Determination of Generalized Fracture Toughness in composite multimaterial closed corners with two singular terms – Part I: Test proposal and numerical analysis

In the present work a general procedure for the experimental evaluation of Generalized-Fracture-Toughness values at multimaterial closed corners is defined. The lack of symmetries in the stress fields at multimaterial corners with non-isotropic materials makes it extremely difficult to define standard test procedures for Generalized-Fracture-Toughness determination. The proposed procedure is suitable for closed corners (all wedge faces being bonded) having two singular terms with real singularity exponents. The procedure begins by finding the load configurations at which one of the singular terms in the asymptotic series expansion vanishes, allowing the failure to be controlled by the other, non-vanishing, singular term. An example of a typical bimaterial corner in an adhesively bonded joint with composite materials is extensively analyzed and suitable test configurations for the experimental evaluation of the Generalized-Fracture-Toughness values K1C and K2C associated to the singular terms are defined. The experimental part of this work using a novel modified configuration of the Brazilian test will be described in a follow up paper.