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Laminated steel body panels are used in different applications in vehicles, such as dash panels and wheel wells. A part made out of laminated steel has the potential to provide structure-borne noise reduction and also improve the airborne noise reduction of the part compared to a monolithic part. The use of laminated steel has been more critical when there are deep draws on the part as the deep draws cause localized resonances which degrade the acoustic performance significantly. However, due to lightweighting demands, hybrid laminated panels, commonly known as acoustic patch laminates have become very attractive. This paper discusses the damping and sound transmission loss performances of a dash panel part with monolithic, laminated, and acoustic patch panels.

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.

A study was conducted to understand the acoustic viability of using post consumer rebond seat foam materials in vehicles for floor carpet underlayment applications. These foam materials were obtained from two different sources: 1) polyurethane foam dismantled from seats of end of life vehicles (ELV or scrap vehicles), and 2) polyurethane foam recovered and cleaned from auto shredder residue (ASR) by the Argonne National Laboratories (ANL) using their cleaning method. The study was conducted using three North-American cars, each serving different market segments. Based on both laboratory and on-road tests conducted on each vehicle, the study concluded that the acoustical performance of the floor carpet underlayment part made of post consumer rebond foam is comparable to that of the current production part mostly made of shoddy materials.

The SAE International standard for testing Oberst bars has been used in the industry for many years with predictable results. Growing interest in testing wider samples to incorporate more of the variability in liquid applied sprayable dampers has led to increased use of a center point damping test method based on a Japanese standard JIS G 0602. This method is similar to that of the ISO 16940 standard for testing laminated glass. Theory shows us that an Oberst test with a free length equal to the half length of a bar used for center point testing will provide the same resonances. This paper intends to show a relationship between the resonances of bars tested with the Oberst and center point test methods. A correlation between the composite loss factor for samples tested with each of the methods will be illustrated.

Sealant materials are used in todays automobiles for many applications such as, sealing of body seams, sealing access holes and the filling of hollow cavities. The primary reasons for these applications are to prevent corrosion, prevent water intrusion, and to reduce the noise level in the passenger compartment. However, the noise control capabilities of sealant materials have not been explored until recently. This paper discusses the requirements that a noise control material must possess, and reviews how a sealant material can fulfil these requirements. Properly designed sealant materials can possess sound transmission loss (barrier) properties, vibration damping properties over a given frequency and temperature range of interest, and often sound absorption properties with proper formulation. This paper provides case studies to substantiate the acoustical capabilities of sealant materials.

Traditionally, the damping performance of a visco-elastic material is measured using the Oberst bar damping test, where a steel bar is excited using a non-contacting transducer. However, in an effort to reduce the weight of the vehicles, serious effort is put in to change the body panels from steel to aluminum and composite panels in many cases. These panels cannot be excited using a non-contacting transducer, although, in some cases, a very thin steel panel (shim) is glued to the vibrating bar to introduce ferrous properties to the bar so it can be excited. In the off highway vehicles, although the panels are made of steel, they are very thick and are difficult to excite using the Oberst bar test method. This paper discusses a measurement methodology based on mechanical impedance measurements and has the potential to be a viable/alternate test method to the Oberst bar testing. In the impedance method, the test bar is mounted to a shaker at the center (Center Point method).

The performance of damping materials is generally evaluated by experimental methods. However most damping materials used in the transportation industry cannot be excited by itself. Therefore, the measurements are generally made by exciting a damped system, where the damped system extends from a bar to a panel. The paper reviews various damped systems and excitation methodologies and discusses some of the limitations of a bar to study the damping performance for different applications. It discusses a methodology where a damped panel is mounted on a fixture and the fixture is excited with a shaker. The paper discusses data acquisition and data reduction procedures to obtain the damping performance of laminated steel acoustic patch products on a third octave band frequency basis.

The use of sealant materials to improve interior acoustics has increased significantly in todays automobiles. One such application is to use expandable sealant materials in rails, pillars, and cavities to reduce noise propagation. However, there is no standardized method for evaluating the acoustical performance of these materials. This paper reviews the basics of noise control engineering and discusses a proposed laboratory based test methodology that has been developed for properly evaluating the acoustical performance or expandable sealant materials. The test method is intended to simulate actual applications so that different materials can be evaluated to achieve optimum acoustical performance within a channel representing the rails or pillars in automobiles.

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.

Automotive noise control involves many aspects of the total vehicle design - the powertrain, body structure, chassis and so forth. Noise control materials in conjunction with intelligent vehicle design can help produce a pleasant, desirable vehicle. Understanding the basic functions and uses of noise control materials is one of the objectives of this paper. In some situation, thermal insulation materials are combined with or used in conjunction with noise control materials, and an understanding of the thermal properties of materials can be useful. Vibration isolators are important devices in controlling the transfer of sound and vibration energy and these are discussed.

Heat reactive expanding sealer materials are used as acoustical “baffles” to block noise propagation in rails, pillars, posts, and rockers. However, should moisture enter and collect in vertical pillars water damage may occur. Therefore, effort is being made to implement a drainage system for these problem applications. This paper discusses an effective way to prevent water damage by adding an acoustical drain plug to the baffle system with a minimal reduction in acoustical performance. The paper also discusses the performance and the effect of adding this plug to the baffle system. Finally, results of design variations of the plug on the baffle system are reported.

This paper discusses a development procedure that was used to evaluate the acoustical performance of one type of dashpanel construction over another type for a given application. Two very different constructions of dashpanels, one made out of plain steel and one made out of laminated steel, were studied under a series of different test conditions to understand which one performs better, and then to evaluate how to improve the overall performance of the inferior dashpanel for a given application. The poorly performing dashpanel was extensively tested with dashmat and different passthroughs to understand the acoustic strength of different passthroughs, to understand how passthroughs affect the overall performance of the dash system, and subsequently to understand how the performance can be improved by improving one of the passthroughs.

Constrained layer damping (CLD) is a well known technique to efficiently damp low frequency vibration. CLD employs a viscoelastic material sandwiched between two very stiff, typically metal, layers. While effective over essentially flat surfaces, CLD has not been applicable to cylindrical shapes. In order to damp low frequency vibration in metal pipes, users have been forced to rely on extensional layer damping, typically consisting of thick layers of extruded or molded rubbers. This paper discusses a novel product to damp cylindrical articles such as metal pipes with a constrained layer heat shrink tubing. This product utilizes a stiff heat shrinkable polymeric jacket bonded on the inside with a viscoelastic layer. When shrunk on a metal pipe or rod, a CLD system is produced. The product is typically thinner than an extensional layer damper and is more effective. It also meets the other physical and environmental requirements for a pipe covering.

The paper discusses the process of developing an SAE damping measurement test method that is suitable for testing bars that are not made of steel or are difficult to measure with the traditional Oberst bar method. The method is based on measuring mechanical impedance (force over velocity) of a vibrating bar. The bar is excited at the center using a shaker and hence it is also called a CenterPoint method. The paper discusses the round robin tests that have been conducted so far and discusses the test results that will help develop the standard. The paper discusses the variability of the round robin test results within a laboratory, between laboratories, as well as the coefficient of variation for these measurements. The paper also discusses various parameters that should be carefully monitored in this study, that otherwise could affect the precision of the test procedure.