This paper investigates on failure mechanisms of turbine blades occurring during operation. Experimental mechanics is utilized to identify critical frequencies leading to blade fracture. Stroboscopic holographic interferometry served to record vibration patterns that are then analyzed quantitatively. Strains are computed from interferometric patterns and hence expressed in local coordinate system of the curved blade surface. Stress distributions are recovered from the Hookean model. Stress trajectories of the blade surface finally allow us to get the isostatic lines. Stress trajectories match with the initial crack surface trajectory. This made it possible to identify the excitation modes causing blade fracture. Furthermore, initial crack trajectories follow the isostatics thus failing in a similar mode to the maximum-tensile-strain law: as the larger principal strain reaches a critical value, cracks will develop in the direction perpendicular to the principal strain direction. The paper discusses blade failure mechanisms justifying the experimental evidence. The observed failure seems a form of the principal normal stress fracture criterion. In this study, we recovered the geometry of the minimum resistance of the crack path rather than the actual applied stress causing failure. Hence, an argument based on damage accumulation should be introduced to explain the observed behavior.
|Autori interni:||CASAVOLA, Caterina|
|Titolo:||Fracture of turbine blades under self- exciting modes|
|Data di pubblicazione:||2006|
|Digital Object Identifier (DOI):||0.1007/1-4020-4972-2_212|
|Appare nelle tipologie:||4.1 Contributo in Atti di convegno|