Acoustic Modeling for Three-Dimensional Lightweight Windshields

In the auto industry, lightweight window designs are drawing more attention for improved gas mileage and reduced exhaust emission. Corning’s Gorilla® Glass used in laminate design enables more than 30% weight reduction compared to conventional soda-lime glass laminates. In addition, Gorilla® Glass hybrid laminates (which are a laminate construction of a thick soda-lime glass outer play, a middle polyvinyl butyral interlayer, and a thin Gorilla Glass inner ply) also show significantly improved toughness due to advanced ion-exchange technology that provides high-surface compression. However, the reduced mass also allows increased transmission of sound waves through the windshield into the vehicle cabin. A system-level measurement approach has always been employed to assess overall vehicle acoustic performance by measuring sound pressure levels (SPL) at the driver’s ears. The measured sound signals are usually a superimposition of a variety of noise sources and transmission paths. It is challenging to quantitatively isolate the impact of replacing a thick windshield with a thin windshield. A reverberation room measurement is another standard component-level testing approach but it is usually limited to flat glass evaluation. To enhance understanding of sound wave transmission through windshields, a 3D windshield acoustic model was developed using ANSYS Acoustics ACT. The model was validated for a 24″ x 24″ flat laminated panel with reverberation data. It was then extended for simulating a 3D production windshield with curved surface and tri-layer polyvinyl butyral (PVB) interlayer. The model has been employed to characterize windshield acoustic performance under either plane wave incidence or diffuse field. Through modeling simulation, an optimal inner layer glass thickness was identified at 1 mm which is able to maximally shift critical frequency further away from human being’s sensitive hearing range while maintaining reasonable sound transmission loss (STL) at damping control region. Windshield geometry was also evaluated and impact observed especially on transmission loss at spectra regions below the critical frequency.