Showing papers in "Materials Testing-Materials and Components Technology and Application in 2009"

Computed Tomography Metrology in Industrial Research and Development

Abstract: In non-destructive testing, Computed Tomography (CT) is increasingly used for dimensional measurement tasks such as the industrial inspection of work pieces. Besides the determination of the measurement uncertainty, the improvement of the image quality is subject of current research in order to establish CT as a measuring device.

Fatigue Assessment and Fatigue Life Calculation of Metals on the Basis of Mechanical Hysteresis, Temperature, and Resistance Data

Abstract: Mechanical stress-strain hysteresis, temperature, and electrical resistance measurements were performed for the microstructurerelated characterisation of the cyclic deformation behaviour and for the fatigue life calculation of metals. The electrical resistance is strongly influenced by the defect density, and allows the detection of a proceeding fatigue damage under cyclic loading and during load-free inspection intervals as well. On the basis of comprehensive mechanical, thermal, and electrical fatigue data the physically based fatigue life calculation “Phybal” was developed at the Institute of Materials Science and Engineering at the University of Kaiserslautern. This method requires only one load increase test and two constant amplitude tests for a fast and nevertheless precise calculation of S-N (Woehler) curves, leading to a significant reduction in experimental time and costs.

Influence of Service Temperatures on the Fatigue Behaviour of Railway Wheel and Tyre Steels

Abstract: The current investigations are focussed on high-speed passenger-traffic and commercial-freight transportation railway wheel and tyre steels, which were provided by a system supplier of the DB AG in technically relevant heat treatment conditions. As a consequence of the industrial heat treatment, microstructural gradients emerge in the rim of monobloc wheels and tyres, leading to a local-dependence of the fatigue behaviour. Fatigue specimens, representing the local microstructure were machined from defined depth-positions. The fatigue behaviour at ambient temperature and elevated service temperatures was assessed by mechanical stress-strain hysteresis and electrical resistance measurements. The local microstructure influences the fatigue behaviour in a characteristic manner.

Fatigue Life Calculation of Metastable Austenitic Stainless Steels on the Basis of Magnetic Measurements

Abstract: Monotonic and cyclic plastic deformation of metastable austenitic steels lead to a phase transformation from paramagnetic austenite into ferromagnetic α′-martensite. The deformation-induced changes of the magnetic properties are directly related to the accumulated plastic strain and therefore to the actual fatigue state. This paper includes a detailed characterization of the deformation-induced austenite-martensite-transformation in metastable austenitic steels. The cyclic deformation behaviour was evaluated by mechanical stress-strain hysteresis and temperature measurements. With in-situ Ferritescope magnetic measurements, the development of the α′-martensite, and the change in the magnetic induction due to the Villari effect were investigated. On the basis of far-reaching cross effects of mechanical and magnetic properties, measurements of magnetic-mechanical hysteresis loops were performed. Hence a method for fatigue life calculation based on the change in magnetic properties was developed.

Wasserverteilung in PEM-Brennstoffzellen

Abstract: KurzfassungIn-situ-Neutronenradiografie wird erfolgreich eingesetzt, um flussiges Wasser in Niedertemperatur-PEM-Brennstoffzellen wahrend des Betriebs zerstorungsfrei abzubilden und das sogenannte Wassermanagement — eine der grosten Herausforderungen der Entwicklung — durch Anpassung der Materialeigenschaften zu optimieren. Dabei werden die besonderen Eigenschaften der Neutronen genutzt, die metallische Bauteile relativ leicht durchdringen, wahrend selbst kleine Wassermengen durch ihre starke Streuung leicht nachweisbar sind. Die relativ langen Messzeiten fur die Neutronentomografie werden durch den Betrieb der Zelle im „angehaltenen‟ Zustand realisierbar, sodass die dreidimensionale Wasserverteilung darstellbar wird.

