Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specimen clamp – holder – or support
Reexamination Certificate
1999-08-03
2001-12-18
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specimen clamp, holder, or support
C073S860000
Reexamination Certificate
active
06330830
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to grips which are used to hold a compact fracture specimen while it is loaded in tension and compression by a hydraulic load frame.
Initiation and controlled propagation of cracks must be produced in various types of materials such as beryllium, ceramics, and various steels under tension/compression cycling in order for subsequent fracture toughness or crack growth rate testing to be valid. Such testing is described in S-200 Grade Beryllium Fracture Properties,
Journal of Testing and Evaluation
, JTEVA, Vol. 1, No. 2, March 1973, pp. 110-118.
The above described testing may be carried out with, for instance, an 810 Material Test System, manufactured by MTS, Inc., Eaton Prairie, Minn. However, the sample holding grips supplied by MTS are not suitable for holding the specimen to be tested in both tension and compression. The standard grips allow for only tensile loading of the specimen through two tension pins that are of smaller diameter than corresponding holes in the specimen. It is the clearance of the pins that pass through holes in the specimen that precludes cyclic loading of the specimen in both tension and compression.
The use of set screws to apply pressure to the top and bottom edges of the specimen, in order to achieve the compressive part of the loading cycle, are not effective. The set screws are not capable of producing an adequate pressure on the specimen to prevent vibration during the loading cycles. This will lead to frequent loosening of the assembly which, in some cases, will result in the tension pins falling out and the test terminating early. The use of an adjustable pin, as suggested in the Journal of Testing and Evaluation, supra, also proved ineffective. Vibration during testing resulted in a loosening of the tension pins.
Accordingly, it is an object of the present invention to provide grips for tension/compression cycle testing, which hold the specimen tightly in position and do not loosen during the testing cycle.
SUMMARY OF THE INVENTION
A pair of grips for holding a specimen which includes a pair of through openings for receiving tension pins and a pair of spaced apart, parallel edges. Each of the grips includes a pin, a Davis adjustable key, and a housing. The Davis adjustable key includes a key housing, a movable key portion and a mechanism to move the key portion relative to the key housing. Each housing includes a bore for receiving the Davis adjustable key, a bore for receiving the pin, and a slot for receiving that portion of the specimen which includes the through opening and the edge. The Davis adjustable key bore and the pin bore are substantially parallel to each other. The slot is substantially perpendicular to and completely bisects the pin bore. The slot also partially intersects the Davis adjustable key bore to, when the specimen is received in the slot, the pin received in the through opening (of the specimen) and the in the bore (of the housing) and the Davis adjustable key is received in the Davis adjustable key bore, permit the moveable key portion to be moved into engagement with the edge. The Davis adjustable key bore is oblong and includes two substantially parallel sides. The Davis adjustable key also includes two substantially parallel sides. The spacing between said parallel sides on the Davis adjustable key is slightly less than the spacing between the parallel sides of the David adjustable key bore to provide a close fit therebetween.
The method of holding the specimen for testing in both tension and compression, includes the steps of inserting a tension pin in each of the through openings, and moving the movable key portion of each of a pair of Davis adjustable keys into engagement with each of the edges.
REFERENCES:
patent: 4276771 (1981-07-01), Wesch, Jr.
patent: 4721000 (1988-01-01), Scanlon
patent: 4875376 (1989-10-01), Fischer
patent: 5948994 (1999-09-01), Jen et al.
S-200 Grade Beryllium Fracture Toughness Properties, W. O. Shabbits and W.A, Logsdon, Journal of Testing and Evaluation, vol. 1, No. 2, Mar. 1973, pp. 110-118.
Jacobson Loren A.
Sandoval David Lynn
Fuller Benjamin R.
Morgan DeWitt M.
Stevens Maurice
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