Component S/N Curve Testing Methodology for Exhaust System Validation

The exhaust system design and development need to be more flexible and easily adaptable for the requirement of dynamic changes to meet the upcoming emission and noise regulations. Durability of exhaust system components are evaluated through conventional bending moment testing using specified standard load conditions. Road load re-production test is an improvement of the conventional approach to predict component weld durability. It involves the systematic and 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 road load reproduction testing. It involves prediction of rough force using transient response analysis followed by Bi-Ax testing for the derived high and low load forces to meet the target number of cycles to failure. Targeted fatigue damage factor (< 1.0) is evaluated by comparing S/N curve low load force with RLDA maximum force magnitude. Fatigue damage factor, which is the deciding parameter for road load reproduction test, is established with simulation and component S/N curve testing for a representative exhaust system. This method is preferred when the failure mechanism is not clearly known. It also helps to propose maximum sustainable load caused by engine vibration. The maximum force from RLDA is found to be less than the S/N curve low load force and the calculated fatigue damage factor 0.95 (which is <1.0) and therefore fatigue failure will not occur.