Fixture for environmental exposure of structural materials under compression load

The present invention relates to a device for stressing a deformable material specimen. The apparatus consists of top plate 11 and bottom plate 12 sandwiching a guide cylinder 13. The specimen 14 is positioned on the bottom plate 12 and attached to a load piston 20 (FIG. 2). Force is applied through top plate 11 into guide cylinder 13. Once specimen 14 has been loaded, the stress is maintained by tightening tie bolt nuts 17.

BACKGROUND OF THE INVENTION 
The present invention relates to a device for stressing a deformable 
material specimen and maintaining the load on the specimen after the 
stressing force has been removed. 
Mechanical tests of a small specimen often are used to simulate the 
behavior of a material under conditions of its service usage. Materials 
used in the construction of vehicles and equipment for use in aerospace 
applications must be able to withstand both extreme compression loads and 
extreme fluctuations in environmental conditions. To test the qualities of 
various materials, it is necessary to be able to simultaneously stress the 
materials and subject the specimens, while under stress, to changes in 
environmental conditions. 
PRIOR ART 
The prior art devices for stressing material specimens are not suitable for 
tests involving exposure of the stressed material to extreme environmental 
conditions. The prior art devices, although adequate for producing 
compression load, are too large and complex to be efficiently useful in 
the study of environmental effects on the test material. 
Thus, a need exists for an economical and compact device suitable for the 
simultaneous testing of material specimens under compression load and 
during exposure to extreme environmental fluctuations. 
Accordingly, it is an object of the present invention to provide an 
apparatus which permits the simultaneous testing of the effects of 
compression load and environmental fluctuations on material specimens. 
It is a further object of the present invention to provide an apparatus for 
stressing materials which is both compact and economical. 
These and other objects are achieved by providing a specimen loading 
fixture of two plates sandwiching a guide cylinder and held together by 
two tie bolts. A material specimen is positioned within the guide cylinder 
and load is transmitted to the specimen by a load piston. Load is applied 
to the specimen by adjusting a loading bolt to a desired value; placing 
the fixture in a test machine; applying load to the fixture until the 
plates are secure against the guide cylinder; and tightening the tie bolt 
nuts to maintain the specimen at the load value.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now more particularly to FIG. 1, there is shown a loading fixture 
10 comprising a top plate 11 and a bottom plate 12 sandwiching a guide 
cylinder 13. A load piston 20 (FIG. 2) is located within guide cylinder 
13. A material test specimen 14 is secured to bottom plate 12 by retainers 
33 and 33a. Specimen 14 is also secured by retainers 33 and 33a to load 
piston 20 (FIG. 2). Loading bolt 15 extends through the center of top 
plate 11 into guide cylinder 13 where it contacts lood piston 20 (FIG. 2). 
Tie bolts 16 are provided with hex heads 23 and extend from bottom plate 
12 to top plate 11 and are bolted on the upper surface of top plate 10 by 
tie bolt nuts 17. An area, indicated by reference numeral 19, of guide 
cylinder 13 is cut away near specimen 14 to permit exposure of the 
specimen to varying environmental conditions. 
The positions of material test specimen 14 within guide cylinder 13 can be 
readily seen by reference to FIG. 2. Retainers 33 and 33a are attached to 
bottom plate 12 by screws 21. Retainers 34 and 34a are attached to load 
piston 20 by screws 22. Screws 21 and 22 fit into slots (32) in retainers 
33, 33a, and in similar slots, not shown, in retainers 34 and 34a. When 
screws 21 and 22 are loosened, retainers 33, 33a, 34 and 34a are free to 
move in the slots either toward or away from specimen 14. To secure 
specimen 14, retainers 33, 33a, 34 and 34a are moved to snugly contact 
specimen 14 and screws 21 and 22 are tightened. Thus, loosening or 
tightening screws 21 and 22, retainers 33, 33a, and 34, 34a can be 
adjusted to accommodate varying specimen dimensions. As can be seen, guide 
cylinder 13 provides axial alignment for load piston 20. 
Referring now to FIG. 3, there is shown a top view of retainers 33 and 33a 
sandwiching specimen 14. Slots 32, approximately 0.3 inches in length, 
accommodate screws 21. Retainers 33 and 33a are free to move either toward 
or away from specimen 14. In assembly, retainers 33 and 33a are moved to 
contact specimen 14, screws 21 are tightened to secure retainers 33 and 
33a to bottom plate 12. Screws 31 are tightened to secure retainer 33 to 
retainer 33a. Retainers 34 and 34a, are adjustable in like fashion and 
further description thereof is omitted herein in the interest of clarity. 
OPERATION OF THE INVENTION 
The operation of the present invention apparatus is now believed apparent. 
The calibrated loading fixture 10 and a specimen 14 are assembled, and 
retainers 33 and 34 are adjusted to assure axial loading of the specimen 
14. The tie bolt nuts 17 are loosened, and the loading bolt 15 is adjusted 
to achieve the desired compression load by noting the angular position 
indicated by reference point 30 relative to reference lines 25 scribed on 
top plate 11. The tightening of tie bolt nuts 17 pushes top plate 11 and 
bottom plate 12 securely against guide cylinder 13 and concurrently pushes 
loading bolt 15 against load piston 20, thereby delivering the desired 
load to specimen 14. With the tie bolt nuts tightened, the load on the 
specimen will be maintained and the loading fixture can be placed in an 
environmental testing apparatus. 
The calibration of the loading fixture is achieved by the following steps: 
(1) A gaged specimen is positioned in loading fixture 10. (2) Loading bolt 
15 is loosened to clear load piston 20; tie bolt nuts 17 are tightened; 
and the loading bolt 15 is tightened to contact load piston 20. The 
angular position indicated by reference point 30 of loading bolt 15 is 
noted on the upper surface 26 of top plate 11 by reference lines 25 
scribed on top plate 11. This represents the zero-load position. (3) Tie 
bolt nuts 17 are loosened and loading bolt 15 is advanced to the estimated 
position of the specimen target strain level. Tie bolt nuts 17 are 
tightened. (4) Loading fixture 10 is positioned in a test machine (not 
shown) which loads the fixture through bottom plate 12 and top plate 11. 
Loading force is applied to bottom plate 12 on the tie bolt heads 23. 
Loading force is applied to top plate 11 at points indicated by reference 
numeral 27. (5) Load/strain recording equipment (not shown) records 
specimen strain versus load. The loading fixture 10 is loaded to the 
estimated target strain level by the test machine. The tie bolt nuts 17 
are tightened. The strain reading at this point is the strain locked in 
the specimen. Because the specimen is loaded through the fixture with the 
test machine and not by deflecting the loading bolt, no torque is applied 
to the specimen. 
Although the invention has been described relative to a specific embodiment 
thereof, it is to be understood that numerous modifications may be made 
therein without departing from the spirit and scope of the instant 
invention. It is therefore to be understood that within the scope of the 
appended claims, the invention may be practiced otherwise than as 
specifically described herein.