Search Results

Standards organizations develop standards depending on the need in the market place. With the change in vehicle design, lightweighting structures, and body panels made out of aluminum and composites, SAE’s Acoustical Materials Committee is developing a new damping standard. This standard is also very suitable in determining the damping performance of materials used in the off-highway applications, where the thickness of the steel body panel is much greater than in the automotive application. The general methodology of this standard is based on the mechanical impedance measurement method and has been developed with the general consensus of automotive engineers, suppliers, and independent test laboratories. This method is essentially based on the fact that a bar is excited at the center by a shaker. The force exerted by the shaker and the corresponding vibration is measured at that point to determine the frequency response function of the mechanical impedance signal.

This paper focuses on the development of treatments to control airborne noise through the dash panel. For a noise control material supplier, these treatments can be the most challenging to design because of the number of pass-throughs and design constraints. The dash panel development process includes extensive in-truck testing and analysis to identify sound paths (location and magnitude) and establish design criteria, laboratory material testing to aid in the selection of appropriate materials, laboratory component testing to select areas requiring treatment and to design the shape of the treatments, and in-truck testing to verify the performance of the new treatments.

This paper discusses the thought process that one needs to go through for developing an appropriate sound package treatment for a vehicle. In the development process one needs to put proper emphasis on understanding the source, path, and the receiver system. One needs to have an understanding on how to reduce the noise at the source, path, and/or receiver location. One may need to conduct a feasibility study of the benefits of various noise control options. In terms of sound package treatments one needs to understand the fundamentals of acoustical materials how they work and why one material performs differently than another one, as well as the importance of a well documented specification that every supplier has to meet.

Advances in vehicle noise control are leading the automotive industry to place increasing emphasis on weatherseals to block exterior noise. As a result, properly evaluating the acoustical performance of automotive weatherseals is of increasing importance. There is no current specific standard for this testing. Rather, there has been reliance on adaptations of SAE Standard 51400 “Laboratory Measurement of the Airborne Sound Barrier Performance of Automotive Materials and Assemblies” by testing laboratories. However, the 51400 standard addresses testing of flatstock materials and does not readily lend application to pre-formed parts such as weatherseals. For this reason, adaptation of the standard can vary significantly from facility to facility and manufacturer to manufacturer. These differences can be significant and can render comparisons between test results on competing materials very difficult.

The paper discusses the importance of a well documented standardized laboratory test procedure to evaluate damping material performance for the automotive industry, and to understand the parameters that influence the precision of the test method. The standard outlines a methodology which was developed with the general consensus of automotive engineers, suppliers, and independent test laboratories. The methodology is based on the Oberst bar test method where a damping material is bonded to a specific size steel bar and the system is excited at its various modes of vibration under a cantilevered configuration. The damping performance is expressed in terms of composite loss factor, ηc, within the frequency range of approximately 100 Hz to 1000 Hz, and over the useful range of temperatures for the given application.