Contribution of MoS2 additives to the Microstructure and Properties of PM Copper Based Brake Material

Abstract: The effect of a MoS2 additive on the microstructural evolution and properties of copper based brake linings has been investigated in this study. It was found that the quantity of additive as well as sintering cycle has significant effect on the density and hardness values of the produced material. The microstructure of designed brake lining materials showed that copper based matrix was surrounded by MoS2 particles. The microstructural investigation also proved that the lower boiling point elements such as Pb in the as-supplied powder vaporise during sintering from the structure, and this result in an increase in the porosity amount by lowering the overall density of brake linings. The Vickers hardness of brake linings decreased with the addition of molybdenum disulphide particles. MoS2 addition reduces wear rate of samples due to the solid lubrication effect.

Vibration Behaviour of Servohydraulic Dynamic Tensile Testing Machines

Abstract: The oscillation behaviour of the Schenck and Roell-Amsler servohydraulic dynamic tensile testing machines used at the RWTH IEHK has been investigated [1]. The dynamic longitudinal and bending oscillations, propagating through the test set-up, have been characterised with a Fast Fourier Transformation (FFT) and a simple analytical model. When increasing the strain rate, the Eigen frequency of the test set-up becomes a limiting factor. With higher testing speed the oscillations amplitude and inertia effects also increase, which makes it difficult to determine accurately the mechanical properties as usually done with quasistatic tensile tests. A set-up optimisation can be reached by decreasing the mass between the load cell and the sample, either by moving the load cell closer to the sample, or with a lighter machine design and grip shape. A combination of both possibilities has been followed at IEHK. A global piezoquartz load cell, a quasilocal calibrated strain gage load cell on the grip, and a loc...

Fatigue Life According to Cyclic Strain Characteristics Determined from Variable-Amplitude Loading*

Abstract: The paper includes the analysis of influence of cyclic stress-strain curve parameters on the fatigue life estimation. The parameters of cyclic stress-strain curve, described by the Ramberg-Osgood relation, were determined by a new method from the variable-amplitude loading histories. The variable-amplitude stresses were used to calculate strain courses based on different values of cyclic stress-strain curve parameters. The calculated and experimental strain courses were applied to calculate fatigue life with use of damage accumulation hypothesis by Serensen-Kogayev.

CO2-Potenzial durch Leichtbau beim PKW*

Abstract: Kurzfassung Die Frage nach dem Differenzverbrauch fur eine Differenzmasse von 100 kg im europaischen Typprufzyklus NEFZ wird fur Fahrzeuge mit Otto- und Dieselmotor beantwortet. Dazu wird die vom Gewicht verursachte mechanische Arbeit im Fahrzyklus berechnet und mithilfe des relativ konstanten Differenzverbrauchs-Wirkungsgrades von Verbrennungsmotoren im unteren Lastbereich in Kraftstoffverbrauch und CO2-Emission umgerechnet. Der maximale Differenzverbrauch von 0,15 l/100 km pro 100 kg im NEFZ kann bei einer Anpassung von Motor- oder Getriebe auf 0,4 l/100 km ansteigen. Angaben in den Medien mit bis zu 1 l/100 km Mehrverbrauch fur eine Differenzmasse von 100 kg werden eindeutig widerlegt.

Optimierung von Nutzfahrzeug- sicherheitskomponenten aus Eisengraphitguss

Abstract: KurzfassungDie Betriebsfestigkeit von Bauteilen wird grundsatzlich durch die Interaktion von Belastung, Werkstoff, Formgebung und Fertigung bestimmt. In jedem dieser einzelnen Parameter ist ein groses Optimierungspotenzial fur den Leichtbau vorhanden, das nicht ausgeschopft ist. Anhand eines Panhardstabes, eines stabilisierenden Elements im Fahrwerk von Nutzfahrzeugen, wird gezeigt, wie zunachst durch eine Werkstoffsubstitution, namlich des konventionellen Eisengraphitgusses EN-GJS-400-15 (GGG 40) durch die ADI (Ausferrite Ductile Iron)- Variante EN-GJS-800-8 mit der entsprechenden Warmebehandlung, eine deutlich hohere Schwingfestigkeit erzielt wird. Zu bemerken ist, dass der ADI-Guss gefugebedingt gegenuber dem konventionellen ferritischen Werkstoff unter variablen Betriebsbelastungen eine deutlich hohere Schwingfestigkeits- bzw. Lebensdauersteigerung aufweist als unter konstanten Amplituden und somit ein Leichtbaupotenzial. Da Panhardstabe, ebenso auch gummigelagerte Gusszapfen, im Betrieb auch Missbrau...

