Search results for "Fatigue"
showing 10 items of 651 documents
New simplified approach for obtaining a reliable plateau value in fatigue analysis of bituminous materials
2017
The Plateau Value (PV) based on the Ratio of Dissipated Energy Change (RDEC) approach has been proven to provide a unique relationship with the fatigue life, N-f, independent of loading mode, temperature and frequency. In this paper, a new simplified approach is proposed to compute the unique energy parameter PV. The results of this study show that applying the proposed method allows a unique fatigue power law to be produced and eliminates the ambiguity and variability in calculating PV. However, the study also shows that the PV-N-f fatigue curves for bituminous materials are dependent on material type which is contradictory to other studies dealing with PV. The study also highlights the im…
Fatigue methodology for life predictions for the wheel-rail contact area in large offshore turret bearings
2016
The present report presents a fatigue life prediction method for large roller bearings applied in the turret turn table for large loading buoy units. The contact points between wheel and rail in these bearings are subjected to a multi-axial fluctuating stress situation and both surface wear and fatigue cracking may occur. A methodology based on the Dang Van fatigue criterion is adopted. The criterion is based on an equivalent stress defined as a combination of the fluctuation of the shear stress from its mean value at a critical plane and the associated hydrostatic stress at the given time. The present work is supporting the theoretical model by extensive laboratory testing. Both full scale…
Re-analysis of fatigue data for welded joints using the notch stress approach
2010
Abstract Experimental fatigue data for welded joints have been collected and subjected to re-analysis using the notch stress approach according to IIW recommendations. This leads to an overview regarding the reliability of the approach, based on a large number of results (767 specimens). Evidently, there are some limitations in the approach regarding mild notch joints, such as butt joints, which can be assessed non-conservatively. In order to alleviate this problem, an increased minimum notch factor of Kw ⩾ 2.0 is suggested instead of the current recommendation of Kw ⩾ 1.6. The data for most fillet-welded joints agree quite well with the FAT 225 curve; however a reduction to FAT 200 is sugg…
Covariance between components of biaxial stress state in fatigue life calculations
1992
In this paper influence of correlalions between components of random stress tensor on the calculated fatigue life of the machine element has been analysed. Two groups of covariance matrices for components of biaxial stress state were considered. The first group was arbitrarily assumed and the second one was determined on the basis of the measured strains in the element of the vibrating screen for aggregate. Computer simulation was realized with four criteria of multiaxial random fatigue. Cycles were counted with the method of rain flow and damages were cumulated according to Palmgren-Miner hypothesis. It has been shown that covariances between components of stress state tensor strongly infl…
Proof of concept of wayside railroad wheel inspection using a laser-air hybrid ultrasonic technique
2003
Non-destructive inspection of railroad wheels is performed in maintenance shops, where wheels are removed and inspected individually. No technique is yet available to the railroad industry to perform wayside inspections of wheels on a moving train. The characteristics of laser and air-coupled ultrasound are discussed to justify the use of a laser-air hybrid ultrasonic technique. Laser generation of ultrasound is combined with air-coupled detection to provide a flexible non-contact and remote technique that would enable the railroad industry to perform wayside inspections of moving railroad wheels. The present paper describes Proof of Concept set-up and results of the experiments performed a…
Proposal for a more accurate physically based S–N curve for welded steel joints
2009
Abstract The present article proposes a more accurate S–N curve in the high cycle fatigue regime for fillet welded joints in steel subjected to constant amplitude loading. The S–N curves are constructed based on a physical model of the fatigue damage evolution. It is a two phase model where the crack initiation is treated by a local weld notch approach. The subsequent growth is based on the concept of the stress intensity factor at the crack front by applying the Paris law. According to the proposed model, the time to crack initiation becomes the dominant part of the fatigue life at low stress range levels. The resulting S–N curves are non-linear for a log–log scale and they do not predict …
Fatigue life prediction under wide band random loading
2004
In this paper, a method for the high-cycle fatigue life prediction of components subjected to gaussian, stationary, wide band random loading is presented. It allows the user to evaluate the fatigue life of components subjected to uniaxial stress states directly from the stress power spectral density (PSD), avoiding onerous simulations in time domain. The proposed method can be applied to random stress processes having PSD of any shape, and the fatigue life predictions obtained are more accurate than that provided by most of the frequency domain techniques proposed in literature.
Fatigue life calculation by means of the cycle counting and spectral methods under multiaxial random loading
2005
The paper contains a new algorithm for estimation of fatigue life in HCF regime under multiaxial random loading using spectral methods. Loading of Gaussian distribution and narrow- and broad-band frequency spectra were assumed. Various characteristic states of multiaxial loading were considered. The equivalent stress history was determined with use of the failure criteria of multiaxial fatigue based on the critical plane. For determination of the critical plane position, the method of variance was applied. During simulation, the authors compared the results obtained by a spectral method in the frequency domain with those from the rain-flow algorithm in the time domain. The paper also contai…
Energy models for fatigue life estimation under uniaxial random loading. Part II: Verification of the model
2001
Abstract The paper concerns verification of the energy model for the fatigue life determination under the uniaxial random and variable-amplitude stress state. Application of the energy parameter for the fatigue life calculation using the algorithmic method under the random and variable-amplitude uniaxial tension–compression proves that most results of the fatigue life calculation are included in the scatter band with the coefficient determined during the uniaxial cyclic tests. The strain energy density parameter seems to be efficient for the fatigue life determination in the ranges of high and low numbers of cycles. The analysis was based on the author's tests and the data from literature. …
Application of an energy model for fatigue life prediction of construction steels under bending, torsion and synchronous bending and torsion
2003
Abstract The paper contains a mathematical model of the material’s behaviour under cyclic loading taking into account the dynamics of the fatigue process, including the number of cycles to failure, induced by the mean stress value. The coefficients in the proposed model have been obtained from experimental tests under symmetrical and nonsymmetrical loading (with the stress ratio R =0). The proposed model has been used in order to modify an energy criterion with the aim of accounting for the influence of the mean stress on the fatigue life. The fatigue tests have been performed for structural steels 10HNAP and 18G2A subjected to cyclic bending, torsion and synchronous bending with torsion, b…