What is Dynamic Mechanical Analysis Used For?

Dynamic mechanical analysis, sometimes abbreviated to DMA, is a workhorse technique used to investigate the various mechanical properties of materials as a function of frequency, temperature, and time. The goal is to ultimately get an in-depth assessment of the stress and strain mechanics of materials in simulated real-world conditions.

Temperature is typically the central function of dynamic mechanical analysis; hence the technique is sometimes described as dynamic mechanical thermal analysis – or DMTA. However, there are two primary test modes used: frequency and temperature sweep. Before discussing the specific use cases of dynamic mechanical analysis, it is worth distinguishing these two operating modes in more depth.

Frequency Vs. Temperature Sweep Mode: What’s the Difference?

Dynamic mechanical analysis is carried out by applying a sinusoidal stress – typically an oscillatory force – to a sample and measuring the resulting strain. Frequency sweep tests are isothermal analyses where the frequency is varied over time. As the temperature remains constant, changes in the complex modulus (storage and loss moduli) can be accurately plotted, yielding accurate insights into the material’s energy dissipation at set frequencies.

Conversely, temperature sweep tests use a set frequency for the duration while temperature varies. User-defined thermal profiles typically ramp-up the temperature in small increments to closely observe temperature-dependent variations in the complex modulus up to, and beyond, key transition points.

We have already touched on some of the core principles of application in distinguishing frequency from temperature sweep dynamic mechanical analysis. The aim is to observe the physicochemical properties of materials under finely controlled, user-defined conditions. So, what are the most common properties under test via DMA techniques?

Glass Transition Temperature

Dynamic mechanical analysis is one of the go-to techniques for probing the glass transition temperatures (T_g) of amorphous polymers and semicrystalline materials. Materials below their glass transition points are extremely brittle and rigid. Exposing them to a gradually increasing temperature under a constant low frequency will eventually cause them to transition to a more flexible state. Between this glass transition point and the melting point is a rubbery region where materials can withstand elongation under relatively low loads. Dynamic mechanical analysis is subsequently ideal for determining different flexible and rigid applications of amorphous and semicrystalline materials.

Extent of Crosslinking

Dynamic mechanical analysis can also be used to determine the effects of changes in composition of polymeric materials on the mechanical properties. The complex modulus of polymers is inherently determined by inter- and intramolecular forces which vary depending on the concentration, presence, and position of distinct cross-linkers and monomers. It is subsequently possible to evaluate performance changes imparted by novel processing aids or different blend compositions. It is an excellent way to examine differences in polymer extent of crosslinking.

Interested in DMA Techniques?

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