Neue Auswertungsmethode zur Bestimmung der Kennwerte der Dehnungswöhlerlinie und der Spannungs‐Dehnungs‐Kurve unter Berücksichtigung der Kompatibilität

New method for evaluation of the Manson‐Coffin‐Basquin and Ramberg‐Osgood equations with respect to compatibility A new method for determining the stress‐strain and strain‐life curves for metals is presented. The method involves fitting the curve to experimental data points in a three‐dimensional strain‐stress‐life space. With the plastic part of strain, stress and fatigue life as coordinates, a straight line is used for fitting the experimental data points. The material constants are calculated directly from the directional vector R and the coordinates of the point P , which determines the fitted straight line. It is shown that the assumption of equality of the plastic and elastic components in Manson‐Coffin‐Basquin and Ramberg‐Osgood equations leads to the so called compatibility condition. This new method retains the mathematical and physical relationships between the considered curves. The results obtained from this new method using high‐strength aluminium alloys subjected to different manufacturing conditions and different test temperatures are presented. These results are compared to results obtained with a conventional method for determining the fatigue parameters.     

Einfluß der Mahlbedingungen und der Qualität der Ausgangsprodukte auf die Eigenschaften von Al-C-Strangpreßprodukten

Influence of the Crinding Parameters and the Quality of the Starting Materials on the Properties of Extruded AIC Products Dispersion strengthened aluminium has been produced by grinding aluminium powder with carbon black in a high energy ball mill, heat treating of the milled powder and subsequented hot extrusion. Tensile strength, elongation, hardness and impact strength were determined. The influence of griding parameters, such as duration, speed of rotation of the rotation arm and the weight ratio of powder to milling balls on the mechanical properties of the extruded rods were investigated. Other important variables are the oxygen content of the aluminium powder, the quality of the carbon black and additions of control agents such as oil or water.     

Anwendung der holografischen Interferometrie in der zerstörungsfreien Werkstoffprüfung

Usage of Holographic Interferometry for Non-Destructive Materials Testing . Holographic interferometry has meanwhile developed into a usable method for non-destructive materials testing, which permits even large-area components to be tested by using high-power lasers. Recording the fringe structures makes a subsequent detailed resolution evaluation possible. Appraisal of the video recordings makes the origin and change of the secondary interference fringes clearly recognizable and interpretable and thus substantiates very informatively the introduction of holographic interferometry for non-destructive materials testing.     

Grundlagen der Werkstoffauswahl bei der Bekämpfung des Strahlverschleißes

Fundamentals of Material Selection in the Conditions of Erosive Wear Problems of proper selection of materials for parts subjected to wear by a stream of abrasive particles are discussed. Considering the main laws governing such kind of wear, the author concludes that target material selection in the case of erosion, like in any other case of abrasive wear, will depend on the ratio of abrasive grain hardness to material hardness. Special attention should be given to hard components in the abrasive. It has been established that a 10-15% content of quartz particles in the abrasive is enough to cause an abrupt fall in the wear resistance of chilled steels, white iron and hard surfacing alloys, thus making their use questionable. Finegrained WC-Co-type sintered carbides have shown the highest wear resistance in such conditions. The conclusions drawn in this paper are borne cut by a considerable body of experimental data.     

Anwendungen der Oberflächentechnik in der Raumfahrt

Ever more challenging missions for the scientific investigation of space as well as the increasing use of satellite‐based services in the fields of telecommunication, navigation and earth observation require the development of more efficient, more economical and more resistant space technologies and systems in the future. A study of the VDI Technology Center on behalf of the German Aerospace Center points out, that nanotechnology, in particular in the range of surface technologies, could supply significant contributions and technological breakthroughs for the development of future space travel systems. Applications of friction and wear reducing layers, thermal protection layers, magnetoelectronics, x‐ray astronomy and thin film technologies for space structures are presented.     

