Dissipative mechanisms during the debonding of high performance foam pressure sensitive adhesives for automotive

Dissipative mechanisms developing in high performance pressure sensitive adhesives (called PSA foam) are extensively studied. New assembly techniques in the automotive domain are based on those materials. Their proper functioning depends on their ability to dissipate energy when they undergo high deformations. Such a large deformations behavior comes from their soft character. The literature on adhesion problems or, more recently, on the fracture mechanics of soft materials has laid the foundations for the study of this type of material. Nevertheless, previous works always focused on the study of thin and unfilled polymers. In this thesis, one emphasizes foam adhesives. They are at least 10 times thicker and filled with hollow glass spheres with diameters ranging from 10 to 100µm. In particular, this structure gives foam PSA, new types of dissipative mechanisms. The latter make it possible to reach adherence levels rarely achieved with conventional adhesives. These dissipative mechanisms appear at three levels during debonding. For low adhesions, the entire dissipation comes from debondings between the microspheres and the matrix in a volume close to the interface between the adhesive and the substrate. These detachments generate a fibrillation phenomenon that remains confined to a small area near the interface. Then, as the adhesion increases, the entire volume of the adhesive deforms. This deformation causes the spheres to detach from the matrix in volume. These volume decohesions generate cavities (cavitation phenomenon) which gradually deconfines the adhesive. The latter then loses its continuum. During the growth of these cavities in volume, instabilities occur at the micrometric scale to minimize the strain energy. Once the material has been deconfined, the adhesive moves in a preferential direction. This orientation is allowed by adopting a millimeter-scale fibrillar structure. A model explains this process well where each of these fibrils is assumed to be loaded in uniaxial tension. Thus, the extensional non-linear rheology of these equivalent fibrils drives the energy dissipation process. The relevant parameter is then the strain rate of the equivalent fibrils. Eventually, we explained quantitatively the link existing between the shape of the debonding region and the adherence level.