Rubber components used in aerospace, mining, defense, and motorsport face extreme mechanical loads in real operation—far beyond what standard testing can replicate. High-Force DMA makes it possible to measure and simulate these stresses, revealing critical behaviors such as heat build-up, fatigue, and the Payne and Mullins effects. With advanced testing technology, manufacturers can better predict performance, prevent failure, and design safer, longer-lasting rubber materials.
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NETZCH high-force DMA product range |
The Behavior of Rubber Under Heavy Load
Whether it's aircraft tires, mining conveyor belts, military track pads, or Formula 1 racing tires – rubber is often exposed to extreme mechanical stress. But how does this complex material behave under real-world conditions? And how can manufacturers reliably test and simulate these loads? This is where High-Force Dynamic Mechanical Analysis (DMA) by NETZSCH becomes essential.
Why High-Force DMA?
DMA is a non-destructive testing method used to analyze the dynamic mechanical behavior of viscoelastic solids. While conventional DMAs are suitable for small samples and linear viscoelastic testing, they reach their limits when materials are exposed to high forces, high frequencies, or large deformations –- all of which are common in real-world applications.
NETZSCH offers high-force DMA instruments like the DMA 503 Eplexor® and DMA 523 Eplexor®, capable of applying static forces up to 6000 N and dynamic forces up to 4000 N. These systems make it possible to test large specimens and simulate realistic loading conditions –from heavy-duty tires to vibration dampers.
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Figure 1: Heat Build-Up experiment on a rubber sample showcasing the temporal evolution of temperature based on different temperature sensors |
Heat Build-Up & Blow-Out – Pushing Elastomers to the Limit
One of the major challenges in rubber testing is heat accumulation under cyclical loading. Elastomers have poor thermal conductivity. When subjected to high dynamic stress, more heat is generated than can be dissipated, leading to internal temperature rises – a phenomenon known as Heat Build-Up (HBU).
Blow-Out tests go a step further: the sample is dynamically stressed until it fails. With High-Force DMA, it’s possible to measure not just temperature rises, but also the viscoelastic properties such as storage modulus, loss modulus, and damping behavior (tan δ) – all in one test.
A practical example revealed that while a surface thermocouple measured only a 20°C temperature increase, the internal temperature – captured using a needle thermocouple – rose by up to 70°C. Such insights are crucial, as internal overheating can lead to cavity formation, crack growth, and ultimately, catastrophic failure.
The Payne Effect – When Rubber Softens with Movement
The Payne effect describes the decrease in stiffness (storage modulus) of filled elastomers under increasing dynamic strain. This effect becomes relevant when rubber components such as tires, windshield wipers, or vibration dampers are subjected to repeated deformation.
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Each of the four subsequent Up and Down cycles of the Load Sweep performed for the measurement of the Payne effect |
Using the NETZSCH DMA 503 Eplexor®, a load sweep test demonstrated how the storage modulus remained constant in the Linear Viscoelastic Region (LVER), then dropped significantly – by nearly two-thirds – once nonlinear behavior began. The loss factor (tan δ) rose initially, peaked when the internal filler networks were most damaged, before falling again.
When the dynamic strain was reduced, the material did not return to its original state. Instead, it exhibited hysteresis: partial recovery, but not full restoration. This proves that the Payne effect is only partially reversible in the short term – full recovery requires longer rest periods as filler-filler bonds re-agglomerate.
Mullins Effect – Irreversible Softening
While the Payne effect is reversible over time, the Mullins effect describes permanent softening of a filled elastomer after repeated loading and unloading under quasi-static conditions.
This effect plays a critical role in applications such as:
• Tire break-in behavior
• Long-term seal performance of O-rings
• Changes in damping performance of mounts
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Quasistatic up and down cycles with increasing maximum static strain values in tension for the measurement of the Mullins effect |
High-Force DMA testing shows that after an initial loading cycle, subsequent stress-strain curves follow softer paths. This indicates irreversible structural changes, including damage to polymer-filler bonds and rearrangement of polymer chains. The difference between original and subsequent stress-strain curves is known as Mullins damage – a key parameter for predictive modeling and material simulations.
Final Thoughts
Rubber is a highly versatile yet complex material. Its behavior under stress involves a combination of mechanical, thermal, and microstructural effects – all interacting simultaneously. Understanding these requires advanced testing techniques. High-Force DMA systems by NETZSCH Analyzing & Testing enable engineers and researchers to simulate real-world loading conditions and capture critical data about fatigue, heat build-up, damping performance, and microstructural changes. As famed Formula 1 designer Adrian Newey once said: “These bits of rubber that actually transmit grip to the tarmac are probably the least well understood – yet they’re the most crucial.”
At NETZSCH, specialists may not have all the answers, but they provide the tools that help take material testing – and understanding of rubber – one step further.
By Sascha Riegler, NETZSCH
Pictures: NETZSCH
