Identification of mechanical properties of biopolymer composites sensitive to interface effect using hybrid approach S. Guessasma a , D.H. Bassir b,c, * a INRA, unité BIA, rue de la géraudière, 44316 Nantes, France b Faculty of Aerospace Engineering, TU Delft, The Netherlands c FIT/ESTP/Constructability Research Institute, 28, Avenue Président Wilson, 94234 Cachan, France article info Article history: Received 27 April 2009 Received in revised form 9 November 2009 Keywords: Composite material Finite elements Genetic algorithm Artificial neural network elasticity parameters Microstructure generation abstract The mechanical behaviour of biopolymer composites is intimately dependent on the phase properties and microstructure features, especially interfacial properties. In this introduc- tive work, a numerical method is proposed to assess the role of the interface on the elas- ticity behaviour of a biopolymer composite characterised by randomly structured phases. A hybrid approach is developed based on finite element calculation and inverse/genetic algorithm to allow the correlation between the interface, intrinsic properties and the effec- tive properties of the composite to be identified. Idealised 2D microstructures are gener- ated in order to represent the main features of real starch-based microstructures in the full phase content range. Monte Carlo scheme is used for such purpose allowing the control of both phase ratio and interface content. Microstructures are meshed using a regular scheme with plane and interface elements. Imperfect interface behaviour is handled using a cohesive zone model. The effective elasticity modulus is computed based on the simula- tion of a simple uniaxial test. Based on the finite element results, the identification of the effective law is obtained using a hybrid artificial neural network/genetic algorithm approach. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction The use of biopolymer-based composites like starchy materials to replace oil-based materials is a challenging route that led to several recent research developments. The improvement of the mechanical performance of bio- composites is a key prerequisite to increase the potential of use of these materials in packaging, single use compo- nents, among other applications. In the case of thermo- moulded glassy biocomposites, the improvement of mechanical performance is correlated to the basic knowl- edge of the correlations between elastic properties and microstructure attributes. In several composite-manufacturing processes, com- posites are usually characterised by random microstruc- ture (de Jong et al., 2009). This is, for example, the case of thermo-moulded starch–zein composites where both phases percolate in all space directions (Guessasma et al., 2009). The effective properties of these composites were studied as function of the intrinsic properties neglecting the possible effect of imperfect interfaces. Recently, the tai- loring of the elastic properties of such composites has been proved to be dependent on the intrinsic properties, spatial arrangement of phases as well as on the interface behav- iour (Rjafiallah et al., 2009). Local measurement confirmed that the interface in the starchy material is imperfect (Guessasma et al., 2008a). The present work is dedicated to the study of effective Young’s modulus of a typical biopolymer composite under the hypothesis of an imperfect interface effect. The present work is divided into four main parts. The first part gives an 0167-6636/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.mechmat.2009.12.001 * Corresponding author. Address: Faculty of Aerospace Engineering, TU Delft, The Netherlands. Tel.: +31 15 278 1382; fax: +31 15 278 5337. E-mail addresses: D.H.Bassir@tudelft.nl, david.bassir@utbm.fr (D.H. Bassir). Mechanics of Materials 42 (2010) 344–353 Contents lists available at ScienceDirect Mechanics of Materials journal homepage: www.elsevier.com/locate/mechmat