Comparing Vibration Data (Turbofan Blades) 1

[jscheel15]

I am performing Impact vibration tests on turbofan blades and when comparing data the peaks are in the appropriate areas as predetermined with FEA analysis but the breadth of these peaks differs with different blades. I know this is due to damping but am having problems trying to figure out why certain blades harmonics are more damped (have a larger breadth) than others when the blades are all within the same tolerance limits (mass, stiffness, thickness, etc. ) I am new to developing a testing proceedure in this area though i do have experience in other vibration analysis, any ideas would be much appreciated. thanks

 

[btrueblood]

Damping can be affected by variations in the metallurgy (grain size, inclusions/voids, etc etc), size/form of parts, stress history, case hardening depth...among a variety of other factors.

However, the mounting of your blades, or the mounting of the accelerometer to the blades (and thickness of adhesive) can also affect the apparent damping.

 

[EricZhao]

In this case, your damping might mainly came from two aspects. One is material’s hysteretic damping, the other is the structural damping at the mounting boundary. For assembly, the damping introduced by boundary friction is usually more than the material’s hysteretic damping. Check the assembly condition between the blade and the disk.

 

[thomasjoseph]

Your case seems like developing a new blade design. I feel when it comes to real world, you might getaway as long as the campell diagram shows no natural frequencies are in the operating speed.