Evaluation of MAST Transfer Function in the Vehicle Exhaust System Full System Durability Test

A major priority of the vehicle industry is to reduce the cost and time of new product development. To achieve that, there are mainly two approaches: developing an inhouse testing facility to replace the vehicle road test; and integrating the CAE technique into the new product development and analyses. This paper focuses on the methodology in the vehicle exhaust system durability test.

The MTS Multi-Axial Simulation Table (MAST) has been used in the vehicle exhaust system durability test since the late 90's. The objective of this equipment is to duplicate the road damage along the exhaust system in the lab. Ultimately, exhaust system durability can be validated without vehicle prototype testing.

Six hydraulic actuators are required to provide 6 DOF motion of the vibration table. The Frequency Response Function (FRF) is calculated to define the transfer function between each actuator. The drive files of actuators are developed based on the FRF results; thus, the iteration to generate FRF is critical to a successful vibration test. MTS provides two methods to calculate FRF. The H1 function is based on the inputs and outputs Cross-Spectral Density (CSD) and the Drive file Auto-Spectral Density (DSD). The H2 function is based on the output Response Auto-Spectral Density (RSD) and the inputs and outputs CSD. This paper addresses these two methods and evaluates their effects on the iteration of the MAST drive files and test.