Ein neues Wärmedämmsystem für Architekturglass

Vacuum coated glass plays an outstanding role for the energy saving of buildings. The basis of such low emissivity coatings is a 10 nm thick silver layer causing an effective reflexion of room temperature radiation. With conventional coatings k‐values of 1,3 W/m²K are realized. In the frame of a research project funded by the BMBF reactive mid frequency sputtering (Leybold TwinMag®) has been introduced for manufacturing of low e glass. The new developed system glass — TiO₂ — ZnO — Ag — NiCrO_x — Si₃N₄ enables a k‐value of 1,1 W/m²K and an improvement of optical properties.     

Schubtragfähigkeit von Mauerwerk aus Wärmedämmziegeln

Der Beitrag berichtet über zentrische und exzentrische Schubversuche an Mauerwerk aus Wärmedämmziegeln. Die Ergebnisse werden mit den aktuell gültigen Bemessungsansätzen in DIN 1053‐1 verglichen. Es wird gezeigt, dass die Versuchsergebnisse immer eine ausreichende Sicherheit gegenüber den Bemessungswerten nach DIN 1053‐1 aufweisen. Auch für Mauerwerk aus Wärmedämmziegeln mit allgemeiner bauaufsichtlicher Zulassung können somit die vereinfachten Bemessungsregeln der DIN 4149 ohne Abminderungen angewendet werden. In plane shear resistance of thermal insulating vertically perforated clay brick masonry. In plane shear tests on thermal insulating vertically perforated clay brick masonry are presented. The results are compared with the design rules from DIN 1053‐1. The test results exceeded the design predictions of DIN 1053‐1 by a significant safety margin. The simplified design rules from the German earthquake standard DIN 4149 can be applied to thermal insulating clay unit masonry with technical approvals without any reduction.     

Entwicklung von Oxid – Keramik zur Anwendung als Wärmedämmschichten

Development of Oxide Ceramics for an Application as TBC The standard thermal barrier coating material yttria stabilised zirconia (YSZ) is limited in long term operation to a maximum temperature of about 1200°C. As a result further increase of the gas inlet temperature and hence the efficiency of gas turbines are hardly to achieve with YSZ coatings. In a screening procedure especially perowskite (ABO₃, A = Sr,Ba, B = Zr) and pyrochlore (A₂B₂O₇, e.g. A = La and other rare earth elements, B = e.g. Zr) materials have been identified as possible candidates for thermal barrier coatings. Basic physical properties (e.g. thermal expansion coefficient, thermal diffusivity and conductivity) of several candidates have been determined using sintered, dense samples. The possibility of optimization of the properties by using specific compositions will be discussed. From promising materials powders which are suitable for plasma‐spraying have been produced by spray‐drying. New TBC systems consisting of new materials (BaZrO₃, La₂Zr₂O₇) deposited by atmospheric plasma spraying and vacuum plasma sprayed MCrAlY bondcoats were tested in a gas burner facility. Especially La₂Zr₂O₇ coatings gave promising results. A further improvements could be achieved by the use of layered or graded coatings with a YSZ coating at the bondcoat interface and on top a layer of the new TBC material. First results of thermal cycling tests with 1250 and 1350°C surface temperature will be presented.     

Röntgenografische Eigenspannungsmessungen an plasmagespritzten Wärmedämmschichten aus Zirkonoxid vor und nach thermischer und mechanischer Beanspruchung

X-Ray Stress Measurements on Plasma Sprayed Zirkonia Thermal Barrier Coatings Turbine blades for aero engines with plasma sprayed zirconia thermal barrier coatings were subjected to typical component loads as thermal fatigue and creep. Before and after testing residual surface stresses in the coatings were determined by X-ray stress measurements. Different substrate temperatures during the plasma spraying process caused tensile or compressive stresses on the surfaces of the thermal barrier coatings. Coatings with compressive stresses failed after only a few thermal cycles whereas those with tensile stresses sustained 700 to 1500 cycles without visible damage. Thermal fatigue and creep tests lead to stress changes reducing tensile stresses and increasing compressive stresses.     

Bauweise mit Zukunft: Durch und durch mineralisch —Wärmedämmendes Mauerwerk mit mineralischem Putz

Hat Mauerwerk eine Zukunft? Oder dienen Wände bald nur noch als Trägermaterial für Dämmschichten? Dabei ist gerade wärmedämmendes Mauerwerk aus gutem Grund im Wohnungsbau nach wie vor die Nummer Eins — und wird es nach Einschätzung der Fachleute auch bleiben. Dieser Beitrag schildert aktuelle Entwicklungen und beleuchtet Hintergründe. Construction with a future — theral insulating brick with mineral plaster. Does brickwork has a future? Couldn’t it be that walls will soon only serve as backing material for insulation layer? However, there are good reasons that heat insulating brickwork is still the number one in domestic constructions — according to experts this will remain so. The following article will characterize current developments und backgrounds.     

Der Einfluß von thermozyklischer Beanspruchung auf den Eigenspannungszustand in elektronenstrahlgedampften Wärmedämmschichten aus Zirkonoxid

Influence of Thermal Cycling on Residual Stresses in Zirconia Thermal Barrier Coatings Produced by Electron Beam – Physical Vapor Deposition. Flat specimens and aircraft turbine engine blades were coated with partially stabilized zirconia by electron beam - physical vapor deposition. Residual stresses of these thermal barrier coatings were measured before and after thermal cycling by x-ray stress analysis. All flat specimens and blades showed compressive residual stresses. Stress values in the longitudinal direction were significantly greater than those measured in the transverse direction. No changes of stress states and line widths were observed after thermal cycling. The specimens showed considerable differences in texture which made evaluation of the stress measurements difficult and which may have influenced degradation behaviour during thermal cycling.     

