Finite Element Simulation on Thermal Fatigue of a Turbine Blade with Thermal Barrier Coatings

In this paper, a finite element model was developed for a turbine blade with thermal barrier coatings to investigate its failure behavior under cyclic thermal loading. Based on temperature and stress fields obtained from finite element simulations, dangerous regions in ceramic coating were determined in terms of the maximum principal stress criterion. The results show that damage preferentially occurs in the chamfer and rabbet of a turbine blade with thermal barrier coatings and its thermal fatigue life decreases with the increase of thermal stress induced by high service temperature.

Harmonic balance-based approach for optimal time delay to control unstable periodic orbits of chaotic systems

As a classical technique for chaos suppression,the time-delayed feedback controlling strategy has been widely developed by stabilizing unstable periodic orbits(UPOs)embedded in chaotic systems.A critical issue for achieving high controlling precision is to search for an appropriate time delay.This paper proposes a simple yet effective approach,based on incremental harmonic balance method,to determine the optimal time delay in the delayed feedback controller.The time delay is adjusted within the iterative scheme provided by the proposed method,and finally converges to the period of the target UPO.As long as the optimal time delay is fixed,moreover,the attained solution makes it quite convenient to analyze its stability according to the Floquet theory,which further provides the effective interval of the feedback gain.

Pb-DOPING EFFECTS ON THE DIELECTRIC AND PYROELECTRIC PROPERTIES OF(Sr,Pb)TiO_(3)SYSTEM

Lead strontium titanate(Sr_(1-x)Pbx)TiO_(3)(0.20≤x≤0.45,step=0.05)ceramics were prepared by conventional mixed oxide method.The X-ray diffraction patterns indicate that the prepared samples have perovskite-type structure.With the increase of Pb content,there is a tendency from the cubic to tetragonal structure.The scanning electron microscopy micrographs reveal that the addition of Pb can affect microstructure.The dependent temperature dielectric permittivity and dielectric loss were investigated in the frequency range from 100 Hz to 1MHz.The maximum peak of the dielectric permittivity versus temperature curve was broadened and a frequency dispersion of the dielectric permittivity was observed for the(Sr_(0.8)Pb_(0.2))TiO_(3)ceramics.The results obtained at the frequency of 10 kHz reveal the Curie temperature linearly increased with the lead content.Thefitted curves of temperature versus inverse dielectric permittivity at 10 kHz for(Sr_(1-x)Pbx)TiO_(3)ceramics are consistent with Curie-Weiss law.The Pyroelectric properties were also investigated.The high pyroelectric coe±cients andfigure of merits indicate that the SPT ceramics are potential materials for pyroelectric sensors.