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Description / Table of Contents: Knowledge about stress corrosion cracking and corrosion fatigue until 1970; specific aggressive media to cause stress corrosion cracking: alkali solution, nitrates, ammonia salts - meaning of the constant strain rate technique and stress corrosion cracking in bicarbonate solutions - dependence of tensile stress, strain and strain rate upon time; significance of strain rate - investigations in bicarbonate, carbonate and hydroxide solutions - critical potential ranges - relation between strain rate and low cycle fatigue - theoretical differences between stress corrosion cracking and corrosion fatigue in spite of gradual transient in physical appearances.

Description / Table of Contents: Investigation of Steel Fiber Reinforced Aluminium under Torsional and Compressive LoadingA fiber-shaped composite material which, due to its fabrication process and internal structure may be called a double fiber composite, and whose strength behaviour is significantly influenced by boundary layers and porosity has been tested by means of two test methods: 1The possibility is demonstrated to determine by a non-destructive elastic torsional test the useful cross section for the utilization of the material, taking the quality-reducing factors into consideration.2Pressure tests have shown good agreement with Timoshenko and Gere's wave theory extended in this particular case. .

Description / Table of Contents: Mechanical and Technological Properties of Nickel Containing SuperferritesHigh chromium ferritic stainless steels with molybdenum and nickel additions, containing low amounts of interstitials, show remarkably good mechanical properties besides their excellent corrosion behaviour. Yield strengths of these materials can be more than the twofold, compared with that of austenitic stainless steels. In contrary to commercial ferritic stainless chromium steels, the Superferrites exhibit remarkable notch impact toughness also at temperatures below 0 °C. These properties as well as their permanent toughness after a welding process permit a good technological workability and, because of the high strength properties, the application of thinner dimensions in construction.

Description / Table of Contents: The growing interest in the use of graphite as a material for chemical equipment is occasioned by the highly corrosion resistant properties of this low-cost material.Economic and safety specifications require a thorough knowledge of the material's properties and performance and also of the effect of these factors on a particular unit. It is to be considered for instance that the material's compressive strength is 3 to 5 times higher than its tensile strength.Another important characteristic is its static strength: the smaller the stressed volume, the higher the breaking strength. This comparatively good performance is of advantage in cases of high voltage gradients as encountered as edge stresses at the openings of tube plates and nozzles. In such cases the breaking strength may reach twice the value of the rupturing strength.A third characteristic to be mentioned is the high dependence of strength on the parameters of production; the strength decreases, for technological reasons, with increasing size.The following design principles are based on the specific properties and performance of the material: units to be preferably subjected to compressive stressuse of the smallest possible stockmaterial of higher strength to be used in hightension zones (smaller semiproduct dimensions)No cemented joints in highly stressed zones .

Description / Table of Contents: ESCA - Investigations of the Passive Films Formed on Austenitic Stainless Steels in Nitric AcidBy means of ESCA the composition and the thickness of passive films formed on austenitic stainless steels were investigated after the attack of nitric acid at various temperatures and acid concentrations.The outermost layers of the oxide film consist of SiO2, then a layer rich of Cr-oxid follows, containing also some Mo in the four- and six-valent state. Ni does not contribute to the oxide film. Cr is also enriched in the metal just below the oxide film.

Description / Table of Contents: The Improvement of Fatigue Limit as a Result of Hardening and Macrostresses Due to a Surface TreatmentSurface treatments, that increase the hardness as well as induce surface residual macrostresses, are universaly able to improve the fatigue limit. It is shown, that depending on the shape of specimens both effects together are responsible for the raise of the fatigue strength, which is in contrast to former opinions. The increase of hardness increases the stress required for crack initiation and is thus decident for unnotched specimens, whereas in this case the influence of permanent residual stresses is relatively smaller. Notched specimens of sufficient stress concentration factor kt are determined by the crack propagation conditions, which can be controlled decisively by mean loads. The increase of hardness improves the resistance against crack initiation proportional to the 1/kt portion of the unnotched fatigue limit, but cracks remain nonpropagating as long as a certain minimum alternative stress, which can be raised by compressive residual stresses, is not exceeded. Depending upon concentration factor, mean compressive load and hardness the transition from crack initiation to crack propagation as the criterion for fatigue fracture can be estimated by several fatigue-strength-diagrams, which are evaluated for specimens of constant hardness but are valid for surface hardened specimens as well.

