Verbesserung der Lebensdauerabschätzung durch Berücksichtigung des Lebensdauervielfachen

Fatigue life assessments of parts are frequently undertaken using the nominal stress concept. The main element in the process is the linear damage accumulation concept according Palmgren and Miner. Statistical analyses show the calculated fatigue life to commonly be on the unsafe side and the accuracy to be low. A higher accuracy would be advantageous, as the present use of effective damage sums is only an adaption. Improvements of the original Palmgren‐Miner rule made use of in practical calculations have mainly been achieved by taking into account amplitudes below the fatigue limit as further damage. The method described in the following utilises a different approach. The influence of the spectrum shape and the inclination of the S‐N curve under constant amplitude loading on the progression of the S‐N curve under variable amplitude loading, easily made visible in statistical comparisons of calculated and experimental fatigue lives, shall be included in a new correction function. The verification of the improvement of the fatigue life estimation can be undertaken using existing experimental data of steel specimens. Furthermore calculations are carried out to find optimized parameters of two Palmgren‐Miner modifications (Haibach, Liu/Zenner).     

Verbesserung des Verschleißverhaltens von Al-Werkstoffen

Improvement of Wear Resistance of Al-materials Wear behaviour of ductile materials can be improved by embedding suitable hard particles of appropriate size. With the Al materials tested here, embedding was achieved by extrusion of the powder mixtures. Wear resistance of the materials thus produced was determined using pin-disc and Klüber testers, commercially available fine grinding discs being used as abrasive partners. Thus, the effect of various parameters on wear behaviour and mechanical strength could be investigated. The mechanical properties are generally deteriorated by embedding hard particles, the amount of embedded material being of primary importance, but there is also a profound influence of the matrix-particle interface strength and, to a lesser degree, of particle size and shape. With regard to the wear resistance, the hard particles result in the desired improvement which is the more pronounced the higher the particle content and hardness. Even at low interface strength the particles are not torn of the matrix during wear stress. At lower matrix hardness (plain Al, Al alloys) better wear resistance is observed, as the abraded particles are more effectively rembedded and thus protect the matrix from wear. If suitable materials are used, excellent wear resistance combined with only insignificantly lowered mechanical strength is obtained.     

Glas,Glasuren, Email und Lack: Gebiete paralleler Forschung von gegenseitiger modellmäßiger Bedeutung

Glass — Glazes — Emaille and Lacquer: Areas of research in parallel with a significant working model. — A phenomenological survey of the interfacial surface energy behaviour of liquid materials applied as thin coatings. Initial observations with molten glass have drawn attention to the interfacial surface energy behaviour of other materials during their technological processing. The extensive parallelism observed during formations of largely undesirable honeycomb structures associated with thinly applied coatings suggests reason for undertaking research concerning the morphology this and related phenomena. It is intended that a summary be written to report this research.     

Lasererwärmung zur Verbesserung des Umformergebnisses beim Kragenziehen von Aluminium‐ und Magnesiumknetlegierungen

Laser heating for improvement of forming results in hole flanging of magnesium and aluminium wrought alloys Warm sheet metal forming has proven itself for the production of parts made of magnesium and aluminium wrought alloys. In many cases, e.g. in deep drawing, the heating of large surfaces makes sense. If only small areas of a larger part have to be formed, as with hole flanging, a local heating by means of laser irradiation is more advantageous. So the heat quantity can be brought in well metered temporally and locally. The expanding ratio could be increased, depending on material, with a local temperature of about 200 °C by more than double in comparison to cold conditions. It was shown that a narrow process window is to be kept, since material failure arises not only from too low, but also from to high forming temperatures.     

Nutzung von Werkstoffstrukturgrößen als Messnormale

Use of material structure sizes as measuring‐normal Lengths measurement is a comparison/evaluating of received measuring signals with a standard/calibration yardstick. The nano‐technology requires measuring accuracies from the submeter to the nanometer range, i.e. a range over 9 orders of magnitude. Strobes and possible measuringnormal are classified according to their requirements and analyzed on requirements, accuracy, stability, data sets and feasibility. For nano‐position‐ and nano‐measuring‐maschine are summarized suggestions for a feasibility.     

Kenngrößen von Turbo‐Molekularpumpen

Graphs of “high‐vacuum pressure as a function of backing pressure” (“p_HV versus p_VV”) and “compression as a function of backing pressure” (“K versus p_VV”) are presented in this article. The performance of any turbomolecular pump can be fully and reliably evaluated with the aid of these graphs. Until now these graphs have only seldom been shown in catalogs. The catalogs generally lack the so‐called “limit lines” (“Q as a function of p_{VV, Kmax}”). For a prescribed gas throughput Q, the limit line indicates what minimum pressure must be generated by the backing pump at the fore‐line port of the turbomolecular pump so that a stable pressure exists at the high‐vacuum side of the turbomolecular pump. Using the gas‐type‐specific limit line and the corresponding, usually well‐documented pumping‐speed curve, one can already describe the functional proficiency and performance of a selected combination of turbomolecular pump plus backing pump in an approximate manner – but not yet completely. In this article we also indicate analytical functions which excellently describe the pressure dependence of the compression and pumping speed.     

