Fixture for Environmental Exposure of Structural Materials Under Compression Load

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.

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.

A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily apparent as the same becomes better understood with reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a side perspective view of the specimen loading fixture of the present invention;

FIG. 2 is a sectional view of the specimen loading fixture shown in FIG. 1 and taken along line II--II thereof, and

FIG. 3 is a view of the specimen loading fixture taken along line III--III of FIG. 2.

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.

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.