Description / Table of Contents: Influence of Microstructure on Mechanical Properties of (α + β)-Ti-AlloysThe amount of α- and β-phase in (α + β)-Titanium alloys for example in the alloy TiAl6 V4 may be altered to a large extend by annealing procedures. In the alloy TiAl6 V4 each temperature corresponds to a certain amount of each of these phases, the composition of which is also dependent on annealing temperature. Above about 970 °C the homogeneous β-phase appears. Additions of Iron, Oxygen, Nitrogen and Hydrogen have a great influence on the transition temperature and the distribution of the α- and β-phase. There is a great influence of the distribution of the phases on the mechanical properties. The β-phase and the α-solid solution can be quenched from high temperature and decomposed at a lower temperature, so that intermediate phases as ω from β and α2 from α may be precipitated. The α-solid solution is anisotropic so that texturized samples have different properties in various directions. Based on these fundamental aspects it is shown to what extend these microstructures may influence the mechanical properties especially the fatigue behaviour of (α + β)-Ti-alloys.

Description / Table of Contents: On the Interaction of CracksStress intensity factors for multiple cracks in a plate under tension are reviewed. In addition to the known results for symmetrically arranged cracks the interaction effects due to rotation of one of the cracks relative to the load direction are calculated and in some cases examined experimentally. The results are discussed with reference to the safety assessment of structural components.

Description / Table of Contents: The State of the Art in the Fatigue Live Evaluation of ComponentsFor fatigue life estimations of components many compromises must be entered in the utilization of available fatigue design data. The parameters of the chosen design data which do not fit the component to be evaluated are in most cases taken into consideration by very global factors. These factors and the inaccuracies of Miner's Rule provide only a rough estimate of the fatigue life of a component. When the component is allready available, these uncertainties can be reduced by performing a fatigue test with service like load-time histories and a relative Miner's Calculation. For the same reason the total knowledge about the service fatigue behaviour of similar components should be taken into account in the life estimation.

Description / Table of Contents: Ultrasonic Attenuation Measurements of a Maraging SteelThe objective of this study was to investigate the influence of nm-precipitation of a precipitation hardening steel on the ultrasonic attenuation. The applied steel X 2 NiCoMo 1885 was solution annealed and subsequently precipitation hardened at 480 °C at different holding times. A clear correlation between ultrasonic attenuation coefficient for 4 Mc and hardness values measured in the range of the hardness increase can be seen. The particle density of the microstructure given is considered as the common cause of the influence of both parameters. The increase in the particle density leads to a decrease in the ultrasonic attenuation coefficient. The reneward increase in the US-attenuation coefficient may additionally be influenced by the beginning austenit reformation and has not been investigated in more details here.

Description / Table of Contents: Investigations on the Effect of Microstructure on Crack Propagation during Unidirectional Loading of TiAl6V4Fracture mechanics tests were performed with the titanium alloy Ti-6 Al-4 V between -196°C and room temperatur. Crack propagation behaviour was characterized by the K-Δa-curve, KIo at the onset of stable crack extension and by KQ, determined with the 5% secant method. KQ is strongly dependent on the microstructure, whereas there is a less effect on KIo. For a material with a microstructure with a low fracture toughness the value KQ can be increased considerably by vaccum annealing at 750°C. There is only a small decrease of the yield strength.

Description / Table of Contents: Shift vectors for the comparison of Cv-T-curvesIt is shown in this paper that a shift in the Cv-T-curves caused by mechanical or thermal treatment, or by irradiation with particles of high energy can be better described by a shift vector given by the inversion points of a functionally determined curve than with the currently used empirical criteria. Moreover, the shift of a whole curve can be described by a vector whose components are the shifts of all parameters used for the calculation of the curve.The resulting vector of a Cv-T-curve may, for instance, be connected functionally with the neutron fluence. This makes it possible to compute shift vectors.

