CRANFIELD UNIVERSITY A. J. LAMB EXPERIMENTAL INVESTIGATION AND NUMERICAL MODELLING OF COMPOSITE-HONEYCOMB MATERIALS USED IN FORMULA 1 CRASH STRUCTURES SCHOOL OF APPLIED SCIENCES PhD THESIS CRANFIELD UNIVERSITY SCHOOL OF APPLIED SCIENCES PhD THESIS Academic Year 2004-2007 A. J. LAMB Experimental Investigation and Numerical Modelling of Composite-Honeycomb Materials used in Formula 1 Crash Structures Supervisor: Professor A. K. PICKETT January 2007 This thesis is submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy. © Cranfield University 2007. All rights reserved. No part of this publication can be reproduced without written permission of the copyright owner. ABSTRACT This thesis has investigated composite-honeycomb sandwich materials commonly used in Formula 1 nosecone structures. Experimental work has investigated their failure behaviour under static and dynamic crash loading, from which new constitutive failure laws for implementation in the explicit Finite Element code PAM-CRASHTM have been proposed. An investigation using an improved Arcan apparatus has been conducted to establish the mixed shear-compression properties of the honeycomb. An investigation has also been performed to establish relationships between in-plane deformation and out-of- plane compression properties. These relationships have been identified and successfully implemented into a honeycomb solid element material model available in PAM- CRASHTM. A further investigation to represent honeycomb using geometrically accurate shell representation of the honeycomb has also been presented. This model was shown to reproduce trends observed during testing. The composite skin material has also been experimentally investigated and presented. This investigation made use of digital image correlation to examine the onset of intra- laminar shear failure mechanisms, from which a non-linear damage progression law was identified. This law was successfully implemented into the Ladevéze damage model in PAM-CRASHTM for composite material modelling and has been shown to improve the representation of in-plane shear damage progression and failure. A series of experimental investigations to examine the energy absorbing properties of the sandwich have been conducted and presented. These investigations include three point bend flexural testing and edgewise impact loading. Failure mechanisms in the skin and core have been identified for each loading case. Experimental findings were used to assess the capability of PAM-CRASHTM for sandwich material modelling. This investigation has highlighted deficiencies in the material models when representing the sandwich, specifically with the existing composite skin and honeycomb models. Improvements introduced to the core and skin material models have shown some improvement when representing sandwich structures. i ACKNOWLEDGEMENTS I wish to thank my supervisor Professor Anthony Pickett. His guidance has been invaluable towards to production of this work and success at the 2005 IOM3/SAMPE student presentation contest in London. I wish him all the best in his new role at ESI and at Stuttgart. There are my fellow PhD research colleagues, who have both finished and begun their working careers, Dr. Gavin Creech and Dr. Michel Fouinneteau who welcomed me into the group and helped me with many issues encountered during this work. A special thank you also goes to Jim Hurley, Ben Hopper, Michael May, Mathieu Colin De Verdiere, Fabien Chaudoye and all those who I have had the pleasure of working with during this research. I would also like to thank the assistance of Mark Oxley and those at Honda Racing F1 who provided valuable information and the test samples used throughout this research. In addition, I wish to thank the EPSRC for funding this research and thus giving me the opportunity to pursue a PhD. Finally there are my family and friends, who have provided support and guidance over the years. Thank you! ii TABLE OF CONTENTS 1 Introduction ........................................................................................................... 1 1.1 Aims and Objectives......................................................................................... 2 2 Literature Review.................................................................................................. 5 2.1 Formula 1 Structures and Crash Testing .......................................................... 5 2.1.1 A Brief History of Motorsport Safety and Materials................................ 6 2.1.2 BAR-Honda 006 Frontal Impact Structure............................................... 7 2.1.3 Design of a New Nosecone .................................................................... 11 2.2 Composite-Honeycomb Sandwich Materials ................................................. 12 2.2.1 Honeycomb Materials............................................................................ 12 2.2.2 Composite Materials............................................................................... 26 2.2.3 Sandwich Structures............................................................................... 40 2.3 Finite Element Analysis ................................................................................. 47 2.3.1 FE in Automotive Applications.............................................................. 48 2.3.2 Honeycomb Modelling........................................................................... 48 2.3.3 Composite Modelling............................................................................. 52 2.3.4 Composite Sandwich Modelling ............................................................ 57 2.4 Summary of Literature Review ...................................................................... 59 3 FE Modelling of Composite-Honeycomb Materials ........................................... 62 3.1 Honeycomb Core Modelling Requirements................................................... 65 3.2 Composite Laminate Skins............................................................................. 67 3.3 Sandwich Structure......................................................................................... 69 3.3.1 Mode-I Crack Propagation ..................................................................... 69 3.3.2 Sandwich Flexural Properties................................................................. 73 3.3.3 Wedge Impact Testing............................................................................ 73 3.4 Nosecone Representation............................................................................... 76 3.5 Section Summary............................................................................................ 76 4 Experimental Procedures and Results ................................................................. 78 4.1 Digital Image Correlation............................................................................... 78 4.1.1 Benefits of Digital Image Correlation .................................................... 80 4.2 Test Samples................................................................................................... 82 4.3 Honeycomb Experimental Testing ................................................................. 82 iii 4.3.1 Principal Direction Compressive Properties........................................... 83 4.3.2 Pre-Crushing In-Plane effect on Out-of-Plane Properties ...................... 89 4.3.3 Testing Procedure and Results for the Multi-axial Loading of Honeycomb Material ............................................................................................ 102 4.4 Composites Sample Testing......................................................................... 111 4.4.1 Tensile Properties of the Composite in the Fibre Direction ................. 112 4.4.2 In-Plane Shear and Cyclic Shear Loading............................................ 115 4.4.3 Compressive Loading........................................................................... 121 4.5 Composite Sandwich Structure .................................................................... 124 4.5.1 Flatwise Loading Test .......................................................................... 124 4.5.2 Cracked Sandwich Beam Testing......................................................... 128 4.5.3 Three-Point Bend Flexural Testing ...................................................... 135 4.5.4 Axial and Oblique In-Plane Sandwich Loading................................... 139 4.6 Section Summary.......................................................................................... 154 5 Computational Modelling of Sandwich Materials ............................................ 157 5.1 Honeycomb Modelling................................................................................. 157 5.1.1 Macro-Scale Modelling........................................................................ 158 5.1.2 Meso-Scale Modelling Investigation.................................................... 167 5.2 Laminate Modelling..................................................................................... 177 5.3 Sandwich Modelling..................................................................................... 181 5.3.1 ‘T’ Direction Sandwich Loading.......................................................... 181 5.3.2 Crack Propagation Modelling............................................................... 182 5.3.3 Three-Point Bending Modelling..........................................................