How to Prepare Samples for Dynamic Mechanical Analysis (DMA)

How to prepare samples for measurements in DMA

This video demonstrates how to prepare samples for dynamic mechanical analysis (DMA) using single and dual bending clamps.

The preparation required for tension samples, and the use of the fluid bath for immersion studies, are also explained.

The cooling performance of the DMA is very impressive and samples can be analyzed from –190 °C. Secondary transitions (β-relaxation) can be studied, as well as larger re-organizations at higher temperatures, such as the glass transition (α-relaxation).

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Sample preparation for DMA is also detailed in our TA tips and hints guide

Dynamic Mechanical Analysis (DMA)

The Mettler Toledo DMA, is a versatile, easy to use DMA allowing you to measure properties in all kinds of materials such as amorphous and semi-crystalline polymers, blends, composites, metals, ceramics and reactive polymers, to name a few.

Apart from DMA measurements, it is also possible to make measurements using the static force. Examples include creep, determination of coefficients of thermal expansion and stress-strain measurements.

To cope with different sample geometries, the DMA offers the following measurement modes.

Three Point Bending
Single and dual cantilever
Tension
Compression and
Shear

The sample holders, clamps, clamping tools and screws are stored in an accessory box that comes with the DMA.

With the Fluid bath option, it is also possible to perform DMA experiments in liquids. This option is available with all measurement modes.

Today, we will show you DMA sample preparation for the more commonly used modes. These being three point bending, single cantilever and tension.

For the three point bending mode and single cantilever, we will make use of printed circuit board as the sample.

For tension, we will use a polyethylene terephthalate film with a thickness of 0.18 micrometer.
In the fluid bath we will use sewing thread in tension mode.

Let's start with the sample preparation for a three point bending mode.

First we can measure the metal sample's width and thickness with a Vernier caliper. The sample length is given by the distance of the outer clamps.

The sample holder is set up for three point bending mode.

Initially, we need to bring the measuring head into the vertical position.
Then, we need to fix the two outer clamp bars with the V shaped edge facing upward with screws. Now carefully place the sample in the three point bending clamp.
Once this is done, we can fit the middle clamp bar with the V shaped edge facing downward. Then gently screw the two extended nuts onto the middle clamp bar without tightening them.

Now we need to check that the sample is positioned straight in the clamps and the sides are not in contact with the clamps.

Once we are happy with the position of the sample, we can finger tighten the two extended nuts on the central clamp. Be careful not to cause unwanted force on the sample by tightening the nuts too much.

You can check the force applied when tightening the central screws in the preparation dialog on the touch screen.

Once the force has been applied, loosen the securing screw of the temperature sensor with a one point two seven millimeter Allen key. Position the temperature sensor as close as possible to the sample without touching it. Then tighten the securing screw.

The sample is now ready for measurement.

Next we will look at the sample preparation for Single cantilever.

First we can measure the PCB sample width and thickness using the Vernier calipers. The sample length is given by the distance of the inner to the outer clamp.

Rotate the measuring head to the vertical position. Now we need to fit two lower clamp bars. One in the central position and the other on the outer clamp position, on the temperature probe side.

Following this, we then place the sample on the clamp bars. Now we can fit the upper two clamp bars. Screw on the four extended nuts and tighten equally, so they are just finger tight.

Loosen the securing screw of the temperature sensor with a one point two seven millimeter Allen key. Position the temperature sensor as close as possible to the sample without touching it. Then tighten the securing screw.

After checking that the sample has not moved, we can proceed to tighten the outer 2 nuts and the middle 2 nuts evenly with a Torque wrench.

The measuring head must be rotated to the horizontal position.

The sample is now ready for a measurement in single cantilever mode.

One additional point is if you are cooling the sample to low temperatures, it may be required that the sample has to be re-clamped to compensate for shrinkage.

Dual Cantilever:

This has a similar setup to single cantilever, except that the sample needs to be clamped in the center and at both outer ends. This involves the use of an extra outer clamp setup and 2 nuts.

Sample preparation for a tension measurement.

A polyethylene terephthalate sample of six millimeter width and twenty five millimeter length is prepared for the measurement.

First we need to bring the measuring head into a horizontal position.

Before we clamp the sample, it is important that we enable a preload force. This is done on the touch screen of the DMA. By default, the preload force is one Newton. If this is too small or too large for your sample, you can change it on the preparation screen.

Place the sample in the clamps. Fit the two clamp bars and screw the four screws by hand.

Check that the sample is straight, horizontal and centrally positioned in the clamps.

Once you are happy with the positioning, tighten the two screws on the drive shaft part of the clamp using the T10 Torx key. While tightening the screws, support the drive shaft part of the clamp with your fingers. Be careful not to cause unwanted clamping effects on the sample.

Now tighten the two screws on the fixed part of the clamp using the
T10 Torx key. Now you can rotate the measuring head to the vertical position.
Loosen the securing screw of the temperature sensor with a one point two seven millimeter Allen key. Position the temperature sensor as close as possible to the sample, without touching it. Then tighten the securing screw.

The sample is mounted and ready for measurement.

With thin films or fibres, reclamping at lower temperatures is not common practice. With thicker samples, run in tension, reclamping may be necessary at lower temperatures as a result of shrinkage.

A measurement using all standard DMA onedeformation modes is also possible in liquids using the fluid bath option.

Install the sample, in this example, a sewing thread in tension mode. The measuring head should be in the vertical position. Now fill the bath with the liquid, in this case, water.

Loosen the clamp handle on the bath. Slowly rotate the bath inward so that it is underneath the measuring head. Lift the bath and dock it to the docking collar on the measuring head. Ensure that there is no gap between the top of the bath and the collar. Hold the bath with one hand while you firmly tighten the clamp handle with the other hand.
The sample is ready for measurement.

We have now shown you how to prepare DMA measurement modes in: