Volume 52, Issue 11-12

Kurzfassung Der Sonderforschungsbereich 747 „Mikrokaltumformen – Prozesse, Charakterisierung, Optimierung“ der Deutschen Forschungsgemeinschaft (DFG) beschäftigt sich seit 2007 mit der Bereitstellung von Prozessen und Methoden für die umformtechnische Herstellung metallischer Mikrokomponenten. Im Teilprojekt B4, Bauteilfestigkeit, in dem drei der Autoren arbeiten, geht es um die statische und dynamische Untersuchung der mechanischen Eigenschaften von Mikroproben und -halbzeugen. Die Prüfung derartiger kleiner Prüflinge erfordert eine an deren Dimensionen angepasste Prüftechnik. Vor dem Hintergrund dieses besonderen Anforderungsprofils werden die infrage kommenden unterschiedlichen Prüfmaschinenklassen vergleichend diskutiert. Zur Durchführung des genannten Projekts wurde ein Prüfsystem beschafft, welches am geeignetsten erschien, bestehend aus der elektrodynamischen Prüfmaschine des Typs Instron ElectroPuls™ E1000 und dem berührungslos arbeitenden Videoextensometer AVE. In diesem Artikel werden einige Erfahrungen mit diesem Prüfsystem beschrieben.

Small mass impacts pose a threat to modern lightweight materials even at low velocities. In this study we describe a test method with a suitable setup to access the materials impact response to masses below 500 g and velocities up to 20 m/s. The setup uses a highspeed camera and adapted semi-automatic image processing algorithms to extract the time-force history of the indenter. The results show good agreement to analytical impact models for hollow core sandwich structures.

Accuracy of indirect fatigue crack length measurement by potential drop method or by compliance technique may be affected at low load ratio due to fracture surface contact, crack closure or mixed mode fracture. As an alternative, the maximum value of crack opening displacement, COD max , from a clip gauge was utilized. Middle crack tension M(T) specimens were used to obtain conservative data at a low load ratio (R = 0.1). Thin sheet specimens (B = 3.2 mm) with different widths (100 mm ≤ W ≤ 400 mm) of AA6056-T4 were investigated in the mid-regime (Paris regime), which is of interest for damage tolerance analysis. The use of COD max is found to provide crack lengths equivalent to those measured optically. Hence, the method is very suitable for indirect crack length measurement. Furthermore, small width specimens provided data equivalent to large width specimens. Insofar, the size effect is found to be absent, and fatigue crack propagation data can be acquired on small width specimens when material availability is limited.

Kurzfassung Fur den Beitrag wurden FSW-Stumpfstose aus AA2024 und AA6013 analysiert. Die Eigenspannungen wurden mittels der Cut-Compliance- Methode in Form von an der Rissspitze wirkenden Spannungsintensitatsfaktoren K rs erfasst, die direkt mit lastbedingten Spannungsintensitatsfaktoren uberlagert werden konnen. Die Schwellenwerte der Schwingbreite des Spannungsintensitatsfaktors ΔK th wurden fur kleine Lastverhaltnisse R mit konstantem R-Wert, fur grose Lastverhaltnisse dagegen mit konstantem K max -Wert ermittelt. Die konventionelle Auftragung der Schwellenwerte uber dem Lastverhaltnis lasst fur geschweiste Proben bei kleinen R-Werten deutlich grosere Schwellenwerte als fur den Grundwerkstoff erkennen. Die Auftragung nach dem 2-Parameter-Konzept verdeutlicht, dass der bei hohen K max -Werten ermittelte effektive Schwellenwert ΔK th,eff werkstoff- und zustandsunabhangig ist. Die Unterschiede werden somit ausschlieslich vom zweiten Schwellenwert K max,th verursacht, der fur FSW-Verbindungen deutlich groser als fur den Grundwerkstoff ist. Dieser Unterschied kann den beim Schweisen eingebrachten Druckeigenspannungen zugeordnet werden. Basierend auf der analytischen Beschreibung des Schwellenwertverhaltens in einer fruheren Veroffentlichung [1] wird gezeigt, dass bei bekanntem Verhalten eines geeigneten Grundwerkstoffs zusatzlich nur ein charakteristischer K rs -Wert benotigt wird, wenn das Schwellenwertverhaltens einer FSW-Verbindung beschrieben werden soll.

The rotation of principal stress/strain axes, which takes place under conditions of non-proportional fatigue loading, may significantly worsen the fatigue life. An explanation of this phenomenon can be found through microstructure examination. In this paper, we present the results of a microstructure examination of a X5CrNi18-10 steel subjected to fatigue loading, both, proportional and non-proportional. The variability of the positions of the principal stress axes was controlled by a fatigue loading program that consisted of alternatively realised blocks of torsion and tension-compression. The microscopic investigations were carried out by X-ray structural analysis and the micro-hardness of the material was examined. The results revealed that the application of cyclic loading caused a plasticity-induced martensitic transformation. Comparative analysis showed that the transformation depended on intensity and the kind of applied loading.

