The main negative effect of added mass is obvious: mass is the exchange ratio between energy and movement (kinetic energy). If one needs to improve the energetic performance of vehicles, trains, airplanes… one way is to limit or reduce the mass dedicated to NVH or robustness issues. For decades engineers have successfully worked to make lighter structures with limited impact into the acoustical comfort or vibration robustness.
Further reduction will always be required as long as energy is a limited resource on our planet, so to keep up with the demand for reduced energy consumption, innovative methods must be combined with well-established good practices. White body mass reduction of a car would be one kind of application. New key ingredients to this equation are perhaps the urgency of limiting GHG emissions and the corresponding collective awareness.
For several decades, engineers have been working successfully to make structures lighter, with limited impact on acoustic comfort or vibration resistance.Making structures lighter, however, remains a constant concern as long as energy is a limited resource on our planet. To reduce energy consumption, innovative methods must be combined with well-established best practices. The need to limit greenhouse gas emissions and the associated collective awareness gives new impetus to the theme of “lightweighting structures” and encourages the application of innovative concepts in the field of materials.
Lightweight design challenges
Noise and vibration control can be a challenging task since several constraints are often imposed by the design and functional performance of specific products. Among them we find: size, cost and of course the added mass associated with dedicated noise and vibration solutions. The latter is perhaps the simplest solution to tackle NVH (noise, vibration and harness) problems : added mass can reduce the amplitude response of vibrating structures, it can shift resonance frequencies and finally mass is inherently added to a structure when passive damping elements such as viscoelastic materials are used.
Lightweight design specifications
How to make the difference?
One of the innovative ideas behind lightweight design and vibration control of structures is to incorporate into the structures means of passively reducing the propagation of elastic waves, or the unwanted vibrations – that means that vibrations and noise can no longer propagate freely in the structures in addition to be highly damped or attenuated. This can be achieved by designing adequate conditions to control (elastic) waves – such as periodic variation of mechanical properties or local resonances which results in frequencies range where wave propagation is highly damped. The development of such new ‘materials’ is part of a research partnership with Le Mans university – the goal of the joint program is to apply this outstanding technology into the industrial world. Big names from the aerospace, automotive, railway and energy sectors have already shown their interest.
These newly developed ‘engineered materials’ such as periodic structures will certainly be part of tomorrow lightweight structures such as satellites and automotive parts. However lightweight and robust design still requires the know-how of structural dynamics and vibro-acoustic, core competencies of Metravib. One cannot dismiss the importance of dynamical characterization of structures, estimation of operational dynamical forces and damping, key parameters used in designing with the aid of numerical methods (such finite elements) : this industry-proven approach combining numerical design and experimental qualification has been used and perfected by Metravib engineers for decades.