Charakterisierung des Ermüdungszustandes in zyklisch beanspruchten Schweißverbindungen durch röntgenographische und mikromagnetische Kenngrößen

Characterization of the Fatigue of Cyclically Loaded Welded Joints by X-Ray Diffraction and Micromagnetic Testing The fatigue behaviour of welded Joints is influenced by the state of the material, its microstructure and residual stresses. By means of the micromagnetic Barkhausen-noise testing method in connection with x-ray diffraction the behaviour of cyclically loaded welded joints of the steel S355 is investigated. Proved by the results of the present investigations, the macro-and micro-residual stresses, micromagnetic and strain characteristic values are strongly connected with each other. Plastic deformations in the HAZ and base material during cyclic loading were identifies by a significant relaxation of the micro-residual stresses and a characteristic change in the micro-residual stresses determined by X-ray profile analysis. Analogous to the growing plastic strain amplitude an advancing damage process in the material is accompained by a significant change in the micromagnetic parameters. As a conclusion the micromagnetic testing method can be suited for the identification of fatigue processes in the material before a final damager of the specimen.     

Bestimmung des Elastizitätsmoduls aus der Nachgiebigkeit angerissener Bruchmechanik-Proben

Determining the moduls of elasticity from the compliance of precracked specimens . A new method is described which allows the determination of the modulus of elasticity of solid materials. Compliance tests with precracked fracture mechanics specimens in a simple tensile test machine yield accurate measurements of the modulus of elasticity in the orientation and material condition desired for fracture mechanics calculations.     

Geometrieunabhängige bruchmechanische Werkstoffkenngrößen – Voraussetzung für die Zähigkeitscharakterisierung von Kunststoffen

Geometry independent fracture mechanics values – Requierenent for toughness characterization of polymers Starting from the history of introducing the Charpy test to the characterization of plastics, polymer‐specific requirements for the specimen geometry relevant for the determination of fracture mechanics parameters of plastics are summarized. Here, the influence of the specimen thickness, the specimen configuration and size, and a/W‐ratio are considered. In order to characterize the geometry independence of fracture mechanics parameters, in this connection, geometrical factors are used to estimate requirements for the specimen geometry without an experimental determination of the geometry influence. For plastics, these experimentally determined factors vary in a wide range. For this reason, the use of constant geometrical factors must cause a pronounced under‐ or overevaluation of the requirements on the specimens. The relationships between the geometrical factors and the fracture mechanics parameters those are universally valid for plastics are independent from the kind of loading (static, dynamic) and the crack propagation behaviour (stable, unstable).     

Einflußgrößen bei der Analyse von Schallemissionen

Factors Influencing Acoustic Emission Analysis . The interpretation of AE measurements requires careful consideration of the prevailing conditions, to ensure reproducable results. By the use of simulated signals in a small steel plate, an analysis of the effect of these various conditions, on the frequency and amplitude distribution of these signals, is possible. In this way the accuracy of location of emission sources can be improved.     

Auswertung von Stichproben normalverteilter,quantitativer Merkmalsgrößen

Estimates for the standard deviation of samples of metrical, normally distributed statistical variables can be determined by a number of different approaches leading to different results. In order to evaluate these approaches, a large number of samples were generated randomly with the help of a computer from a normally distributed population and evaluated in relation to the mean x and the standard deviation s. The hereby generated Characteristic statistical values x and s can then be compared to the Values of the underlying normal distribution. As this study shows, only the position probabilities Pì (normal ranks) derived by Henning and Wartmann deliver standard deviations ture to the expected values. Rosows commonly applied equation P_i = (3i – 1)/(3n + 1) is equally correct. All other methods examined result in systematic statistical deviations (bias) from the expected value. This includes the estimate s = $ \sqrt v $, taken from the variance v, which is used almost exclusively. The bias, however, is known due to this study and therefore can be corrected. Should outliers be eliminated, none of the appreaches investigated deliver standard deviations true to the expected values. The treatment of outliers is complex, however, and discussed in the paper. The confidence fpr the estimate of the standard deviation is independent of the method chose, i.e. none of the examined methods has an advantage over the others.     

Saphir-Entladungsgefäße zur Plasmadiagnostik

The energy demand for lighting is tremendous, and thus the reduction of costs by using more efficient light sources is an important challenge. Research and development in this field will also be essential in future. The application of new materials and procedures may lead to the development of new light sources. Some years ago, ceramic materials introduced a new quality of high pressure sodium lamps. Recently developed ceramic metal halide lamps have good future expectations. Sintered materials are used because of low costs. These materials are translucent but not transparent; that is why spatially resolved investigations are not possible. Basic research requires transparent discharge tubes. A special technique is introduced which allows the use of transparent sapphire. The present article shows that by selection of adequate materials and proper variation of essential parameters the sealing problem of a temperature firm, vacuum tight, electrically conducting connection can be solved. Especially for cases where experimental investigations on comparable bulk goods are not possible it is necessary to use this method in order to get experimental discharge tubes and employ optical diagnostics.