Einfluss der Härtung auf die Materialeigenschaften eines Harnstoffharzes

Abstract: Kurzfassung Uber die in der Technik weit verbreitete typisierte Harnstoffformmasse UF 131.5, ein Aminoplast, wird berichtet, dass sie im Zuge der thermisch aktivierten Vernetzungsreaktion wegen „Uberhartung‟ mangelhafte Eigenschaften annimmt. Zur Verifizierung dieses Effektes werden mithilfe der Ultraschall-Prozesskontrolle gezielt Proben unterschiedlicher Aushartegrade hergestellt. Sie werden mit verschiedenen Methoden, wie der „Kochprobe‟ und der Thermoanalyse, charakterisiert und auf ihre Materialeigenschaften untersucht. Dabei zeigt sich ein deutlicher Einfluss der Hartezeit auf die Glasubergangstemperatur der Formmasse. In den mechanischen Eigenschaften ist eine Veranderung allerdings nur in der Schlagzahigkeit festzustellen, die sich mit steigender Hartezeit sogar wesentlich verbessert.

Factors Affecting the Intrinsic Anti-Oxidative Activity of Carbon-Nanofibers — Metallic Impurities

Abstract: It is reasonable to assume that the existence of inherent anti-oxidizing activity of nanotubes and nanofibers (CNT, CNF) would be a good tool for solving the problem of oxidative stability of polymer composites. CNT/CNFs have electron affinities similar to those of fullerenes and are therefore capable of acting as radical traps in free radical chain reactions, we found good evidence in our earlier works. Here, the anti-oxidizing activity of commercial carbon nanofibers of herringbone structure CNF-HB was examined with the aim to quantitatively assess the interference of Ni impurities. The model initiating the aerobic oxidation of cumene was used to determine the kinetic parameters of anti-oxidizing activity of commercial and purified CNF-HBs. CNF-HB inhibits the model reaction according to the mechanism of trapping of peroxy radicals: the oxidation proceeds with pronounced induction period and kinetic curves linearly at the semi-logarithmic coordinates (especially in the case of purified samples)....

Influence of Tool Geometry on Microstructure and Mechanical Properties of a Friction Stir Welded 7075 Aluminum Alloy

Abstract: The effectiveness of a friction stir welded joint is strongly dependent on several process parameters such as the tool geometry, including the height and the shape of the pin and the shoulder surface of the tool. In this study, two pin parameters, namely the pitch dimension (1.25 and 0.75 mm) and the helix angle (right and left helices), are varied in order to study their influence on the micro-structural, hardness, and tensile properties of friction stir welded 6 mm thick aluminum alloy 7075. The results reveal that the best combination has been obtained when welding with a pitch dimension of 0.75 mm using a right helix pin.

Bewertung des Spannungszustandes und der Materialschädigung von Komponenten industrieller Anlagen

Abstract: Kurzfassung In zunehmendem Mase gilt es fur Betreiber industrieller Grosanlagen oder Bauwerke, deren mogliche Betriebsdauer auszureizen bzw. zu verlangern. Hierzu ist die Kenntnis des aktuellen Spannungs- und Materialzustands der Komponenten unabdingbar, um daraus auf die mogliche Restlebensdauer zu schliesen. Fur die Charaktersierung ferromagnetischer Materialien steht dabei die Barkhausen-Pruftechnik als zerstorungsfreies Verfahren zur Verfugung. Die fraktale Analyse des Barkhausenrauschens generiert eine neue Kenngrose, die fraktale Dimension, die zusammen mit dem der mechanischen Spannung proportionalen magnetischen Parameter eine wesentliche Charakterisierung des Materialzustandes erlaubt. Das Verfahren wird ausfuhrlich erlautert und anhand von Beispielen werden verschiedene industrielle Abwendungen demonstriert.

