US2896448A - Materials testing machine grips for thin sheet material - Google Patents

Description

- July 28, 1959 A N s 2,896,448

' MATERIALS TESTING MACHINE GRIPS FOR THIN SHEET MATERIAL Filed Oct 11, 1956 INVENTOR LEW/S 6. HAINES A r TORNEY United States Patent TESTING MACHINE GRIPS FOR THIN SHEET MATERIAL Lewis G. Haines, Washington, Pa.

Application October 11, 1956, Serial No. 615,346

2 Claims. (Cl. 73-103) This invention relates to grips for thin sheet metal specimens subject to tensile testing.

Various types of grips have been proposed and used for holding thin sheet metal specimens when subjected to tensile test loads but generally such grips required a wedging action that distributed the stress so unevenly as to produce undesirable fractures on thin specimens. The prior art has also had other deficiencies either structurally, functionally or economically.

It is an object of my invention to provide an improved grip for testing thin sheet metal specimens so as to distribute the stress evenly over the entire cross section of the specimen whereby tests of a high order of reliability in accuracy and reproducibility can be obtained.

A further object is to provide a grip for thin sheet metal tensile specimens that is relatively simple and economical in construction, operation and maintenance and does not in any way sacrifice the desired reliability and characteristics above mentioned.

Other objects and advantages will be more apparent to those skilled in the art from the following description of the accompanying drawings in which:

Fig. 1 is an elevational view of my improved grips disposed in materials testing machine platens;

Fig. 2 is a sectional View taken substantially on the line 22 of Fig. 3 and showing one end of a specimen in its initially inserted unclamped position;

Fig. 3 is a sectional view taken substantially on the line 3-3 of Fig. 2;

Fig. 4 is an enlarged side view of my grip showing a gripping pin in section with the specimen shown at the beginning of its gripping action;

Fig. 5 is a view similar to Fig. 4 but showing the specimen in its completely clamped position; and

Fig. 6 is a section taken substantially on the line 66 of Fig. 2.

In the particular embodiment of the invention disclosed herein I have shown upper and lower specimen loading platens 1 and 2. of any usual materials testing machine in which loading rods 3 and 4 are mounted within usual swivel joints 5. The holders 3 and 4 are threadedly connected to upper and lower grip bodies 6 and 7. Inasmuch as the grips are identical, except for extending toward each other, it will suflice to describe only one. The grip body has a transverse cylindrical opening 8 while a slot it extends upwardly from a curved lower end 10 for communication with the opening. A short aligned continuation 11 of the slot 9 extends from the other side of the opening. A pin 12 of smaller cross sectional area, i.e., diameter, than the opening and of substantially the same length thereof is provided with a slot 13 disposed diametrically and extending the length of the pin. This slot is substantially the same width as the body slots 9 and 11 so as to permit the end of a sheet metal specimen 15 to extend upwardly to the depth of the short slot 11 whereupon the pin 12 is rotated so as to bend the end 16 of the specimen in a position shown in Fig. 4 and to start pulling the specimen within the space between the pin 12 and the lower side of hole 8. The pin 12 is rotated until its full gripping position is obtained, as shown in Fig. 5, at which time the specimen portion 16 overlaps another portion of the specimen. However, under certain conditions it may be sufficient to merely rotate the specimen to a partial position. It is thus seen that the space between the pin and opening is determined by the thickness of the specimen.

Rotation of the pin 12 is effected by a, shaft continuation 17 of the pin and whose diameter is preferably substantially equal to that of the opening 8. A knurled knob 18 is slidable axially on shaft 17 and imparts rota-.

tion thereto by a suitable longitudinal spline 19. A pair of locking pins '20 extend inwardly from knob 18 and after rotation of the slotted pin to its gripping position the knob 18 is moved along the shaft 17 to cause the pins 20 to enter fully a set of openings 21 or 22 depending upon the angular position of the knob, thereby to prevent reverse rotation of the slotted pin during loading. When the specimen is similarly gripped in the lower grip body 7 a load may be applied to the specimen.

Because of my improved gripping action there is no wedging action and the stress is distributed so evenly over the entire cross section of the specimen that in many cases full cup type fractures are obtained on material as thin as .002 inch in thickness. It is also seen that the device is extremely simple in operation and is economical in manufacture and maintenance.

It will, of course, be understood that various changes in details of construction and arrangement of parts may be made by those skilled in the art without departing from the spirit of the invention as set forth in the appended claims.

I claim:

1. A specimen grip for holding sheet material to which load is applied in a straight line direction lengthwise of that portion of the sheet under test comprising, in combination, a grip body having a transverse opening therein, of substantially circular cross section and having a specimen receiving slot therein extending from one end of the body to the opening substantially radially thereof and lying in the plane of the lengthwise portion of the sheet under test, a pin disposed within said opening about the axis thereof and being of less cross sectional area than the opening so as to provide a space within which an end portion of the specimen may be drawn, said pin having a substantially radial slot which in one position is in alignment with the body slot so as to receive a specimen, and means for rotating said slotted pin so that a portion of the specimen is drawn within said space between the pin and opening.

2. The combination set forth in claim 1 further characterized in that the body has a continuing slot substantially diametrically opposite to said other slot so as to receive the end of a specimen when initially inserted in the grip whereby said specimen end is bent over onto the pin upon rotation thereof.

References Cited in the file of this patent UNITED STATES PATENTS 1,272,944 Green July 16, 1918 2,293,084 Sedam Aug. 18, 1942 2,704,466 Way Mar. 22, 1955 FOREIGN PATENTS 294,447 Great Britain July 26, 1928

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