SIMPLE TENSILE WEDGE GRIPS

As also noted in Section E-1, there are two basic types of mechanical wedge grips. Either the wedges move as they tighten on the specimen and the bodies of the grips remain stationary, or the grip bodies move and the wedges remain stationary while being tightened on the specimen. In Wyoming Test Fixtures, Inc. terminology, the former are termed “simple grips” and the latter are termed “standard grips“.

The “simple” wedge grips are easier to fabricate and thus are less expensive. The “standard” wedge grips, because the wedges do not move axially relative to the specimen during clamping, do not have the potential of putting the tensile specimen in compression, possibly damaging it as they are tightened. But of course, with most specimen materials this may not be a damaging effect. And when using simple wedge grips it is possible to disconnect the one grip from the testing machine while engaging the specimen, thus avoiding the potential problem.

An example of a simple wedge grip is shown in the following photograph. Note that a screw on each side of each grip, pushing on a plate against the tops of the wedge grip inserts, is used to tighten the grip onto the specimen prior to the test.

10,000 lb. Capacity Simple Wedge Grip
1” Wide Flat Specimen, 1.5” Grip Length

Of course, once a loading is applied to the test specimen, the wedging action takes over, to grip the specimen in proportion to the magnitude of the loading being applied, just as for a standard grip. The springs retract the grip inserts when opening the grips.

The photograph below shows a similar simple grip, but with the tightening screws in the top of the grip, another option. Although the screws cannot be seen in this photograph, the push plate can. Note that this grip has vee-grip inserts mounted in it, for gripping round specimens. All types of grip inserts can be provided (see Section F-3).

15,000 lb. Capacity Simple Wedge Grips
Thermal Sprayed Vee-Grips for Round Specimens

The next photograph is another example of simple grips with top screws and pusher plates. These grips are for wide specimens such as geotextiles tested per ASTM D 4595.

Four-Inch Wide Tensile Wedge Grips, 1000 lb Capacity

Sometimes space is very limited, such as when performing tensile testing at cryogenic temperatures in a dewar. The next photograph shows 20,000 lb capacity compact wedge grips fabricated of 310 stainless steel.

Compact Tensile Wedge Grips, 310 Stainless Steel, 20,000 lb. Capacity at Cryogenic Temperatures

A very attractive version of simple wedge grips is that shown in the following photograph. Rather than using screws, at either the top or at the sides of the grip body, to push the wedges against the test specimen, these grips have a hand wheel to tighten the grips.

 Simple Wedge Grips with Hand Wheels for Tightening Wedges

Grips Shown are 5,000 lb Capacity, 1” Wide