Microstructural Changes in a Duplex Stainless Steel During Low Cycle Fatigue

Abstract: Low cycle fatigue of SAF 2507 duplex stainless steel has been studied at different temperatures in two thermal conditions: unaged (as-received) and aged (100 hours at 475°C). The corresponding cyclic flow stress components, the friction, σF, and the back stresses, σB, have been analyzed in relation to the observed microstructure. σF attains higher values at room temperature than in the intermediate range of temperatures in both thermal conditions due to the influence of the lattice friction stress on screw dislocations in the ferrite phase. The cyclic softening observed at all temperatures in aged samples is caused by the decrease of the back stress σB. The increase of σB in unaged samples at 300°C is consistent with the high dislocation density observed in the ferrite phase ascribed as a typical manifestation of dynamic strain aging.

Mechanical Material Properties of Polymethylmethacrylate (PMMA) for Medical Applications

Abstract: Polymethylmethacrylate (PMMA) also known as bone cement is a frequently used material for medical applications. This study investigated the material properties of the bone cement Palacos R. Flexural, tensile, and compression tests on Palacos R, following common standard, revealed typical brittle material behaviour with high compression (83 MPa) by rather low tension stress (35 MPa). No significant difference was measured between dry stored and 37°C saline solution stored specimens regarding tensile, compression and flexural properties. As bone cement can be considered as a visco-elastic material, additional tests under varied strain rates revealed an increasing Young's modulus and ultimate strength of Palacos R with increasing strain rate. To evaluate long-term load-cycling behaviour an S-N curve was determined. The material parameters of Palacos R may help to predict and evaluate failure of bone cement and improve its medical application.

Bruchmechanische Prüfverfahren für die Kennwertermittlung bei statischer, zyklischer und dynamischer Beanspruchung*

Abstract: Kurzfassung Der vorliegende Beitrag gibt einen Uberblick zu den bruchmechanischen Prufmethoden bei statischer, dynamischer und zyklischer Beanspruchung. Die prinzipielle Vorgehensweise bei der experimentellen Ermittlung der entsprechenden bruchmechanischen Kennwerte wird erlautert. Auf die zurzeit aktuellen Prufstandards wird aufmerksam gemacht. Die Kennwertermittlung wird am Beispiel spezieller Werkstoffe demonstriert. Auf bestehende Korrelationen zwischen den bruchmechanischen und den konventionellen mechanischen Kennwerten wird hingewiesen. Die Auswertung des Schrifttums erfolgt unter Hinweis auf spezielle, auserhalb der Prufstandards zum Einsatz kommende Prufmethoden und auf Beispiele fur die geforderte und erfolgreich praktizierte bruchmechanische Bauteilbewertung.

Validation of a Constitutive Material Model with Anisothermal Uniaxial and Biaxial Experiments

Abstract: The dynamic behaviour of steam turbine components is currently a key issue in terms of the discontinuity in the power supply from regenerative energy systems like wind-mills. These systems call for a combined and flexible use of conventional steam power plants. The influence on fatigue behaviour with superimposed creep on lifetime of large plant components is still unknown. Fatigue loading of such components is induced by temperature transients during start-up and shut-down processes. This requires an anisothermal inspection of the thermo-mechanical fatigue (TMF) loading at design. Hence, a viscoplastic constitutive material model of the Chaboche type was adapted to a 10% Cr forged steel. As a verification of the constitutive material model, uniaxial TMF experiments were performed. These experiments were derived from a temperature cycle on the surface of a turbine rotor during a hot start. The mechanical loading depends on the start temperature and the temperature rate of the start up, and the in...

Low Cycle Fatigue of the Single-Crystal Nickel-Base Superalloy CMSX-4 — Anistropy and Effect of Creep Damage*

Abstract: Low cycle fatigue of the single-crystal nickel-base superalloy CMSX-4 was investigated in the temperature range 700—950°C under strain controlled cyclic loading. The points of interest were the crystallographic anisotropy of low cycle fatigue behaviour and the effect of creep damage on low cycle fatigue life. For the testing conditions used the low cycle fatigue life of CMSX-4 is strongly orientation dependent as well as very sensitive to the formation of rafted γ/γ’-microstructure.

