108 DEPARTMENT BULLETIN 12 16, U. S. DEPT. OF AGRICULTURE 
seated shackles or with a spherical-seated bearing block to insure as nearly 
axial loading as is possible. The arrangement shown in Figure 45 is suggested 
Spherical 
/ Bearing 
Upper Head 
Of 
testing 
■^ Machine 
Specimen 
with 
Threaded 
Ends, 
Split 
Socket 
Solid 
Clamping 
Ring 
Testing 
Machine 
Fig. 45. — Testing arrangements for tension 
jSpherica/ 
I Bearing 
v\ Upper Head 
of 
Testing 
Machine 
Specimen 
with 
Shouldered 
Ends. 
Movable 
Head of 
Testing 
Machine 
for tension bars, and the arrangement shown in Figure 46 is suggested for 
compression bars. 
11. (a) The calibration device shall be of such size that under the greatest 
load for which the device is to 
Cross-Head of 
Testing Machine 
Spherical Seat- 
>.\ El— Center of 
Spherical Surface 
Specimen 
be used (called its full load) the 
stress on any cross-section will 
not be more than 80 per cent of 
tbe elastic limit of the material, 
as determined in accordance 
with Method II for the deter- 
mination of elastic limit as de- 
scribed under the definition of 
the term " elastic limit " of the 
tentative definitions of terms re- 
lating to methods of testing (se- 
rial designation E6-25T) of the 
American Society for Testing 
Materials (2) on a test specimen 
cut from the bar, forging or cast- 
ing for the device after its final 
heat treatment. 
(ft) Before the calibration de- 
vice is used for verification pur- 
poses, it shall be loaded to its 
full load at least six times, and 
between successive loadings it 
shall be heated to a temperature of 100° C. (212° F.) for a period of 30 min- 
utes or shall be allowed to rest for a period of 24 hours. The object of this 
treatment is to adjust the device to its bearings and to relieve internal strain. 
^1 .-- Bearing Block 
''W////////}//////)//////' ■ 
Weighing Table of 
Testing Machine. 
Testing arrangement for compression 
bars 
