Aircraft Engine Turbine Blades Research Articles

Damage evolution in EB-PVD thermal barrier coatings for turbine blades in aircraft engines under close to reality testing conditions

In advanced gas turbines for aircraft engines, internally cooled turbine blades have a ceramic thermal barrier coating (TBC) to reduce the thermal load of the metallic substrate. Exhausting the full potential of the TBC to increase the turbine inlet temperature requires reliable lifetime prediction methods, since failure of the TBC will entail the immediate failure of the blade. A lifetime prediction concept for TBCs based on lifetime analyses of close to reality tests is given. The basic idea is to ensure that failure mechanisms during testing are the same as in a turbine engine. Specimens with an electron beam physical vapour deposited (EB-PVD) TBC were tested under realistic fatigue load but drastically reduced holding times. The results exhibited that the as-coated properties of the ceramic coating are sufficient to survive the required load alternations in service. The influence of kinetic damage mechanisms on the TBC-lifetime will be determined in tests with pre-aged specimens.

Determination of trace impurities in nickel-based alloy using neutron activation analysis

A radiochemical neutron activation analysis procedure has been applied to investigate 40 major, minor, and trace impurities in nickel-based alloy. The extensive use of these alloys in the electronic industry, telecommunications, manufacturing of aircraft engine turbine blades and chemical equipments desires for their precise characterization. The concentration of nickel in the nickel-based alloy was found to be 56.8%, whereas Fe, Cr, Ca, Mg, Ce, Mn, Na and V were the major components of the alloy, which constituted to more than 26%. The rest of the elements was present in minor or trace levels. Most of the rare earth elements except Ce were also present in trace amounts. Neutron activation analysis technique was preferably used because of its good sensitivity and multielement determination capabilities for the characterization of high purity materials. The comparison of RNAA and INAA indicated improvement in the detection limits utilizing radiochemical separation procedures developed in the present work.

A Design Method to Prevent Low Pressure Turbine Blade Flutter

A design approach to avoid flutter of low pressure turbine blades in aircraft engines is described. A linearized Euler analysis, previously validated using experimental data, is used for a series of parameter studies. The influence of mode shape and reduced frequency are investigated. Mode shape is identified as the most important contributor to determining the stability of a blade design. A new stability parameter is introduced to gain additional insight into the key contributors to flutter. This stability parameter is derived from the influence coefficient representation of the cascade, and includes only contributions from the reference blade and its immediate neighbors. This has the effect of retaining the most important contributions to aerodynamic damping while filtering out terms of less significance. This parameter is utilized to develop a stability map, which provides the critical reduced frequency as a function of torsion axis location. Rules for preliminary design and procedures for detailed design analysis are defined. [S0742-4795(00)01401-0]

Acoustic emission inspection of aircraft engine turbine blades for intergranular corrosion

The depth of the intergranular corrosion on turbine blades is of decisive significance with regard to their suitability for continued use. An acoustic emission method is introduced that is suitable for examination of blades during regular engine overhaul and which permits a statement on the depth of the corrosion to be made.

Missile Firing Tests at Stationary Targets in Support of Blade Containment Design

Compressor and turbine blades of aircraft engines are liable to failure from a number of causes. Their subsequent containment within the immediate confines of the engine has long posed problems for the designer aiming for minimum weight designs. To assist the understanding of the dynamics of the containment problem, a series of small scale model tests have been conducted. The particular tests reported, deal with the failure mechanism at the point of impact. A theoretical analysis in support of the results obtained is developed. Fairly good agreement is obtained between tests and theory and the read-across to full scale containment tests indicates that the containment problem is capable of scaling if linear velocities are kept constant. A discontinuity in the behavior of materials with respect to their just contained energy capacity has been identified. While several contributory factors can be suggested, a fully satisfactory explanation is not found.

Effect of load variability on the fatigue strength and endurance of EI617 alloy at elevated temperatures

The article describes the results of programmed fatigue tests on a heat-resistant alloy used in the fabrication of aircraft-engine turbine blades. The test program employed was based on the analysis of operational loads acting on turbine blades.