Die Qualitätsprüfung geschweißter Rohre in der Schweißstraße unter besonderer Berücksichtigung der Indikation der Kalt- oder Mattschweißung

Testing of Welded Pipes to Indicate Pasting or Stuck Welding . Inspecting the seams of continuously welded tubes by the aid of electromagnetic or ultrasonic methods it was up to now impossible to indicate the so-called ?pasting”? or ?stuck welding”?. This defect causes no discontinuities but results in a reduced strength of the welding. By additionally using an infrared method by which the welding seam is scanned 1000 times per second immediately after the weld station over a width of 1 mm, the transformation of energy which answers for the occurence of the above mentioned defect can be traced minutely. Two infrared scanners at a distance of about 50 cm inform about any internal or external undertemperature during the welding process. Hereby, the last up to now undetectable weld defect can be indicated by an automatic test equipment, too.     

Ausgewählte Ergebnisse der Untersuchung der Prozesse des Schmelzens und der Erstarrung beim Schmelzschweißen und Schmelzlöten mittels der materiellen Modellierung

In the article a method for the material modelling is described under application of visually transparent materials of the thermal and chemical solidification processes when welding and soldering. All solidification processes carried out independently of the form of the primary crystals, first about the planar one, then cellular and in the end dendritically growth the solidification structure. It is determined by the chemical composition of the weld and soldering good, the weld, soldering, crystallization or solidification speeds and by the temperature gradients at the solidification front particularly. The vacancy concentration is made by the temporary formation of so‐called zipper primary grain boundaries in the solidification structure when welding. Among other things a preferential growth direction of the primary crystals explains itself by the fast growth of so‐called victim crystals which completes the known theories of the preferential growth.     

Probleme der Kriechstromfestigkeit: Untersuchungen über den Einfluß der Prüflösung

Problems of Tracking Tests: Influence of the Test Solution. This Paper reports on the influence of different electrolyts to the results of tracking tests. Specially the influence of the resistivity and the chemical components were explored. 34 materials were tested and the measured values of 16 are fixed in a table. In case of some of them the results are graphically described.     

Zum Einsatz der Mikrosonde im Rahmen der Betriebsüberwachung und der Untersuchung von Schadensfällen

Contribution to the application of the X-ray microprobe within production control and investigation of failures . On the basis of several selected cases the application of the X-ray microprobe within production control and investigation of failures is discussed. The influence of sulphur on nickel as well as that of vitriolic acid on cast iron is demonstrated to show examples of reciprocal actions between metals and environment. The final state of diffusion processes which occur during welding of copper and aluminium as of unsufficiently cleaned low carbon nickel is described. The effects of high temperatures are demonstrated for a X 8 CrNiNb 16 13 header exposed to long time service and of a 14 NiCr 8 pinion being heated and quenchend in a very short period of time. The influence of microchemical composition on the shape of fracture surface of stressed X 2 CrNiMoSi 19 5 3 corrosion test specimens is examined. The identity of the materials of a damaged X 10 CrNiMoTi 18 10 shaft case from a chemical pump and a piece of sintered metal found adjacent to the bearing is demonstrated.     

Zur Plausibilität der Methode der Zugdreiecke

On the Plausibility of the Method of Tensile Triangles (MTT) The shape optimization of components, developed in Forschungszentrum Karlsruhe after the design rules of nature [1] has during the last 15 years very well spread and proven itself in industry, especially in automotive engineering. The limits for using the CAO‐method (Computer Aided Optimization) are more or less of economical nature. In this paper the plausibility for a new pure graphical method is shown, which works without any FEM or optimization software.     

Wasserstoffversprödung von Feinkornbaustählen in Abhängigkeit von der Legierungszusammensetzung,der Gefügeausbildung und der mechanischen Belastung

The Influence of Chemical Composition, Structure, and Mechanical Strain on the Hydrogen Embrittlement of Fine-Grained Low-Alloy Steels On specimens from fine-grained low-alloy steels StE 51 and StE 36 strain induced hydrogen embrittlement has been studied under increasing, pulsating, and static load conditions in hydrogen sulphide at various strain rates, gas pressures, gas compositions, and surface qualities. Both steels displayed equal sensitivity compared to mild constructional steels, Hydrogen pick-up occurred only during plastic-deformation of the specimens and led mainly to a decrease of the reduction of area and to the formation of side cracks in the necking zone. This type of embrittlement is important for constructions subjected to pulsating load conditions causing plastic deformation in areas with constructional notches. As part of the research and development project “Corrosion and Corrosion Prevention” this investigation was supported by the Federal Ministry of Research and Technology.     

