A History of Research and a Review of Recent Developments
A History of Research and a Review of Recent Developments
A History of Research and a Review of Recent Developments
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References 69<br />
in Los Angeles Harbour, USA, at Christmas 1976, <strong>and</strong> in the Norwegian<br />
tanker King Haakon VII.<br />
3.5 THERMAL FLASH<br />
A final characteristic <strong>of</strong> explosions must be examined before we end this brief<br />
survey.<br />
Structural damage <strong>of</strong> a quite different nature can result from the extremely<br />
high temperatures created by the fireball <strong>of</strong> a nuclear explosion. The maximum<br />
fireball diameter for a 1 megaton bomb yield is about 1.4 miles, <strong>and</strong> for a 10<br />
megaton weapon it would be 3.4 miles. The thermal flash from bombs <strong>of</strong> this<br />
magnitude can cause changes to properties <strong>of</strong> materials, <strong>and</strong> can weaken the<br />
resistance <strong>of</strong> metal structures that contain material <strong>of</strong> relatively low melting<br />
point. It might well be that an aluminium alloy structure would be robust enough<br />
to withst<strong>and</strong> the shock pressures <strong>and</strong> blast winds from a large nuclear explosion,<br />
but be seriously weakened because <strong>of</strong> a reduction in pro<strong>of</strong> strength <strong>of</strong> the material.<br />
For a low yield nuclear explosion, heat pulses at a range <strong>of</strong> 1000ft from<br />
ground zero are <strong>of</strong> the order <strong>of</strong> 50 to 150 cals/cm 2 . A heat pulse <strong>of</strong> 1000 cals/<br />
cm 2 is about equivalent to a maximum surface temperature in structural<br />
aluminium <strong>of</strong> 250° C, <strong>and</strong> for aluminium plating between 0 <strong>and</strong> 0.5 inches<br />
thick, this will lead to a reduction in strength by annealing. If a heat pulse <strong>of</strong><br />
100 cal/ cm 2 is applied to the front face <strong>of</strong> a slab inch thick, the front <strong>and</strong> back<br />
faces will have both reached 250° C after 2 seconds. However, if the slab is<br />
inch thick, it has been shown by Parkes [3.20] that the behaviour is different.<br />
The front face, after reaching a maximum temperature <strong>of</strong> 200°C, falls gradually<br />
in temperature to reach a final value <strong>of</strong> 120°C after 2.5 seconds. Meanwhile the<br />
back face rises more gradually in temperature to reach the same final value.<br />
By analysing structural members as a number <strong>of</strong> laminations, each with<br />
varying strain <strong>and</strong> properties, Parkes showed that it is possible to estimate the<br />
residual stress distribution after a period <strong>of</strong> uneven cooling. A high residual<br />
tensile stress means that a subsequent tensile loading <strong>of</strong> the member will cause<br />
failure at a relatively lower applied stress. Care should therefore be taken to<br />
inspect apparently undamaged aluminium alloy structures after a nuclear<br />
explosion to check for minor deflection <strong>and</strong> distortions that signify a noticeable<br />
reduction in structural strength.<br />
3.6 REFERENCES<br />
3.1 Fletcher, R.F. (1968) Characteristics <strong>of</strong> liquid propellant explosions, Prevention<br />
<strong>and</strong> Protection against Accidental Explosion <strong>of</strong> Munitions, Fuels <strong>and</strong> Other<br />
Hazardous Mixtures, New York Academy <strong>of</strong> Sciences, 432.<br />
3.2 High, R.W. (1968) The saturn fireball, Prevention <strong>and</strong> Protection against<br />
Accidental Explosion <strong>of</strong> Munitions, Fuels <strong>and</strong> Other Hazardous Mixtures, New<br />
York Academy <strong>of</strong> Sciences, 441.