Grips for Fatigue Testing

Written by Chris Thomas, Universal Grip Company · Reviewed by Frank Bertini · Updated October 17, 2026

Fatigue testing grips hold a specimen through thousands or millions of load cycles on a dynamic universal testing machine without loosening, slipping or adding play, and they do it in both directions: a fatigue grip must carry tension and compression through the same jaw faces, so the specimen cannot shift at every load reversal. Universal Grip machines fatigue grips to order from hardened steel in 10 kN, 50 kN and 100 kN capacities, with quick-action, environmental-chamber and wide-specimen versions, plus the ASTM E399 clevis grips used for fracture and crack-growth testing and an ISO 14801 fixture for dental implants.

This page explains what makes a fatigue grip different from a static tensile grip, how to choose a capacity and jaw arrangement, what each of our grips is built for, the standards they serve, how they mount to servo-hydraulic and electromechanical frames, the setup details that keep cyclic data clean, and the mistakes that end fatigue tests early. For the grips used in monotonic tensile tests, see the tensile grips range; for fixtures that hold specimens in bending, shear or compression fatigue, see the bend, shear and compression fixture pages.

In this guide: What a Fatigue Grip Does · How to Choose a Fatigue Grip · The Fatigue Grip Range · Standards Served · Machine Compatibility and Mounting · Setup and Best Practices · Common Mistakes · Related Products · FAQ

What a Fatigue Grip Does

A static tensile grip only has to hold the specimen while the load rises in one direction. Wedge and roller grips exploit that: the harder the pull, the tighter they clamp. Reverse the load and the same geometry lets go. A fatigue grip has to be rigid in both directions, so it is built as a vise-action fixture with a solid backstop: the specimen end sits against a block that reacts compression, side screws clamp the jaw faces laterally so the specimen cannot slide in tension, and the whole body is a single hardened-steel block with no wedge angles, no pivots and no springs to work loose over a million cycles.

That construction is what makes fatigue grips useful on dynamic machines for the tension-compression and tension-tension tests of ASTM E466 (force-controlled axial fatigue of metals), ASTM E606 (strain-controlled low-cycle fatigue), ASTM D3479 (tension-tension fatigue of composites), ISO 1099 and ISO 12106, and for the cyclic loading of components such as implants, springs, fasteners and bonded joints. The same grips also work for static tests; the reverse is not true.

Who uses them: metals and alloy producers qualifying fatigue curves; aerospace and automotive labs running composite and joint fatigue; biomedical companies testing implants, stents, sutures and orthopaedic devices to ISO and FDA protocols; universities and research institutes with servo-hydraulic frames; and any quality lab that has to show a part survives a stated number of cycles at a stated load.

How to Choose a Fatigue Grip

Four decisions set the right grip. Work through them with your specimen drawing in hand.

• Capacity. Pick the grip for the peak force in the cycle, not the mean: a fully reversed test at ± 40 kN needs a 50 kN grip, and the grip should be matched to the actuator and load cell rather than oversized, because a heavier grip adds mass that the machine has to accelerate at every cycle. Our 10 kN grip covers biomedical and polymer specimens, 50 kN most metal coupons, and 100 kN large coupons, components and composites.

• Specimen shape. Flat coupons need flat serrated faces at least as wide as the specimen; round specimens need V-faces or button-head and threaded holders (see our bolt grips and shoulder grips for round and shouldered ends). The 10 kN grips are available for both rounds and flats.

• Clamping method. Standard fatigue grips clamp with several side screws, which gives the most even pressure. If specimens change many times a day, the quick-action version with oversized bolts cuts the changeover time, provided the specimen and loads suit it.

• Environment. Tests at elevated or sub-ambient temperature need grips that fit inside a chamber and resist corrosion: our chamber version mounts on long tubes so the jaws sit in the working zone of an environmental chamber while the actuator and load cell stay outside.

Then check the mounting: fatigue grips attach with a high-thread-count fatigue stud, preloaded so the joint never opens under reversed load, and the stud size must match the load cell and actuator threads of your machine. Our adapters page lists the common thread and stud sizes by machine brand; tell us the make and model and we supply the matching stud or coupling.

The Fatigue Grip Range

All fatigue grips are custom designed and machined to order from hardened steel, so delivery takes a few extra weeks compared with stock tensile grips. The standard capacities below are the starting points; jaw faces, openings and mounting are then matched to your specimen and machine.

10 kN mechanical fatigue grips

The 10 kN grips (about 2,250 lbf) suit lower-force cyclic testing and are available for both round and flat specimens. The capacity covers most of the biomedical field, where specimens such as polymer coupons, sutures, small implants and fixation devices rarely exceed a few kilonewtons, and it keeps the moving mass low on small servo-hydraulic and electrodynamic frames, which helps the controller hold the waveform at higher frequencies.

