Random Vibration Testing Development for Engine Mounted Products Considering Customer Usage

In this paper, the development of random vibration testing schedules for durability design verification of engine mounted products is presented, based on the equivalent fatigue damage concept and the 95th-percentile customer engine usage data for 150,000 miles. Development of the 95th-percentile customer usage profile is first discussed. Following that, the field engine excitation and engine duty cycle definition is introduced. By using a simplified transfer function of a single degree-of-freedom (SDOF) system subjected to a base excitation, the response acceleration and stress PSDs are related to the input excitation in PSD, which is the equivalent fatigue damage concept. Also, the narrow-band fatigue damage spectrum (FDS) is calculated in terms of the input excitation PSD based on the Miner linear damage rule, the Rayleigh statistical distribution for stress amplitude, a material's S-N curve, and the Miles approximate solution. Vice versa, the input excitation PSD is directly derived in terms of a given FDS and test duration. Finally, a random vibration test profile in PSD is obtained by varying the test duration such that the FDS calculated from the customer usage data equals the FDS from the test PSD. Two reliability demonstration test methods such as attribute testing and extended testing are introduced to ensure the tested parts will meet the required reliability and confidence target with a limited sample size.