Papers by Author: Hélène Welemane

Abstract: A new micromechanical modelling approach for brittle damage in initially orthotropic materials is presented. The proposed strain-based energy formulation allows to derive a fully anisotropic multilinear model for microcracked materials with arbitrary oriented defects. The thermodynamics framework provides a standard procedure for the damage evolution law. The new model explicitly accounts for the interaction between primary and induced anisotropies. Moreover, the very challenging issue of opening-closure effects (unilateral behavior) is addressed in this framework.

Abstract: This work deals with the Liquid Resin Infusion (LRI) process developed within the research program “FUSelage COMPosite” of DAHER SOCATA. This manufacturing process enables the realization of complex composite structures or fuselage elements in a single phase (mono-material), which considerably reduce connections and relative difficulties. The concern here is the investigation of non destructive testing (NDT) methods that can be applied to LRI-structures in order to define their capacities for defect detection, and especially their associated critical defect size. In aviation industry, the AITM standards require the ultrasonic testing as NDT for composite materials. Therefore the aim of this work is to characterize and compare three different and complementary ultrasonic techniques on composite specimens. Such analysis allows to define the NDT application field of each method in term of defect detection.

Abstract: The work of this study concerns the fine modelling of the thermomechanical and metallurgical behavior of interface ceramic-metal in order to determine the residual mechanical state of the structures during brazing process. For these cases, difficulties mainly arise in the modelling of the solid-solid phase transformations as well as in the modelling of the mechanical behavior of the multiphasic material. Within an original theoretical framework - generalized standard materials with internal constraints – we proposed models for the behavior of multiphasic material. The design of joints in engineering structures and the optimisation of the industrial brazing process require determining and analysing such a phenomenon. In this way, the present work aims at predicting the thermally induced stresses (localisation and level) through numerical simulations and then, at defining the main parameters which influence their development