50 kN mechanical fatigue grips

The 50 kN grips test specimens in both tension and compression. The body is machined from hardened steel and phosphate coated for corrosion resistance, and the grip faces can be customised to the specimen, for example a 2 × 4 in (height × width) face for wide flat coupons. This is the general-purpose size for metal fatigue coupons per ASTM E466 and E606 and for composite coupons per D3479.

100 kN mechanical fatigue grips

The 100 kN grips are machined from A6 tool steel with a nickel coating, which lets them operate across a wide range of temperature and humidity. The serrated jaw faces accept specimens up to 100 mm wide and 60 mm deep, and the grips attach to the dynamic machine through a high-thread-count fatigue stud so the connection stays preloaded through reversed loading. Use them for large coupons, structural components and thick composite laminates.

Quick-action fatigue grips

Tightening a row of screws for every specimen is the slowest part of a fatigue program. The quick-action version secures the specimen with oversized bolts instead, so there are fewer fasteners to tighten between tests. It does not suit every specimen or load case, but where it fits it shortens the changeover without giving up the rigid, two-direction clamping that fatigue testing needs.

Fatigue grips for environmental chambers

Many fatigue tests run hot or cold. For those, nickel-alloy-plated fatigue grips are mounted on long tubes so the jaws reach into the chamber while the load cell and actuator stay in room air. Universal Grip also offers temperature chamber add-on kits that fit any dual-column universal testing machine; see the environmental chambers page for ranges and sizes.

Fatigue grips for wide or thick specimens

Extra wide or extra thick specimens get a custom-designed grip. The example in the photo holds specimens up to 40 mm wide and 20 mm thick (the tightening screws are removed in the picture to show the body). Tell us the specimen envelope and the peak load and we design the jaw opening, face size and screw pattern around it.

Dental implant fatigue fixture (ISO 14801)

The dental implant fatigue fixture holds an endosseous implant at the specified angle inside a fluid bath so it can be loaded cyclically, as in ISO 14801 fatigue testing of dental implants. The angle, the embedding and the fluid environment are all part of the standard; the fixture sets them so the test reproduces the loading of an implant in the jaw.

ASTM E399 clevis grips

Clevis grips load compact-tension specimens through pins for fracture toughness (K Ic) per ASTM E399 and fatigue crack growth per ASTM E647. The pin loading lets the specimen rotate freely as the crack opens, which the standards require, and the clevis flats and pin holes are machined to the standard's proportions for the specimen width. The same grips serve E647 pre-cracking and crack-growth cycling on a fatigue machine.

Standards Served

A fatigue grip is not standard-specific the way a peel or shear fixture is; it is matched to specimen shape and load. These are the methods our customers most often run with them:

• ASTM E466: force-controlled constant-amplitude axial fatigue of metals. Flat or round coupons in the 10, 50 or 100 kN grips depending on section and stress.

• ASTM E606 / ISO 12106: strain-controlled (low-cycle) fatigue, with an extensometer on the gauge length; grip rigidity matters most here because compression half-cycles buckle a loosely held specimen. See our clip-on extensometers.

• ASTM E647 and E399: fatigue crack growth and fracture toughness on compact-tension specimens, with the clevis grips.

• ASTM D3479: tension-tension fatigue of polymer matrix composites, usually in the 50 kN or 100 kN grips with tabbed coupons as in ASTM D3039.

• ISO 14801: dynamic fatigue of endosseous dental implants, with the implant fixture.

• Component and product fatigue: springs, fasteners (ASTM F1554 anchor bolts, A370 products), bonded joints (ASTM D1002 lap shear in fatigue), orthopaedic and cardiovascular devices, and sandwich panels in flatwise fatigue.

If a specification names the grip or the alignment class, send it with the inquiry; fatigue grips are custom-built anyway, so the drawing is the fastest route to a quote.

Machine Compatibility and Mounting

Fatigue grips are used on servo-hydraulic and electrodynamic frames from Instron, MTS, Shimadzu, ZwickRoell and others, and on electromechanical universal testing machines for low-frequency cyclic tests. The grip body is the same; what changes is the connection. Three things decide it:

• The fatigue stud. A high-thread-count stud, preloaded against the load cell and actuator faces, so the threaded joint never sees a gap under reversed load. The thread size follows the machine; we match it from the make and model.

• Alignment. Fatigue standards limit bending strain in the specimen, and most of the bending comes from the load string, not the specimen. Rigid, concentric mounting through a straight stud is the first step; an alignment fixture (ASTM E1012) and shimming the grip faces is the second. Grips are supplied with parallel, square faces so that a correctly mounted specimen is straight.

• Clearance. Check the daylight between actuator and load cell with both grips fitted, especially with the chamber version on tubes, and check that the grip body clears the chamber door and ports.

For standard capacities and thread conventions by brand, see our adapters page. Hydraulic machines with large load strings may prefer our hydraulic grips for static work and the fatigue grips for cyclic programs.

