The sun. [volume] (New York [N.Y.]) 1833-1916, 1898-03-06

will cause congratulation among Yale men.
FA UE ~ I~NANIMATE THINGS.
about the Only Thing That Doesn't Got Tired
by Use IL Cast Iron.
From the Phiiadeiphia Record.
Aconstitutionally lazy man is. in ordinary con.
versation. commonly said to have been born
tired" This capacity for becoming fatigued by
slight %cxertion was always supposedto be cherac-
teristic of animate bodies; but the scientists,
who have been probing with their microscopes,
spectroscopes, and other scopes into the molec.
ular constitution of steel or iron and testing
their strength under varying conditions, have
discovered that even such inanimate objects
grow tired, and positively lose much Of their
strength and elasticity by long-continued sub
lection to quite moderate stress or vibrations.
When allowed to rest for q timo these metals
recuperate and recover their pristine strength.
This observation has been made so often. and
has been SO thoroughly proved by repeated lab
oratory tests, not only on q small scale, con-
Quoted with the greatest care and accuracy.
but also upon a large scale. with full-sizcd
bridge members and other commercial forms of
steel and iron. that it has become generally nc
cepted by engineers as q positive and well-un-
derstood law.
The old saying that there is an exception to
every law has again been verified by a re:
port OF the Committee on Science and Arts of
the Franklin Institute. upon whose recon.
mendation the city of Philadelphia has recently
n msa nl sdr the sn 'o orIri nGp'' in 1Ssafx bffemin proy ana
that cast iron is an exception to this law. Two
years ago the announcement was made ut a
Engineers that cast iron when subjected to long
continued shocks or vibrations increased in
strength. the explanation being given that the
gain in strength is due to the release Of internal
cooling strains. owing to o rearranGement OF the
molecules under the influence Of shock. This
is. in effect. a process of mechanical annealing
analogous to annealing by heat. Upon a test
ing machine over 1000 test bars were broken.
or vibrations in a revolving iron barrel; the
other bars. cast in the same moulds and from the
the bars that had been subjected to Shock were
found to be stronger than their companions.
tho average hcing over 10, per cent, and the
bies. being nearly 20 per cent. This surprising
statement created y sensation and excited wide.
The tests were repeated by expert ironmasters
everywhere. and the experiments subsequently,
published by many observers not only corrob-
of these independent Investigations in most
cases far exceeded the original claims.
great number Of tests showing large gains in
most cases; and the maximum gain in strength
s sSsH 100 f per cent OF the r 2hrlsii n7es fissff BY o % tSs
committee extended over a period of moro
than a year, and no evidence was offered; or
loUtu ilbtl i'ioiiEt SS"tbL iiltdtl tltuD
such. tests had eyer been previously made.
On tho contrary. these experiments explained
for the first time the certain peculiar and here
tofore mysterious ply steal properties of cast
iron.
improved by age. and over thirty years ago
Sir Frederick. Bramwell. then the director Of
the metallurgical work a. Woolwich Arsenal,
tested by him were immensely stronger than
precisely similar guns made and tested within
thirty days after having been cast. TESTS to
destruction" Of both the old and the new guns
were then ordered to be made: and IT was found
that a gun which had been Kept for six years
i isas H. Of ' time. did fpG not burst Est" aft ksp ha ing sfs i Seee
Bramwell reported in 1860 that guns of tho
same description tried thirty days after cast.
Ing S sH r ons at az Sgse sbtghty,f@ouTE!!hhb and rs one at
said he, Showed that 1t was not impossible that
tho superior manner n which guns cast some
work as COMPARED with those OF modern make
was not due. as was commonly supposed. to the
hut to their having been cast n long time. and to
tho strains that existed in then, from unequal
contraction Internationally cast having ceased,
ing n prejudicial ~efoct."
The recent discovery. 50 fully ,corroborated
Franklin Institute. proves the correctness of
these assumptions. But it. does much more
tatively the force and value of these internal
strains In cast iron, but the Important discovery
mas been maze mat snch strains can be quickly
removed by subtccting castings to shocks or
vibrations. Steel and forged iron are inner
emily different metals. and are differently treat
ed, from east iron In the process of manufacture.
1t is, therefore, not incomprehensible that the
effect of vibration upon steel and iron, is to
cause fatigue and consequent weakening of
the metal. Lord Kelvin thirty years ago d.
rected attention to the fact that iron wires kept
h In tSTSi Sniie GaIiGf Iersh3Iv d nfFsp tb 5eS E senG. BE-
rest, and It has recently been shown that owing
to molecular rearrangement which occurs dur:
ing rest II al. overstrained bar the modulus of
elasticity will rise 10 per cent. after three
weeks holiday: This remarkable statement
was made by Sir BENJAMIN Bake in his Prssi-
denIfal address two years ago at the meeting
of the English, Institution OF Civil Engineers.
II is naturally to be expected that many facts
arc still 10 be learned about the physical quail
ties OF steel, because Its application to very
large engineering work Is of comparatively re-
cent origin; but II was said at the meeting Of
the mining engineers two years ago that 1t was
long thought that practically all properties OF
cast iron were known and that the discovery OF
east Iron at this late day was, therefore, a com.
plete %surprise to tho mctallurgical world. The
Franklin Institute committee In its report says:
The principal result has boon to largely mp.
IeCt OF cast iron. and whore formerly 1t was con-
sidercd essential that small or light castings
must be protected from shock, 1t Is now be.
n andre rel heSs IH of tR %fiy i Ps SgnGr soGIjn 9sre sfstlns ed
Judlclous treatment In this way"
Recent specifications for certain castings re-
CURED TO be made Of iron OF guaranteed
strength contain n new clause STIMULATING that
tho test bars must not be subjected to shock ina
tumblinE barrel or otherwise have their strength
Increased by mcchnhicaI vibrations. A practi-
raj result OF this Investigation will BIO TO give In.
creased confidence In the use of cast iron for
structural ana other purposes where the metal
is subject 10 vibrations of moderate shocks.