Filtern
Erscheinungsjahr
- 1998 (28) (entfernen)
Dokumenttyp
- Beitrag zu einem Sammelband (28) (entfernen)
Sprache
- Englisch (19)
- Deutsch (7)
- Französisch (1)
- Mehrsprachig (1)
Referierte Publikation
- nein (28)
Schlagworte
- Biochemical reaction mechanisms and kinetics (1)
- Chemical analysis (1)
- Cordierite (1)
- Glass-ceramics (1)
- Laser irradiation surface effects (1)
- Lattice parameter refinement (1)
- Photochemical reactions of biomolecules (1)
- Rietveld analysis (1)
- Solid solutions (1)
- Surface and interface chemistry of polymers (1)
Catalyst characterization
(1998)
High performance composites and other light weight materials are generally a comple problem to the performance of nondestructive testing methods. X-ray refraction provide unconventional X-ray scattering techniques to meet the actual demand for improve nondestructive characterization of these advanced materials. Scanning the samples across collimated narrow incident X-ray beam permits to image integral micro-structures (a present) with a resolution of 10 µm. Investigations of samples after strain-induced micro cracks and fibre debonding in impact damaged epoxy are shown.
The physics of X-ray refraction are analogous to the well known refraction of light b optical lenses and prisms, governed by Snell's law. The special feature is the deflection a very small angles of few minutes of arc, as the refractive index of X-rays in matter i nearly one. Due to the density differences at inner surfaces most of the incident X-rays ar deflected. As the scattered intensity of refraction is proportional to the specific surface of sample, a reference standard gives a quantitative measure for analytical determinations.
Figure 1 represents a two-dimensional damage distribution of an impact in a 0/90° CFR laminate of 3 mm, thickness. Unlike in ultrasonic testing, there is no shadowing effect o the successive layers. By use of X-ray refraction the exact concentration of debonde fibres is calculated for each position. Additionally the refraction allows the selection of th fibre orientation.
Gas turbine efficiency is significantly influenced by the pressure losses caused by the inevitable gap between the rotating turbine blades and the stator parts.
Because contact between rotor and stator cannot be completely avoided with a small gap, systems are designed to allow for some rubbing. Honeycombs or abradable MCrAlY stator coatings are normally used to minimize the wear of the rotor blades when rubbing occurs. But, more efficient solutions must be developed on modern engines, because both suffer temperature limitation and standard MCrAlY have usually poor abradability. For higher temperature and closer control of the gap, a thick thermal-barrier coating must be applied on the stator, but presently with no rub-tolerance.
To increase the abradability of the stator coating, its composition and structure can be modified, but such changes must be strictly limited with respect to the loss of erosion resistance.
The solution can then lie in the hardening of the rotating blade tip to permit the use of harder ceramic or metallic coatings on the stator with greater resistance to erosion. These systems typically consist, on the blade tip, of hard particles embedded in a softer metallic matrix.
In the present programme, it is therefore intended:
- to assess the present European solutions, standard or in development, for outer air seals and blade tips.
- to develop coated grits or new grits for the hardening of the blade tips, as well as to improve the matrix and the stator coating for long life systems.
- to optimize the most promising of these systems, that will be tested on development rigs and on engine.
The consortium includes several engine manufacturers, which are the potential users of the innovating solutions to be developed, companies having a large experience in the field of abradables and tip coatings
and non industrial partners involved in tribology and materials science.