By Arya Shahrostambeik, Laboratory Scientist (M.ScE)
In today’s industrial landscape, tools, gears, and equipment are increasingly subjected to high-frequency forces during operation. These forces often lead to unwanted vibration and noise, which can significantly impact both performance and safety. While these issues might initially seem like minor inconveniences, they can have far-reaching consequences. Excessive vibration and noise not only reduce the comfort and usability of machinery for operators and consumers, but they can also accelerate wear and tear, leading to premature equipment failure and costly downtime. In some cases, they may even pose serious risks to human health and safety.
Figure 1: Noise and Vibration Quality Assurance in the Automotive Industry [1]
Dynamic mechanical analysis (DMA) allows researchers and engineers to study the mechanical properties of materials under varying frequencies, temperatures, and stress conditions. By analyzing how materials respond to dynamic forces, DMA provides valuable insights into damping characteristics, stiffness, and energy dissipation—all of which are critical for minimizing vibration and noise.
Figure 2: Sample Mounted in clamp for tension testing
EV Noise and Vibration Challenges
Electric vehicles are inherently quieter in operation than traditional gasoline cars, since they lack the loud combustion engine. However, this quietness actually makes other sources of noise and vibration more noticeable.
Whirring electric motors, gearboxes, tire-road contact, wind, and chassis vibrations that were once masked by engine noise are now exposed. EV powertrains also operate at much higher frequencies (up to the kilohertz range), generating a distinctive high-pitched noise. Meanwhile, the absence of low-frequency engine rumble means there’s no background noise to cover up road bumps or rattles. All these factors amplify the need for superior noise, vibration, and harshness (NVH) control in EV design.
Figure 3: Tesla at charging station [2]
Why is a Quiet EV Important?
Electric car buyers and passengers have high expectations for a smooth, silent ride. Excessive noise and vibration can make driving uncomfortable and fatiguing, reducing overall enjoyment. Poor NVH can even pose safety risks. Constant droning or buzzing can distract the driver or cause fatigue, increasing accident risk over time. From a market standpoint, quietness is a key selling point of EVs; if an EV exhibits a lot of noise or harshness, it can negatively impact customer perception of quality. Additionally, minimizing vibration isn’t just about acoustics – it can help protect vehicle components. For example, high vibration levels can reduce powertrain efficiency (affecting driving range) and may shorten battery life by stressing internal connections.
Thus, EV manufacturers are investing in NVH solutions to ensure comfort, safety, and component longevity. Engineers are exploring new materials and designs (like acoustic foams, tuned motor mounts, and constrained-layer dampers) to isolate and damp vibrations at the source. Thus, it is critical to investigate NVH solutions to ensure comfort, safety, and component longevity.
To develop these next-generation damping materials and systems, quantifying their effectiveness is essential. This is where Dynamic Mechanical Analysis (DMA) becomes a critical tool. DMA measures how well a material can absorb and dissipate vibrational energy across the relevant frequency and temperature ranges. In the EV era, with unique noise profiles and stringent comfort demands, DMA-driven insights help ensure the materials chosen will deliver a quieter, smoother ride.
Figure 4: Testing the Future of Quiet Mobility [3]
What is Dynamic Mechanical Analysis (DMA)?
Dynamic Mechanical Analysis (DMA) is an analytical technique used to characterize the viscoelastic properties of materials, essentially how a material responds to deformation that changes with time (or frequency). In a DMA test, a small oscillatory force (dynamic stress) is applied to a specimen of the material, and the resulting deformation (strain) is measured.
By monitoring the force and displacement signals, DMA determines how much of the deformation energy is stored elastically versus dissipated as heat in the material.
Some key parameters from DMA include:
- Storage Modulus (E’ or G’): This measures the elastic stiffness of the material – its ability to store energy and spring back. A high E’ means the material is relatively rigid and elastic, like a spring.
- Loss Modulus (E” or G”): This measures the viscous response – how much energy is lost as heat each cycle. A higher E” indicates the material dissipates more energy (internal friction), behaving more like a damper.
- Loss Factor (tan δ): This is the ratio E”/E’ (often called tan delta). Tan δ is essentially the damping ability of the material. It indicates the fraction of energy lost per cycle relative to energy stored.
A higher tan δ means the material is better at absorbing vibrational energy and converting it to heat (greater damping).
In practical terms, imagine deforming a piece of material back and forth (like bending a rubber strip rapidly). The storage modulus tells us how stiff the rubber is, while the loss modulus tells us how much energy it’s converting to heat (and not giving back). DMA measures both, and tan δ gives a single metric of damping performance. A perfectly elastic material (like an ideal spring) has tan δ = 0 (no energy lost), whereas a highly damping material (like a shock absorber or a viscoelastic polymer) will have a larger tan δ value, indicating significant energy dissipation each cycle.
