In-plane mechanical and thermal conductivity properties of a rectangular–hexagonal honeycomb structure A. Bezazi a , C. Remillat b , P. Innocenti b , F. Scarpa b, * a Laboratoire de Me ´canique & Structures (LMS), BP. 401 Universite ´ 08 Mai, 1945 Guelma, Algeria b Department of Aerospace Engineering, University of Bristol, Queens Building, University Walk, BS8 1TR Bristol, UK Available online 23 August 2007 Abstract In this work, the mechanical in-plane and thermal conductivity properties of a novel cellular configuration for multifunctional appli- cations are described using analytical and finite element models. The hexagonal–rectangular honeycomb proposed allows one more geo- metric parameter in the unit cell compared to the classical hexagonal honeycomb configurations. The added geometric entity provides enhanced in-plane flexibility and tailoring of properties, such as the in-plane Poisson’s ratio, which can become negative under specific geometry configurations. The thermal conductivities are modeled using the electric-thermal analogy, allowing closed-form solutions for the thermal properties of the honeycomb. Comparison between analytical models and finite element simulations provides good conver- gence of results. Crown Copyright Ó 2007 Published by Elsevier Ltd. All rights reserved. Keywords: Honeycomb; Auxetic; In-plane; Mechanical; Thermal conductivity 1. Introduction Since the maiden flight in November 1940 of the De Havilland Mosquito aircraft, sandwich constructions with honeycomb core have become a widespread structural fea- ture in aerospace, naval and packaging applications. Devel- opments in the field of rapid prototyping, resin transfer moulding and composite manufacturing have led also to the design of novel honeycomb concepts differing from the classical hexagonal centresymmetric shapes used in structural sandwich components. Moreover, the use of cel- lular structures as microactuators and displacement ampli- fiers has been suggested in different MEMS designs [1], with focus on the in-plane mechanical properties of configura- tions providing extreme properties [2]. Between cellular configurations exhibiting anomalous characteristics, special mention should be made on the auxetic ones [3,4], initially developed from re-entrant configurations of the classical hexagonal honeycomb topology [5,6], and from non-cen- tresymmetric or chiral symmetry [7,8]. Other configura- tions featuring anomalous mechanical properties are Poisson-shear cellular structures [9], combined anisotropic and negative thermal expansion behaviour [10], pure Pois- son shearing [11], and star-shaped honeycomb assemblies [12]. The thermal properties of honeycomb structures are also important in view of specific applications such as thermal heat sinks in the nacelles of aeroengines, or conversely heat shielding technologies [13]. Although aluminium-based and non-metallic carbon–metallic interwowen cellular struc- tures have been proposed to overcome low thermal con- ductivity in non-metallic cores [14], additional thermal management capabilities could be achieved by tailoring the geometry of honeycomb configurations. Recent devel- opments in that sense occurred in the field of multifunc- tional honeycombs, involving optimisation of the performance of cellular structures in view of thermal management and structural integrity [15–18]. 0263-8223/$ - see front matter Crown Copyright Ó 2007 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.compstruct.2007.08.005 * Corresponding author. Tel.: +44 117 9289861; fax: +44 117 9272771. E-mail addresses: ar_bezazi@yahoo.com (A. Bezazi), f.scarpa@bris. ac.uk (F. Scarpa). www.elsevier.com/locate/compstruct Available online at www.sciencedirect.com Composite Structures 84 (2008) 248–255