ASTM D5026 DMA of Plastics in Tension
ASTM D5026 tests dynamic mechanical properties in tensile mode, which suits materials that are too thin or too flexible to test in bend mode. The material, whether a film, fiber, or elastomer strip, is placed in two clamps with a static load and then subjected to dynamic strain. MatX Lab performs tensile DMA testing per ASTM D5026 for films, thin sheets, fibers, and elastomers.
What Is ASTM D5026?
ASTM D5026 is the standard test method for dynamic mechanical properties of plastics in tension. The instrument applies a sinusoidal displacement, measures the resulting force, and resolves the phase lag between the two into storage modulus, loss modulus, and tan delta.
Static force control is what makes the geometry work. The instrument keeps a static preload above the dynamic amplitude at all times so the specimen never goes slack, and that ratio is a setup parameter that affects the result.
When bending is not possible, tension testing is preferred. The 50 µm film has no bending stiffness, and the unfilled elastomer sags in the three-point system, so tension testing is required.
Select tension testing when bending is not possible. The bending stiffness of the 50 µm film cannot be measured because it has no bending stiffness. The elastomer without any fillers sags in a three-point bend testing fixture; thus, both must be tested in tension.
ASTM D5026 Scope and Applications
The procedure applies to films, thin sheets, fibers, tapes, and strips of elastomers over the temperature range possible in the instrument and the clamps.
Data application areas:
- Film transitions mapping. Determination of glass transition and secondary relaxation transitions in films used for packaging and other technical purposes, where bending geometry is inapplicable.
- Elastomer properties determination. Determination of modulus and damping as a function of temperature of rubber-like materials, including low-temperature stiffening effect that affects seal properties.
- Coatings and laminates evaluation. Testing free films of coatings and adhesives for softening temperature.
- Orientation and anisotropy. Comparing machine and transverse direction response on oriented film, which frequently differ substantially.
ASTM D5026 Test Procedure
Gripping is where tensile DMA succeeds or fails. Slip inside the clamp reads as material compliance, and over-tightening cuts the specimen.
| Step | What happens |
| Specimen cutting | Strips are cut with clean parallel edges, since a nicked edge concentrates stress and the specimen fails partway through a run. |
| Dimensional measurement | Width and thickness are measured at several points and averaged, because modulus scales directly with cross-sectional area. |
| Conditioning | Condition specimens at standard laboratory conditions, bringing hygroscopic films to a defined moisture state. |
| Mounting | Clamp the strip at both ends, measure the free length accurately, and align it so the load path is straight. |
| Preload Configuration | Determine the static force and static-to-dynamic ratio such that the sample remains in tension throughout the entire experiment, including the softening stage. |
| Strain Validation | The strain sweep is performed to ensure the strain is within the linear viscoelastic range before starting the temperature program. |
| Temperature Program | The sample is cooled to the starting temperature and heated at a controlled rate, typically between 2 to 3 °C/min. |
| Data Acquisition | Measure the storage modulus, loss modulus, and tangent delta continuously at the desired frequency, which is usually 1 Hz. |
Limitations:
Clamp slip is the main source of error and often goes unnoticed until the modulus decreases where it should not. Free length needs to be measured carefully, because modulus depends upon it, and an error of 1 mm in a 10 mm specimen would give a 10% error in modulus. Soft specimens may stretch under the static preload and ultimately relax, rendering the experiment useless. The transition temperature depends on the rate and frequency of heating, so comparisons between laboratories are valid only if the same values apply.
Thin films can be particularly sensitive during mounting. Even a small crease near the clamp edge can create a weak point and cause the specimen to fail there.
As with any DMA test, the glass transition temperature can vary depending on how it is determined. Values based on storage modulus onset, loss modulus peak, and tan delta peak may differ by 10 °C to 20 °C for the same specimen. For this reason, the reported basis for transition temperature matters when interpreting and comparing results.
ASTM D5026 Specimen Requirements and Test Conditions
| Parameter | Typical requirement |
| Specimen form | Rectangular strip, film, tape, or fiber bundle |
| Free length | Commonly 10 mm to 30 mm between clamps |
| Width | 4 mm to 6 mm typical |
| Thickness | Up to around 2 mm, down to tens of micrometers for film |
| Replicates | Three per material and direction |
| Frequency | 1 Hz standard, multi-frequency on request |
| Heating rate | 2 °C/min to 3 °C/min for transition work |
| Material required | Enough for the replicate count plus spares for mounting losses |
Mark the machine direction on oriented film. Modulus and transition breadth both differ between directions, and unmarked material makes the whole dataset ambiguous.
ASTM D5026 Test Results and Reporting
Your report includes plots of storage modulus, loss modulus, and tan delta against temperature for each specimen.
You also tabulate transition temperatures and clearly identify the basis for each value, including storage modulus onset, loss modulus peak, and tan delta peak. Each curve includes the relevant test parameters, such as free length, cross section, frequency, heating rate, static force, static-to-dynamic ratio, and strain amplitude.
If a specimen draws, slips, or fails during the test, the report notes what happened and identifies the temperature where the results are no longer considered reliable.
This makes it easier to separate true material behavior from changes caused by specimen movement or a test failure. If a curve continues after the specimen has slipped, do not treat that portion of the data as representative of the material.
ASTM D5026 FAQs
Which transition value should I report?
Whatever your specification says, please let us know which test you are requesting. The tan delta peak temperature is the highest, the storage modulus temperature is the lowest, and the difference between those two temperatures for the same material sample may be over 15 °C.
Can you test a fiber?
Yes, it depends on the fiber type and the number of fibers per bundle. Please specify this at the time of quotation, and we will check the instrument range before running your sample.