Analytical and experimental investigations of crack propagation in adhesively bonded joints with the Mixed Mode Bending (MMB) test Part II: Investigation of cohesive stresses distribution with backface strain monitoring

Backface strain monitoring is used for probing the peel and shear cohesive stresses distribution along an adhesive layer during a crack propagation test under mixed mode conditions. An elastic model consisting of two Timoshenko beams attached with an elastic layer is derived to obtain simple analytical estimate of the specimen deformation from which a simple data reduction procedure is proposed. Taking benefit of the specimen symmetry, a proper experimental arrangement allows to separate the mode I and mode II contributions. Such protocol is less affected by the experimental artifacts which are observed on classical force versus displacement measurements from which are based the traditional fracture mechanics data reduction protocols. Additionally, backface strain measurements show superior sensitivity to non-linear interface behavior which should improve the quality of cohesive zone models identification.