Figure 5: A delay in strain (deformation) observed following the application of stress (force)
Metravib DMA instruments can perform tests over a wide frequency range (from very low, 10-5 Hz, to high, 103 Hz for advanced instruments) and temperature range (from -150 °C up to 500 °C). This is crucial because material damping behavior is strongly dependent on frequency and temperature. Many polymers have a peak in tan δ around their glass transition temperature; for example, at that point they are especially effective in damping. Likewise, a material might damp well at certain frequencies but not others. By sweeping through frequencies and temperatures, DMA reveals the full viscoelastic profile of a material.
Figure 6: Damping behavior of rubber vs frequency
How Does DMA Help to Address NVH Control?
To reduce noise and vibration, engineers use materials that can damp out mechanical energy, for example, rubber bushings that absorb road shocks or polymer coatings that deaden panel vibrations. The effectiveness of these materials comes from their viscoelastic nature, which DMA can directly measure. Using DMA, we can evaluate a material’s damping performance by measuring its loss factor (tan δ) across the relevant frequency range. A high tan δ at the frequencies of interest means the material will effectively absorb vibrational energy at those frequencies, converting it to heat and preventing it from radiating as sound or structural vibration
An important factor is temperature dependence. EV components experience a range of temperatures (cold winters, hot motor operation). Materials often damp best near their glass transition temperature (Tg), where they are softest. DMA temperature sweep tests can find at what temperatures tan δ peaks. Engineers might choose a polymer whose Tg is tuned to near room temperature if most noise is at ambient conditions, or use a blend to broaden the temperature range of effective damping.
Crucially, DMA also helps in understanding how real-world conditions or manufacturing processes affect damping. For instance, the bonding or curing process can alter a material’s viscoelastic properties. In one DMA study, an adhesive’s damping dropped when it was co-cured with a carbon fiber laminate (its tan δ decreased because the resin from the laminate made it stiffer).
Interpreting DMA for NVH Design
When looking at DMA data for noise/vibration applications, engineers focus on a few questions:
- What is the peak damping (max tan δ) of the material, and at what frequency and temperature does it occur? Ideally, you want that peak aligned with your problem noise frequency and operating condition.
- How wide is the effective damping range? A broad plateau in tan δ over a range of frequencies/temps is often desirable so the material works under various conditions.
- Is the material stiff enough while providing damping? A component like a motor mount must support load with sufficient stiffness and damp vibrations. DMA provides storage modulus E’ to ensure it’s not too soft.
- How does the material behave under different strain amplitudes? (For large vibrations, sometimes damping behavior changes; DMA can do strain sweeps to check linear vs nonlinear range.)
Figure 7: Damping behavior of rubber vs temperature
Testing Materials Beyond Experimental Limitations
Considering the EV motor noise again the dominant whine is around 1000 to 5000 Hz [4]
. Due to the experimental limitations, it is challenging to evaluate the materials at higher frequencies than 1000 Hz. DMA can address this issue by running frequency-sweep tests at different temperature stages. By having this data according to time-temperature superposition principles a mastercurve can be built. Time-temperature superposition principles state that the behaviour of materials at low temperatures simulates the high frequency behaviour and high temperature response simulates the low frequency behaviour. Based on this principle, a mastercurve can be built to evaluate materials frequency response above 1010 Hz.
Figure 8: High frequency evaluation of the materials using time-temperature superposition
Conclusion
Conclusively, dynamic mechanical analysis (DMA) is a powerful technique for measuring the viscoelastic properties of materials. These properties are essential for understanding how materials dampen noise and vibration. With this knowledge, engineers and scientists can design materials that effectively mitigate the harmful effects of vibration and noise.
Today, materials are frequently exposed to significant levels of noise and vibration from various sources. High-frequency testing capabilities are particularly valuable, as they allow for the simulation of real-world conditions and ensure maximum accuracy under application-relevant environments.
Interested in Learning More?
C-Therm is the sole distributor of Metravib instruments in North America. These advanced tools are ideal for characterizing the viscoelastic properties of materials. Contact us at info@ctherm.com to learn more or request a demo.
Our Thermal Analysis Labs (TAL) team also offers expert contract testing services tailored to your material characterization needs. Book a FREE technical consultation with a subject matter expert today by contacting info@thermalanalysislabs.com.
Tel: +1 (506) 457-1515
References
[1] [Online]. Available: https://www.nti-audio.com/en/applications/quality-control/noise-vibration.
[2] [Online]. Available: https://vehicleanswers.com/can-tesla-vehicles-use-other-charging-stations/.
[3] [Online]. Available: https://www.assemblymag.com/articles/96607-making-electric-vehicles-quieter.
[4] Q.D.W.L.C.Y.J.H.X.L. Chenghao Deng, “Analysis of Vibration and Noise for Powertrain System of Electric Vehicles under Speed-Varying Operating Conditions,” Mathematical Problems in Engineering, 2020.
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.