Description / Table of Contents: Progresses in the application of plastic compound materialsPlastics possess a number of various properties one cannot find in another material in this combination. Beyond that the desired properties can be reached by compounding several different materials. The best known example is the glass reinforced plastic. The arguments for the application of compound materials are very different: increase of strength and stiffness, cheaper injection moulded parts due to shorter cycle times, thinner wall-thicknesses and therefore less raw material consumption, lower distortion and thermal elongation for technical parts and excellent thermal insulation of the foams.Research on the topic of the bonding between the plastic and the carbon, glass and organic fibres led the way to an ever spreading field of the application of reinforced plastics.

Description / Table of Contents: Thermally Induced Structural Changes in Nickel Composite Coatings

Description / Table of Contents: Dynamic strength variationThe Weibull probability function or the arcsin √P distribution suffices for description purposes provided that considerations are confined to failure or survival probabilities between 20 and 80%. Beyond these limits more sophisticated analysis of the test results - as too in the case of the design engineer when estimating the statistically induced component of the safety margin - must make use of more realistic distribution functions.

Description / Table of Contents: Carbon Fibre Reinforced Al2O3 and MulliteThe hydrolysis process from metalalkoxides has been investigated to prepare carbon fibre reinforced Al2O3 and mullite composites. Carbon fibres (SIGRAFIL HF with 10,000 monofilaments) were im pregnated with metalalkoxides (Al-tri-sec-butylate to form Al(OH)3, mixtures of tetramethoxy-silan and Al-tri-sec-butylate to form mullite), hydrated in air and hot-pressed in a graphite mold at about 1700 °C, 10 min. Beside this also the preparation of composites with chopped fibres is described. The mechanical properties were measured in a three point bending test. Composite material with more than 10 vol% fibres show plastic deformation with matrix cracking during testing. For Al2O3 an additional SiC-interlayer (0.5-1 μm SiC by a CVD-process from CH3SiCl3 and H2 at 1280 °C) is necessary to obtain a bonding between fibre and matrix. Only in this case with fibre content higher 10% it is possible to increase the fexural strength of Al2O3. The strength values lie on a line with 60% of the fibre strength. The rule of mixture cannot be applied for Al2O3 as matrix. Low fibre contents decrease the flexural strength. It appeares that in this case the Al2O3 matrix is damaged before testing. But with mullite as matrix the measured values of flexural strength lie on a line which is 65% of the rule of mixture. This is caused by a relative good bonding between fibre and matrix and is independend of an additional SiC-interlayer. The Young-modulus of Al2O3 is drastically decreased with 10% carbon fibre content (for mullite matrix: 28 vol%). It was possible to calculate the beginning of the formation of cracks in the Al2O3 matrix caused by the mismatch of the components. This value does agree with the measured decrease of Young-modulus. The toughness of both materials measured by the critical intensity factor KICV (for a composite material) with notched speciments (0.1 mm notch width) is increased with fibre content. (These KICV-values are a function of notch length and width in a range of the probable error and therefore the uncorrected values are considered). For Al2O3 matrix the KICV-values increase only if SiC-scoated fibres are used. For mullite as a matrix KICV increases with fibre content for both of the SiC coated and uncoated fibre composites. With higher fibre volume than 50% the values decrease because the interspace between the fibres is not filled with matrix. The increased KICV for these composites compared to that of the matrix alone can be explaned by energy absorption at the fibre-matrix interface. In the case of mullite matrix this mechanical behaviour is caused by a good bonding between the components. Therefore the fracture energy of these mullite composites is drastically increased with fibre content. This means that a strong mullite material with good toughness is formed. These properties are a function of the preparation method. The hydrolysis process formes a very fine grain starting material, which formes a relative dense mullite by reaction sintering between the carbon fibre monofilaments. During this reaction also a good bonding between the fibres and the matrix is formed.

