Test specimen grip apparatus

Improvements in test specimen grip apparatus for tensile stress testing machines includes replaceable grip inserts that are able to accommodate wider than usual test specimens, particularly textile test specimens. The specimen grip means or grip inserts are threadedly retained on and may be substantially wider than their supporting jaw members. The grip housing, moreover, is provided with apertures for access to the threaded retainers for ease of grip insert removal and replacement. In addition, fluid actuation is preferably provided for the jaw members of the improved grip apparatus and a thumb screw is also disclosed for temporarily locking the jaw members in a selected open position, when mounting test specimens or removing and/or replacing grip inserts.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to improvements in test specimen grip apparatus for 
testing machines and, more specifically, to improvements in grip apparatus 
for tensile stress testing machines. The grip apparatus disclosed is 
capable of holding test specimens, such as textile test specimens, that 
are wider than usual dog bone specimens or the like and, in addition, is 
provided with desirable fluid actuation, a thumb screw lock for its jaw 
members and an arrangement whereby grip inserts can be rapidly and easily 
removed and replaced. 
2. Description of the Prior Art 
This invention is an improvement in wedge grips for testing machines and, 
in particular in the grip apparatus disclosed in applicant's U.S. Pat. No. 
4,662,229, issued May 5, 1987, entitled Grip Assembly, the disclosure of 
which is incorporated herein by reference. Disclosed in applicant's said 
prior patent is test specimen grip apparatus for use with universal type 
testing machines. The grip apparatus disclosed includes a grip housing 
having a connecting end adapted for securing the housing to tensile stress 
testing apparatus and a test specimen receiving end opposite the 
connecting end of the housing. A pair of passages extend through the 
connecting end of the housing and converge toward the housing's receiving 
end. A cavity in the housing is in operative communication with the pair 
of passages and with the receiving end of the housing and is adapted for 
receiving one end of a test specimen within the grip housing. A grip bar 
is slidable mounted in each of the converging passages and each grip bar 
extends above the connecting end of the housing. Moreover, each grip bar 
is provided with specimen grip means carried on its lower end, the grip 
means being opposed and being adapted to compressively engage oppose 
surfaces of a test specimen, whereby application of tensile stress to the 
test specimen increases the compressive engagement of the grip means with 
the test specimen. 
Notwithstanding the patentable features and advantages of the foregoing 
grip assembly over those known in the prior art, applicant's prior grip 
assembly was not well suited for tensile testing textile materials, 
particularly as the tensile test specimen increased in width. A review of 
the prior patents disclosed or cited in applicant's U.S. Pat. No. 
4,662,229, including U.S. Pat. Nos. 1,510,896; 2,419,711; 2,447,660; 
2,537,322; 2,613,941; 2,676,381; 3,224,259 and 3,403,549, the disclosures 
of which are incorporated herein by reference, provided no structure by 
which textile test specimens of varying widths, such as up to at least 
twelve (12) inches or more in width, could be accommodated for tensile 
testing. Moreover, a review of additional patents disclosed in U.S. Pat. 
No. 4,662,229, including Canadian Pat. No. 446,096 and Soviet Union Pat. 
No. 800,797, the disclosures of which are also incorporated by reference, 
was similarly of no avail in providing or suggesting a suitable grip 
structure for tensile testing textile specimens of such widths as 
heretofore stated. 
Accordingly, there remained a need for a grip apparatus for use with 
conventional tensile stress testing devices that was readily adaptable for 
use with test specimens of varying widths, including textile test 
specimens of up to at least twelve (12) inches or more in width. Moreover, 
the need for such grip apparatus included the further need for an 
apparatus which permits easy and rapid removal and replacement of test 
specimens, as well as easy and rapid removal and replacement of the 
specimen grip members without removal of the grip apparatus from the test 
device and without substantial disassembly of the grip apparatus. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided a novel and 
improved grip apparatus for tensile stress testing machines that includes 
replaceable grip inserts that are able to accommodate wider than usual 
test specimens, particularly textile test specimens. The specimen grip 
means or grip inserts are threadedly retained on and may be substantially 
wider than their supporting jaw members. The grip housing, moreover, is 
provided with apertures for access to the threaded retainers for ease of 
grip insert removal and replacement. In addition, fluid actuation is 
preferably provided for the jaw members of the improved grip apparatus and 
a thumb screw is also disclosed for temporarily locking the jaw members in 
a selected open position, when mounting test specimens or removing and/or 
replacing grip inserts.

