Tensile testing grips include manual vise grips, pneumatic grips, wedge grips, hydraulic grips, rope and thread grips, webbing grips, pinching, and self-tightening grips. Choosing the most appropriate tensile grips to effectively secure your samples is critical in getting accurate measurements of tensile properties such as tensile strength, peak load, elongation, tensile modulus, and yield. This post will walk you through the different tensile grips while showing how each grip is best suited to specific tensile test specimens.
Manual Vise Tensile Grips
Manual vise grips are versatile tensile grips with capacities up to 50kN. Their ease of use and large opening width make them the most popular tensile grips. However, the manual tightening mechanism of vise grips does not provide as high of a clamping force as some other tensile grip options like pneumatic and self-tightening eccentric roller grips. Depending on the material properties of your test specimen and the specific test application, consider exploring different tensile grip options if you’re experiencing problems with manual vise grips.
Pneumatic Tensile Grips
Pneumatic vise grips and eccentric roller grips are often used with high-elongation materials such as rubber and are recommended for ASTM D412 and ASTM D624 testing as they ensure constant clamping force throughout the test as the material elongates. In addition, pneumatic grips feature dual acting jaw faces that move to the centerline of the sample with air pressure, assuring correct sample alignment while allowing the user to adjust the pneumatic pressure to securely grip the samples.
Wedge Tensile Grips
The recommended tensile grips for materials that require a high clamping force at higher forces are wedge grips, which operate with a self-intensifying clamping mechanism.
ADMET’s lower capacity wedge grips operate with springs and a handle to open and close the dual acting jaw faces that move to a centered position when tightened. Depending on the model chosen, higher capacity wedge grips may come with handle extrusions (GW-10T), a retaining knob, or a door (GW-XT) that must be closed after the tensile specimen is secured in the jaw faces. ADMET also offers moving body wedge grips (GW-527) that avoid applying compressive loads on the samples as well as wedge grips that are designed to be installed in environmental chambers for high temperature testing (GW-T-T).
Wedge grips are the most common tensile grip types for metals testing as they are recommended in ASTM E8 test method.
Hydraulic Tensile Grips
Hydraulic grips provide the highest force for gripping samples. ADMET hydraulic grips can go up to 3,000kN capacity and are often used with hydraulic machines and their hydraulic pumps. These grips are ideal for testing rigid materials that require high force.
Pinching Tensile Grips
For low capacity testing where sample sizes are too small or non-standard to be secured by vise grip jaws, we recommend using pinching grips. Pinching grips are often used to test electronic components and biomaterials. Pinching grips can be chain mounted for flexible positioning or pneumatically controlled to provide easier clamping and automatic sample alignment.
Tensile Grips for Rope, Thread, and Webbing
Tensile grips for certain samples such as rope, thread, and webbing come with custom designs. Thread grips (GT-T) are applicable for cords, fine wires, and narrow ribbons whereas rope grips (GR-T) are used with larger diameter samples such as yarns, cords, and wire strands. Self-tightening scissor grips (GSS-T) are recommended for thick elastomers and materials with non-standard shapes such as plastic belts. Webbing grips (GRW-T) are designed with a center slot and a drum that is rotated and then pinned to lock it in place. As the material is pulled, it tightens itself and the drum offers stress relief and prevents the breakage of the specimen in the clamping area. Coated textiles that may easily slip from other tensile grip types can be securely gripped and pulled with webbing grips. We offer standard as well as custom rope, thread, webbing, and scissor grips where the customer can modify drum, roller, or jaw dimensions to accommodate their samples.
Other Tensile Grips
Other tensile grips include hook grips, loop testing grips, and o-ring tensile testing grips. ADMET also makes grips and fixtures conforming to many testing standards. Check out our ASTM Grips & Fixtures and Other Grips pages or contact an engineer to discuss the details.
Getting the Right Grips with ADMET
In order to determine the best suited tensile grips for your tests, our Sales Engineers will walk you through a diagnostic sales process where the details of your test application and test specimen material characteristics such as sample material, dimensions, shapes, and elongation properties are discussed in detail.
In addition to grips, ADMET offers a full line of testing accessories. Certain ASTM standards, such as ASTM E8 and ASTM D638, require the use of an extensometer to measure elongation. Check our extensometers page or talk to one of our engineers and we’ll recommend the right equipment for your testing needs.