BDC develops tools and methods for evaluating and controlling how mistuning affects the vibratory response of Integrally Bladed Rotors. Mistuning refers to the fact that each blade has a slightly different natural frequency.
Mistuning has been identified as a primary factor in High Cycle Fatigue failures in Integrally Bladed Rotors. Even very small amounts of mistuning can cause some blades to vibrate much more than others. It has been documented that mistuning can cause an amplification of resonant response by up to 400 percent.
BDC develops new methods and tools to inspect IBRs in the depot, during the manufacturing process, or for use in R&D.
In order to extend the life of Integrally Bladed Rotors, BDC technologies identify and predict the effects of mistuning and vibration on these critical and expensive engine blades. The BDC IBR management approach includes:
This is especially critical in measuring high frequency modes since very small errors in locating measurement points can result in large errors in measured response. An important application of the test equipment is that it can be used in the depot as basis for an automated inspection system to track changes in Integrally Bladed Rotors caused by engine usage, e.g. wear, FOD, and repairs such as blending. As a result, a critical objective of BDC is to develop test equipment that has excellent repeatability and reproducibility so that the inspections produce a meaningful historical record of changes in a partís vibratory response.
This approach can be used to process vibration data from spin-pit and engine tests on conventional bladed disks as well as non-rotating tests on Integrally Bladed Rotors. More specifically, BDC has developed methods for extracting information about forces, damping and frequencies that can be used to construct a reduced order mistuning model of the test part. The reduced order model can then be used as the basis of a Monte Carlo simulation to relate the vibratory response of the tested part to the fleet. These techniques can be:
It is our experience that each stage has its unique aspects that need to be understood and taken into account when developing a quantitative understanding of its vibratory response. BDC engineers analyze vibration test data to extract information, develop mistuning models, and predict fleet response.
The high local stress concentration caused by FOD can reduce the fatigue strength of a titanium blade by as much as a factor of four. Blending is a relatively low cost machining operation that may be done by hand while the rotor is still in the engine. However, blending changes the geometries of the blades so that they no longer meet specifications. More specifically, blending changes the frequencies of the blades as well as their aerodynamic characteristics.
SMART BLEND™ is being developed by BDC and refers to the idea of using part-specific information to make a decision about whether or not the part can be repaired by blending. This will be done by measuring the mistuning in the part, determining how the blends affect the aerodynamic forces (excitation and damping) that act on the blades, and integrating this information to predict how the blended part will respond in the engine. DoD contracts are supporting BDC to develop SMART BLEND™.
This PDF explains the benefits of the Force ID™ & AutoPoint™ processes behind BDCís R&D.
This PDF explains BDCís work in MIM, Traveling Wave Testing & Parametric Studies.
Carnegie Mellon University Mechanical Engineering Magazine published this article on BDC.