Persistent Slip Bands

Abstract: The slip activity and shear strain of persistent slip bands (PSBs) in polycrystalline nickel were studied after half-cycle deformation on well-polished specimen surfaces at different stages of fatigue life using the combination of atomic force microscopy (AFM) and scanning electron microscopy (SEM). Although the local shear strain of PSBs seems to be nearly independent of the stage of fatigue life, the half-cycle slip activity of PSBs significantly depends on it. In-situ deformation experiments in the scanning electron microscope (SEM) showed that during half-cycle loading the slip steps do not proportionally develop to the applied plastic strain and not the whole accumulated PSB volume is active. The reactivation of the cumulative PSB volume is different for individual PSBs and grains, and evolves more slowly than the reactivation of grains. PSBs in polycrystals are subjected to a development history — their activity changes both temporally as well as spatially. Possible reason for this behaviou...

Mischbau und Funktionstrennung im Automobilbau

Abstract: Kurzfassung Die Erwartungen der Automobilkunden an mehr Funktionalitat und Effizienz der Fahrzeuge stellen die Werkstofftechnik vor neue Herausforderungen. Neue Systeme fur effizientere Verbrennungsmotoren, elektrisches Fahren, Wasserstoffantrieb, Komfort und Sicherheit mussen in ein stimmiges und zuverlassiges Gesamtkonzept integriert werden. An neue Werkstoffe wird ein breiteres Spektrum von Anforderungen gestellt, um die Konstruktionen mit multifunktionalen Werkstoffen zu unterstutzen. Durch die Analyse aktueller Konstruktionen wird ersichtlich, dass oft die Trennung von Funktionen oder Mischbau zu interessanten Leichtbaulosungen fuhrt. Anhand von Beispielen aus dem Automobilbau werden die Vor- und Nachteile von Funktionstrennung und Funktionsvereinigung aus Sicht der Werkstofftechnik diskutiert.

Active Thermography for Quantitative Analysis of Defects in Composites

Abstract: The method of Pulsed Thermography has been used for the investigation of carbon as well as glass fibres reinforced plastics. We have studied material properties like porosity and density, ...

Functionalized Nanodiamonds as Nanoagents in Materials and Life Sciences

Abstract: Ultradisperse nanodiamonds can be implemented as nanoagents in materials and life sciences by chemical or biological activation. In this paper we show the potential of nanodiamonds for spe...

Hochgeschwindigkeitszugversuche an Stahl

Abstract: Kurzfassung Viele Stahle weisen eine positive Dehnratenabhangigkeit auf, d.h., mit zunehmender Dehnrate steigt die Fliesspannung an. Dies wird zum Beispiel bei der Beurteilung der Crashsicherheit von Fahrzeugstrukturen, die in der Automobilindustrie zunehmend mittels numerischer Methoden erfolgt, berucksichtigt. Zur Kennwertermittlung werden heute in Industrie und Forschung unterschiedliche Prufsysteme eingesetzt. Der vorliegende Beitrag informiert einerseits uber den Stand der Pruftechnik, behandelt aber auch den Status und den Fortgang aktueller Normungsvorhaben. Erganzend wird ein Uberblick uber die Einbindung dieser technisch anspruchsvollen Pruftechnik in den Werkstofffreigabeprozess bei der Entwicklung neuer Stahle im Automobilbau gegeben.

Thermal Fatigue of Magnesium Base Alloy AZ91

Abstract: Thermal fatigue tests of the magnesium-base alloy AZ91 were carried out under total strain control and out-of-phase-Ioading conditions in a temperature range between 50°C and +190°C Specimen produced by a vacuum die casting process were loaded under constant total strain and uniaxial homogeneous stress To simulate the influence of different mean stresses, experiments were started at different temperature levels, i e the lower, mean or upper temperature of the thermal cycle The thermal fatigue behaviour is described by the resulting stress amplitudes, plastic strain amplitudes, and mean stresses as a function of the number of thermal loading cycles Depending on the maximum temperature, and the number of loading cycles, cyclic softening as well as cyclic hardening behaviour is observed The upper temperatures or the respective temperature amplitudes determine the total fatigue lifetime