Description / Table of Contents: On the relationship between the properties and the microstructure of multiphase materials. Part IV: Microstructure and thermal expansion coefficient. The properties of multiphase materials depend on the properties as well as on the geometry and geometrical arrangement (microstructure) of their phases. In many cases, where the material exists under extreme conditions (e. g. high temperatures, radioactive irradiation) not admitting direct property measurements or making them difficult and less accurate two dimensional pictures (micrographs) are available as the only reliable source of information.A stereologic image analysis then provides the tool to characterize the microstructure of multiphase materials quantitatively from their micrographs. Knowing equations describing the dependence of the properties on the microstructure characterized by appropriate parameters direct property measurements would become substitutable by stereologic analyses of the microstructure. Due to the fact, that this holds not only under extreme conditions the stereological microstructure analysis could also be used in conventional quality control to obtain properties without measuring them directly. Furthermore quantitative relationships between properties and microstructural parameters provide a better insight into the property-microstructuredependence thus enabling theoretically the pre-calculation of property improvements by optimalisation of the microstructure (“taylormade- materials”).This paper - subdivided in four articles - considers the derivation and the experimental proof of quantitative relationships between the microstructure and the conductivity, elastic modulus and thermal expansion coefficient of two phase matrix materials.In the present fourth part of this paper the derivation of the equations is considered which describe the dependence of the linear thermal expansion coefficient on the microstructure of two phase matrix materials quantitatively, the phases of which show linear elastic and isotropic behaviour. Calculated and measured thermal expansion coefficients of two phase materials from about 15 binary systems are compared agreeing sufficiently well. The general equation describing mathematically the relationship between the microstructure and the linear thermal expansion coefficient of two phase materials confirms theoretically, that closed pores do not affect the thermal expansion coefficient of porous materials. - At the end of the present article an engineering statement is made summarizing and judging the results obtained in the alltogether four parts of this publication.

Description / Table of Contents: Wear testing and wear behaviour of cemented carbidesWear resistance is not a mater constant but a quantity of a system. For the judgement of a case of wear or for the choice of the suitable grade of cemented carbide it is necessary to investigate exactly the limiting conditions and the appearance of wear.The wear test can only be considered with exactly defined limiting conditions and only be compared with application of similar limiting conditions.

Description / Table of Contents: Internal Pressure Loading of Hollow Cylinders with excentric welded-in NozzlesInvestigations were carried out on nozzles welded on to the basic pipe with a V-seam without counter welded root; the material was of St 35 and WB 36. Flat specimens St 37 and BH 51 with a cross seam were delivered for comparative fatigue tests.The highest stressed part was established on the hole edge in the base material for nearly all types during static measurements (with and without longitudinal force compensation). The stress concentration factor αK, plastic support factor n0,2 and weakening factor v0,2 were determined for the highest stressed part on samples of St 35 (exception WB 36). Stresses with longitudinal force compensation were somewhat larger than without, that means the results of internal pressure pulsating tests can be regarded as the lower limit of loading types.With internal pressure pulsating, cracks were predominantly on the hole edge in the base material, i. e. the negative influence of the (ground) seam was mostly smaller than the differences in maximum strains between hole edge and weldment. Compared with the test results of polished test bars, a surface factor f0 would be defined. As far as the crack was within the range of the weld a “weld factor” fS could be added so that the fatigue can be calculated with the total factor fges - f0 × fS from the strain amplitude of the polished bar. When utilizing the static design basis it turns out that the higher strength of WB 36 as against St 35 allows only a factor 2 ÷ 10 lower fatigue life (pulsating loading).

Description / Table of Contents: Acoustic Emission Analysis on Short Glass Fibre Reinforced Thermoplastics (GRP). - The Influence of Fibre length DistributionIn this work a model is developed which relates the length of the glass fibres to the acoustic emission curve. In this model if one assumes that it is possible to strain the matrix infinitely then the emitted acoustic emission due to fibre fracture can be qualitatively analysed. It is also assumed that the mean length of the fibres, as related to their diameter, is considered to be the most important parameter for the probability of a fibre to fracture. This probability B, is 1 for a long thin fibre, and with an ever decreasing fibre length, this value tends towards O. It is possible, with these assumptions, to predict that the acoustic emission curve will have the form ∊B exp∊B, where ∊ is the applied strain. This model is supported by experimental results.