Description of the Preferred Embodiment 
The construction and operation of conventional tensile stress testing 
apparatus, such as universal type testing machines, is well known and is 
suitably described in applicant's U.S. Pat. No. 4,662,229. As therein 
disclosed, the stress testing apparatus is generally comprised of a top or 
cross member and a base member or platen. A grip apparatus, such as the 
grip apparatus of the present invention, is attached by its connecting end 
to the top member of the testing apparatus and an identical grip apparatus 
is attached by its connecting end to the base member of the testing 
apparatus. Opposite ends of a test specimen are received and secured in 
the opposed, specimen receiving ends of the grips for testing. Stress 
measuring means, such as a load cell, is employed with the testing 
apparatus and may be interposed between one of the grips, such as the top 
grip, and its attached machine support. With such an arrangement, tensile 
stress is applied directly through the load cell to the test specimen, 
and, stress measurements, of the amount of tensile stress so applied, are 
recorded simultaneously by a device attached to the load cell. 
Shown in FIGS. 1 and 2 is a preferred grip apparatus of this invention. The 
preferred grip apparatus is indicated generally by the reference numeral 
10 and comprises a generally U-shaped housing 12 having a front surface 
14, a rear surface 16, a connecting end surface 18, a specimen receiving 
end surface 20, and opposed side surfaces 22. In a preferred embodiment of 
this invention, housing 12 is of unitary construction consisting of a 
single piece of material. Housing 12 can be constructed of any suitable 
material that provides the strength and rigidity required for the 
particular range of tensile stress to be applied to a selected work piece 
or test specimen. For example, for high stress use, housing 12 can be 
constructed of steel or other suitable metal. For low stress use for 
testing materials having low tensile strength, such as thin gauge wire or 
plastic materials, housing 12 can be constructed of plastic or other 
strong, rigid, non-metallic materials. In a preferred embodiment of this 
invention, for use with high tensile strength materials having tensile 
strength in excess of thirty thousand (30,000) pounds per square inch, 
housing 12 has been constructed of aluminum. 
With particular reference to FIG. 2, an inwardly opening, generally 
V-shaped cavity 24 extends from the specimen receiving end surface 20 of 
the housing 12 through a portion of the housing 12 and also extends from 
the front surface 14 to the rear surface 16 of the housing. A pair of 
bores or passages 26 extend from the connecting end surface 18 of housing 
12, through housing 12, to the specimen receiving end surface 20. Bores or 
passages 26 mutually converge and open into cavity 14, as bores or 
passages 26 extend toward specimen receiving end surface 20 of housing 12. 
In a preferred embodiment of this invention, bores or passages 26 are 
circular in transverse cross-section; however, in other embodiments of 
this invention, bores or passages 26 may be either polygonal or of curved, 
non-round transverse cross-section. 
In each of the bores or passages 26, there is slidable mounted a grip bar 
28, which extends downwardly through housing 12 and has a bottom surface 
30 which may be flush with the specimen receiving end surface 20 of 
housing 12. An upper portion 32 of grip bar 28 extends beyond connecting 
end surface 18 of housing 12. A pair of mutually spaced aligned holes 34 
extend through upper portion 32 of grip bar 28. Each hole 34 contains a 
pin 36, extending outwardly from grip bar 28 toward rear surface 16 of 
housing 12. Laterally adjacent and normal to each hole 34 and each pin 36, 
a threaded bore 38 extends through grip bars 28 into holes 34 and secures 
a threaded set screw 40 which abuts pins 36 and secures pins in place. The 
function of pins 36 is discussed more fully below. 
The peripheral transverse configuration of grip bar 28 conforms to the 
shape of the transverse cross-section of bore or passage 26 in a manner 
adapted to provide a close tolerance, readily slidable fit between the 
surfaces of bore or passage 26 and grip bar 28, while preventing damage to 
those surfaces while the grip apparatus is in use. In a preferred 
embodiment of this invention, grip bar 28 is cylindrical and conforms to a 
circular transverse cross-section of bore or passage 26. In another 
embodiment of this invention, the transverse cross-section of grip bar 28 
can be polygonal or of a non-round, curved configuration. In all 
instances, the cross-sectional configuration of grip bar 28 conforms to 
the cross-sectional configuration of bore or passage 26. 
A groove 42 is formed in the side of grip bar 28, opposite threaded bores 
38, and extends a portion of the length of grip bar 28 adjacent the side 
surface 22 of housing 12. A key or guide 44 is secured by fasteners 46 to 
the connecting end surface 18 of housing 12 adjacent groove 42. A 
forwardly projecting portion 48 of key or guide 44 extends into groove 42 
to enable proper slidable alignment of grip bar 28 and to prevent turning 
of grip bar 28 when grip apparatus 10 is in use. Of course, key or guide 
44 and groove 42 may be omitted when grip bars 28 and bores or passages 26 
have a polygonal transverse cross-section, or other configuration, that 
prevents turning of the grip bars 26 in use. 