Investigations on Local Fatigue by Infrared Thermography

Abstract: Modern infrared (IR) thermography as a non-contacting, high resolution and full-field measurement technique offers a promising tool for various applications in experimental fatigue studies. Despite the tremendous advances in IR-camera, computer and data processing technology, infrared measurements have so far rarely been applied to the assessment of localized fatigue phenomena. The aim of this paper is to present basic considerations and experimental results of an application of infrared thermography for damage studies during fatigue tests on mild steel S355. For this purpose high-resolution infrared image sequences have been acquired during high cycle fatigue testing. The data is analyzed with respect to linear thermoelastic and nonlinear phenomena, which allows characterizing the local fatigue behavior. Experimental studies on unnotched, mildly notched, and welded specimens under different testing conditions are presented. The results confirm the high potential of the application of infrared the...

Energiebasierende Lebensdauerbewertung von Nickellegierungen

Abstract: KurzfassungZyklische Beanspruchung bei konstant steigender oder variabler Temperatur fuhrt bei metallischen Bauteilen zu einer komplexen Schadigungsentwicklung, die nur schwer mit einfachen Mitteln zu beschreiben ist. Wahrend des Betriebes tritt in vielen Bauteilen thermomechanische Ermudung (TMF) auf, z.B. in Kokillen in der Stahlproduktion, Turbinenscheiben, Zylinderkopfen. Daher ist es wichtig, die thermomechanischen Ermudungseigenschaften dieser Materialien zu untersuchen und zu charakterisieren. TMF-Versuchsserien wurden durchgefuhrt, um eine Basis fur Schadigungsparameter und energiebasierende Ansatze zu finden. In diesem Beitrag werden die TMF-Ergebnisse von galvanisch beschichtetem Nickel, kaltgewalztem warmebehandeltem Nickel (Ni200/201) und einer geschmiedeten Nickelbasislegierung fur Turbinenscheiben (IN718) dargestellt und verglichen.

FatiRAN – Optimized Generation of Spectra for Random Vibration Testing*

Abstract: Random vibration testing with stochastic broad band noise signals is a commonly used procedure in qualification testing of vehicle parts. However, there are no standard procedures for deriving adequate test power spectral densities from road load data; hence test spectra can be defined far too low leading to tests not covering the loads of service life. In this paper, a new method is presented that gives consideration to the aspects of material fatigue during the whole process of windowing, overlapping, amplitude correction, and averaging that all have vital influence on the test spectra obtained. This allows for deriving test spectra with calculated damage equivalent to a defined set of design load histories, and thus helps minimizing the effort for calibration runs of test spectra on a test rig. The theoretic derivation will be shown as well as a comparison with the commonly used procedures using an exemplary case study.

Cyclic Softening Behaviour of a Duplex Stainless Steel

Abstract: This second part aims to propose an extension of the bi-phased polycrystalline model shown in a previous contribution [1], in order to simulate the cyclic softening observed in an austenitic-ferritic stainless steel under uniaxial and non-proportional biaxial cyclic loading [2]. Assuming that the cyclic softening for uniaxial and biaxial non-proportional cyclic loading is due to a rearrangement of dislocations in hard (rich in dislocations) and soft (poor in dislocations) zones in ferritic grains [3], the ferritic single crystal law is modified. The new model parameters are identified from TEM observations [3] and by inverse procedure. Finally, the new model is validated for other cyclic loading paths. A good agreement is observed between simulation and experimental data.

Deformation Character of the Aluminum Alloy AA 6063 Depending on the Homogenization State

Abstract: In the work for this contribution, homogenization heat treatment was evaluated with respect to its effect on deformation ability of AA6063 aluminum alloy which is a widely used extrusion alloy. The samples machined from extrusion billets were homogenized at 540°C, 560°C and 580°C for a time period of 2, 4, 6, 8 and 10 h. The homogenization state of the samples was assessed via microstructure examination. The hardness of the samples was determined using Brinell hardness method. Tensile test was carried out in order to evaluate the deformation ability. Tensile strength and elongation at rupture were compared depending on the homogenization state of the alloy. Depending on the homogenization grade, the elongation at rupture was increased, and samples showed a gradual shift from brittle fracture to ductile fracture.