Bedarf an Qualifizierungsmaßnahmen aus Sicht der Großindustrie in der Oberflächentechnik

Future‐oriented quality production in the surface technology requires more than the accurate fulfilment of the customer requirements. In the external customer‐supplier relationships the co‐workers of large enterprises are increasingly in demand as advisors for their customers, they regularly take part in the product development phase at the customer contribution their know‐how in order to ensure the optimal conditions for the surface treatment. Because of this the importance of social and methodical skills is increasing for technological, technical and high‐level personnel. Personal with these qualifications are hard to find in the job market. The enterprises specialising in surface‐technological services are not even able to cover their needs at a purely technical know‐how level. The consequence: “We have to train the people ourselves”. Training activities initiated by the enterprises are becoming more important parallel to this more is being invested in public relations work and advertising. This conclusion was arrived at after carrying out a analysis of the future training requirements for the large‐scale industry on the basis of four case studies in the mechanical engineering, chemistry, steel industry and automotive industry. The analysis of these case studies is supplemented and rounded off by the postal questioning of a further 28 large‐scale enterprises. The investigation was carried out by the Institute for knowledge transfer at the University of Bremen (IfW) on behalf of the Federal Ministry for education and research (BMBF) by the VDI Technologiezentrum and is a component of the project “Technology transfer surface technology”.     

Berechnung der Dauerschwingfestigkeit unter Berücksichtigung der spannungsmechanischen und statistischen Stützziffer

Fatigue Limit and Geometrical and Statistical Size Effect The ratio of the fatigue limit of an unnotched specimen to that of a notched one, the fatigue notch factor K_f, is usually smaller than the theoretical stress concentration factor K_t. With the assumption of a plastic cyclic deformation ?_apW at the level of the fatigue limit the fatigue limit for a notched specimen can be calculated. According to formula (4) this fatigue limit σ_naD is a function of K_t, ?_apW, the notch stress amplitude σ_a, the cyclic strengthening exponent n′ and the fatigue limit of a smooth specimen σ_W. Moreover, taking into account the statistical size effect with the known “weakest link concept”, see flow chart Fig. 9, the calculation is in a good agreement with 77 test results for steel.     

Simulationsuntersuchungen der Wärmeeinflußzonen von Schweißverbindungen der Legierung Hastelloy B-2

Simulated Heat-Affected Zone Studies of Hastelloy B-2 Gleeble studies show that as-welded HAZ corrosion resistance of a low carbon nickel-molybdenum alloy can be preserved by using gasshielded-arc or covered electrode welding. A heat-affected zone study was conducted on a low carbon, nickel-molybdenum, corrosion resistant alloy, commercially known as Hastelloy alloy B-2. Six different production heats were thermally cycled with the Gleeble apparatus to 1300 °C (2372 °F) under several conditions to simulate the heat-affected zones produced by a number of different welding processes. Specimens were subsequently tested in boiling 10% HCl and in 20% HCl at 150 °C (302 °F) in an autoclave. Most of the corrosion penetration measurements were found to be less than the maximum allowable limits, reaffirming that the as-welded heat-affected zone corrosion resistance of alloy B-2 can be preserved when welding is accomplished with the recommended shielded metal rec, gas tungsten arc, and gas metal arc processes.     

Zwillingsbildung bei der thermischen Ermüdung der Mg‐Basislegierung AZ31

Twinning at thermal fatigue of magnesium alloy AZ31 In this paper results of thermal fatigue tests of the magnesium base alloy AZ31 carried out in a temperature range between ‐50 °C and +290 °C are presented. Specimens were loaded under constant total strain and uniaxial homogeneous stresses. The resulting materials behaviour is described by stress amplitudes, plastic strain amplitudes and mean stresses as a function of the number of thermal loading cycles. It is well known that AZ31 shows different stress‐strain behaviour during tensile and compressive loading resp. at lower temperatures due to the fact that mechanical twinning depends on the loading direction. However untwinning processes may occur during unloading and reloading in the opposite direction. As a consequence, during the first thermal loading cycles, typical consequences of the formation and the dissolution of twins are observed. The interaction of deformation, recovery and recrystallization processes, characteristic for individual temperature ranges are discussed in detail to analyze the damage progress during thermal fatigue.