Duval, A., Crignon, G., Goret, M., and Roux, M., "Comprehensive Hybrid Stiff Insulators Family: The Chips Urethane Contribution," SAE Technical Paper 2017-01-1883, 2017.
The lightweighting research on noise treatments since years tends to prove the efficiency of the combination of good insulation with steep insulation slopes with broadband absorption, even in the context of bad passthroughs management implying strong leakages. The real issue lies more in the industrial capacity to adapt the barrier mass per unit area to the acoustic target from low to high segment or from low petrol to high diesel sources, while remaining easy to manipulate. The hybrid stiff insulator family can realize this easily with hard felts barriers backfoamed weighting from 800 g/m2 to 2000 g/m2 typically with compressions below 10 mm.Above these equivalent barrier weights and traditional compressions of 7 mm for example, the high density of the felts begins to destroy the open porosity and thus the absorption properties (insulation works anyway here, whenever vibration modes do not appear due to too high stiffness…). The felt costs begin to be critical for these intermediate weights above 2000 g/m2 as well. From 2000 g/m2 up to 3000 g/m2 or 3500 g/m2 equivalent barriers, the use of a traditional intermediate heavy layer is still not relevant from a process and cost point of view (ABA - Absorber/Barrier/Absorber systems).An original way to circumvent the issue consists in using a double porosity material like compressed chips urethane bound with bicomponent thin fibers. Airflow resistivities and porosities remain high while reasonable even at high compressions and thus deliver very good absorption, while being stiff enough to allow mass-spring like insulation slopes, as well as not too stiff in order to avoid bad modal resonances. The acoustic performance of this unconventional hybrid stiff insulator solution will be discussed with poro-elastic finite element modeling compared to measurements and to other hybrid stiff or ABA existing solutions of the same mass per unit area.