Fatigue Damage Modeling Approach Based on Moving Power Spectrum Density
Fatigue damage estimation has long been treated as an important area of research in order to design machines and structures dependably during their entire lifetime. The durability of engineering components and structures under expected vibrational environment must be assessed to meet design requirements for the reliability and safety in the service life. In past decades, fatigue damage estimation approaches in both time domain and frequency domain have been developed to simulate the operational life of the structures under severe vibrations. ^ Current frequency fatigue prediction methods for accelerated vibration loading conditions, however, are based on stationary Power Spectral Density (PSD) inputs. Machine components such as jet engines, rotating machines, and tracked vehicles are subjected to non- stationary (sweeping) PSD conditions under real service loadings. This thesis is aimed to develop a Fatigue Damage modeling approach to predict fatigue damage for structures subjected to non- stationary PSD loading conditions. This modeling provides the fatigue damage estimation using the frequency domain method, where only the input PSD and the attributes of a structural system are required. In this thesis, a computational mathematical model was developed to estimate fatigue damage of simplified structure(s) subjected to non-stationary PSD, which includes sweeping narrowband and stationary wideband. The non-stationary PSD was divided into a number of PSD stations on the basis of sweeping rate. Each PSD station represents the excitation energy level at a certain time duration. And each PSD station was sliced into small segments for fatigue damage estimation on the basis of the Bands method. A numerical finite element (FE) method using ANSYS software package was used to simulate the vibrational PSD response and fatigue damage of three simplified structures to validate the proposed computational modeling. Estimated fatigue damages obtained from the computational modeling showed a good correlation with finite element analysis results. The modeling fatigue damage approach on the basis of the non-stationary PSD loadings is more efficient, better simulates real environmental vibration loadings and provide more accurate fatigue life predictions. Techniques and modeling methods developed here can be easily adapted to optimize design of engineering structural components experiencing a spectrum of complex loading conditions.^
Ayhan Ince, Purdue University.
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