Einfluß von Sauerstoffspuren auf die Eigenschaften von Wolfram-Schwermetallen

Influence of Oxygen Traces on the Properties of Tungsten Heavy Metals Investigation carried out with differently sintered W heavy metals showed that careful pre-reduction before liquid phase sintering is essential for obtaining satisfactory mechanical properties; otherwise oxide layers at the phase boundaries deteriorate the interface strength and thus cause premature fracture. Understandably, the water vapour content of the furnace atmosphere is of considerable importance. Appropriate sintering anticipated, even severely oxidized green compacts result in highly ductile heavy metals. Addition of scavengers, e.g. Cr or V, instead of the pre-reduction improves the interface strength, the mechanical properties however remain unsatisfactory.     

Einfluß von unverformbaren Teilchen auf die Strangpresstexturen von Verbundwerkstoffen

Influence of undeformable particles on the extrusion texture of composite materials The influence of α-Al₂O₃ particles on the extrusion texture of Ni-, Cu or CuZn30-composites has been investigated, variing particle size and interparticles spacing. The rods show a 〈100〉-recrystallization texture, which decreases with greater values of the interparticle spacing. In the case of the addition-free Cu and CuZn30 a random orientation distribution of the crystals was found. These results are discussed in comparison with the results found on Al? Al₂O₃-composites.     

Einfluß der Belastungsfrequenz auf die Lebensdauer von Punktschweißverbindungen

The Effect of Different Test Frequencies on the Lifetime of Spot-Welded Joints In general lifetime prediction of welded joints is basing on S-N-curves where the influence of the variation of the S-N-curve is not taken into consideration. Moreover, it is not possible to specify the valid frequency range for the endurance limit of spot-welded joints. The test frequency defines the load velocity as a function of the phase relation of the strength. At the same time, the strength properties of the base material, the HAZ and the weld nugget are affected by load velocity. This means that the endurance limit of spot-welded joints is a function of the test frequency. This correlation was confirmed with tests on spot-welded deep-drawing sheets of R St 1403 (similar to AISI C 1008). In the report test results and the different fracture mechanisms are presented.     

Oxidierende Nachbehandlung von Nitrocarburierschichten - Einfluß auf die Schwingfestigkeit

Oxdiation treatment of nitrocarburized layers and its influence on fatigue strength This paper deals with the investigation of the fatigue strength of salt bath nitrocarburized specimens of the steels SAE 1015, SAE1034, SAE 1042, SAE4135 and SAE4140 in a normalized or in a quenched and tempered state, and additionally cooled after nitrocarburizing in different media (salt water, oil, oxidizing salt bath). In statistically ascertained rotating bending fatigue tests the oxidized specimens of the alloyed steel showed improved fatigue lives in comparison with the oil-quenched ones. In contrast with the case of unalloyed steel the low cooling rate during the oxidizing treatment leads to a decrease in fatigue life. The result of corrosion fatigue tests with specimens of SAE4135 and SAE4140 show that the 5% NaCl environment drastically reduced fatigue life but nitrocarburizing plus oxidation treatment was found to improve the corrosion fatigue life over that of untreated specimens. The beneficial effect of nitrocarburizing followed by oxidation treatment on corrosion fatigue life results from the protection rendered by the compound layer by means of a well-sealed oxide layer, whereby the pores present in the compound layer fill up with oxides.     

Der Einfluß der Feuchteaufnahme auf die mechanischen Eigenschaften von Phenoplasten

The Effect of Moisture on the Mechanical Properties of Phenolic Moulded Materials In order to use thermosetting moulding material it is necessary to know how the mechanical properties are changed by absorption of water. Therefore, multiphase systems based on phenolic resin, with varying quantities of wood flour and/or powdered minerals as fillers, were examined. The relationship between moisture absorption and the change in Young's modulus, flexural strength and the strain of the outer fibre at fracture was determined. It could be shown that the increase in flexural strength as water absorption began is a result only of the swelling stress.     

Einfluß der Oberflächenbeschaffenheit auf die Schwingfestigkeit von Aluminium-Druckguß

Effect of Surface Condition on Fatigue Strength of Die-Cast Aluminium Surface processing like milling or shot peening involves modifications of the surface and subsurface condition of a material that can be described by changes of the residual stresses, the hardness, and the surface roughness. Moreover, there is the possibility of introducing additional surface defects. In this paper the influence of these modifications on the fatigue behaviour of the aluminium die-casting alloy GD-AlSi8Cu3 is presented. S-N curves are determined for four surface conditions produced by milling, shot peening, and a combined treatment. The improvement of fatigue limit by shot peening is confirmed for this material. The additional effect of mean stresses is determined. Investigations of the fatigue fracture surfaces show that pores and pipes as well as surface defects induced by shot peening act as fatigue crack initiation sites.     

