Measuring and testing – Testing by impact or shock
Reexamination Certificate
2000-08-11
2003-04-08
Noori, Max (Department: 2855)
Measuring and testing
Testing by impact or shock
C073S835000
Reexamination Certificate
active
06543273
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to methods and apparatuses for testing properties of materials, more particularly to methods and apparatuses for testing impact fracture toughness (resistance) of metallic materials such as titanium.
The “dynamic tear” (DT) test is a conventional procedure for characterizing impact fracture toughness properties of both ferrous and nonferrous materials. The “one-inch standard” DT test was developed at the United States Naval Research Laboratory (NRL) in the early 1960's.
Since the mid-1960's, the one-inch DT test has been used extensively by the U.S. Navy to characterize the impact fracture resistance of high strength steels, titanium alloys and aluminum alloys. Numerous U.S. Navy specifications require the use of the standard specimen for measuring the impact fracture toughness of candidate marine construction materials. DT test facilities have been established by the U.S. Navy at various research laboratories and production plants in this country and abroad.
Incorporated herein by reference, and appended hereto marked “APPENDIX A,” is the following U.S. Navy report (NRL FR-6851) which describes the standard specimen and procedure in accordance with the one-inch DT test: Puzak, P. P. and F. A. Lange, “Standard Method for the 1-inch Dynamic Tear Test,” NRL Report 6851, February 1969. Essentially, as described by Puzak et al. in APPENDIX A, the standard one-inch DT test involves the impacting of a large beam which contains a brittle crack starter weld on the tension side of the standard specimen. The dimensions of the standard specimen are 1 inch thick×4.75 inches wide×18 inches long.
Also incorporated herein by reference are the following U.S. Navy reports: NRL FR-7159, E. A. Lange, P. P. Puzak and L. A. Cooley, “Standard Method for the ⅝ Inch Dynamic Tear Test,” 1970; NRL FR-6975, E. A. Lange and F. J. Loss, “Dynamic Tear Energy—A Practical Performance Criterion for Fracture Resistance,” 1969; NRL FR-6991, C. N. Freed and R. J. Goode, “Relationship between Fracture Toughness and Estimated Plastic Zone Size in Steel, Titanium and Aluminum Alloys,” 1969; NRL FR-6873, R. W. Judy, P. P. Puzak and E. A. Lange, “Characterization of Fracture Toughness of 5Ni—Cr—Mo—V Steel by Charpy V-Notch and Dynamic Tear Tests,” 1969; NRL FR-6864, G. E. Nash, “An Analysis of the Forces and Bending Moments Generated during the Dynamic Tear Test,” 1969; R-1969-14151, G. E. Nash, E. A. Lange, “Mechanical Aspects of the Dynamic Tear Test,” 1969; NRL MR-1826, G. E. Nash and E. A. Lange, “Mechanical Aspects of the Dynamic Tear Test Specimen,” 1967; R-1970-14063, E. A. Lange and F. J. Loss, “Dynamic Tear Energy—A Practical Peformance Criterion for Fracture Resistance,” 1970; NRL FR-7056, F. J. Loss, “Dynamic Tear Test Investigations of the Fracture Toughness of Thick-Section Steel,” 1970; NRL FR-6993, L. A. Cooley and E. A. Lange, “Vertical Drop-Weight Machine for Conducting Drop-Weight NDT, Drop-Weight Tear and Dynamic Tear Tests,” 1970; R-1977-14178, T. G. Heberling, E. S. Harris and E. A. Lange, “Results of Interlaboratory Test Programs to Evaluate the ⅝-in. (16-mm) Dynamic Tear Test Method,” 1977.
According to the one-inch standard DT test, the brittle crack starter weld is prepared by machining a shallow 1.75 inch long groove across the width on each of both sides of the specimen. A small amount of embrittling material is diffused in an electron beam weld through the 1-inch plate thickness. For a titanium specimen, steel wires are placed in the grooves and upset by light hammering to ensure uniform distribution of the embrittling materials during electron beam (EB) welding. After EB welding the crack starter weld is notched to assist initiation of the crack in the embrittled weld. The specimen is fractured using a pendulum machine (or drop-weight machine), and the total energy for fracture is recorded.
The main disadvantage associated with use of the standard one-inch DT test (to characterize the fracture toughness of materials) is the requisite large size of the test specimen. Although usually one-inch DT testing of flat plate material is readily accomplished, one-inch DT testing of many different product and pre-product forms, such as used in submarine and surface ship construction, are problematical or impractical.
For instance, forgings and castings are frequently of a shape that does not allow the removal of an 18-inch long flat specimen. This necessitates the design and fabrication of special forging dies that produce a sufficient amount of excess material to allow the removal of a DT specimen blank for testing. Another example of the limitedness of the one-inch DT test is its inability to test small mock-up or pre-production forgings, which typically are on the order of 9-12 inches in diameter. The cost of fabricating special forging dies for mock-up or pre-production testing can be prohibitively expensive.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide method and apparatus for testing dynamic tear of a metallic material when there is an insufficient and/or unsuitably dimensioned amount of available metallic material for properly performing the one-inch standard DT test.
It is further object of the present invention to provide method and apparatus for testing dynamic tear of a limited amount of metallic material so that one or more other tests of the metallic material can be properly performed.
The present invention provides a methodology for measuring the dynamic tear toughness properties of metallic materials (such as titanium, steel and aluminum alloys), particularly in cases of limited material availability or incompatible size and geometry. The inventive DT test procedure features utilization of a modified (“nonstandard”) DT specimen in lieu of the “standard” one-inch DT specimen. Inventively implemented is a smaller, “nonstandard” DT specimen which will generate energy values equivalent to those which would be measured for the larger, “standard” one-inch DT specimen.
According to this invention, the nonstandard one-inch dynamic tear specimen comprises a center (middle) test section and a pair of end-tabs. The center test section is made of the test material, and is joined (preferably, welded) to each of the two end-tabs. The two end-tabs, when appropriately combined with the center test section, accomplish complete dimensional standardization of the nonstandard one-inch DT specimen.
In other words, according to this invention, the center test section and the two end-tabs each have the standard width and standard thickness, but a “non-standard” length which is something less than the standard length. In typical inventive practice, the two end-tabs will each have the same “non-standard” length, which will exceed the “non-standard” length of the center test section. Once the center test section and two end-tabs are united in the lengthwise direction, the integral whole has become characterized by the standard length as well as the standard width and standard thickness.
In accordance with the present invention, a method is provided for obtaining a rectangular parallelepiped section from an object for the purpose of being subjected to dynamic tear testing of the kind wherein a rectangular parallelepiped specimen made of a metallic material is impacted, wherein the specimen has a prescribed length, a prescribed width and a prescribed thickness, and wherein the specimen has provided therein a crack through the thickness and a portion of the width for initiating fracture of the specimen when impacted. The method comprises: determining the extent of lengthwise plastic deformation of the specimen which would result if the specimen were subjected to the dynamic tear testing; and, obtaining from the object the rectangular parallelepiped section having the prescribed width, the prescribed thickness and a nonprescribed length which is shorter than the prescribed length, the nonprescribed length being at least as great as the determined extent of lengthw
DeNale Robert
Judy, Jr. Ralph W.
Lindauer Roy A.
Wells Michael E.
Kaiser Howard
Noori Max
The United States of America as represented by the Secretary of
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