Tensile Machine Fixtures: Pneumatic Tensile Grips – Types, Principle & Selection

Tensile machine fixtures are core accessories of universal material testing machines, which directly affect test accuracy, sample clamping stability and repeatability of test data. Following our previous introduction to peel test fixtures and wedge tensile grips, this article focuses on pneumatic tensile grips. We will explain their working principle, main types, applicable test materials and key points for proper fixture selection, helping laboratories and manufacturers pick suitable pneumatic grips for tensile, elongation and strength tests.

What Are Pneumatic Tensile Grips?

Pneumatic tensile grips, also called air-operated tensile clamps, are sample holding fixtures for universal material testing machines. They use compressed air to drive jaw movement to securely fasten test specimens. Unlike manual or wedge grips that require hand tightening, pneumatic grips deliver consistent clamping force via air pressure control. They are widely adopted in high-volume testing laboratories for standardized material tensile tests.

Working Principle of Pneumatic Tensile Grips

The core working principle relies on compressed air power. When the air supply is turned on, compressed air enters the built-in air cylinder inside the grip body. The cylinder piston pushes the jaw assembly to close, applying even clamping pressure on both sides of the test sample.

Operators can adjust air pressure on the regulator to change clamping force. This design ensures uniform pressure across the sample width, minimizing sample slipping during tension loading. When a test finishes, air pressure releases automatically, and the jaws open to release the specimen quickly.

Common Types of Pneumatic Tensile Grips

Pneumatic tensile grips are categorized mainly by jaw insert configurations to match different specimen properties.

1. Flat Smooth Jaw Inserts Smooth flat jaws are designed for thin, soft materials such as films, foils and non-woven fabrics. They prevent surface damage while holding flexible samples firmly.
2. Flat Serrated Jaw Inserts Serrated flat jaws feature fine teeth on contact surfaces. They are the most universal type for rigid and semi-rigid samples like plastic sheets, composite panels and rubber strips, to avoid specimen slippage.
3. V-Type Jaw Inserts V-shaped inserts are used for round specimens, including metal wires, rods, cables and cylindrical extrusions. The V groove centers round samples automatically to guarantee axial alignment during tensile loading.
4. Custom Profiled Jaw Inserts Custom jaws are manufactured to match special-shaped samples, such as extruded profiles, hoses and pre-cut unique test pieces for bespoke material test requirements.

Applicable Test Samples & Relevant Standards

Pneumatic tensile grips fit a broad range of materials for tensile, breaking strength and elongation tests.

• Flexible materials: plastic film, textile, adhesive tape, nonwoven fabric
• Polymer materials: rubber, plastic sheets, composite materials
• Metal specimens: thin metal sheet, copper foil, aluminium wire, small metal rod

These grips support tests compliant with major international standards including ASTM D638, ASTM D412, ISO 527 and ISO 37, ideal for quality control labs, R&D departments and third-party testing institutions.

Key Factors to Select Pneumatic Tensile Grips

Selecting the correct pneumatic grips is critical to avoid test failure, sample slippage or premature specimen breakage at the clamping area.

1. Maximum Test Load Match grip rated load to your universal tester capacity and expected maximum breaking force of samples. Overloading will damage air cylinder and grip body.
2. Specimen Shape & Dimension Confirm sample width, thickness and geometry. Flat samples use flat jaws; round wires require V-type jaw inserts.
3. Material Hardness Soft delicate materials need smooth jaws to prevent jaw piercing. Hard, slippery materials need serrated jaws for high friction.
4. Air Pressure Range Check the operating air pressure requirement. Most standard pneumatic grips work within 0.4–0.7 MPa compressed air supply.
5. Machine Connection Interface Ensure the grip top adapter matches the crosshead connection of your existing tensile testing machine.

Wrap-up

Pneumatic tensile grips offer repeatable, fast and evenly controlled clamping compared with wedge or manual grips, which makes them a top choice for high-frequency material tensile testing. Understanding grip types, working principle and selection criteria helps you avoid common testing pitfalls. If you need custom jaw inserts or have special specimen testing demands, feel free to contact our engineering team for tailored fixture solutions for your universal tensile machine.