A new micromechanical damage model accounting for progressive interface debonding is developed for composite materials. It consists of an original evolution law of the damage at the interface and an appropriate load transfer law at the matrix-fiber interface integrated into a generalized incremental Mori-Tanaka homogenization scheme. The interface damage evolution is driven by the interfacial stress state while the load transfer is obtained from a new model inspired by the shear lag model. Specifically, such damage evolution is supported by experimental microscopic observations for short glass fiber reinforced polyamide-66. The proposed model is validated based on numerical reference solutions provided from finite element analyses of a representative unit cell of a composite, where imperfect interfaces are represented using cohesive elements. A further comparison with experimental data proves that the proposed model is an alternative to micromechanical models involving weak interfaces in the case of spherical reinforcements. It is shown that the proposed model is able to accurately reproduce the non-linear effective response of composite materials for a broad range of reinforcement shapes, including spherical particles and matrix mechanical properties.

International audienceNumerical studies of squeal in brake systems are carried out with unreal perfect surfaces. In this paper, a methodology to introduce geometric imperfections in the multi-scale contact problem is proposed. Two kinds of geometric imperfections are taken into account separately: the first is “disc thickness variation” as function of the disc while the second is the “plateau” as function of the friction pad. A complete resolution strategy is proposed with a combination of finite element analysis and a lumped-mass model for a simplified pin-on-disc system. A complex modal analysis is performed for different static configurations in which only the contact pressure evolves. Parametric studies for both cases are performed to study the influence of these geometric imperfections on mode lock-in. It is shown that the introduction of both kinds of geometrical imperfections have an influence on dynamic behavior and mode lock-in (through modification of the eigenfrequencies of the system). The pad mode is mostly influenced by bumping which modifies the contact localization. Considering plateaus on the pad surface highlights the importance of the theoretical contact length parameter