Installing windows in composite thermal insulation systems / Fenstermontage in Wärmedämm‐Verbundsystemen

According to the German Association for Composite Thermal Insulation Systems, about 780 million m² of composite thermal insulation systems (ETICS) have up to now been installed in both existing and new buildings in Germany ? a trend that is set to continue. Correct window installation in ETICS with a permanent and functional connection to the building fabric requires architects, engineers and contractors to be familiar with the special details of this external wall system [1], [2]. However, experience from expert witness reporting has shown that this is frequently not so and that eliminating any defects subsequently is only possible at great expense.     

Langzeitverhalten und Einsatzgrenzen von plasmagespritzten CeO2‐ und Y2O3‐ stabilisierten ZrO2‐Wärmedämmschichten

Long‐term behaviour and application limits of plasma‐sprayed CeO₂‐ and Y₂O₃‐stabilized ZrO₂ thermal barrier coatings Investigations of changes in phase composition and mechanical properties of CeO₂ – and Y₂O₃ – stabilized plasma‐sprayed ZrO₂‐based thermal barrier coatings (TBC) after long‐term heat treatments at typical service temperatures were performed. Experimental studies include X‐ray diffraction and mechanical testing. TBCs with a high amount of the tetragonal equilibrium phase t (8 mol‐% CeO₂) show strong degradation due to the high amount of transformation to the monoclinic phase and the related decrease in strength. TBCs with a high amount of tetragonal or cubic non‐equilibrium phases t′ or c′ are more suitable. Among these, TBCs with higher CeO₂‐stabilizer contents (19.5 mol‐% CeO₂/1.5 mol‐% Y₂O₃ and 35 mol‐% CeO₂) show less amounts of monoclinic phase with respect to Y₂O₃‐stabilized TBCs (4.5 mol‐% Y₂O₃), as commercially used. Therefore they seem to have a high potential for long‐term applications.     

Untersuchungen zum Mindestversuchsaufwand bei Lebensdaueruntersuchungen an einem Wälzgetriebe

Investigations Concerning the Minimal Experimental Expenditures for Fatigue Tests on Wheels for Friction Drives Results of fatigue tests on wheels for friction drives show always great scatter. The reliable experimental evaluation of the interesting scatterregions (scatter at constant stress in the range of finite life or the width of the range of transition) demands a great number of samples. In practice minimal experimental costs are aimed at and therefore the general possibilities of lowering the necessary number of samples are discussed on the example of a friction drive. The reduction of the numbers of samples, levels of load and the limiting value of stress cycles endured are especially investigated in the range of transition. Considerations concerning the reduction of the levels of load to minimal two lead to a method of testing known as ?boundary technique”? from the literature. Some remarks are made to the statistical background of this method.     

Einkristalline Gasturbinenschaufeln aus Nickelbasis-Legierungen. Teil II: Wärmebehandlung und Eigenschaften

Single-Crystal Blades for Gas Turbines Part II: Heat Treatment and Properties The article gives an overview of current single-crystal technology used in fabricating highly stressed blades and vanes for gas turbines. After a short outline of the demands placed on gas turbine blades and the resulting necessity for improvement of nickel-base alloys, and following a short definition of the “technical” single-crystal, the principal of directional solidification with suitable methods of grain selection and the realizable solidification front morphologies were described in Part I. The usuable range of casting parameters for industrial production was fixed using the alloy SRR99 as an example. The major mictrostructural characteristics of single-crystal comoponents made of nickel-base alloys namely crystallographic orientation, microporosity, morphology of the γ′-hardening phase, dendritic segregation and residual eutectic were presented. After casting, the microstructure is not in a condition which yields optimum service properties. Therefore, heat treatment is necessary. Part II describes how, with appropriate heat treatment, residual eutectic can be dissolved, segregations homogenized and the morphologly of the γ′-phase optimized. Finally, the mechanical properties are discussed. The dominant influence of the crystallographic anisotropy on elastic and plastic properties are shown as well as the dependence of the creep behaviour on the morphology of the γ′-phase and the correlation between fatigue strength and microporosity.     

Temperaturabhängigkeit des Verformungsverhaltens von PTFE-Schälfolie. Versuche an Material mit künstlichen Fehlstellen

The Deformation Behaviour of Skived PTFE Film as a Function of Temperature. Tests on Material with Artificial Defects When manufacturing anti-corrosion liners made from skived PTFE film for use in chemical engineering equipment, a knowledge of the force-deformation behaviour of this skived film is a necessary pre-requisite for a successful operation marked by a low level of scrap. A particularly important factor is a knowledge of the effects of notch-like surface injuries to the film, such as can occur during manufacture and handling of this scratch-sensitive material. Tensile tests on specimens of PTFE skived film that had been prepared with defined pierced and cutted notches showed that in the temperature range between room temperature and 380°C surface notches have an adverse effect on tensile stress and elongation at break up to the melting point, but in particular below 100°C. Strength and deformability of notched specimens fall sharply as the temperature drops to room temperature. A notch 0.2 mm in depth, cut in a 4 mm thick skived PTFE film, can reduce ultimate stress and elongation at break at room temperature to about half the level of an unnotched specimen. Since in the case of PTFE, a soft sintered material, the occurrence of notchlike defects can never be completely ruled out, their effect on the manufacture of anticorrosion liners made from skived film should be mitigated by increasing the processing temperature. Under the application conditions that are often marked by elevated temperature and result in relatively slight film deformation, the notch problem can probably be rated as less critical that during the actual manufacture and fitting of the anticorrosion liners, when high localized stretching of the skived PTFE film often must be accepted.