Acoustic requirements for product design became a major task in the product development process due to more stringent legal sound regulations and customer demand of quieter products. Numerical methods are widespread tools in this process. However, accuracy and applicability of predictive numerical models are limited by availability and precision of material properties. These data has to be investigated by measurements only.

Experimental Modal Analysis (EMA) has demonstrated to provide significant results when applied to automotive components. However, traditional impact modal testing with hand-held hammers shows its limitations during brake pad measurements. Major reasons for this effect are the composite structure and the anisotropic material of brake pad components. Such nonlinear structures are sensitive to excitation amplitude and direction. Therefore, automatic and repeatable excitation is needed in order to achieve precise results.

Brake pad samples are excited in this study with an adjustable and repeatable force with the assistance of a custom-designed automatic test facility. Using the same brake pad type, a series of tests was performed on new and used samples. The modal parameters natural frequency and modal damping are extracted from these measurements up to 15 kHz. Repeatability of the results has been demonstrated.

All data can be extracted dependent on excitation force, frequency, and temperature. Repeatability of experimental results suggests that this technique can be used in validation, development, end-of-line tests, and in quality management applications.

Peter Blaschke, Daniel Alarcón, Robert Paeschke, Torsten Schneider - Technical University of Applied Sciences Wildau