An experimental and numerical investigation of stress wave propagation across interfaces.

摘要

In this dissertation the propagation of stress waves across interfaces has been studied. The stress waves of interest in this research are those that can be used in diagnostics for detecting defects or impending failure. The stress waves considered are acoustic emission (AE) waves released during crack propagation and stress waves arising due to impact in the pitted region of gear teeth or bearings. These stress waves carry valuable information and if they are successfully detected, they can serve as early warning signs of impending failure.; The stress waves are detected by using transducers. On their path from the source to the sensor, these stress waves experience multiple reflections, refractions and mode conversions. These waves have to transmit across a number of mechanical interfaces before they reach the sensor and they lose a significant portion of their strength at each interface. In order to efficiently detect these stress waves, strategic location of sensors becomes important. In order to judiciously locate sensors, the losses for different paths of transmission need to be evaluated and for this the losses across different types of interfaces have to be quantified. This research uses a combination of experimental and numerical methods to come up with guidelines for transducer locations.; In this dissertation several issues regarding stress wave propagation have been addressed. The detectability of stress waves arising from AE and from pits on gear teeth has been studied. The feasibility of detecting pits on gear teeth by using an AE sensor has been established. The losses across different types of interfaces commonly encountered in mechanical systems have been quantified. A dynamic transient finite element code has been developed to numerically model the propagation of AE waves. The ability of this code to model wave phenomena like propagation, reflection, refraction and mode conversions has been shown. A spatial and temporal resolution criterion for accurately modeling wave phenomena has been established. Finally a combined experimental and numerical approach to identify optimal sensor location has been developed.