Probleme der Kriechstromfestigkeitsprüfung

Problems of Tracking Tests. The influence of the electrolyte, the material of the electrodes and the test voltage on the results were explored. Furthermore tracking tests with D. C. were described. A table of test results, obtained with D. C. and A. C. and also different electrolytes allows a comparision of the tracking behavior of a large number of materials.     

Bedeutung der Unregelmäßigkeit Gauß'scher Zufallsfolgen für die Betriebsfestigkeit

Significance of Irregularity of Gaussian Random Sequences on Random Fatigue The results of investigations concerning the influence of the irregularity factor which are found in the literature are often contradicting. The cause may be, that with the variation of the irregularity factor in some cases other influencing parameters were unintentionally varied too. To help clarify the situation a test program was conducted. Notched specimen and single shear lap joints of the aluminium alloy 2024 were tested under axial random loading sequences to determine the influence of irregularity on fatigue life. The irregularity factors (l = 0,99, 0,7, 0,3) cover the range interesting in practice. The method to generate random sequences ensures that the factor of irregularity is the only variate among the usual parameters of the random sequence.     

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.     

Vorbeanspruchungsabhängige Schadensakkumulation bei der Kriechermüdung warmfester Stähle

Influenced prior loading on the creep fatigue damage accumulation of heat resistant steels On two heat resistant power plant steels the influence of prior strain cycling on the creep rupture behaviour and the influence of prior creep loading on the strain cycling behaviour is investigated. These influences concern the number of cycles to failure and the rupture time being the reference values of the generalized damage accumulation rule and they are used for a creep fatigue analysis of the results of long term service-type strain cycling tests.     

Über den Einfluß der Probengeometrie auf die Rißausbreitungsgeschwindigkeit bei Spannungsrißkorrosionsversuchen

The influence of specimen geometry on stress corrosion cracking rates The fracture mechanics characterization of stress corrosion cracking phenomena established the quantitative relation between the stress field around the crack front and the stress corrosion cracking rates. In order to apply the results successfully in structural design, the influence of specimen geometry and test conditions have to be eliminated or minimized. Great experimental efforts are applied worldwide to develop such a testing procedure. The following work is directed to some of the effects resulting from specimen geometry, such as the numerical equations used to obtain the stress-intensity factors, the specimen thickness and crack length.     

Einfluss der Netztopologie der künstlich neuronalen Netze auf das Ergebnis der Abschätzung zyklischer Kennwerte

Several estimation methods have been developed to estimate the cyclic material parameters out of the static material properties. Most of these methods are based on empirical equations. Increasing numbers of input‐ and influencing parameters lead to an rising effort for determining these equations and the accuracy decreases. For this reason new suitable methods are sought to estimate the cyclic material behaviour. A very promising approach is the application of the artificial neural networks, which can derive self‐depended a relationship between in‐ and output parameters. Static parameters such as yield strength, tensile strength …? etc., which can rapidly be determined used as input parameters. The output parameters are the cyclic material parameters of the strain‐life curve and stress‐strain curve according to the Manson‐Coffin‐Basquin‐ and Ramberg‐Osgood curve. Many different artificial neural networks with different structures and complexity can be applied. In this paper the influence of the topology of an artificial neural network on the estimation accuracy will be investigated. Based on the results of a reference artificial neural network it will be shown, that more complex topologies in the network do not lead inevitably to better estimations.     

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.     

Flächeneinfluss bei der PACVD‐Beschichtung

Impact of the active surface on properties of DLC films in the PACVD coating chamber. In the automotive industry, economic and stable industrial processes to apply hard coatings for tribological applications are required. Hence detailed knowledge about the influence of coating parameters on the film characteristics is essential. the following paper deals with the process of plasma activated chemical vapor deposition with focus on the effect of the parameter “active area in the coating chamber“ on the properties of diamond‐like‐carbons (DLC). the coatings are deposited in an industrial coating chamber using reactive magnetron sputtering with a pulsed bias voltage (40 kHz) and at constant pressure. During the investigation of the influence of active area and current density on the mechanical and tribological properties of the DLC films, the expected correlation between active area and current density could be confirmed. By regulating the current density, consistent film properties could be achieved, independently of the active area in the chamber. Furthermore improved wear characteristics of the film – crucial for the endurance of heavily loaded automotive components – were achieved by adapting the load pattern of the chamber.     

