Possibilities and extension of XRD material response analysis in failure research for the advanced evaluation of the damage level of Hertzian loaded components

Due to clearly distinguishable damage symptoms, it is differentiated between the surface and sub‐surface failure mode of rolling bearings. Material states red out by X‐ray diffraction (XRD) residual stress measurements point to a variety of loading conditions especially at raceway surfaces that are associated with several competing failure mechanisms. The corresponding lifetime reduction can range from the lower fatigue strength region to material ratcheting in extreme cases. Relevant position of the microstructural changes and nature of the failure mechanisms are characterized. The time alteration of the XRD material parameters measured at or near the surface and at the depth of the maximum equivalent stress correlates, in a different manner, with the statistical parameter of the 10 % bearing life. Both failure modes are illustrated by concrete examples. Contaminated lubricant and boundary lubrication, which represent practically important surface‐induced failures, are discussed in more detail. Gray staining, i.e. shallow pitting, often occurs without distinct indication of global material aging by means of XRD characteristics. Here, scanning electron microscopy observations and electron microprobe analyses point to corrosion fatigue as acting surface failure mechanism. The interaction between material and lubricant under complex loading regimes particularly of mixed friction and corrosion opens further failure research areas in the field of tribology.     

Verbessertes Widerstandsgesetz für Stufendiffusoren

Zusammenfassung Es wird ein allgemeines Widerstandsgesetz für Stufendiffusoren hergeleitet, bei dem die Widerstandszahl den Zusatzverlust gegenüber den Verlusten der bis zum Kontursprung reichenden fiktiven Kanal- bzw. Rohrstr?mungen in der Zu- und Abstr?mung beschreibt. Unter vereinfachenden Annahmen reduziert sich dieses Gesetz auf die bekannte Carnot-Formel. Insbesondere wird dabei der Anteil des Zusatzverlustes, der vom Unterdruck an der Stufe und von der Wandschubspannungs?nderung unmittelbar hinter der Stufe herrührt, vernachl?ssigt. Die Berücksichtigung dieses Anteils führt zu einem gegenüber der Carnot-Formel verbesserten Widerstandsgesetz. Herrn Prof. Dr.-Ing. Martin Fiebig zum 60. Geburtstag     

Production and properties of micro‐porous glas bubble zinc and aluminium composites

Micro‐porous syntactic foams were produced by means of integration of glass bubbles into aluminium and zinc matrices. Preforms of glass bubbles were pressure infiltrated with the alloys AlSi9Cu9 ans ZnAl4Cu using squeeze casting. The preforms were sintered thermically without the use of bonding agents. Using the combination of different sintering steps syntactic foams with locally different densities could be produced. The mechanical properties of the foams were tested indicating a high compression strength of the foams and a very good compression energy absorption. Furthermore, corrosion behaviour and behaviour at higher temperatures were investigated.     

Fast method to compute the scalar product of gradient and given vector

The paper deals with a special problem in Automatic Differentiation. Letf be a rational function ofn variables, let #(f) denote the number of operations to evaluatef(x), letg denote the gradient off. Many algorithms for minimizingf(x) require the scalar productg(u) ^tv. In the standard method for computingg(u) ^tv the amount of work grows withn·#(f). In this note a new method for computingg(u) ^tv is presented. The new method is considerably faster, its amount of work only grows with #(f).     

The possibility of evolving a theory for predicting the service life of reinforced concrete structures

The development in recent years with increasing air pollution, increasing need of energy saving and last not least the growing number of damage in old structures leads to a raising demand to calculate the durability of structures, too. The paper has been prepared by request of the RILEM Technical Committee 45-LTO to show that, in principle, it is possible to evolve a theory for predicting the service life of r.c. structures and to sketch a way how that could be achieved. A lot of necessary basic data can be found scattered in the literature. To collect these data will be the first step to take.     

How to avoid logarithms in comparisons with uniform random variables

In many algorithms for sampling from non-uniform distributions the logarithm of a uniform deviate must be compared with some test quantity. It is shown that all these comparisons can be done efficiently without calling a logarithm subprogram: two procedures for this task are presented and compared.     

On plastic potentials for anisotropic metals and their derivation from the texture function

Summary Plastic yielding of anisotropic metals can be either described by a macroscopic constitutive relation or assessed by means of a model which correlates single and polycrystal behaviors. The mathematical identification of the plastic work rate derived from the two approaches, for all strain rate tensors, leads to a fit of the polycrystal yield surface by an analytical function. When a quadratic from is assumed, the macroscopic anisotropy parameters become explicit functions of the texture coefficients. This identification method is applied to calculate yield surfaces andR-values of rolled and annealed steel sheets: theR-values and in general the flow rule, are more significantly modified by the fitting than the yield surface. Thus, it is worth extending the method to more general constitutive relations which may be given by the form of their work function: alternative forms of the work function for plastic materials are explored, especially in the bearing of convexity and homogeneity where quadratic forms have a distinct advantage. Finally, it is shown that the identification of the work function allows to express the phenomenological coefficients as analytical functions of the texture parameters for many forms of the work function; in the other cases, these coefficients may be obtained by linear or non-linear regression.