This paper presents a linear model for the dry sliding wear behaviour of a PM copper based brake lining material with the addition of MoS 2 . The model was based on experimental results related to standard pin-on-disk wear tests of the brake material with various MoS 2 contents at constant applied load and sliding velocity. The wear load was considered as the input parameter, whereas the wear rate and friction of coefficient as the output parameters. The predicted results were compared with experimental results by simulating a linear process for each MoS 2 content of the material, and it was found that the results obtained from such linear process modelling were satisfactory. The results showed that the linear process model represents an useful tool for the prediction of the brake lining material properties, and that it is more effective than timeconsuming experimental procedures.

In automotive engines, the connecting rod is subjected to high cyclic loads. These are represented by high compressive loads due to combustion, and high tensile loads due to the connecting rod mass of inertia. The main objective of this study is to optimize the shape of a connecting rod in an automobile engine. A model of the connecting rod has numerically been built and has been solved by the Finite Element Method (FEM) using the ANSYS package to determine the stresses distribution over the entire rod. In addition, the transition force analysis of the connecting rod and the verification of the analysis are shown. The aim of the optimization has been to minimize the respective Von Mises stresses which occur at connected rod in both cases, i. e. compressive loads coming from the gas pressure at maximum engine output and the bending loads resulting from the inertia force at the maximum engine power. The weight of the connecting rod should be maintained to prevent increasing of the inertia force. The results of this study indicate that the maximum compression stress occur at compressing loads at the small end section of the connecting rod. Optimizing the radius at the small end decreases such stresses. On the other hand, the inertia forces of the connecting rod mass cause a maximum bending stress at the large end section. By changing the shape and geometry of this section the maximum Von Mises stresses are reduced by 16.5 %, as compared to the original design. A buckling analysis has been carried out for the original and the optimized model and the results have been compared. The load factor (critical load / applied load) is increased by 7 % compared to the original design. Finally, a shape optimization for connecting rod reduces the stresses over the entire rod.

By definition, Functionally graded materials (FGM) are new advanced composite materials which are used to produce components featuring engineered gradual transitions in microstructure and/or composition. FGMs permit tailoring of material composition so as to derive maximum benefits from their inhomogeneity. The aim of the study behind this contribution is to optimize the composition variation between the ceramic and the metal in order to minimize the maximum stress concentration around the hole in a plate made of FGMs in case of the plate is subjected to pressure, heating or both pressure and heating. The finite element method (FEM) has been used to optimize the material composition of functionally graded materials made from Al 1100 as the metal portion and SiC as the ceramic portion using the ANSYS package. The objective has been to minimize the stress concentration factor around a hole in a plate expressed by the ratio between the principal stress calculated by the ANSYS and the applied stress at different volume fractions of the metal and the ceramic. The investigations have shown that when applying pressure or heating to the plate the optimum for minimizing the stress concentration is to have a ceramic-rich plate and when the plate is subjected to both pressure and heating the optimality is to have a metal-rich plate.

In this study, a newly developed Boron alloyed armor steel is presented and its mechanical properties as well as its ballistic applications are given. Further, a description of ballistic terms is included to understand the development of armor steel for the use in civil and defence applications. The main subject of the study is the microstructural design of these steels. For this purpose a Boron alloyed experimental steel has been produced by quenching and tempering. The microstructures obtained after such heat treatments have been examined by light microscopy (LM) and scanning electron micoscopy (SEM). The application of precipitation hardening is highlighted by the effect of alloying elements and the resulting matrix hardening potential. As a result, a suggestion is given for the alloy design of the new armor steel with Boron additions. The effect of microstructure and mechanical properties (strength, hardness, toughness, etc.) of this experimental armor steel have been evaluated by methods similar to homogeneous rolled armor steels (MIL-A-12560) targeted at a good ballistic performance. Also the effect of heat treatment on the mechanical properties of armor steel is shown. The impact toughness values at different test temperatures are comparatively given in addition to the relationship between ballistic performance and hardness for armor steels. Attempts have been undertaken to explain the cause of deformation and failure occurred in the steel plates due to projectile penetration with light and scanning electron microscopical studies.

Kurzfassung Die Ansprüche an qualitativ hochwertiges Kunststoffrohmaterial steigen zunehmend. Als „high grade“ ausgezeichnete Granulate erzielen besonders hohe Gewinnmargen und sind weniger verantwortlich für Schwierigkeiten während des Weiterverarbeitungsprozesses als „low grade“-Materialien. Ziel der Pelletkontrolle ist also die Steigerung der Produktqualität und Verhinderung von Ausschussproduktion, die wiederum am effektivsten durch eine stichprobenartige Überprüfung mittels sogenannter Online-Testsysteme erreicht wird. Wesentlich aktuellere Messergebnisse ermöglichen einen zeitnahen Eingriff in den Produktionsprozess. Die neue Generation der Pelletkontrollsysteme ermöglicht jedoch eine Qualitätskontrolle in Produktionsmaßstab und sortiert gleichzeitig die detektierten Fehler aus, so dass nahezu eine 100%ige Qualitätskontrolle erreicht wird.