Citation

Nguyen SN, Greenhalgh ES, Olsson R, Iannucci L, Curtis PT. Int. J. Impact Eng. 2010; 37(5): 502-514.

Copyright

(Copyright © 2010, Elsevier Publishing)

DOI

10.1016/j.ijimpeng.2009.11.006

PMID

unavailable

Abstract

Stones and foreign objects on runways or roads can cause considerable impact damage to vehicles and high repair costs if thrown up by the wheels onto vulnerable structures. Damage tolerant design of vehicles such as aircraft requires a methodology to predict the likelihood of critical impacts occurring over the operational lifetime of the vehicle. Such information could be provided by examination of the damage caused in previous incidents, so that the locations of severe impact damage can be mapped out. In practice, the limited availability of such detailed records makes this approach very difficult to utilise. Additionally, such impact data would have fairly limited use in scenarios involving different aircraft and runway conditions. An alternative approach relies on understanding the complex lofting processes of objects by wheels, which may be considered as an impact event given the high speed at which a tyre may contact the object. This paper aims to develop knowledge about the physical processes underlying the lofting of stones by aircraft tyres, and report on the conditions that lead to the most critical impact events.

The influence of various factors affecting the severity of runway debris lofting mechanisms was investigated by performing numerical simulations and drop-weight impact experiments to assess the likelihood of a stone impact. Geometrical characterisation of stones collected from airfields led to a generic model of a tyre rolling over stones of various shape with different overlaps, orientations, and densities. In numerical simulations of a 0.4 m diameter aircraft tyre rolling at 70 m/s, a 10 mm diameter spherical stone was lofted at a maximum vertical speed of 35 m/s. For equivalent mass prolate spheroid stones, the loft speeds were 11-34% lower depending on the stone orientation. Objects with flat surfaces exhibited different lofting mechanisms and lower angular velocities. The conditions most conducive to stone lofting were very stiff, small diameter, sharp cornered tyres rolling on ground with a high friction coefficient over spherical stones such that just under half the stone diameter was covered by the tyre. The stone loft speed was approximately proportional to the square root of the tyre tread stiffness. Finally, tyre tread grooves could throw stones upwards at the tyre-ground separation speed, which was 17 m/s for the conditions mentioned earlier.