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Multiaxial Fatigue (multiaxial + fatigue)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

Multiaxial fatigue of rubber: Part I: equivalence criteria and theoretical aspects

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 6 2005
W. V. MARS
ABSTRACT This paper investigates commonly used approaches for fatigue crack nucleation analysis in rubber, including maximum principal strain (or stretch), strain energy density and octahedral shear strain criteria. The ability of these traditional equivalence criteria, as well as a recent equivalence criterion (the cracking energy density) to predict multiaxial fatigue behaviour is explored. Theoretical considerations are also introduced relating to the applicability of various fatigue life analysis approaches. These include the scalar nature of traditional equivalence criteria, robustness of the criteria investigated for a wide range of multiaxial loadings, effects of crack closure and applications to non-proportional multiaxial loadings. It is shown that the notion of a stress or strain amplitude tensor used for the analysis of multiaxial loading in metals is not appropriate in the analysis of rubber due to nonlinearity associated with finite strains and near incompressibility. Taken together, these considerations illustrate that traditional criteria are not sufficiently consistent or complete to permit confident analysis of arbitrary multiaxial loading histories, and that an analysis approach specific to the failure plane is needed. Of the three traditional criteria, maximum principal strain is shown to match most closely to the cracking energy density criterion, in terms of a failure locus in principal stretch space. [source]

Multiaxial fatigue of welded joints under constant and variable amplitude loadings

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2001
C. M. Sonsino
Flange-tube joints from fine grained steel StE 460 with unmachined welds were investigated under biaxial constant and variable amplitude loading (bending and torsion) in the range of 103 to 5,×,106 cycles to crack initiation and break-through, respectively. In order not to interfere with residual stresses they were relieved by a heat treatment. In-phase loading can be treated fairly well using the conventional hypotheses (von Mises or Tresca) on the basis of nominal, structural or local strains or stresses. But the influence of out-of-phase loading on fatigue life is severely overestimated if conventional hypotheses are used. However, the hypothesis of the effective equivalent stress that is introduced leads to fairly good predictions for constant as well as for random variable amplitude loads. Therefore, the knowledge of local strains or stresses is necessary. They are determined by boundary element analyses that are dependent on weld geometry. This hypothesis considers the fatigue-life-reducing influence of out-of-phase loading by taking into account the interaction of local shear stresses acting in different surface planes of the material. Further, size effects resulting from weld geometry and loading mode were included. Damage accumulation under a Gaussian spectrum can be assessed for in- and out-of-phase combined bending and torsion using an allowable damage sum of 0.35. [source]

A fatigue criterion for general multiaxial loading

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2000
Jiang
An incremental fatigue damage model is proposed. The model incorporates the critical plane concept in multiaxial fatigue, plastic strain energy and material memory in cyclic plasticity. With an incremental form the model does not require a cycle counting method for variable amplitude loading. The model is designed to consider mean stress and loading sequence effects. Features of the new model are discussed and the determination of material constants is detailed. Verification of the model is achieved by comparing the predictions obtained by using the new model and experimental data of four materials under different loading conditions. [source]

Lebensdauerermittlung bei mehrachsigen wechselnden Beanspruchungen im niedrigen und hohen Temperaturbereich

MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 9 2003
E. Roos
multiaxial fatigue; creep fatigue; stress theories; material laws Abstract Zur Berechnung der Dauerfestigkeit von Bauteilen aus duktilen Werkstoffen bei komplexer Schwingbeanspruchung stehen unterschiedliche Verfahren zur Verfügung. Hierbei wird im Wesentlichen zwischen den Festigkeitshypothesen der Integralen Anstrengung und denen der Kritischen Schnittebene unterschieden. Als typische Repräsentanten werden die Schubspannungsintensitätshypothese (SIH) sowie die Methode der kritischen Schnittebene (MKS) ausgewählt und für körperfeste und nicht körperfeste Hauptspannungsrichtungen gegenübergestellt. Für synchrone Beanspruchungen wird darüber hinaus das Berechnungsverfahren mit dem Anstrengungsverhältnis nach Bach verglichen. Die Berechnungsmethodik wird deutlich komplexer, wenn zeitabhängige Werkstoffeigenschaften bei entsprechend hohen Temperaturen mit in die Betrachtung einbezogen werden müssen. Für diesen Fall wird die Anwendung von viskoplastischen Stoffgesetzen erforderlich, die eine Beschreibung von Kriechen und Ermüdung in Kombination ermöglichen. Am Beispiel eines modifizierten Werkstoffmodells nach Chaboche / Nouailhas wird die Berechnung mehrachsiger Kriechermüdungsversuche vorgestellt. Life time assessment on multiaxial cyclic loadings at low and high temperatures For the calculation of fatigue strength of components made out of ductile materials under complex cyclic load different assessments are present. As typical representatives of stress theories the shear stress intensity hypothesis (SIH) as well as the method of critical plane approach (MKS) are considered and compared for rigid and non rigid principle stress directions. Furthermore for synchronous loads the calculation methods are compared with Bach's method. The calculation method becomes more complex, if time dependent material properties at corresponding high temperatures have to be taken into account. In this case the application of viscoplastic material models is necessary, which allows the consideration of combination of creep and fatigue. As an example a modified material model by Chaboche / Nouailhas is used in order to present the calculation of multiaxial creep fatigue tests. [source]