Lebensdauervorhersage auf Basis von Finite Elemente Ergebnissen

Fatigue Life Prediction Based on Finite Element Results The ever‐increasing pressure of competition leads to continuously decreasing product development cycle times. Therefore, information about the life time and the dimensioning of machine parts is required already in the early stages of development. Frequently, a weight optimization is desired, which implies that the local stress must come as close as possible to the strength limit for wide regions of the component under concern. This leads to an increasing use of simulation methods in design as well as in testing. For a life time prediction based on stress results from finite element computations, local S/N curves are needed, which frequently have to be deduced from S/N curves obtained from laboratory specimens. In the present contribution, the transferability from specimen S/N curves to component S/N curves is pointed out exemplarily by taking into account the influences of notches, component size, and microstructure of cast aluminum. Based on such S/N curves, which are computed for each material point in the component, the life time may be calculated by taking into account the local stresses and stress gradients obtained from finite element simulations.     

Flussmittelfreies Hartlöten unter reaktiver Prozessgasatmosphäre – ein alternatives Verfahren zum Fügen von Aluminiumwerkstoffen

Flux‐free brazing under reactive process gas atmosphere – an alternative process for joining of aluminium materials Due to the high affinity of aluminium towards oxygen, joining of aluminium materials has ever been a challenge. In particular the efficiency of the process and the abandonment of fluxes during controlled atmosphere brazing have been within the focus of current research projects. The specific addition of reactive gases to the inert process gas atmosphere offers a suitable possibility of aluminium brazing without the use of fluxes. Under the application of hydrogen chloride the activation of the brazing and the workpiece surfaces is to be initiated, thus leading to dissolving the oxide layers. Moreover, the strongly reducing gas silane is used, which specifically removes oxygen and water residuals from the controlled atmosphere. Through a suitable controlled atmosphere brazing process the combination of both, reductive and activating additions, is to be used and tested upon their influence on the gas mixtures and materials used [1–5].     

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).     

Löten von Diamant – Grenzflächenreaktionen. und Benetzung

Diamond Brazing – Interfacial Reactions and Wetting Diamond tools are increasingly gaining importance as cutting materials for various construction materials. The quality of synthetic diamonds, monocrystalline as well as polycrystalline or CVD‐diamonds has been significantly improved over the last years. Integrating these cutting materials requires adequate joining technologies that produce sound joints without exposing the temperature sensitive diamond to too elevated temperatures. The paper highlights current developments in the joining of synthetic diamonds to steel and cemented carbide. Owing to their covalent atomic bonding diamonds cannot easily be wetted and joined by employing conventional brazing alloys. Hence, active agents are needed to foster an interfacial reaction. Different active filler concepts are presented and discussed regarding their joint formation. The brazing temperatures influence not only possible diamond degradation but also the interfacial decomposition of the diamond due to the formation of corresponding reaction layers.Active brazing, monocrystalline     

Charakterisierung von Randentkohlungsvorgängen bei der Austenitisierung des Wälzlagerstahls 100Cr6. Teil 1: Korrelation zwischen Randschichteigenschaften und Kohlenstoff‐Tiefenverlauf

Characterization of Decarburisation Processes During Austenitising of the Rolling Bearing Steel 100Cr6. Part 1: Correlation between Rim Zone Properties and Carbon Concentration Profile The influence of a decarburisation process during austenitising of the through‐hardenable rolling bearing steel 100Cr6 (SAE 52100) on the rim zone properties of the martensitic through‐hardened material was investigated by means of material analysis and diffusion calculations. For this purpose, two specimens were prepared under defined heat treatment conditions, and the near‐surface carbon distribution was determined micro‐chemically by using secondary ion mass spectrometry (SIMS). In part 1 of the present work, these concentration profiles are compared with the depth variation of the micro‐hardness and with the distance curves of the residual stresses and the line broadening ({211} α'‐Fe diffraction line) both measured by X‐ray diffraction (XRD). In addition, microstructure investigations were performed. In part 2, a refined kinetics model of a diffusion‐controlled reaction based on the finite element method (FEM) will be applied to the decarburisation process in order to describe the carbon distributions obtained.     

Energy Conservation Ordinance 2014 – On the way to the nearly zero energy building / EnEV 2014 – auf dem Weg zum Niedrigstenergiegebäude

The tightening of the Energy Conservation Ordinance in 2016 provides the first step toward the introduction of nearly zero energy buildings. The level of performance for residential buildings after 2020 will most likely attain an energy quality close to the primary energy consumption of the KfW Efficiency House 55 today, at least regarding performance. The following report describes the requirements methodology of the Energy Conservation Ordinance 2014, including the KfW promotion, and provides calculation examples to clarify the issues.     

Werkstoffkennwerte für die Lebensdauerberechnung von Strukturen aus Stahlfeinblechen für den Automobilbau

Materials Data for Fatigue Life Calculation of Steel Sheet Structures for Automotive Engineering Within a joint project of the steel and automotive industry 17 steel sheet materials for automotive engineering in various delivery and forming conditions at temperatures of –40 °C, 22 °C and 100 °C were investigated. In the course of 37 test series strain controlled fatigue curves to crack initiation and stress‐strain‐curves under monotonic and cyclic loading were determined. All experimental data, hysteresis loops and determined cyclic properties are available in a database. A correlation between the mechanical properties from tensile tests and the properties from strain controlled cyclic experiments seems to be possible.     

Chemische Zusammensetzung und Mikrostruktur polymerabgeleiteter Gläser und Keramiken im System Si–C–O. Teil 2: Charakterisierung der Gefügeausbildung mittels hochauflösender Durchstrahlungselektronenmikroskopie und Feinbereichsbeugung

Chemical Composition and Microstructure of Polymer‐Derived Glasses and Ceramics in the Si–C–O System. Part 2: Characterization of microstructure formation by means of high‐resolution transmission electron microscopy and selected area diffraction Liquid or solid silicone resins represent the economically most interesting class of organic precursors for the pyrolytic production of glass and ceramics materials on silicon basis. As dense, dimensionally stable components can be cost‐effectively achieved by admixing reactive filler powders, chemical composition and microstructure development of the polymer‐derived residues must be exactly known during thermal decomposition. Thus, in the present work, glasses and ceramics produced by pyrolysis of the model precursor polymethylsiloxane at temperatures from 525 to 1550 °C are investigated. In part 1, by means of analytical electron microscopy, the bonding state of silicon was determined on a nanometre scale and the phase separation of the metastable Si–C–O matrix into SiO₂, C and SiC was proved. The in‐situ crystallization could be considerably accelerated by adding fine‐grained powder of inert fillers, such as Al₂O₃ or SiC, which permits effective process control. In part 2, the microstructure is characterized by high‐resolution transmission electron microscopy and selected area diffraction. Turbostratic carbon and cubic β‐SiC precipitate as crystallization products. Theses phases are embedded in an amorphous matrix. Inert fillers reduce the crystallization temperature by several hundred °C. In this case, the polymer‐derived Si–C–O material acts as a binding agent between the powder particles. Reaction layer formation does not occur. On the investigated pyrolysis conditions, no crystallization of SiO₂ was observed.