Crack-Detection Experiments on Simulated Turbine Engine Disks in NASA Glenn Research Center's Rotordynamics Laboratory

The development of new health-monitoring techniques requires the use of theoretical and experimental tools to allow new concepts to be demonstrated and validated prior to use on more complicated and expensive engine hardware. In order to meet this need, significant upgrades were made to NASA Glenn Research Center’s Rotordynamics Laboratory and a series of tests were conducted on simulated turbine engine disks as a means of demonstrating potential crack-detection techniques. The Rotordynamics Laboratory consists of a highprecision spin rig that can rotate subscale engine disks at speeds up to 12 000 rpm. The crack-detection experiment involved introducing a notch on a subscale engine disk and measuring its vibration response using externally mounted blade-tip-clearance sensors as the disk was operated at speeds up to 12 000 rpm. Testing was accomplished on both a clean baseline disk and a disk with an artificial crack: a 50.8-mm- (2-in.-) long introduced notch. The disk’s vibration responses were compared and evaluated against theoretical models to investigate their applicability to and success of detecting cracks. This paper presents the capabilities of the Rotordynamics Laboratory, the baseline theory and experimental setup for the crack-detection experiments, and the associated results from the latest test campaign. I. Introduction HE development of fault-detection techniques for the in situ health monitoring of gas turbine engines is of high interest to NASA’s Aviation Safety Program (AVSP). The rotating components of modern gas turbine engines operate in severe environmental conditions and are exposed to high thermal and mechanical loads. The cumulative effects of these loads over time lead to high stresses, structural deformity, and eventual component failure. Current risk-mitigation practices involve periodic inspections and schedule-based maintenance of engine components to ensure their integrity over the lifetime of the engine. However, these methods have their limitations, and failures are experienced leading to unscheduled maintenance and unplanned engine shutdowns. To prevent these failures and enhance aviation safety, the NASA Integrated Vehicle Health Management (IVHM) Project, as part of the overall AVSP, is investigating new types of sensor technologies and methods for the in situ structural health monitoring and detection of flaws in gas turbine engines. The successful development and implementation of such technology and health-monitoring techniques requires the use of both theoretical and experimental tools to allow new concepts to be investigated and demonstrated prior to use on more complicated and expensive hardware. In order to meet this need, research has been conducted at the NASA Glenn Research Center to develop both global and local approaches for monitoring critical rotor components. 1-6