172 APPLIED MECHANICS 
the altered length of a 1 inch length on the specimen before testing, and 
this length contains the 
fracture near its centre, oe 
The other lengths, in order, $5 
are the altered lengths of .& 
S 
2, 4, 6, 8, and 10 inch »04 Vi 
lengths respectively on the 803 \ 
specimen before testing, . Papen 4 mies 
and the fracture is approxi- 
mately in the middle of 0-1 
each of these lengths. 5 
The altered lengths of the oC (2) (3) (4) (5) 16) : 
original inch lengths num- Inches of Lede 9) (10) 
bered (1), (2), (3), ete., are Fig. 245. 
given above the specimen 
in Fig. 244, and the elongations of these inch lengths are plotted 
in Fig. 245. 
It will be seen that the elongation per inch is fairly uniform, except 
for about 1} inches on each side of the fracture, and the elongation in 
the immediate neighbourhood of the fracture is much greater than in any 
other part of the specimen. 
Coming next to the actual elongations and the elongations per cent. 
of length in the 2, 4, 6, 8, and 10 inch lengths, which contain the fracture 
near their centres, the results are tabulated below. 
Gauge length, inches . , 1 2 4. 6 8 10 
Elongation, inches. ; 0°58 0°92 1:43 191 2°40 2°87 
Elongation, per cent. . ‘ 58°0 46°0 35°7 318 30:0 28°7 
It will now be seen how important it is, in stating. the elongation, 
to give the gauge length on which it is taken. It is also very important 
that the gauge length used in getting the elongation should contain the 
fracture, and if possible the gauge length should contain the fracture 
near its centre. For example, the elongation on the 4 inch length con- — 
taining the inch lengths numbered (1) to (4) in Fig. 244 is only 24°6 
per cent., while the elongation on the 4 inch length puipuis the fracture — 
near its centre is 35°7 per cent. 
To be able to select the gauge length so that it shall if posatile contain — 
-the fracture near its centre, it is desirable that the whole length of the 
parallel part of the specimen be marked off in half-inch lengths. 
When tests are made on specimens of the same material it is found — 
that the elongation is influenced by the area of the cross section of the 
specimen as well as by the gauge length. 
The elongation may be divided into two parts, one, the general, and 
the other, the local. The general elongation takes place over the whole 
length of the parallel part of the specimen, and is produced mainly before 
7 
the maximum load is reached. This general elongation is practically 
uniform over the length, and is independent of the area of the cross section 
of the specimen, After the maximum load is reached, local contraction 
