There are many types of jigs that are used on UTMs. 

Let’s focus bit more on the most common types used in tensile tests. 

Wedge action grips and side action grips. 

Let’s find out how they work and when they are used so that we can choose the right grip for the right material testing.

Wedge action grips are recommended for samples that need to be held tightly. 

Ex: Metals, hard plastics etc.

Side action grips are for softer samples that have risk of breaking 

or tearing if too much tension is applied upon the sample. 

Ex: soft plastic, textiles, films etc.

WEDGE ACTION GRIPS

Just as the name explains this grip has a funnel shape groove with a set of jaws in a wedge shape. 

The wedge shaped jaws slide on the slanted “funnel” shape wall on the grip to adjust opening sizes. 

*When the wedge shaped jaws are pulled upwards towards the 

larger area of the funnel shape their spaces between becomes greater. 

As the wedge shape jaws are pulled/pushed downwards towards the 

smaller area of the funnel shape the jaw spaces become tighter.

Once the tensile test begins with the samples gripped in the jaws, the tension of the grip pulling upward 

and the sample being held down by the bottom jaws will drag the top jaws down along with the sample. 

This action creates the jaws to slide down the funnel shaped walls creating a tighter space.

1.During a tensile test the cross head pulls upward along with the attached grips. 

2.The sample held by the bottom jaws resist the tension that’s being pulled upwards thus creating an opposite force. 

3.The jaws gripping on to the sample gets dragged downwards holding on to the sample tigher and tigher.

Advantages

-The more sample tries to slip, the wedge action grip hold the sample tighter keeping it from slipping out.

-Less force is required to hold a sample compared to side action.

(If 100kN wedge grip is needed to hold a sample during a test, in order to grip the sample with equal amount of force a much larger side action grip will be needed.)

 Disadvantages

-Symmetrical sample clamping only recommended

-Heavy fixture

-Clamping force on the sample is hard to adjust

Availiable types of Wedge grips

Mechanical (Manual), Penumatic and Hydraulic.

SIDE ACTION GRIPS

Side action grips are a type of grip that jaws grip the samples from both sides. It has an equal holding force through out the test which is more suitable for “softer” material. Materials that are pron to tear or rips would use such grips.

There are single bolt action(single action) or double side action grips. Single side has one side that is fixed at a certain position and the other side will move to grip the sample. On the other hand you will be able to control the movement and claming of both jaws on the grips on the double side action grips.

Side action grips are usually recommended for tests/samples that does not require high capacity clamping. Side action grips decreases in clamping force as tension builds and the sample tries to slip out. This can be good because softer samples do not rip or tear. This also can be bad because the samples can slip out of the grips.

Advantages

-Force control on clamping is easier to control than the wedge action. (Good for tests that require clamping force)

-Since the jaws hold on to the sample with equal or less amount of force through out the test,

a tare or rip is less likely to happen on film/softer sample materials.

-Light fixture on low capacity testing.

-Able to grip symmetrical and asymmetrical samples

Disadvantages

-Requires larger grip to hold sample in the same amount of force as a wedge action grip.

-More chance of sample slippage compared to wedge action

Availiable types of Wedge grips

Double and Single Mechanical (Manual), Penumatic and Hydraulic.

Please visit our previous blog post to see more grips and jig types that may interest you.

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