Measuring Damping Loss Factors of High Performance LASD Coatings

One of the most effective NVH solutions used in the automotive industry to reduce structure-borne noise is to apply vibration damping treatments to the vehicle structure. These damping treatments need to meet increasing weight reduction targets, while offering the same or better damping properties. While Liquid Applied Structural Dampers (LASD) are now delivering high damping performance at lower densities, traditional damping measuring techniques are falling short in describing the performance of these extensional layers when applied onto more realistic test samples or real structures. This paper discusses the damping performance of LASD technology, in particular the newer generations of acrylic-based waterborne LASD materials, which through improvements in polymer architecture are achieving increased damping efficiencies together with reduced density. The paper further describes a test method for evaluating the composite damping loss factor (CDLF) properties of LASD treatment layers applied to metal panels used as test samples. The panel test method is based on the calculation of the reverberation time as determined from the initial decay rate of the band filtered impulse response functions. The damping data determined by using this test method is found to be in good agreement with similar data measured independently by using power injection methods (PIM). Correlations between damping performance of LASD treatments measured by using panel testing, one dimensional beam testing, and body-in-white testing methods are also discussed. The damping measurement technique described was used as a validation tool for the latest generation, lower weight, high performance, LASD materials. Panel measurements correlate well with existing test techniques and provide useful information on damping performance, in a high modal density environment, which can be used as input into advanced NVH modeling techniques.