Setup and Best Practices

• Torque the side screws evenly in a star pattern, in two or three passes, so the jaw pressure is uniform across the face. Uneven clamping is the usual cause of specimens walking out of a grip during the first thousand cycles.

• Seat the specimen against the backstop before clamping, so compression half-cycles load the block and not the screws.

• Preload the stud to the machine maker's figure and re-check it after the first run at load; a stud that works loose shows up as a growing phase lag between force and displacement.

• Check alignment with a strain-gauged specimen when the standard limits bending (E466, E606), and after any change of grips or load cell.

• Use the right faces. Serrated faces for metals and composites; smoother or softer inserts for polymers and thin-walled parts that serrations would notch. A notch at the jaw edge is a fatigue crack starter, so grip failures count as invalid tests.

• Keep moving mass low at high frequency. The lighter 10 kN grips let a small frame hold its waveform; the 100 kN grips are meant for the loads that need them, not for small specimens.

• Inspect faces and screws between programs; a million cycles of fretting at the jaw face dulls serrations and loosens hardware.

Common Mistakes

• Running reversed (R < 0) loading in wedge or roller grips, which let go in compression.

• Sizing the grip to the machine's capacity instead of the specimen's peak load, adding mass the actuator has to drive.

• Clamping with the specimen off the backstop, so the screws carry the compression.

• Serrated faces on a polymer or thin-wall part, starting the failure at the jaw.

• A loose or wrong-thread stud, giving play at every reversal and a false hysteresis loop.

• No alignment check after changing grips, in a strain-controlled test that limits bending.

• Chamber tests with standard grips, which corrode or lose hardness, instead of the plated chamber version on tubes.

Related Products

• Tensile grips for static tests: wedge, pneumatic, vise, roller and more.

• Bolt grips and shoulder grips for threaded and shouldered round specimens.

• Hydraulic grips for high-capacity static testing.

• Environmental chambers and chamber add-on kits.

• Clip-on extensometers for strain-controlled fatigue and video extensometers for non-contact strain.

• Adapters and fatigue studs for any machine brand.

• Universal testing machines for low-frequency cyclic and static programs.

Fatigue Grip FAQ

What is the difference between a fatigue grip and a tensile grip?

A tensile grip only has to hold the specimen while the load rises in one direction, so wedge and roller designs tighten with the pull and let go when it reverses. A fatigue grip is a rigid vise-action fixture with a solid backstop that holds the specimen in both tension and compression without play, so it can run reversed loading for millions of cycles.

What capacities do Universal Grip fatigue grips come in?

Standard capacities are 10 kN (about 2,250 lbf), 50 kN and 100 kN, each machined to order from hardened steel. Quick-action, environmental-chamber and wide-specimen versions are built on the same designs.

Can fatigue grips do compression as well as tension?

Yes. A solid block backstops the specimen for compression and the side screws clamp it laterally for tension, so the grips carry fully reversed (tension-compression) cycles.

How do fatigue grips attach to the machine?

Through a high-thread-count fatigue stud that is preloaded against the load cell and actuator so the joint never opens under reversed load. The stud thread is matched to your machine's make and model; see the adapters page.

Which standards are fatigue grips used for?

ASTM E466 and ISO 1099 force-controlled fatigue, ASTM E606 and ISO 12106 strain-controlled fatigue, ASTM D3479 composite fatigue, ASTM E647 crack growth and E399 fracture toughness (with clevis grips), ISO 14801 dental implant fatigue, and cyclic tests of components, fasteners and bonded joints.

Do you make fatigue grips for environmental chambers?

Yes. Nickel-alloy-plated fatigue grips are mounted on long tubes so the jaws sit inside the chamber while the load cell and actuator stay outside, and we supply chamber add-on kits for any dual-column universal testing machine.

What specimen sizes do the 100 kN grips take?

The 100 kN grips have serrated jaw faces that accept specimens up to 100 mm wide and 60 mm deep. Larger or thicker specimens, such as 40 mm wide by 20 mm thick coupons, are handled with a custom-designed grip.

How long does delivery take?

Fatigue grips are custom designed and machined to order, so allow a few extra weeks compared with stock tensile grips. Sending the specimen drawing, peak load and machine model with the inquiry shortens the design stage.

What are quick-action fatigue grips?

A version that secures the specimen with oversized bolts instead of a row of small screws, so there are fewer fasteners to tighten between tests. It suits programs with frequent specimen changes but not every specimen or load case.

Will fatigue grips work on an electromechanical universal testing machine?

Yes. The grips are mechanical and mount through a stud or coupling, so they run low-frequency cyclic tests on electromechanical frames as well as high-frequency tests on servo-hydraulic and electrodynamic machines.

Need fatigue grips for a specific specimen or machine? Contact Universal Grip with the specimen drawing, the peak load and R-ratio, the test temperature and your machine's make and model, and we will design and quote the grips, stud and any chamber tubes as one setup.