 61 (2013) 311-324
  • D. Dalmas, E. Barthel et D. Vandembroucq, "Crack front pinning by design in planar heterogeneous interface", J. Mech. Phys. Solids 57, 446 (2009).