How Noiseless steel ( Vibration-damping Steel | Quiet steel ) work?
Noiseless steel is a new material, with at least two ordinary steel plates, and visco-elastic material viscoelastic sound absorbing combinations and oscillating to reduce noise and vibration of motor vehicles.
It is a specific material, which allows not only to reduce its own oscillations, but also has the effect of reducing weight and cost. Particularly for the automotive industry, noise and vibration are factors that are very important in customer satisfaction for high quality. Noiseless steel has been proven by modern rigorous testing methods and techniques that are currently used by the three major automakers of the United States (Ford, GM, Chrysler) and European companies.
As a general rule, products constructed of thin metal sheet have very low internal loss. In other words, their ability to convert vibration energy into thermal energy is poor. This means that the resonant vibrations that may occur when they are subjected to vibration and structure-bound noise can be considerable, and will usually result in the radiation of a great deal of air-borne noise.
The internal losses in a material or structure are usually stated in terms of acoustic loss factor (η) by reference to the amount of vibration energy converted into heat, and thus not emitted as sound. A high loss factor reduces a structure’s level of vibration and consequently the amount of sound it emits. Where a material or structure is made up of several layers, the combined loss factor is stated as ηcomb.
The highest realistically possible loss factor is approx 1. In the case of sheet metal structures it is usually between 0.001 and 0.01. Consequently, in structures of this type the internal loss is negligible, but it can be improved considerably if structure-borne sound damping materials are used. The most common methods involve coating one side of the sheet or using a sandwich construction. NM is an example of the latter method and, in optimum conditions, can achieve loss factor figures of around 0.4. These results are achieved using a sound damping core that is only 2 – 4mils (0.05-0.1 mm) thick.
Results as good as these are rarely obtained by coating one side of the sheet. This is because coatings are exposed to elongation/compression when subjected to bending waves, whereas the core of an NM panel is subjected to shear (see Fig 1). Shear converts larger amounts of energy than does elongation, resulting in higher energy losses and thus in a higher loss factor.
Noiseless Metal sandwich constructions make higher loss factors possible even with thick panels.