ABSTRACT
The purpose of this paper is to better understand the strength of the Buncefield explosion by attempting to quantify the external pressures necessary to de-bead/deflate vehicle tyres. A series of tyre tests were designed and conducted where a tyre was mechanically pushed off its rim and the force required to de-bead and deflate the tyre was measured as a function of loading rate and inflation pressure.
The inflated tyre was positioned between two specially designed plates in a hydraulically-driven test frame. The loading plate surfaces were contoured to match the external shape of the tyre sidewalls. Tests were conducted with a range of internal tyre pressures and frame loading rates.
The tests performed at the highest loading rate (60 mm/s) with 30 or 35 psig (207-241 kPa) initial internal pressure are of the most interest. These tests took about 2 s to run, with the depressurization occurring in the last 0.1 s. A peak force of approximately 137-147 kN was required to de-bead/deflate the tyre. This force translates into a sidewall surface pressure of about 800-870 kPa, based upon the tyre-plate contact loading area of 0.17m2 per loaded side.
Actual loading times would have been much smaller (~ 2 to 5 ms) if the explosion had been a detonation. Transient effects make it difficult to predict exactly what external pressure would be required to de-bead a tire for detonation-based loading, but the present results indicate that the required external pressure would be several times the inflation pressure.
Keywords: Buncefield, Pressure, Tyre, De-beading.
