The Locomotive - Lighthouse Survival Blog

1893. J THE LOCOMOTIVE 19
The column hciuled " net width " gives the width of the piece after the diameter of
the hole ha.s been deducted, and the "net sectional area" is obtained by multiplying the
net width by the thickness. It will \)0 noticed that the iron shows a material increase
in strength as the tcmi)crature ri.ses. At 78° it broke at 52,300 lbs. per square inch of
original section, but at 575° an additional stress of seven tons per square inch was re-
quired in order to break it. The iron even .shows a gain in strength^etween 575° and
'.100°, but it is doubtful if all pieces woidd show a gain in strength at this place, for at
925° we are approaching a red heat. The steel also showed a pronounced ^ain in
strength per square inch of original section, as the temperature rose from 68° to 575°,
but after this point was reached it fell off again, though even at 925° it remained materi-
ally stronger than at 68°. A marked and unexpected falling off in the contraction of
area was observed in both the iron and the steel. This is so pronounced in the case of
the steel that if tlie strain is computed per square inch of fractured area the steel appears
to grow continuously weaker as the temperature ri.ses. The lessening of the contraction
is not so marked in the iron test pieces, so that these exhibit an increa.sing strength
whether the original or the fractured area is considered. Although these experiments
were not numerous enough to serve as the ba.sis of any very broad generalizations concerning
the effect of temperature on the strength of iron, we considered that they showed
Temperature
Test.
of
The Tensile Strength of Steel at Various Temperatures.