Accelerated Mission Testing Research Articles

A novel compilation method of comprehensive mission spectrum of aero-engine maneuvering load based on use-related mission segment

Comprehensive Mission Spectrum (CMS) of an aero-engine can reflect the usage characteristics of the engine. It can provide load input for engine life prediction and accelerated mission test. In this paper, a novel compilation method of CMS of aero-engine maneuvering load based on mission segment is proposed. Firstly, the use-related Typical Mission Segment (TMS) of maneuvering load is divided and identified according to spectral characteristics. Secondly, the mathematical model of different kinds of TMS are established based on stochastic process theory. Finally, the CMS of maneuvering load is compiled based on TMS. The proposed method can accurately quantify the compilation of CMS. The compiled CMS shows good agreement with the original load spectrum. According to damage consistency inspection, the compiled CMS is consistent with the damage caused by the original load spectrum in terms of low cycle fatigue.

Structural Integrity Analysis and Life Estimation of a Gas Turbine Bladed-Disc

Turbine blades in an aero-engine are subjected to severe conditions of high temperature and pressure, which cause high levels of stress leading to crack formation and subsequent failure in service. We have investigated the influence of crack on vibration parameters of a typical aero-engine gas turbine blade and have described a life assessment approach for blades and bladed discs. A typical transport aircraft AMT (Accelerated Mission Test) cycle has been utilized for getting operating parameters. Material data is taken from tests conducted on specimens extracted from turbine disc of a transport aircraft. Initial studies are carried out on idealizations involving cantilever beams with uniform cross-section; the procedures are then extended to free-standing turbine blades with asymmetric airfoil cross section mounted at a stagger angle on a rotating disc. Dynamic characteristics of the blade are estimated and free vibrations analysis has been carried out for healthy blades and those with cracks of different sizes. Influence of crack size on natural frequencies and mode shapes is studied. Results show a difference of less than 1% in frequency for cracks less than 1mm in length; for larger crack lengths the frequency shifts are higher. Analytical results are compared with experimental tests on a Laser Doppler Vibrometer set-up. Subsequently, forced vibration analysis is performed and a methodology, using Lazan’s law, is developed to extract modal damping ratios from the strain energy of the blade under nozzle excitation pressure fluctuations. Modal damping ratios, thus obtained, are indicative the energy dissipation in the component under such stress conditions. The ratios show differences of the order of 5% between healthy and cracked blades for the second mode. These observations lead illustrate that modal damping has strong correlation with blade structural integrity. The possibility of employing these modal damping ratios as indicators for the presence of cracks / defects is discussed.

Life enhancement of Nozzle Guide Vane of an Aero Gas Turbine Engine through Pack Aluminization

AbstractPack aluminization of high pressure turbine nozzle guide vane of an aero gas turbine engine has been carried out following a well defined systematic procedure. The process parameters are first optimized on dummy vanes and optimized process is followed for the actual vanes for evaluation and testing. Visual and binocular examination followed by metallurgical evaluation have been carried out to validate the process and to establish the adequacy and correctness of the coating. The coated vanes are then evaluated through engine level tests for performance and durability. The results of engine level tests and inspection post accelerated mission test cycles ensure that the vanes with aluminide coating can withstand severe engine operating cycles without any damage or failure which would otherwise would have happened without the coating. The condition of vanes post endurance test is also an indication of enhanced life of the vanes with coating.

Measurement of service-induced internal elastic strains in a single-crystal nickel-based turbine blade with convergent-beam electron diffraction

Abstract During tensile creep deformation, single-crystal nickel-based superalloys develop a characteristic internal stress state, which leads to counteracting tetragonal lattice distortions of the two phases γ and γ'. The aim of this work was the evaluation of the related elastic lattice distortions in the microstruture of a turbine blade after service in an accelerated mission test with high lateral resolution by convergent-beam electron diffraction. For the determination of the local lattice parameters, the higher-order Laue zone (HOLZ) lines of the central diffraction disc were evaluated under the assumption of a tetragonal distorted crystal lattice. The zone-axis patterns were simulated considering dynamical effects of the diffraction process. In order to reduce the computation time, a set of HOLZ line patterns was calculated in advance. Experimental patterns were compared with dynamically simulated patterns by the analysis of characteristic areas between HOLZ lines. The dependence of two area fractions on the lattice parameters were fitted by an interpolation function. This function was used for the evaluation of the experimental patterns. With this new approach a relatively fast evaluation of lattice strains was possible.

Determination of local strains in a monocrystalline turbine blade by microbeam X-ray diffraction with synchrotron radiation

X-ray peak profiles of the types {400} and {300} of monocrystalline nickel-based superalloy turbine blades were measured with a new microbeam synchrotron radiation X-ray diffraction technique. Under the coating of a turbine blade in the virgin state, a plastically deformed layer was found which is responsible for anomalous rafting. In a turbine blade subjected to an “accelerated mission test”, the phases γ and γ′ were found to be under elastic distortions arising from the superposition of counteracting internal stresses. It is concluded that the investigated section was under tensile creep load during service. In the regions near the surfaces, the lattice parameters of both γ and γ′ increase. The reason for this increase is the diffusion of Al from the NiAl coating into the bulk of the blade. Finally, the differences between the peak profiles measured with the microfocus technique and with a conventional diffractometer are discussed.

Analytical Condition Inspection and Extension of Time Between Overhaul of F3-30 Engine

F3-30 is the low-bypass-ratio turbofan engine developed to power the T-4 intermediate trainer for the Japan Air Self Defense Force (JASDF). The actual field service was started in Sept., 1988. The program to extend time between overhaul (TBO) of the F3-30 has been running. Analytical condition inspection (ACI) and accelerated mission testing (AMT) were conducted to confirm sufficient durability to extend TBO. Most deteriorations of parts and performance due to AMT were also found by ACI after field operation with approximately the same deterioration rate. On the other hand, some deteriorations were found by ACI only. These results show that ACI after field operation is also necessary to confirm the TBO extension, although AMT simulates the deterioration in field operations very well. The deteriorations that would be caused by the field operation during one extended-TBO were estimated with the results of ACI and AMT, and it was concluded that the F3-30 has sufficient durability for TBO extension to the next step.

TF41/Lamilloy accelerated mission test

TF41/Lamilloy accelerated mission test

Accelerated Mission Testing of Gas Turbine Engines

Commercial and military aircraft engines are designed to meet specific usage requirements. In the past, verification of these designs was based on the successful completion of a model endurance test. The model test was a yardstick-type test and was not specifically designed to simulate actual usage. Flight experience has shown that this type of qualification testing is not representative of real usage. Today, new development engines are being tested to accelerated mission test cycles. These test cycles are designed to include all significant engine excursions and time at high power conditions in a representative fashion. The philosophy and methodology of mission-related testing of gas turbine engines are presented.