METHODS OF SAMPLING AXD TESTIXG HIGHWAY MATERIALS 119 
a scale. The elongation should not be reported for any tension-test specimen 
which breaks outside the middle third of the gauge length. 
Note. — If only a few specimens are furnished for testing it is recommended that in 
marking the gauge length for measuring elongation after fracture it be divided into eight 
parts, and that if a specimen breaks inside the gauge length but outside the middle third 
of the gauge length the requirement in the foregoing paragraph be waived, and the 
elongation be measured and reported as follows : 
(1) If the specimen breaks in the middle half of the gauge length (between G and Q), 
Figures 57 (a) and (.b) the elongation is measured directly over the stretched gauge 
lengths (fig. 59 (b)). 
(2) If the specimen breaks between A and C (or between G and I) but nearer B than 
A (or nearer H than J), as shown in Figure 59 (c) the elongation from A to C (or from 
G to /) is measured, and to this is added twice the measured elongation from C to F 
(or from D to G) . 
(3) If the specimen breaks within one-half a division of an end gauge mark (see 
fig. 59 (d)) the elongation from A to E (or from E to I \ is measured and multiplied 
by 2. 
The above method can be applied to specimens with any gauge length, and to turned 
specimens as well as flat specimens. 
This method is not applicable to brass specimens. 
v. 
•—^ 
K • 
Gauge Length 
(a) 
*s 
V. 
ABC 
JLl 
G H I 
k 
j<- Stretched Gauge Length ->| 
(b) 
(C) 
H I 
H I 
Fig. 57. — Method of placing gauge markings where only a few specimens are furnished for 
testing 
24. The measurement of reduction of the dimensions of the cross section 
of a tension-test specimen may be made by the direct measurement with a 
micrometer of the smallest section of the fractured specimen. For round speci- 
mens this measurement can usually best be made by holding the broken pieces 
together in a vise or between centers and then measuring the average diameter 
of the smallest cross section by means of a micrometer fitted with points so 
shaped that they will come in contact with the specimen at its smallest 
diameter. 
PLOTTING STRESS-STRAIN DIAGRAMS 
25. A stress-strain diagram 61 is a diagram plotted with values of stress as 
ordinates and values of strain as abscissas. 
61 The use of the term "stress-strain diagram" is * frequently extended to cover 
diagrams plotted with values of applied load, or applied moment, as ordinates and wi'h 
values of stretch, compression, deflection, or twist as abscissas. 