Beitrag zum Einfluß von Druckwasserstoff auf die mechanischen Eigenschaften von Stählen

Contribution to the Influence of Pressurized Hydrogen on the Mechanical Properties of Steels The investigation method of using hollow specimens in tensile tests to examinate steels for hydrogen service is described. Reduction of area after fracture, Z, resulting from these tensile tests with constant strain rates shows not only a significant but also a constant difference between hydrogen and nitrogen when being plotted versus strain rate. Therefore a newly introduced term named “Index of embrittlement” and characterized by the relation of Z with nitrogen and with hydrogen was found to be independent of strain rate. With strain rate ε = 10^?6 s^?1 chosen for a “critical” one because of lacking in a maximum index of embrittlement several European steels for hydrogen service were tested to find out their individual index of embrittlement. Assisted by light optical microscopy it was found that there is a special correlation between microstructure, index of embrittlement and tensile strength of a given steel grade.     

Einfluß von last- und verformungsgesteuerten mehrachsigen Beanspruchungen auf die Anrißlebensdauer

Influence of load- and deformation-controlled multiaxial tests on fatigue life to crack initiation Generally, areas of components with notches or geometrical transitions are critical because of the resulting stress/strain concentrations. In these areas due to the stress-gradients and constraint local deformations are displacement controlled even if the material's yield stress is exceeded, as long as the deformations are below the structural yield point. Therefore, load controlled tests in the elasto-plastic region with unnotched specimens from ductile materials under combined axial loading and torsion are not suitable for the interpretation of component's behaviour because of uncontrolled local deformations. Thus, the influence of multiaxial stress/strain states on the fatigue behaviour of a component under elasto-plastic deformations can be determined reliably with unnotched specimens only by deformation controlled tests, if cyclic creep is not expected in critical areas.     

Einfluß des Gefüges auf die Zähigkeit von Nitrierschichten

Microstructure and Toughness of Nitrided Layers The redistribution of carbon during the nitriding of chromium alloyed steels leads to a cementite precipitation at prior austenitic grain boundaries more ore less parallel to the surface. The intensitiy of the precipitates dependence on the thickness and phase structure of the coumpound layer. The notch- and indentation fracture thoughness allowables a differentiate evaluation of the toughness of nitrided layers. The toughness of the precipitation layer dependence on its hardness, the microstructure prior the nitriding and the intensity of the cementite precipitates at grain boundaries.     

Der Einfluß von unterschiedlichen Erwärmungen auf die Festigkeit und die elektrische Leitfähigkeit einer ausgehärteten AlCu2MgNi-Legierung

Influence of Various Heating of Age Hardened AlCu2MgNi, Alloy on Mechanical Strength and Electrical Conductivity In-service or unintended heating above certain temperatures and periods affect the mechanical properties of age hardened aluminum alloys. Non destructive evalution of strength reduction is very difficult especially in the case of minor heat damage. The effect and assessment of various heating on tensile strength, hardness and electrical conductivity of an airplane wheel rim is investigated.     

Einfluß einer thermomechanischen Behandlung auf die mechanischen Eigenschaften der Ti6Al4V-Legierung

Influence of thermomechanical treatment on the mechanical properties of Ti6Al4V Thermomechanical treatments of Ti6Al4V including deformation just below the β-transus followed by water quenching and aging were shown to substantially improve the mechanical properties. Especially the fatigue strength was raised well beyond levels known from conventional processed material, for both room and elevated temperatures. The paper shows how other properties like tensile strength, ductility, fracture toughness, creep strength fatigue crack growth and stress corrosion cracking are affected.     

Einfluß verschiedener Wärmebehandlungsverfahren auf die Schwingfestigkeit von Sinterstählen

Influence of different Heat Treatment Methods on the Fatigue Behaviour of Sintered Steels This investigation compares the fatigue behaviour of the alloys Fe-1.5%Cu, Fe-1.5%Cu-0.6%C and Fe-0.8%Mn-0.95%Cr-0.24%Mo-0.6%C in as-sintered and heat treated states. The steel Fe-1.5%Cu is carbonitrided and both other alloys are quenched and tempered. As in practice components are usually notched and will be subjected to different types of loading, the investigation is carried out with unnotched and notched specimens tested under axial loading and bending with and without mean stresses. The selection of these different materials, heat treatment methods, geometries, and loading modes covers a broad field of practical applications.     

Einfluß der Probengröße auf die bruchmechanischen Eigenschaften von Sinterstahl

Influence of Specimen Size on the Fracture Mechanical Behaviour of Sintered Steel Fracture mechanics testing was carried out with small and big specimens using high-temperature sintered Fe-2%Cu-2.5%Ni-alloys in the densities of ρ = 7.1 and 7.4 g/cm³. These steels are often used in the manufacturing of PM-parts. Due to the different dismensions the crack propagation is for the bigger sizes faster than for the smaller sizes. Also the conditional fracture toughness of the big specimens is superiour to the toughness of the small specimens. But under consideration of a plain strain state for the big specimens and of a plain stress state for the small specimens valid fracture toughness values being independent from the specimen size can be calculated applying linear-elastic fracture mechanics. These results were obtained for both densities investigated. The increase of the density delivers principally better fracture mechanical data. Hereby the relation of strength data with the microstructure is also discussed.     

