Test method Towards the development of laser shock test for mechanical characterisation of fibre/matrix interface in eco-composites Am  elie Perrier * , Romain Ecault, Fabienne Touchard, Maria Vidal Urriza, Jacques Baillargeat, Laurence Chocinski-Arnault, Michel Boustie Institut Pprime, CNRS-ISAE-ENSMA-Universit e de Poitiers UPR 3346, D epartement Physique et M ecanique des Mat eriaux, ENSMA, 1 Avenue Cl ement Ader, 86961 Futuroscope Chasseneuil, France article info Article history: Received 16 February 2015 Accepted 3 April 2015 Available online 11 April 2015 Keywords: Hemp yarn composite Laser shock Interface Micro-damage abstract This paper deals with the possibility of using the laser shock test for studying the adhesion between fibre and matrix in composite materials. Single hemp yarn in epoxy matrices - a fully synthetic one, Epolam 2020, and a partially bio-based one, Greenpoxy 56 - specimens have been tested. The water sorption effect on interfacial adhesion quality has been studied. Two different types of damage induced by laser shock have been observed: resin cracks appear only for high laser intensity levels, and specific cone-shaped interfacial damage appears for lower intensity values. The reproducibility of the threshold value evaluation has been demonstrated for the two resins. A numerical simulation by finite elements has also been performed to enhance the understanding of laser shock wave propagation in such samples. These preliminary results demonstrate the ability of the laser shock test to study and quantify the mechanical quality of yarn/matrix interface, which is needed to help design of such composites. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Eco-composites are nowadays increasingly used for their numerous advantages [1]. However, one of the main problems when considering these materials is the weak fibre/matrix adhesion between the hydrophilic reinforce- ment and the hydrophobic matrix. This “mismatch” leads to a lack of compatibility between natural fibres and polymers. It causes poor adhesion between fibres and matrix, which reduces mechanical properties. Adherence can be seen as the sum of different contributions: interac- tion forces (like van der Walls), chemical bonds, residual stresses, etc. The crucial issue of adhesion between natural fibres and polymers has been examined in several review papers on green composites [2e5]. For example, Ku et al. demonstrates that the tensile properties of natural fibre reinforced polymers (both thermoplastics and thermosets) are mainly influenced by the interfacial bonding between the matrix and the fibres [2]. La Mantia et al. presented the role of different adhesion promoters, additives or chemical modifications that can enhance the interfacial adhesion [3]. To better integrate eco-composites on an industrial scale, it is necessary to improve the interfacial adhesion between natural fibres and polymers. Indeed, the best performance strength of a composite material is achieved when the ability to transfer stress across the fibre-matrix interface is high, i.e. when adhesion is the best. Therefore, the char- acterisation of fibre/matrix adhesion is an essential point for composite materials optimisation. Different types of tests are classically available, such as the fibre indentation test (push-out), the fibre extraction test (pull-out), the fragmentation test or the microbond test. In literature, there are plenty of papers dealing with these tests on synthetic fibres, for example on glass fibre with epoxy * Corresponding author. Tel.: þ33 (0)5 16 08 00 80; fax: þ33 (0)5 49 49 82 38. E-mail address: amelie.perrier@ensma.fr (A. Perrier). Contents lists available at ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest http://dx.doi.org/10.1016/j.polymertesting.2015.04.003 0142-9418/© 2015 Elsevier Ltd. All rights reserved. Polymer Testing 44 (2015) 125e134