Machining technique prevents undercutting at the test section in tensile specimens when machining the four corners of the reduced section. Made with a gradual taper in the test section, the width of the center of the tensile specimen is less than the width at the four corners of the reduced section

Moscater, R. E.

Royster, D. M.

English

NASA Technical Reports Server

September 1968
	 Brie I'68-lO32 
NASA TECH BRIEF	
%F 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Machining Technique Prevents Undercutting in Tensile Specimens 
A technique has been devised to prevent undercut-
ting at the test section in tensile specimens when ma-
chining the four corners of the reduced section (transi-
tion section). The tensile specimens are made with a 
gradual taper in the test section, resulting in a width 
at the center of the specimen that is from 0.002 to 
0.006 inch less than the width at the four corners of 
the reduced section. Tensile failures are thus forced 
to occur at the narrow central cross section. 
The tapers are machined on a milling machine 
equipped with a contour-tracer-controlled vertical-
travel table. The specimens are stacked in conven-
ient groups, blanked off, and drilled for locking bolts 
at each end. The locking bolts are used to align and 
secure the specimens for further handling and machin-
ing. The specimens are then set up in the milling ma-
chine. To machine tensile specimens with a I 1/4-inch 
test section having a 0.006-inch (.003-inch on a side) 
reduction, use is made of an arc-shaped template with 
a chord length of 1 1/4 inches and a depth at the 
center of 0.30 inch. The stylus follows this template 
which controls the vertical travel of the table at a 
cousin ued os cricul 
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ratio (vertical to horizontal) of 100 to 1. The spindle 
is stationary and tilted to correspond to a 0.003-inch 
horizontal displacement in 0.3-inch vertical travel of 
the table. The stack of specimens is aligned and tilted 
in the width direction by the same angle as the spindle 
so that the stack and spindle are perpendicular to each 
other. A mill cutter with a diameter corresponding to 
the radius of the transition section of the tensile speci-
mens is placed in the spindle. The cutter and speci-
mens are then oriented with the tracer stylus and 
template so that when the stylus reaches the bottom of 
the arc on the template the cutter is at the center of 
the test section. By following the template with the 
stylus, the table with the specimens is moved up 0.30 
inch at a gradual pace corresponding to successive 
positions of the stylus. This operation causes an el-
liptical shape to be machined on the edges in the test 
section of the specimens with maximum cut occur-
ring at the center. As the stylus passes the mid-
point and starts up the curve on the template, the 
table is controlled to descend at the same pace as in 
ascending. The taper is completed when the stylus 
traverses the arc of the 1 1/4-inch chord. The speci-
men stack is then turned over, realigned, and ma-
chined on the other edge in the same manner as in the 
previous operation. 
Note: 
Details may be obtained from: 
Technology Utilization Officer 
Langley Research Center 
Langley Station 
Hampton, Virginia 23365 
Reference: B68-10352 
Patent status: 
No patent action is contemplated by NASA. 
Source: R. E. Moscater and D. M. Royster 
(LA R-l028l) 
Brief 68-10352	 Category 05


Machining technique prevents undercutting in tensile specimens

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