Testing of an Automotive Frame to Determine Dynamic Properties

The essentially modal behavior of an automotive chassis frame in the 0-30 Hz frequency range is confirmed by investigation of a typical frequency response. A mathematical model is developed for which the parameters are to be obtained directly by analysis of vibration test data. The requirements are determined for the instrumentation system and laboratory test setup necessary to obtain accurate estimates of resonant frequencies, mode shapes, and modal mass and damping properties. The determination and importance of the rigid body properties and the “residual compliance” of truncated modes are discussed. Direct comparisons of predicted frequency responses with the original test data demonstrate the validity of the “test-derived model.”