As shown particularly in FIG. 2, each of the grip bars 26 has a planar 
surface 50 formed on the lower portion of grip bar 28. A rectangular 
notch, seat or recess 52 is formed in the planar surface 50 of each grip 
bar 26 to receive and secure laterally opposed grip jaw inserts 54 and 56 
in grip bars 28. 
Grip jaw inserts 54 and 56, shown in chain line or phantom in FIG. 1, are 
typical of a set of such inserts that can be employed with textile test 
specimens in the practice of the present invention. As illustrated, jaw 
inserts 54 and 56 are wider than their respective supporting grip bars 28. 
For example, grip bars 28 may be of a width or diameter of about 11/8 
inches, whereas the grip jaw inserts 54 and 56, illustrated in FIG. 1, are 
about 9 inches wide.times.11/2 inches high.times.11/32 inch deep. 
Obviously, none of the foregoing dimensions are intended to be critical. 
However, the preferred practice of one aspect of the invention is based on 
the premise that for textile test specimens or the like there is a need 
for, and, the invention provides, a grip apparatus in which the set of 
grip jaw inserts 54 and 56 are wider than the respective width of the 
supporting jaw members or grip bars 28. This difference in width may vary 
from a relatively moderate difference to a rather substantial difference, 
such as a ratio of 12:1 or more. 
For the purpose of securing grip jaw inserts 54 and 56 to jaw members or 
grip bars 28 and, in addition, for ease of removal and replacement of such 
jaw inserts, there is provided an arrangement including bores or apertures 
58 in housing 12 and recessed threaded retainers 60 received in and 
passing through countersunk holes 62 in grip bars 28. The threaded 
retainers 60 are secured in a threaded bore (not shown) located centrally 
in the grip inserts 54 and 56. Threaded retainers 60 are preferably of a 
type having an allen head. It will be understood that, by aligning 
threaded retainers 60 with apertures 58, grip inserts 54 and 56 can be 
easily installed, removed or replaced by use of an allen wrench inserted 
through apertures 58. 
The finish provided on the specimen gripping surface of inserts 54 and 56 
can be chosen to suit the particular material being tensile tested. Thus, 
the gripping surface can be cross-scored, serrated, in the nature of a 
sand paper finish or any other finish that is found to be desirable. It 
will also be noted that the grip inserts illustrated in FIG. 1 are shown 
to be provided on their extreme ends with a clamping arrangement 
comprising a threaded rod 64 pivotally mounted to one grip insert and a 
suitable locking nut 66. As will be understood, the grip inserts 54 and 56 
are provided at their ends with a groove (not shown) to accommodate 
receiving threaded rod 64 therein. Also, as shown, locking nut 66 is 
preferably provided with a convenient hand wheel 68 for ease of 
tightening. 
Grip bars 28 and grip jaw inserts 54 and 56, of the apparatus of this 
invention, can be made of any suitable rigid material having sufficient 
strength to withstand the range of tensile stress to be applied to a 
particular work piece or test specimen. In a preferred embodiment of this 
invention, grip bars 28 and grip jaw inserts 54 and 56 are made of steel. 
A further improvement in the test specimen grip apparatus 10 of this 
invention resides in the provision of fluid actuation means for grip bars 
28 and, accordingly, for the grip jaw inserts 54 and 56 that are secured 
thereon. In this connection, there is mounted on housing 12 a fluid 
control valve 70 and a double acting, piston-cylinder assembly 72. The 
center line of piston-cylinder assembly 72 is parallel to and rearwardly 
spaced from the central longitudinal axis 86 of housing 12, in a plane 
that bisects housing 12. One end of a drive plate 74 is secured by an 
allen head screw 76 to the upper end of piston rod extension 78, of the 
piston cylinder assembly 72. Drive plate 74 is provided with a transverse 
pin 80 secured by a set screw 82 in a bore (not shown) in the opposite end 
of drive plate 74 from its attachment to piston rod extension 78. Drive 
plate pin 80 bridges and loosely nests between the pair of mutually spaced 
aligned pins 36 extending outwardly from grip bars 28 toward rear surface 
16 of housing 12. A collar 84 is secured by set screws at a selected 
position near each end of drive plate pin 80. The position of collars 84 
on drive plate pin 80 sets and determines the length of stroke of the 
piston portion of piston-cylinder assembly 72. 
