An analysis of fretting-fatigue failure combined with numerical calculations to predict crack nucleation (original) (raw)
Three Dimensional Finite Element Modelling of Cracks Under Fretting Fatigue Conditions
2014
The starting of crack initiation from micro-heterogeneities of the structure is often causes degradation of element’s structure. The industrial metallic materials are generally alloys of complex composition with defects (work hardening, dislocation, segregation of addition elements, grain boundaries, and porosities) which locally create an incompatibility of deformation and/or a stress concentration. Microscopic cracks can then start by accumulation of dislocation on the defect, if local crystallography is favorable there. In fretting fatigue, the application of mechanical under pressure contact during the complex loading of fretting fatigue involves cracks born from crystallographic dislocations. In order to understand and to enrich knowledge of the fretting fatigue phenomenon, a complete study of the parameters of elliptical inclined cracks by three dimensional Finite Element Method under conditions of fretting fatigue with complete contact was carried out. An initial crack was su...
Fretting-contact-induced crack opening/closure behaviour in fretting fatigue
International Journal of Fatigue, 2016
Fretting fatigue experiments and finite element analysis of stainless steel (SUS316L) were performed to investigate the crack opening/closure behaviour of a fretting fatigue crack. The crack nucleated at the location of the maximum shear stress range and then propagated in the maximum tangential stress range direction. The crack path could be successfully predicted based on the criterion of the maximum tangential stress range. A crack opening under compressive bulk stress was found in both the experiment and finite element analysis. The crack opening was induced by the restraint of deformation of one side of the crack surface due to the fretting contact. The predicted fatigue lives without consideration of crack opening were significantly longer than those of the experimental results, while the predicted fatigue lives with consideration of crack opening were in good agreement with the experimental results.
Numerical Estimation of Fretting Fatigue Lifetime Using Damage and Fracture Mechanics
Tribology Letters, 2013
Fretting fatigue is a complex tribological phenomenon that can cause premature failure of connected components that have small relative oscillatory movement. The fraction of fretting fatigue lifetime spent in crack initiation and in crack propagation depends on many factors, e.g., contact stresses, amount of slip, frequency, environmental conditions, etc., and varies from one application to another. Therefore, both crack initiation and propagation phases are important in analysing fretting fatigue. In this investigation, a numerical approach is used to predict these two portions and estimate fretting fatigue failure lifetime under a conformal contact configuration. For this purpose, an uncoupled damage evolution law based on principles of continuum damage mechanics is developed for modelling crack initiation. The extended finite element method approach is used for calculating crack propagation lifetimes. The estimated results are validated with previously reported experimental data and compared with other available methods in the literature.
An investigation of fatigue damage development under complete contact fretting test conditions
2016
In this paper evolution equation based multiaxial fatigue model is applied to the analysis of fretting fatigue of a cantilever test specimen made of EN 10083-1 steel. The adopted high-cycle fatigue model is based on the concept of evolving endurance surface and damage evolution equation. For the endurance surface a simple linear relationship between the hydrostatic stress and the reduced deviatoric stress is used. It is observed that such a simple relationship does not model the fretting fatigue phenomena properly due to the high compressive hydrostatic stress state at the contact region. Also stress gradient effects should be taken into account in a more rigorous manner.
Fretting fatigue crack nucleation: A review
Tribology International, 2018
This study aims to provide an overview of numerical and experimental work, related to crack nucleation under fretting fatigue conditions. In fretting fatigue, multiaxial loads and severe stress gradients are present at the contact interface, which can lead to failure. The damage process, in general, is considered as a two-phase phenomenon, namely, nucleation and propagation. Various damage models and approaches are available in literature to model each phase. In the present work, different criteria, related to nucleation phase, are classified based on the approach used to define failure. These approaches include, critical plane approach, stress invariant approach, fretting specific parameters and continuum damage mechanics. Apart from theoretical background, the work related to the applications of these approaches to fretting fatigue problems is also presented. It is observed that, to analyse various aspects, intricate details near the contact interface and mechanisms involved in fretting fatigue, the strength of finite element method can be employed. In the light of numerical and experimental observations, comparison between different approaches, common sources of errors in prediction and generalized conclusions are presented.
Prediction of the crack extension under fretting wear loading conditions
International Journal of Fatigue, 2006
Fretting is associated with small amplitude oscillatory movements between two surfaces in contact. One possible consequence of fretting is the formation and subsequent growth of cracks at the edges of the contact. This paper presents an experimental investigation of the cracking behaviour under fretting loading of two different aluminium alloys: 2024-T351 and 7075-T651. Systematic and controlled experiments with a cylinder-flat contact under partial slip fretting conditions were carried out. A model which combines both crack nucleation and propagation processes is used to predict the crack extension throughout the life of the component. The direction of crack propagation experimentally observed was taken into account by the model. Furthermore, an analytical prediction of crack nucleation based on the process volume approach is made. The predictions of both crack extension and nucleation are compared with the experimental results, and show good agreement.
Analysis of initial crack path in fretting fatigue.PDF
The initial crack path is analysed in a fretting fatigue test with cylindrical contact, where there is a stress gradient and a multiaxial and non-proportional stress state. For this, a cylindrical pad is pressed, with a constant normal load, N, against a dog-bone type fatigue test specimen. Then, the test specimen is subjected to a cyclic axial stress, σ. Due to the cyclical axial stress, the assembly used and the friction between the contact pair, a tangential cyclic load Q is generated. In these tests, both components are made of Al7075-T651 alloy. The crack initiation path along the fracture surface is optically measured using a focus variation technique. The contact stress/strain fields obtained analytically, in junction with the Fatemi-Socie (FS) and Smith-Watson-Topper (SWT) multiaxial fatigue parameters, allow us to determine the controlling parameters of the crack initiation process observed in the tests and to estimate the crack path during the early stage of the crack growth.
Engineering Fracture Mechanics
Finite element analysis was carried out to evaluate the stress and strain on flat-on-flat contact interface as well as around crack tip in fretting fatigue at various contact pressures. The crack path in fretting fatigue could be successfully estimated based on the maximum tangential stress range criterion. While, the fretting-fatigue lives could be successfully predicted by using the effective maximum tangential stress intensity factor range. At stress amplitudes higher than 300 MPa, the predicted lives tended to become longer than the experimental results due to the large plastic zone at crack tip.
A fatigue endurance criterion in two stages with application to fretting contact
Tribology International, 2009
In this paper we propose a fatigue endurance criterion suitable for mechanical components under high stress gradients. It is composed of two stages in order to predict both short and long crack arrest. In the first stage, a non-local multiaxial fatigue criterion measures the potential for crack initiation/short crack arrest. In the second stage, linear elastic fracture mechanics is used to evaluate the possibility of long crack arrest. The predictions of the fatigue criterion are compared with available experimental data obtained with cylinder-flat contacts under partial slip, fretting wear conditions. The results show that the proposed criterion can describe the endurance mechanisms observed in the experimental data.
Tribology International, 2018
In fatigue problems, an accurate estimation of the propagation direction is important for life prediction. We identify the most relevant factors that affect the crack orientation during the propagation stage of fretting fatigue cracks, arising from complete contacts. Contrary to what initially expected, parameters such as normal load, cyclic bulk load, etc. do not have a noticeable influence on the orientation. However the relative Young's moduli of indenter/specimen materials, the indenter width and the surface coefficient of friction are the most influencing factors. Analyses are performed through the extended finite element method (X-FEM) and an orientation criterion for non-proportional loading proposed by the authors. Experimental fretting fatigue tests confirm the predicted trends. An explanation of this behaviour is also given.