If prejudicial stresses exist in the
metal of a hoop before it is put in its place, then, when the gun is
fired, if it had been shrunk on with the degree of tension usually
allowed, the layer situated in the internal radius will be extended
beyond admissible limits, thereby causing the resistance of the gun to
be less than that prescribed.[4]
[Footnote 4: When the inner tube is strengthened by means of
wire, the initial or natural stresses in the latter may be
neglected on account of its thinness; but when the thickness of
the hoops is reduced, and the number of layers thereby increased,
then the value of the initial stresses in these hoops is a very
important factor with respect to the decrease or increase Of the
powers of resistance of the gun.]
It is evident, from what has been said, that in order to determine
precisely the resistance of hollow cylinders to internal pressures, and
to make the correct calculations for hooping tubes, it is absolutely
necessary to know whether internal initial stresses exist in the tube
and in the hoops, and to ascertain what their nature and intensity may
be--that is to say, whether they are useful or detrimental; yet it is
incontestable that in the construction of modern ordnance no attention
has been paid to the investigations indicated.
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