Crack analysis of the first stage blade on a gas turbine

To clarify the physical cause of premature blade cracking during the accelerated mission test(AMT) in a test cell environment,initial fracture graphic investigation and analysis of the cracked blades was carried out and an in-depth analysis of the blade was undertaken using ansis system XactLIFE^TM of Life Prediction Technologies inc(LPTi's XactLIFE^TMM) system.Results show that the blades have suffered excessive airfoil creep damage,leading to excessive blade lengthening and airfoil untwisting particularly in the trailing edge region.It's believed that this uneven rubbing action might have contributed to the fatigue crack nucleation and growth process just below the platform in the shank region of the blade under AMT fatigue cycling conditions.Excessive creep deformation is therefore believed to be the significant contributor to the overall crack nucleation process.