Influence des charges sur le comportement mécanique d'un joint collé cisaillé en traction: Fid-Bau Portal

Influence des charges sur le comportement mécanique d'un joint collé cisaillé en traction

Luhowiak, W. / Cabrillac, R. / Duval, R. / Collot, C.

Résumé Le comportement mécanique d'un joint collé cisaillé en traction dépend de nombreux facteurs tant mécaniques que géométriques. Parmi tous ces paramètres, nous nous sommes proposés d'étudier, tout particulièrement, l'influence des charges sur la tenue d'un collage ainsi que leur rôle sur la microfissuration d'un joint. Après avoir caractérisé la nature minéralogique des charges vulgaires et renforçantes, nous déterminons les contraintes radiales et tangentielles dans la matrice et dans l'inclusion aux points les plus sollicités mécaniquement. La comparaison avec l'état des contraintes autour d'un trou circulaire nous permet, alors, de déterminer un diamètre limite en-deçà duquel les charges ne jouent plus aucun rôle dans la rupture du film d'adhésif.

Summary In the course of study of the influence of fillers on the mechanical behaviour of a glued joint, the author was first led to characterize them by spectroscopic analysis and scanning microscopy. These fillers of essentially mineral origin can be classified as common fillers (chalk, calcite, kaolin ...) and reinforcing fillers (aluminia, titanium oxide, ferrous oxide). Roughly spherical in shape, they may reach a diameter of 15 μm, whereas the maximum pore size is close to 20 μm. In a second phase of research, the author determined the radial and tangential stresses in the matrix and in the inclusion at places in the joint under the greatest mechanical stress by a uniform plane field of compressive stresses. The calculation is based on the Mauskhelisvili formulae and shows that the radial and tangential stresses (σ r andσ θ respectively) in the matrix are fairly equal and maximum at points M2 and M 2 ′ -extremities of the diameter of the circular load, in the direction of monoaxial loading p. The values ofσ r andσ θ are 1.45 and 0.45 respectively whatever the type of reinforcing filler. At M1 and M 1 ′ these stresses are nil (M1 and M 1 ′ are the extremities of the diameter perpendicular to M2M 2 ′ ). In the circular inclusion for the same type of filler, the stress tensor is reduced to a compressive stress of 1,45 p at M1, M 1 ′ , M2 and M 2 ′ . Using these results as a basis and applying the Ishaï fracture criterion, the authors show that the onset of microcraking at points M2 and M 2 ′ in the joints occurs for a value of p equal to two thirds of the tensile elastic limit of the resin. By approaching this value of limit load of a circular hole, it is possible to determine a 7μm limit diameter for an inclusion beyond which the filler plays no role in the microcracking of the glued joint. Finally, the authors show that a common fillter fractures well before the onset of microcracking in the matrix. The singularity then behaves like a circular hole under increasing uniform compressive stress p.