In operation, a fluid, which may be a pneumatic or hydraulic fluid but in 
the preferred embodiment shown in compressed air, is introduced into valve 
inlet fitting 88 of fluid control valve 70. Movement of valve control hand 
lever 90 to a first position allows the compressed air to pass through 
valve 70 to the lower end of piston-cylinder assembly 72, driving the 
piston and the piston rod extension 78 upward and, through the interaction 
of drive plate pin 80 with grip bar pins 36, to raise the grip bars 28 to 
their upper or open operating position, for either mounting or removing a 
test specimen from grip apparatus 10. Retained air in the upper end of 
piston-cylinder assembly 72 escapes through a sintered metal exhaust 
filter 92, shown mounted on fluid control valve 70. Conversely, movement 
of the valve control hand lever 90 to a second position allows the 
compressed air to pass through valve 70 to the upper end of 
piston-cylinder assembly 72, simultaneously closing off the exhaust and 
driving the piston and the piston rod extension 78 downward, and, through 
the interaction of drive plate pin 80 with grip bar pins 36, to lower the 
grip bars 28 to their lower or closed operating position for tensile 
testing of a test specimen. 
An example of a suitable valve 70, for use in with this invention, is a MAC 
1100A Series valve, available from MAC.RTM. Valves, Inc., P.O. Box 111, 
30569 Beck Road, Wixam, Mich. 48096 or their distributors. An example of a 
piston-cylinder assembly 72, that has been found particularly 
satisfactory, is a HUSKY.TM. Square Base Mount Cylinder B158.times.112, 
available from Compact Air Products, Inc., P.O. Box 176, Rt. 1, Hwy. 123, 
Westminster, SC 29693. 
Also, shown in FIGS. 1 and 2, is a convenient thumb screw feature of this 
invention wherein a thumb screw 94 is threadedly secured in the front 
surface 14 of housing 12, directly opposite to one of the grip bars 28, 
such that, by tightening the thumb screw 94, it bears against its 
associated grip bar 28. Thumb screw 94 is useful with grip apparatus, such 
as the grip apparatus disclosed in applicant's U.S. Pat. No. 4,662,229 or 
the grip apparatus disclosed herein, for the purpose of locking 
interconnected grip bars 28 in a selected open position, such as when 
removing and replacing grip inserts 54 and 56. 
A threaded hole 96, in the connecting end surface 18 of housing 12, is 
provided to connect grip apparatus 10 to tensile testing machines. 
Moreover, hole 96 is adapted to receive a connector (not shown) having 
both external and internal threads for the purpose of adapting grip 
apparatus 10 to certain of the testing machines. In any event, hole 96, or 
hole 96 and said connector-adaptor, or other suitable connecting means can 
be used to enable connection of grip apparatus 10 to any type of existing 
tensile stress testing apparatus. 
Maintenance of a suitable angle formed between grip bars 28 is useful in 
providing a grip apparatus of exceptional strength and gripping force, 
even when the housing is constructed of light weight materials, such as 
aluminum. One convenient manner of describing that angle is the angle 
formed between the central longitudinal axis of bores of passages 26 that 
provide required wedging surfaces and the central longitudinal axis 86 of 
housing 12. A suitable range for that angle in the apparatus of this 
invention is from approximately 10 degrees to approximately 40 degrees. In 
a preferred embodiment of this invention, that angle is 15 degrees. 
The apparatus of the invention provides a wedge grip that can be used with 
new or previously known tensile stress testing apparatus to test low, 
medium or high tensile strength materials without risk of failure of the 
grip apparatus. The grip apparatus of this invention is of relatively 
simple and inexpensive construction, can be made of relatively light 
weight materials, and can be so constructed as to have a relatively low 
gross weight for the grip apparatus. The apparatus of this invention 
provides the further advantage of permitting easy and rapid removal and 
replacement of the grip jaw inserts without removal of the grip apparatus 
from the test device and without substantial disassembly of the grip 
apparatus. The apparatus is particularly useful for tensile testing 
textile materials. 
Although the apparatus of this invention has been described with respect to 
its use with tensile stress testing apparatus, the apparatus of the 
invention can be used with other types of material strength or stress 
testing apparatus, such as testing apparatus used to test resistance to 
torsion or bending. 
According to the provisions of the patent statutes, I have explained the 
principle, preferred construction and mode of operation of my invention 
and have illustrated and described what I now consider to represent its 
best embodiments. However, it should be understood that, within the scope 
of the appended claims, the invention may be practiced otherwise than as 
specifically illustrated and described.