Description / Table of Contents: Two Step Fatigue Tests with Copper PolycrystalsPolycrystalline copper specimens have been subjected to axial push-pull two step fatigue tests in stress- and plastic strain controlled conditions. The differences between the amplitudes imposed under two step loading as well as the block length of the program have been varied systematically. At the very moment the amplitude is changed in a test the material shows a characteristic deformation response nearly independent of the test duration. It is therefore concluded that the same deformation processes are involved - independent from duration of the test - which are leading to comparable fatigue work hardening states. In tests with small differences between the two amplitudes the block length was observed to have no influence on the work hardening curve on the contrary to tests with large differences in the amplitudes.

Description / Table of Contents: The Effects of Specimen Size and the Presence of Notches on the Stress Rupture Properties of Round Bars Representative of Structural ComponentsStress rupture tests at 550 °C on smooth and notched specimens of 21 CrMoV 57 steel in three heat-treatment conditions have been carried out for test times of up to 35000 hours. A wide range of notch parameters for specimens of between 8 and 20 mm notch diameter has been investigated, the notch shapes (60°-V-notch, shoulder fillet and cylindrical T-head) being representative of those found in structural components. The effects of material properties, notch geometry and specimen diameter on the stress rupture strength have been determined.

Description / Table of Contents: The Deformation Behaviour of Metallic Materials Under Mechanical LoadingSimple loading conditions are reviewed with load, reaction-diagrams and characteristic mechanical data as well as typical surface appearances. The uniaxial tensile test, the uniaxial creep test, the fracture toughness test and the single-stage fatigue test are dealt with in detail. The basis of plastic deformation is discussed and the reasons for the formation of definite dislocation structures and the type of glide bands are considered. The influence of different parameters of structure on the yield stress is explained in examples together with different hardening mechanisms. The influence of temperature and strain rate on the yield stress is described quantitatively. The deformation processes which are represented in deformation mechanism maps. Finally the influence of environments on the mechanical behavior of materials is considered. In examples, an insight is given into the activity of electrolytes, gaseous environments, organic liquids and liquid metals on the deformation behaviour at typical loading conditions.

Description / Table of Contents: Form and Mechanisms of Cracks and Fractures Caused by Simultaneous Corrosive and Dynamic Stress under Various FrequenciesDistinction of crack nucleation and crack propagation under variable frequencies and electrolytic corrosion. Relationship between crack nucleation and frequency due to differing sliding mechanisms. Crack propagation under decreasing frequencies causes transition from corrosion fatigue to cyclic stress corrosion cracking and finally stress corrosion cracking can be observed. Coordination of that transition with the increasing influence of the KISCC-value as determinant of the crack propagation.The influence of frequency on high temperature materals in hot gas atmosphere is mainly determined by creep mechanisms during top-load phase and the gas-metal-reactions. Accordingly the life time increases with growing load frequency.

Description / Table of Contents: Stress-Strain and Fatigue Life Behaviour of Unnotched and Notched Specimens and ComponentsIn contrast to unnotched specimens where the cross section and the surface area are uniformly deformed, when external loads are applied at the specimens, notched specimens and components show severe concentrations of stress and deformations at the notches. In the paper different type of notches are considered and the effect of the notches under different loading conditions (monotonic, cyclic loading) is described. Some possibilities for predicting the crack initiation of notched components are also outlined and the effect of corrosive environments is briefly discussed.

Description / Table of Contents: Tribological Effect of different Fluorocarbon RefrigerantsFluorine and chlorine substituted organic compounds of the methan and ethan type are used in refrigerators, air conditioners and cooling systems. Besides their physical effect the different fluorocarbons have an effect on the tribological behavior of the different machine parts.

Description / Table of Contents: The Effective Viscosity in Visometric Pressure-Drag-Flow with Application to Extruders and Journal BearingsA number of technologically relevant flows of non-newtonian fluids can be calculated approximately by treating the fluids like newtonian fluids. This can be justified for a class of viscometric pressure-drag-flows provided the pressure gradients are not too large. It is shown that besides the usual viscosity the differential viscosity plays a dominant role. Applications and examples: viscosity pumps, extruders, journal bearings.