Component S/N Curve Testing Methodology for Exhaust System Validation

The exhaust system design and development needs to be more flexible and easily adaptable for the dynamic changes with the introduction of new emission and noise regulations. Conventionally, bending moment testing is used to validate significant components like inlet and outlet pipe/cone joints and bend pipes through Bi-Ax test rig. Road load re-production test is an improvement of the conventional approach to predict component durability. However, it is more time consuming and involves the sequential process of acquiring road load data such as sensor instrumentation, strain measurement at the test track, data processing and input to Bi-Ax testing. S/N Curve testing is introduced recently as an alternate method to minimize the use of RLDA. It can be done upfront during vehicle unavailability and other challenging conditions and also as a parallel activity along with RLDA. Our objective is to show the simulation and validation process of Component S/N Curve testing with a LNT+DPF system special case study. It involves identification of force from virtual simulation and proceed to Bi-Ax testing for each load case to validate critical joint locations. The average bending moment load has been determined through the slope of S/N Curve derived from High load (50,000 ±10% cycles) and Low load (5,00,000 ±10% cycles) forces after testing. This bending moment is used to recommend maximum sustainable load caused by engine excitation as a limiting factor for evaluating component durability. This method is preferred when the failure mechanism is not clearly known and it serves the purpose of predicting fatigue life cycle of components. Also it serves as a major source of data for commonized exhaust system layout. Prediction of fatigue life cycle from virtual simulation, Component S/N Curve testing and RLDA Bi-Ax testing are correlated and details are discussed in this paper.