By Travis Parkman, DMA Product Manager (PhD)
Keywords: Viscoelastic, Adhesives, High-Frequency DMA, Damping, Loss Factor
Vibrations are the periodic motion of a particle or body. A great example of vibrations that most of us encounter is riding in a vehicle. Whether it’s the city bus or our car, it will vibrate during our commute. These vibrations are unavoidable and come from different sources, such as tire-road interaction, engine, wind, or potholes. While some see these vibrations as simple annoyances, vibrations unaccounted for can cause serious problems. Vibrations can cause premature failure of parts through fatigue and abrasive wear, unsafe work conditions through excessive noise, and even small vibrations can have adverse effects on sensitive lab equipment and devices.
These vibrations can be produced from different sources, and in most situations, it is impossible to prevent vibrations from occurring in our life. However, there are ways we can reduce and isolate these vibrations. One way is to use vibration-absorbing materials; these include but are not limited to adhesives, rubber mats, or foams. These materials fall under the category of viscoelastic materials, meaning it has elastic and viscous characteristics.
Review of Dynamic Mechanical Analysis
Just as a quick review, the elasticity describes a material’s ability to store energy as it is deformed and is measured by its Storage Modulus (E’), also known as the real modulus. The word ‘store’ means that the energy is not lost and is used to return the material back to its original shape, like a spring. While viscous represents the material’s ability to dissipate stress and energy to heat. This is quantified by the Loss Modulus (E”). These characteristics can be measured using a Dynamic Mechanical Analyzer (DMA), which periodically applies a load to a sample and measures its response.
If we consider our case of vibration damping, we want a material which has a relatively high loss modulus so it can absorb vibrations (energy) and dissipate them into another form of energy, like heat. A key parameter to describe this is by taking the ratio of the two moduli described above using the following equation .
The loss factor, , indicates the relative amount of energy dissipation for a material or its damping. A higher loss factor or damping means that the material will absorb more vibrational energy resulting in fewer vibrations being transferred through it.
Using a High-Frequency DMA to Evaluate Damping Performance of Different Adhesives
For example, we can consider the work done by Dr. Edith Roland Fotsing and his research group from the École Polytechnique de Montréal. They investigated the damping performance of two viscoelastic materials, an acrylic-based adhesive VHB and Smacwrap (SW), a silicon-based material. These materials are used extensively in the aeronautic industry for structural and damping applications.
Dr. Fotsing’s and his research group provide an extensive analysis of these materials using a Metravib DMA+450, which looked at different layered configurations, thicknesses, bonding quality, and curing procedures. To read about this full analysis, I highly recommend reading this paper titled, “Dynamic characterization of viscoelastic materials used in composite structures”. I will summarize two different comparisons done by this group. Figure 3 shows the first comparison which was the loss factor vs. frequency for the VHB and SW directly after curing .
The results show that VHB and SW have different damping characteristics and that frequency has a unique effect on each. This is expected since viscoelastic materials are time-dependent materials, as I covered in a previous blog post. The cured VHB’s damping properties remain relatively constant from 1 to 600 Hz, while the data suggests that the SW will have better vibration absorption properties above 500 Hz at room temperature. A future recommendation would be to repeat this experiment at different temperatures.
The group further investigated the effect of different curing processes on the viscoelastic properties, where they compared two different samples; (1) VHB directly bonded to the steel fixtures and cured at 80°C and (2) VHB was sandwiched and cocured between carbon/epoxy laminates, which were directly bonded to the steel fixtures. The thickness of the VHB was consistent for each sample. The loss factors are shown in Figure 4.
The cocured sample between the two carbon layers had a lower loss factor and although not shown, had a higher stiffness. The resin from the carbon/epoxy laminate is hypothesized to diffuse inside the VHB layer, causing a decrease in the VHB’s loss factor (damping). The group also states this was expected due to previous results in the literature. This conclusion is further supported when we consider the similar curing/cocuring analysis on the SW material, which is shown in Figure 5.
As Figure 5 shows, the SW adhesive keeps its integrity and experiences no changes when bonded to different surfaces.
In summary, the tradeoffs in terms of damping performance between two different viscoelastic materials were identified using a DMA. VHB, the acrylic-based adhesive was identified to have superior damping performance when adhered to metals but damping performance was reduced when cocuring with composites. While Smacwrap (SW), a silicon-based material, was more stable when applied to composite materials. A recommended next step would be to repeat the analysis at different temperatures and stresses/strains. An extensive data set considering different temperatures and loading conditions, helps you understand your material and is critical in developing a comprehensive model.
If you would like to learn more about the Metravib DMA+ series and some of their new testing capabilities, like the temporal storage module, I recommend checking out our High Performance Rubber Characterization Innovations in Test and Measurements seminar or contact us directly at firstname.lastname@example.org.
 Sperling, L. H. (1990). Sound and Vibration Damping with Polymers: Basic Viscoelastic definitions and concepts. American Chemical Society.
 Fotsing, E. R., et al. (2014). Dynamic Characterization of Viscoelastic Materials Used in Composite Structures. Journal of Composite Materials, 48(30), 3815–3825. https://doi.org/10.1177/0021998313514254.
About the Author
Travis obtained his degree in Mechanical Engineering in 2015 from the University of New Brunswick. After graduation, he began his Masters, where he investigated a new method to measure cutting forces produced during machining. This research was later converted to a Ph.D. program, with a focus on identifying and adjusting for inertial effects present in force measurements used to monitor machining processes. Travis is the Metravib Product Specialist for C-Therm.