Einfluß des Sauerstoffes auf die Entladung bei der Spektralanalyse von Metallen in Edelgasen

Influence of Oxygen on the Discharge during Spectral Analysis of Metals in Inert Gases . This article features new considerations and tests for explaining the various types of discharge as well as the influence of oxygen. It describes a phenomenon hitherto not described in this context, i. e. the elimination of the oxygen effect by gettering. Some practical hints should particularly help checking the influence of oxygen.     

Einfluß von Korngrenzenöffnungen auf die Bruchvorgänge geschweißter AlMgSi-Werkstoffe

Influence of Grain Boundary Openings on Fracture Mechanisms in Welded AlMgSi Alloys In the present investigation AlMgSi0.7 extruded samples were welded with AlMg5 filler metal under conditions which favoured the formation of Grain Boundary Openings (GBO) in the heat affected zone. Fractographic examinations showed that GBO influence the fracture mechanisms. Applyingspecific fatigue block loadings the crack growth could be made visible on the fracture surface. It was demonstrated that a GBO does not behave like a sharp crack in the senseof classical fracture mechanics with immediate growth on application of stress. After a certain time of fatigue a crack is created at a GBO depending mainly on the stress amplitude. It is shown that a weld defect tolerated by standards can cause a more effective risk for fracture than the presence of the above mentioned GBO.     

Einfluß von Überlasten auf die Ausbreitung von Ermüdungsrissen in der Aluminiumlegierung 7075 T 7351

Influence of overloads on the propagation of fatigue cracks in the aluminium alloy 7075 T 7351 For realistic lifetime predictions the crack propagation behaviour under variable amplitude spectrum loads has to be known. In this work the influence of single overloads on the fatigue crack propagation in the alloy 7075 T 7351 was investigated at a constant loading level (K_max and ΔK = const.). The experiments showed, that a single overload causes a short crack acceleration followed by a pronounced deceleration of the crack propagation rate. After this deceleration at higher overloads a zone where the crack propagation rate is slightly increased (lost retardation) was observed. It has been shown, that the minimum crack propagation rate as well as the length of the influenced region depends on the height of the overload. The observed crack acceleration, the deceleration as well as the lost retardation can be explained by internal stresses caused by those overloads which have to be added to the external stresses.     

Der Einfluß der Kohlenstoff-Diffusion auf die mechanisch-technologischen Eigenschaften von ferritisch-austenitischen Schweißverbindungen im Chemie-Betrieb

The effect of carbon diffusion on the mechanical properties of ferritic-austenitic weldments . Weldments between ferritic and austenitic steels indicate a diffusion of carbon from ferritic to austenitic partner as an influence of temperature stresses and due higher solubility of carbon in γ-iron in comparison to α-iron. Investigations on two characteristic weldments (German standard H II/1.4571 and H II/Ni) have been conducted in different annealed conditions to study the effect of carbon diffusion on the various mechanical properties. There is an observable impairement of the mechanical properties of the weldments. Increased hardness in the carburised zone causes cracking and tensile strength as well as notch toughness decrease in the decarburised area.     

Einfluß von Druckvorspannungen auf die Dauerfestigkeit metallischer Werkstoffe bei ein‐ und mehrachsiger Beanspruchung

Effect of compression stresses on the fatigue strength of metals at uniaxial and multiaxial state of loading The calculation of the effect of multiaxial mean stresses on the fatigue strength required to consider the relative direction between the constant and cyclic parts of stresses. For this a new concept for the assessment of stresses has been presented for any fracture behaviour of materials. Experimental investigations on the effect of compression stresses on the fatigue strength of hollow cylinder samples from the steel 20MnCr5 has been used to support the parameter determination of the strength model     

Über den Einfluß von Probendicke und -geometrie auf die Ermüdungsrißausbreitung und die Bruchzähigkeit von Polycarbonat

The Influence of Specimen-thickness and Geometry on Fatigue Crack Propagation and Facture Toughness of Polcarbonate This study deals with the influence of specimen-thickness and geometry of the fracture-behaviour of polycarbonate at room-temperature. With decreasing thickness, an increasing resistance against fatigue crack propagation and an increase of the fracture toughness under static loading conditions was observed. Additional J-integral-evalutions showed a good agreement with the values of the fracture toughness. Scanning electron microscopy studies of the facture surfaces showed the sequence of damage and te individual micromechanisms of fracture. Based on th latter, detailed informations were given for the interpretation of the mechanical properties as a function of specimen-geometry.