By Arya Shahrostambeik, Laboratory Scientist (M.ScE)
Introduction
Viscoelastic materials are unique due to their time-dependent response to force or deformation (see this blog post on viscoelasticity). Rubber is known for its viscoelasticity and plays a key role in various applications. The earliest evidence of rubber goes back to 1600 BC by the Mesoamerican, particularly the Olmec civilization. In 1839, Charles Goodyear accidentally discovered the rubber curing process using sulfur (known as vulcanization) [1]. Since then, rubber has been used in many materials and applications such as tires, gaskets, O-rings, seals, automotive, insulation, construction, vibration dampening, hoses, and belts.
One of the most common applications of rubber is in the tire industry. Apart from chemical formulation and curing process, analyzing the mechanical properties of rubber is critical. Evaluating the mechanical performance of rubber can be challenging since the nature of deformation is dynamic. In other words, the materials’ properties are frequency-dependent, and a technique to study the time dependency is necessary.
How to Measure Viscoelastic Properties of Materials
Dynamic mechanical analysis (DMA) is the most promising technique for measuring the viscoelastic properties of materials. This technique allows you to obtain mechanical testing results at different frequencies, forces, and displacements. Companies such as Michelin, Goodyear, Bridgestone, and many others benefit from Metravib DMA instruments to understand the viscoelastic properties of their materials. These instruments have unique capabilities such as high frequency up to 1000 Hz, high force capability up to 2000 N peak to peak, and 6 mm peak to peak displacement range. Furthermore, the Metravib high-performance DMA provides fatigue testing insights such as crack growth and heat build-up (HBU).
Figure 1: Metravib DMA+ series
Fatigue testing is a method used to determine how long a material can withstand repeated stress cycles before failing (irreversible mechanical change in the structure). This test plays a key role in understanding the durability of the materials under dynamic loads and, consequently, helps engineers design components that are more resistant to failure due to cyclic loading.
What is Heat Build-Up Fatigue?
Across various industrial applications, rubber materials and their composites, such as tires, undergo prolonged and repeated deformations throughout their service life. Not only do rubber materials demonstrate an elastic nature, but they also behave as viscous materials. The viscous component is called the loss modulus, which is the matrix’s ability to lose energy as heat. Due to this inherent hysteresis, the energy dissipated under dynamic loading is converted into heat and accumulates within the material, a phenomenon known as heat build-up.
An instance of heat built up in materials causing failure can be the blowout of rubber materials, including tires. This failure can result in human lives being lost on the roads or significant financial damage to businesses and companies.
What do we mean by blowout in terms of material failure? Blowout refers to the development of high temperatures at the center of the mass causing decomposition, the formation of liquid and gaseous compounds, and finally, the rupture of the solid walls of the mass by the expansion of these decomposition products. In large masses under heavy loads, the temperatures attained have been so high that ignition of the gases has occurred spontaneously [2].
Figure 2: Example of ruptured tire due to heat build-up
The following graphic demonstrates a test result from a Heat Build-Up module on metravib DMA+2000.
Figure 3: Result from a heat build-up test using a Metravib DMA+2000 [3]
How a Heat Build-Up Test is Performed
During this test, the temperature is controlled, and a thermal probe records the temperature of the sample’s surface sitting inside the furnace of the DMA+2000. The second thermal probe is inserted into the sample after applying a certain number of cycles of deformation. For instance, the picture above shows the surface temperature of 66.57 °C while the internal temperature of the sample was to be recorded at 124.8 °C after 5000 cycles of deformation.
Another application of the HBU test is studying the curing process of the materials. In the figure below, the internal temperature increase of the materials is shown after applying deformation cycles. The results indicate that increasing the curing time for sample A increases the ability of the material to dissipate energy as heat. On the other hand, samples B and B-1 depict an opposite trend, and heat dissipation decreases by adding time to the curing process.
Figure 4: Curing study using the Goodrich Flexometer on the first published paper in 1973
Case Study: Heat Generation Inside Tire Materials
Researchers at the Center for Frontier Research and Technology, Zhongce Rubber Group Company Ltd. in China, used the Metravib DMA+2000 to evaluate the heat generation inside their tire materials, in strain-controlled and stress-controlled conditions. Evaluating material properties and the heat generation under these two modes is crucial for the material’s structural integrity. For example, in the tire tread center area, stress-controlled fatigue dominates, while strain-controlled fatigue is the dominant force in the tire sidewall area.
Figure 5: Temperature of the tire material measured using Metravib’s DMA+ 2000
The Metravib DMA allows the operator to run tests on both strain-controlled and stress-controlled modes for all tests. Moreover, the evaluation is not limited to temperature increase, and the viscoelastic properties are simultaneously measured and accessible to the operator. This feature can be pivotal for a full characterization since this phenomenon is directly related to the loss modulus component of viscoelastic properties [4].
Figure 6: Loss modulus component of the tire material measured using Metravib’s DMA+ 2000
Conclusion
Understanding the fatigue behavior and viscoelastic properties of materials, particularly rubber, is crucial for ensuring the safety and durability of various applications, such as tires. The DMA technique, especially with advanced instruments like the Metravib DMA+ series, provides valuable insights into the mechanical performance of rubber under different conditions. By evaluating the heat build-up (HBU) and crack growth, engineers can design components that are more resistant to failure due to cyclic loading. This knowledge not only helps prevent catastrophic failures but also contributes to developing more efficient and reliable materials for industrial use.
Interested in Learning More?
If you are interested in material testing using any of the Metravib DMA+ series or have any other material testing inquiries, contact TAL at info@thermalanalysislabs.com to schedule a FREE technical consultation today! Or, click on the link below:
Tel: +1 (506) 457-1515
References
[1] “The History of Rubber,” [Online].
[2] E.T. Lessig, “The Goodrich Flexometer,” vol.9, no. 12, 1937.
[3] P. Yadav, “Heat Build-Up in Materials Subjected to Cyclic Loading,” 2024.
[4] W. H. P. R. X. W. Shouliang Nie, “Heat Build-Up of Rubber in Different Deformation Modes and its Correlation to Viscoelasticity,” Macro Molecular Rapid Communications, 2025.
About the Author
Arya Shahrostambeik is a Laboratory Scientist at C-Therm Technologies specializing in the Metravib product line. Having completed his Masters Degree in Chemical Engineering at the University of New Brunswick, Arya has extensive experience in the area of DMA and other materials characterization techniques.