Thermal Conductivity Properties and Heat Transfer Analysis of Multi-re-entrant Auxetic Honeycomb Structures P. INNOCENTI AND F. SCARPA* Department of Aerospace Engineering, University of Bristol, BS8 1TR Bristol, UK ABSTRACT: In this work, the static and transient conductivity properties of a novel centersymmetric honeycomb structure are evaluated using analytical and finite element (FE) models. The honeycomb structure features a unit cell geometry allow- ing in-plane auxetic (negative Poisson’s ratio) deformations, and geometry para- meters to be used to design the honeycomb configurations for multifunctional applications. The equivalent thermal conductivity along the two principal directions of the multi-re-entrant unit cell is calculated using a theoretical approach based on Fourier’s law and electric-thermal analogy. To validate the theoretical models, a FE analysis has been carried out on periodic unit cells under thermal steady-state conditions, showing an excellent agreement with the theoretical results. A transient thermal analysis, considering convection and radiation, has been performed numer- ically to evaluate the possible use of this honeycomb configuration for sandwich panels in thermal protection systems. Parametric analysis on the thermal conductiv- ity and maximum temperatures acquired during convectionradiation is performed vs. the nondimensional geometry parameters of the honeycomb cell. The auxetic honeycomb configurations show higher out-of-plane conductivity, strong in-plane thermal anisotropy, and the lowest peak temperatures during heat transfer between the bottom and top faces of honeycomb panels. KEY WORDS: auxetic, honeycomb, conductivity, transient and steady state, radiation. INTRODUCTION M ULTIFUNCTIONAL HONEYCOMBS HAVE been recently developed for combined heat transfer and structural integrity, for a variety of mechanical and aerospace applica- tions. As an example of harsh operative conditions requiring both high thermal and mechanical performance, hypersonic flight vehicles such as the Space Shuttle orbiter are subjected to severe aerodynamic heating during flight missions, requiring a thermal *Author to whom correspondence should be addressed. E-mail: f.scarpa@bris.ac.uk Figures 1–3, 5, 7, 8 and 1114 appear in color online: http://jcm.sagepub.com Journal of COMPOSITE MATERIALS, Vol. 43, No. 21/2009 2419 0021-9983/09/21 241921 $10.00/0 DOI: 10.1177/0021998309344636 ß SAGE Publications 2009 at University of Bristol Library on September 4, 2015 jcm.sagepub.com Downloaded from