High Cycle Fatigue Prediction Research Articles

High cycle fatigue prediction of glass fiber-reinforced epoxy composites: reliability study

The aim of this paper is to develop a probabilistic approach of high cycle fatigue (HCF) prediction of glass fiber-reinforced epoxy composites by taking into account the modifications induced by the variation of the loading parameters (stress and number of cycles) and those of the material parameters (fiber Young’s modulus and fiber volume fraction). Using fatigue curve analytical expression and Monte Carlo simulation assessment, probabilistic Wohler curves are plotted to predict the high cycle fatigue behavior of the material. In this regard, four cases are studied by varying the hypothesis for the stress and number of cycle values to be probabilistic or deterministic. The design of experiment (DoE) techniques are used in this work by varying the factors of interest in a full factorial design to evaluate the effect and the interaction of some factors influencing the fatigue reliability. The controlled input factors of the process are traduced by (i) the materials’ parameters represented by the variation of fiber and matrix Young’s moduli (E f and E m ) and the fiber volume fraction (V f ) and either traduced by (ii) the loading parameters represented by the applied stress and number of cycles.

Prediction of multiaxial high cycle fatigue at small scales based on a micro-mechanical model

An approach for prediction of high cycle fatigue (HCF) at a length scale of 5–100μm is established, which evaluates the accumulated plastic shear strain in slip bands of grains. Damage mechanisms initiated by dislocations and the grain microstructure are the key factors that influence the fatigue of metals in small dimensions. For this reason the HCF model considers the elasto-plastic behavior of metals at the grain level and microstructural parameters, specifically grain size and grain orientation. The HCF model can be applied either as a criterion for deterministic predictions of the failure in individual grains, or as a failure function in probabilistic studies on aggregates of grains, if the input parameters are given by specific distributions. This is addressed in a parameter study and a sensitivity analysis of the failure function with respect to different parameters. For model verification, the predicted results of the failure function are compared with the observed micro-damage in individual grains of nickel micro-samples. It is shown that the overall predictive power of the HCF model is fairly good. Nevertheless, some misclassifications occur as some grains are damaged, which were predicted to be safe. Those misclassifications are addressed in post-fatigue investigations on individual grains.

A probability method for prediction on High Cycle Fatigue of blades caused by aerodynamic loads

A probability method for prediction on High Cycle Fatigue (HCF) of blades caused by aerodynamic loads (PHBA) is erected and two approaches are adopted: improving the numerical method to obtain the dynamical responses of blades caused by aerodynamic loads and introducing probability theory into predicting HCF. The basic governing equations of fluid domain, solid domain and fluid-solid interface are given for flow-blade interaction system. Furthermore a numerical method named bidirectional sequential method is illuminated, and the corresponding physical process of vibration from unsteady state to steady state is described. The dynamical response can be obtained by this time domain method conveniently by the use of commercial softwares. Then PHBA is put forward based on vibration stress according to the probabilistic accumulative damage model. Finally an engineering sample is discussed to illuminate PHBA flow clearly. PHBA is performed on two types of second-stage stators to evaluate the operation security, thus the probabilistic accumulative damages altering with operation time are calculated, and the operational reliabilities are also obtained. The results can describe the possibility of HCF intuitively and quantitatively, which shows PHBA is very helpful in the HCF prediction and failure analysis.

Competition between mesoplasticity and damage under HCF – Elasticity/damage shakedown concept

The aim of this paper is to present new modelling dedicated to multiaxial high cycle fatigue (HCF), and applied to polycrystalline metals. The model presented is based on the experimental characterization of damage during HCF tests, under pure tension and torsion modes. The origin of this approach is a mesoscopic model considering three plastic behaviour stages (hardening, saturation and softening) suggested by Papadopoulos [Papadopoulos I.V. Fatigue limit of metals under multiaxial stress conditions: the microscopic approach. Technical Note No. I.93.101, Commission of the European Communities, Joint Research Centre; 1993. [ISEI/IE 2495/93].], and used by Morel [Morel F. A critical plane approach for life prediction of high cycle fatigue under multiaxial variable loading. Int J Fatigue 2000;22:101–119.]. The principal evolution brought in by this study is a competition description during all the sample lifetime of the plasticity and damage effects. The plasticity mechanisms induce a hardening saturating effects (resulting from movement and accumulation of dislocations), especially significant at the beginning of the crystal life. Damage, present at the end of crystal lifetime, is considered as a degradation process inducing a strong reduction of the crystal ductility, leading to its failure (decohesion). The coexistence and the competition between these two effect (hardening and damage-induced softening) describe cyclic crystal behavior, including shakedown phase. The model is formulated in the framework of the continuum damage mechanics, according to the identified physical mechanisms during the tests. The second purpose is to compare the model predictions with experimental data, after identification of the parameter for a ferritic-pearlitic steel. The case of in-phase loading is merely studied here. In particular, the evolution of a few internal variables is discussed and correlated with the available physical features. It is shown that this model provides a complementary insight into a crystal with respect to the endurance criterion of Dang Van. The model predicts, in a particular stress amplitude range, the damage growth arrest.