SAMPLING AND TESTING HIGHWAY MATERIALS. 
85 
2. Information obtained from the various laboratories in which 
tension tests are made shows that in many oases the forms and 
dimensions of specimens as recommended by the American Society 
for Testing Materials are in use and that in other cases these 
forms and dimensions most Dearly reconcile the differences that 
exist between the various forms employed. 
3. It is therefore recommended that the selection of specimens 
and their forms and dimensions shall conform to the specifications 
for each material as are now adopted by the American Society 
for Testing Materials. 
In the case of flats one-quarter inch or less in thickness, the 
dimensions shall be as follows: Width equal to five times the 
thickness of the specimen, except that in no ease shall the width 
be less than three-quarters inch; gauge length equal to twenty- 
four times the thickness of the specimen, except that in no case 
shall the gauge length be less than 2 inches. 
4. It is believed that the distance between the end of the gauge 
length and the beginning of the shoulders as prescribed in the 
standard specifications of the American Society for Testing Mate- 
rials is ample to avoid interference with proper elongation, and 
no grounds are found for recommending any change. 
5. The pulling speed has a marked influence on the tensile 
properties shown by materials tested, an increase in speed in- 
creasing the values found for yield point and tensile strength. 
In testing steel and wrought iron in grange lengths of 2 and 8 
Inches in accordance with the specifications of the American So- 
ciety for Testing Materials the speed of the machine, by which is 
meant the speed of the crosshead when the machine is running 
idle, shall conform to the following requirements: 
The crosshead speed of the testing machine shall be such that 
the beam of the machine can be kept balance!, but in no case 
shall be values given in the following table be exceeded : 
, Specified minimum tensile 1 /-•„„„„ 
i strength of material | i^il 
(pounds per square inch.; ; ieu s lu - 
Maximum crosshead 
speed in determining — 
Yield 
point. 
Tensile 
strength. 
Inrhf--. 
S0.C00 or under I 2 
Inches 
per minute. 
0.50 
2.00 
• 
Inches 
per minute. 
2.0 
6.0 
1.0 
2.0 
Over 80,000 -j \ 
Crosshead 
speed. 
6. In determining the elastic limit (so called i by the method 
prescribed in the American Society for Testing Materials specifica- 
tions for forgings and cold-rolled axles (serial designation A 18, 
A 19. A 63. and A 22) the crosshead speed for the 2-inch gauge 
length shall not exceed 0.125 inch per minute. 
7. In determining the proportional limit, the crosshead speed 
shall not exceed 0.025 inch per inch of gauge length per minute. 
8. In determining the modulus of elasticity, the elastic limit. 
and the proportional limit, the extensometer should be attached 
to at least two sides of the specimen, to compensate for unequal 
elongation, for improper holding, or any slight bending that may 
exist in the specimen. 
9. All authorities seem to regard it as desirable to measure 
the elongation on two or more sides of the test specimen, and 
most extensometers provide for so doing. 
10. The greatest accuracy is required in determining the 
modulus of elasticity, since small errors in measuring elonga- 
tion are of considerable consequence in the result. 
11. Since the modulus is determined for points well within 
the elastic limit, the total elongation to be measured is much 
smaller than at the elastic limit. 
