Experimental Characterisation of Tyre Indentation by Simulated Runway Debris S. Nguyen*, E. S. Greenhalgh*, L. Iannucci*, S. Longstaff*, R. Olsson † and P. T. Curtis ‡ *Department of Aeronautics, Imperial College, London, SW7 2AZ, UK † Swerea SICOMP AB, Box 104, SE-431 22 Mo ¨ lndal, Sweden ‡ Physical Sciences Department, Dstl Porton Down, Salisbury, Wiltshire, SP4 0JQ, UK ABSTRACT: As part of an investigation to assess the impact threat posed to vehicles by tyre-lofted runway debris, it is important to gain a quantitative understanding of the interaction between inflated tyres and foreign objects. In this paper, experiments involving indentation of an inflated tyre to represent over-rolling of a foreign object were used to estimate the energy that could be transferred to the over-rolled object. The maximum kinetic energy that a 24-mm diameter spherical stone could potentially attain from such an indentation-related loft mechanism by a tyre inflated to 0.34 MPa (50 psi) was 20 J. KEY WORDS: debris, digital image correlation, indentation, lofting, runway, tyre Introduction This paper concerns the characterisation of the indentation behaviour of aircraft tyres. The purpose of this study was to collect aircraft tyre response data to develop and validate accurate tyre models for finite element simulations of runway debris lofting. The digital image correlation (DIC) technique was used to measure both the in- and out-of-plane displacement and strain fields of the tyre. The study formed part of an investigation to provide vehicle structural designers with a more accurate assessment of the risk of impact damage that may occur from stones and debris thrown up by tyres. Knowledge of the likely speeds and trajectories of lofted stones will aid damage tolerant design that aims to minimise the vehicle weight. The investigation also seeks to understand the physics underlying the lofting mechanisms, so that the effect of varying certain parameters can be predicted. Previous simulations of runway debris lofting have used a simple cylindrical solid tyre with material properties taken from the literature [1]. These models were validated by performing experiments with a solid impactor and consequently the pressurisation in the tyre was not taken into account. This pre- liminary study was able to identify potential loft mechanisms for an idealised tyre, but a more realistic tyre model was needed to represent the complex geometry and material properties associated with real aircraft tyres. Construction of an aircraft tyre Aircraft tyre construction can take two main forms, cross (bias) ply or radial ply. Most aircraft tyres are cross ply [2], which use layers of nylon reinforcement that run diagonally across the carcass to form a lattice pattern. Radial tyres have the reinforcement running perpendicular to the tyre centreline, giving them a longer tread life but a harder ride on rough surfaces at low speeds [3]. The curved surface that forms the intersection between the tread and the sidewall is known as the shoulder of the tyre [4]. Around the circumference, the tread often has moulded grooves to increase traction and grip by removing water between the tread and runway during wet conditions. Measurement of tyre behaviour The greater sophistication of tyre models has led to the need for more detailed material property data and reliable measurement methods. Recent advances in instrumentation technologies have explored the possibility of obtaining accurate information about the forces applied to tyres during operation. For instance, an ultrasonic sensor mounted inside a tyre could be used to obtain real-time information about the vertical tyre deflection [5]. An alternative tech- nique involves using capacitive-resistive sensors embedded within the tyre tread [6]. However, robust miniature sensors are still in the early stages of development. Experimental data used for finite Ó 2010 Blackwell Publishing Ltd j Strain (2011) 47, 343–350 343 doi: 10.1111/j.1475-1305.2009.00704.x An International Journal for Experimental Mechanics