Integral bending moment absorber system for mechanical testing of materials

• US 5,431,062 A
• Filed: 05/13/1994
• Issued: 07/11/1995
• Est. Priority Date: 05/13/1994
• Status: Expired due to Fees

• Current Assignee: Francis I. Baratta
• Original Assignee: Francis I. Baratta
• Inventors: Baratta, Francis I.
• Primary Examiner(s): Chilcot, Jr., Richard E.
• Assistant Examiner(s): Olsen, James M.
• Application Number:
  US08/242,303
• Time in Patent Office: 424 Days
• Field of Search: 73/826, 73/830, 73/831, 73/834, 73/856, 73/860
• US Class Current: 73/856
• CPC Class Codes: G01N 2203/0226 High temperature; Heating means
• CPC Class Codes: G01N 2203/0405 Features allowing alignment between specimen and chucks
• CPC Class Codes: G01N 3/04 Chucks

Abstract

An apparatus is invented that accurately determines the failure or fracture stress of materials that behave in a brittle manner while under static or dynamic loadings that applies a stress to a test specimen in tension, compression, shear, or combination thereof, or in the case of cyclic loading stressing a fatigue sample. The bending and twisting of the test specimen due to the inherent misalignments in conventional test systems are drastically reduced by this device, which utilizes a hollow cylinder, termed a bending moment absorber whose ends are fitted and fixed to the ends of a dumbbell or flat specimen. This assembly, in turn, is clamped at each end by commercially available hydraulically-operated grips within the load train. This device causes the combined cross-sections of the hollow cylinder and the specimen to act in concert so as to markedly increase the moment of inertia of the system and thus reduce both the imposed bending stress and the error during testing. If the bending moment absorber and the specimen are of dissimilar materials and their modulus of elasticity ratio is less than 1.0, while their fracture strength ratio is greater than their modulus ratio, then failure will occur in the specimen, and the moment absorber will be reusable. In addition, this apparatus can be operated at cryogenic, ambient, or elevated temperatures.

Claims

1. A method to determine mechanical properties of a material where a sample of said material is prepared for testing, said sample having a top end and a bottom end, top and bottom ends providing grip surfaces for a testing machine and said sample is then enclosed within surrounding means which has a upper end and a lower end;

said surrounding means are then closely fitted to said sample top end and bottom end, and where, said top end of said sample is affixed by affixing means to the upper end of said surrounding means, and where said bottom end of said sample is affixed by affixing means to said lower end of said surrounding means, and where said sample and surrounding means are then clamped by clamping means within a testing device and when, the test device is then activated, the surrounding means, called a bending moment absorber, absorbs the bending moment of said sample reducing errors due to misalignment.

2. The claim in 1 where said sample behaves as a brittle material.

3. The claim in 2 where said surrounding means is a tube.

4. The claim in 2 where said surrounding means is a plurality of strut members affixed to hollow cylinder ends.

5. The claim in 2 where said affixing means is a pin or bolt.

6. The claim in 2 where said affixing means is an adhesive joint.

7. The claim in 2 where said affixing means is a shrink fit between the surrounding means and the top end of the sample and the surrounding means and the bottom end of the sample.

8. The claim in 2 where said affixing means is a threaded joint.

9. The claim in 2 where said affixing means is a soldered joint.

10. The claim in 2 where said affixing means is a brazed joint.

11. The claim in 2 where said affixing means is encapsulation within a cast or poured elastomer.

12. The claim in 2 where said clamping means are mechanically activated joints, such as two drillpress chuck mechanisms or two collet grips located or two hydraulically-operated grips at each end of the surrounding means, called a bending moment absorber.

13. The claim in 2 where said clamping means are two hydraulically-operated jaws located at each end of the surrounding means, called a bending moment absorber.

14. The claim in 2 where said surrounding bending moment absorber tube is a super alloy steel or a ceramic tube, thus allowing a functional bending moment absorbing method for high temperature tests of metals and ceramics.

15. The claim in 2 where said surrounding bending moment absorber tube material is chosen to have a linear coefficient of thermal expansion less than that of the prepared sample, such that a radial compression is provided at the top and bottom ends of the test sample when testing at elevated temperatures.

16. The claim in 2 where said surrounding bending moment absorber tube material is chosen to have a linear coefficient of thermal expansion greater than that of the prepared sample, such that a radial compression is provided at the top and bottom ends of the test sample when testing at cryogenic temperatures.

17. The claim in 2 where said surrounding bending moment absorber material is chosen to have a lower modulus of elasticity than that of the prepared sample, such that the sample will support a greater portion of the applied load and thus fail;

leaving the bending moment absorber intact and allowing it to be reusable.

18. The claim in 2 where said surrounding bending moment absorber is used for static testing.

19. The claim in 2 where said surrounding bending moment absorber is used for dynamic testing.

20. The claim in 2 where said surrounding bending moment absorber is used for cyclic fatigue testing.

21. The claim in 2 where said surrounding bending moment absorber is used to apply a multiplicity of loadings, such as tension, compression, torque and a combination thereof.

22. A device to test materials that behave in a brittle fashion where a prepared sample, which has a top end and a bottom end enclosed within a surrounding sleeve which is called a bending moment absorber which has a top end and bottom end, where said prepared sample is affixed at the top end to the top end of said sleeve and where said prepared sample is affixed at the bottom end to the bottom end of said sleeve and where said top end of said sleeve is gripped by the top jaw of a testing machine and where bottom end of said sleeve is gripped by the bottom end of the bottom jaw of a testing machine, and where said surrounding sleeve, called a bending moment absorber, acts to align said top and bottom ends of said sample within said testing machine;

preventing premature failure of said test sample.

23. A method to test materials that behave in a brittle fashion where a prepared test sample is enclosed within a closely conforming tubular sleeve, called a bending moment absorber, and affixed to the sleeve at each end, and where the ends of the tubular sleeve and the contained sample are gripped within a testing machine, where the the tubular sleeve provides additional moment of inertia to the said prepared test sample it encloses and reduces the effect of the inherent misalignment.