Zur Übertragbarkeit der Schwingfestigkeitseigenschaften im Örtlichen Konzept

Transferability of the properties of fatigue in the local approach This article deals with the uncertainty of lifetime prediction. There are to reasons for still unsatisfying calculation results, known as transferability problems. The first appears when using strength under constant amplitude loading for the prediction of operational loaded structures. The second transferability problem exists only in the local strain approach where the strength of the unnotched small specimen is assumed to be valid for the real component as well. This difficulty is dealt with by separating the independent influences and its individual consideration. The microstructural mechanics influence is derived by a statistical evaluation of experimental data. The proposed concept for regarding the microstructural support effect allows o derive a strain‐life‐curve for an individual component. The results of verification look promising.     

Prüfmethoden zur Ermittlung des Verhaltens von Polyolefinen bei der Einwirkung von Chemikalien

Methods to Determine the Behavior of Polyolefines in Contact with Chemical Agents Two test methods to determine the behavior of thermoplastics in contact with chemicals were compared. These are the immersion test and the internal pressure creep test of pipes filled with a chemical agent. Concerning the immersion test the mechanical properties of tensile bars after the test procedure were determined. The results only are valid for constructions without any load. In the internal pressure creep tests the influence of a chemical agent and the stress is considered simultaneously. By comparison with the long term behavior under the influence of water the chemical resistance factor is given. The test procedure and the evaluation of the results of the immersion tests were strown at two examples. A test station for internal pressure creep tests with pipes which are filled with a chemical agent is described. Many resistance factors were listed up and their application in two examples explained.     

Einfluß des Fe-Gehalts und der Auslagerungszeit auf mechanische,elektrische und magnetische Eigenschaften der Legierung CuNi 10(Fe)

The Influence of the Fe-Content and the Ageing Time on Mechanical, Electric and Magnetic Properties of the Alloy CuNi 10 (Fe) 6 batches of the technical alloy CuNi 10 Fe with Fe-contents varying from 0.04 to 1.52 wt- % were investigated concerning the influence of the Fe-content and of ageing at 400 ° on Vickers hardness, impact properties, tensile strength at 400 °, relative magnetization and electric conductivity. In addition stress rupture tests with continuous strain recording were performed at 400 ° with testing times up to 3000 hrs. The results indicate that when ageing the material at 400 ° the mechanical as well as the physical properties investigated are markedly influenced by the Fe-content in the alloy CuNi 10 Fe. This influence is also clearly perceptible in the stress rupture tests at 400 °. An explanation for this behaviour is given by the formation of Ni-Fe rich precipitates on the grain boundaries as well as in the grain interior in all batches with the exception of those with the lowest Fe-contents     

Strukturmechanische Grundlagen der Werkstoffermüdung

Fundamental aspects of the fatigue processes in metallic materials The present situation in fatigue research is characterized by a great number of scientific as well as of applied work. However, despite of extensive activities no unified theoretical approach of fatigue is to be seen. This paper gives a survey of the well-established fundamentals of fatigue of metallic materials. The research work of the last two decades led to the development of criteria to classify the multi-layered experiences and the detailed assessments of many facts in this field. Considering the fatigue stages, initial-deformation, crack-initiation, crack-propagation and fracture some characteristic experimental and theoretical results are presented and discussed. Cyclic plastic deformation is a prerequisit for fatigue of metals. It changes the mechanical behavior of the whole samples in the crack-free fatigue stage. It also develops surface structures, which act as sites of micro cracks. Crack growth also is a consequence of plastic deformation and needs a tensile component of the applied stress system. Structure-sensitive factors influence the fatigue behavior of metals mainly in the initial stage of fatigue.     

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.     

Bestimmung der Streckgrenze und der Hall‐Petch‐Konstanten des Vergütungsstahles 42CrMo4 unterschiedlichen Gefüges mittels Eindruckprüfungen

Determination of yield stress and Hall‐Petch coefficients of the tempering steel 42CrMo4 with different microstructure by means of indentation testing Yield stress of steels can be determined by tensile tests or by indentation testing. Indentation tests offer the advantage of measuring the yield stress of certain parts that otherwise could not be used to withdraw tensile samples. Furthermore, measurements in parts with a varying yield stress e.g. surface hardened steels can be carried out. This work investigates several methods of indentation tests to measure the yield stress of the tempering steel 42CrMo4. The yield stress of different microstructures is compared to results of tensile tests. Using the indentation test according to GOST 22762‐77 the Hall‐Petch coefficients of microstructures consisting of perlite and ferrite are determined. Thus the influence of grain size and distance of perlite lamellas on the yield stress can be taken into account.     

