Assessing the Vibration Fatigue Life of Engine Mounted Components

Abstract

Abstract As part of the design validation of components mounted on rotating machinery such as a car engine, it is essential to understand the environmental stress in which they operate. In the case of vibration loadings, the reliability must be verified according to accelerated tests that realistically reproduce the in-service stress. Indeed, a representative validation profile permits not only the assessment of the component durability, but also provides a reliable reference for design optimization (downsizing), reducing development cycle costs, and time scale. This paper proposes an innovative methodology to generate tailored vibration signals more representative of the real environment. First, the severity of the test is tailored to the specific engine usage profile, i.e., the time spent at each revolution per minute (RPM) for a given percentile of customer usage. Traditional signals of Power Spectrum Density (PSD) and sine sweep are developed according a fatigue damage approach (test tailoring). Then, a more representative vibration specification is obtained as a multiple-sine-on-random signal. The signal is expressed as a series of multiple sine sweeps (representing the engine harmonics) and a PSD (representing the random leftover signal). A case study applied to an engine mounted heat exchanger (a water-cooled intercooler) is presented. The generated specification is compared to the validation signals developed according to existing procedures. The results show that 1) the tailored approach decreases the risk of unnecessary over-testing and 2) the multi-swept-sine-on-random signal guarantees the best representativeness of the real environment.