A new approach in the mean residual lifetime evaluation of a multi-state system

Dynamic reliability measures are important characteristics for understanding the lifetime behaviour of multi-state systems. This study aims to analyze the mean residual lifetime (MRL) function for a one-unit three-state system.The system considered has just three states such as “0, 1, 2”. State “2” and “1” signify the perfect functioning and partially working states, respectively while state “0” is the failure state. We let [Formula: see text] and [Formula: see text] be the lifetimes of the system spent at state “1” and “2,” respectively. We assess a particular performance characteristic, MRL, of this three-state system via conditional survival functions, when [Formula: see text] and [Formula: see text] are both independent and dependent. In case of independency, MRL functions are obtained and the results are discussed with reference to a case study. The effect of different distributions on the MRLs are also investigated in this case study. In case of dependency, on the other hand, the effect of dependency on MRL functions is especially underlined given that the system is at state “ j” ([Formula: see text]) for [Formula: see text]. To understand the time dependent behaviour of the related MRL functions, certain graphical illustrations are also presented.

The Influence of Metal Diffusion and Interfacial Reactions on the Crystallization Behaviour of Glasses Employed in the Manufacture of Glass-Ceramic-to-Metal Seals

One of the major attributes of glass-ceramics is an ability to tailor their thermal expansion characteristics and this makes them ideal candidates for sealing to a wide variety of metals and alloys; however, during the sealing process, reaction of diffusing metal species with glass constituents may occur, and this can lead to the formation of undesirable phases within the interfacial region. In addition, diffusion of metal species into the bulk glass away from the interface may affect the overall crystallization kinetics and can result in the formation of unwanted crystalline phases which may be detrimental to the lifetime behaviour of a seal component. This contribution outlines and discusses the factors affecting the crystallization behaviour of glasses employed in seal manufacture and describe methods by which undesirable reactions can be alleviated or minimized through effective control of the process parameters and starting glass composition.

Concentration Dependent Fluorescence Lifetime in Nanocrystalline Y2O3:Eu Phosphors

Nanocrystalline (Y1-xEux)2O3 powder was synthesized via a chemical vapour reaction. Xray diffraction revealed the structure of cubic yttria with crystallite sizes of about 5 nm. The Eudopand concentrations x for the samples in the range from 0.003 up to 0.165 were determined by EDX-spectra. The luminescence of the nanopowders was investigated by continuous and timeresolved UV-fluorescence spectroscopy and compared to a microcrystalline Y2O3:Eu phosphor as a reference. The emission spectra show an increasing intensity for higher doping concentrations. However, compared to the microcrystalline material the yield was significantly lower. The lifetime of the 5D0 – 7FJ transition in the nanocrystalline Y2O3:Eu was found to be significantly longer than for the microcrystalline reference sample. For increasing Eu-content the lifetime in the nanocrystalline samples decreased continuously from 3.71 ms to a value of 1.20 ms for the highest doping concentration. The concentration dependent lifetime behaviour was interpreted by energy transfer between Eu ions and from Eu ions to impurities as a competing process to the radiative 5D0 – 7F2 transition.

Fatigue Behaviour of Case-Hardened P/M Steels

Powder-metallurgical (P/M) produced components may be used as mass parts in a very large quantity. Due to the multistage manufacturing process which consists of the pressing of the prepared powder and the sintering of the green bodies also complex shaped components can be produced very economically and precisely. They can be utilised without any further post-processing if the whole production process is optimised. However, it is still difficult and only possible with considerable technical and financial effort to produce highly stressable components profitably using the sinter technique. Therefore, the examinations on hand had the intention to create the basis for the use of the sinter technology also for the production of highly stressable case-hardened components. To this, at first bending specimens were fabricated with modern pressing procedures and sinter facilities and first characterized in the as sintered state. Then the conditions for the case-hardening was analysed and the parameters for an optimised case-hardening procedure fixed. With these parameters specimens were case-hardened and their lifetime behaviour estimated under different bending loading conditions. Finally it should be checked whether the knowledge gained from the specimens could be applied to complex components. To this, gear wheels were produced using powder-metallurgy. The cyclical tooth foot strength of this gear wheels were analysed in the only sintered as well as in the case-hardened state. It could be demonstrated that the improvement of the fatigue strength of the bending specimens by case-hardening also appears at the tooth foot strength of the gear wheels.