Zeitstandverhalten von Schweißverbindungen aus HDPE bei der Einwirkung von Chemikalien

Long Term Creep Tests with HDPE Pipes under the Influence of Several Fluids The results of long term creep tests with unwelded and welded HDPE pipes under the influence of several fluids are presented. It is shown that the resistance factors determined by the investigations of tubes are also valid for welded constructions, when the long term weld factors in DVS 2205, Blatt 1 are taken in consideration.     

Vorhersage der Schwingfestigkeit von Schweißverbindungen auf der Basis des statistischen Größeneinflusses

Prediction of the fatigue strength of welded joints based on the statistical size effect With increasing length of welding seams the fatigue strength decreases. This effect is confirmed in fatigue tests on butt joints and cruciform joints. The influence of the length of the welding seam on the fatigue strength depends on the scatter of the parameters describing the geometry of the welding seam. The theory of the statistical size effect worked well in fitting and predicting the test results. The fatigue strength of welded joints is well predicted, if no other influences like e. g. residual stresses change the fatigue strength. Additionally a method for the calculation of crack propagation is proposed, which takes in account angular and linear misalignement as well as local changes of the geometry of the welding seam.     

Untersuchung der Reaktionsvorgänge zwischen gasförmigen und festen Metallen

Reaction of gaseous with solid metals . The reaction of gaseous zinc and cadmium with solid copper, silver, palladium and palladium silver alloys were investigated at various temperatures. Besides the cleanliness of the metal surfaces various other factors influence the zink tak up e. g. the shape of the surface. More than up to now it has to be kept in mind, that the zinc atoms spread as directed atomic beams. This results in possibilities of influencing the zinz up take.     

Eigenschaften langzeitgealterter,artgleicher Schweißnähte der Ni‐Basislegierung alloy 602 CA

Properties of long‐time aged matching joints of Ni‐base alloy 602 CA The paper presents results about the influence of a 2‐year exposure in the production process of ammonia synthesis on the microstructure and the mechano‐technological properties of matching TIG‐ and e‐manual welds of the high‐temperature resistant Ni‐based alloy 602 CA (NiCr25FeAlY, Material‐No. 2.4633 / UNS N 06025). These results show, that Ni‐base alloy 602 CA possesses a very good resistance against metal dusting. Furthermore typical metallurgical characteristics of the welding process of this extremely hot‐crack sensitive alloy are presented and recommendations for a hot‐crack safe manufacturing of components made of this alloy are given.     

Beständigkeit verschiedener Stähle und Nickelbasiswerkstoffe unter dem Einfluß aufnitrierend wirkender Gase in der Ammoniak-Synthese

Resistance of Various Steel Types and Nickel-Base Alloys Under the Influence of Nitriding Gases in Ammonia Syntheses Plants The paper describes test results obtained during 5 years of practical trials with heat-resisting steels, steels for hydrogen service, austenitic steels and nickel-base alloys under the nitriding operation conditions found in an ammonia plant at temperatures of more than about 400°C. During the test, nitriding rates and depths at high temperatures and under stresses were established, as well as changes in the mechanical properties as a result of nitriding. Based on the test results and the knowledge of the subject matter, recommendations and service condition limits for material selection are given. The superior behaviour of austenitic materials, especially with increasing nickel contents, could be confirmed. An attempt is made to find an explanation for the reduced resistance to hydrogen attack under the influence of nitridation.     

Einfluss der Beschichtungen beim stoffschlüssigen Lichtbogenfügen von Stahl mit Aluminium

Influence of the coating by bonded arc joining of steel to aluminium The firmly bonded joint between steel and aluminium has, so far, not been achieved successfully in joining technology. The problems of joining these metals thermally are caused by the low up to non‐existing solid solubility of the metals and by the development of brittle intermetallic phases. The quality of the joints depends on many influential factors which are, sometimes, also interacting. One of those influential factors is the coating of the steel sheets. Using the example of coatings which are common and others which are unusual in automotive engineering it has been tried to demonstrate the influence on the wetting length and wetting angle of those factors with, otherwise, constant boundary parameters. The results are part of a test series which is currently carried out at the Joining and Welding Institute, Aachen.