The Birmingham age-herald. [volume] (Birmingham, Ala.) 1902-1950, 1903-03-22
STEEL GROWS TIRED AND
BREAKS VERY SUDDENLY

| out takes place-that Is what we must
know In order to prevent accidents.
The experiments at the Institute of
Technology In the strength of materials
were begun by Professor Gaetano LAMA,
who is now in charge of the mechanical
engineering department, more than twen-
ty years ago. What was done before then
was worked out on small scale the
theory being that If a piece of wood two
inches square showed certain effects from
a given test, another piece two feet
square. for example. would show similar
effects In a proportionate degree. Pro-
fessor LAMA, pointing out that such in
ferences were likely to be incorrect on
account of the varying quality of diner-
ent materials. began experimenting with
full-sized beams and shafts and pillars
such as are used in the actual construc-
tion OF buildings and of machinery.
Repeated Stress.
The methods of discovery In use In the
institute laboratories are both interesting
and surprising They disclose one general
fact very plainly; that the trial which
structural materials above all others cam
not stand is the trial of repeated stress"
In other words, if the Brooklyn bridge,
or any other steel structure like it, were
loaded completely full of the heaviest
trains and vehicles 1t was designed to
carry and this load were to remain per-
manently upon II without ever being
moved away, the bridge would last for
ever-barrng rust. But put these same
weights in motion, so that the entire
structure trembles with their going, and
the result is very different indeed. be-
cause each member, instead of bearing
a steady fixed weight, undergoes a sue
cesson of little jerks answering to the
vibration of the bridge as a whole. The
brake-rod under car works under SIM
ilarly adverse conditions, for each time
the breaks are put on they receive
strain one way and each time they are
released there Is a strain in the opposite
direction.
| The case of the steamship shaft that
breaks Unexpectedly Is somewhat differ
| ent. Here a great steel rod-for such it
| may be regarded-is turned rapidly in
one direction by the engine at the same
time that It is twisted in the opposite
direction by the resistance of the water
against the propelling screw. Being sup
| ported at either end, the shaft has
| tendency to sag the least bit somewhere,
even though it is held up by bearings,
and 1t is evident that wherever 1t bends,
! even ever so little, its fibres are alternate
| ~ stretched and compressed. Now If the
| bearings which secure 1t are n IT in proper
| line, the fibres are continually undergoing
alternate stretching and compression,
| and the result Is that, after certain
| number of revolutions of the engine, the
rod finally breaks.
| The plan of the institute of Technology
| is, In other words, to bring about the very
| same conditions in the laboratory as
actually occur in practice. 1t runs ma
| chimes for no other purpose than to de-
| liberately break things while the stu
dents and instructors keep tabs on the
results Finally. after long series of
experiments, the rules governing these
breakages will appear. If shaft of a
certain diameter, subjected to a given
strain. breaks after so many turns. and
one of twice the size under the same
strain after so many more and so on for
different sizes and different strains, then.
ultimately. competent surveyor on dis
covering that vessels machinery was
out of proper line. could, by measure
ments and calculations establish the
possibility of accident and either con-
denim suspected parts before their break
ing time arrived. or at least see to II that
they were thoroughly and accurately test
ed. The same rules could be applied to
the shafting of elevator machinery to
locomotive axies, to the thousand and