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Showing papers on "Vibration fatigue published in 1988"


Journal ArticleDOI
TL;DR: In this paper, the authors summarized some studies in fatigue reliability research and demonstrated how reliability methods can be effectively utilized by designers to avoid fatigue in marine structural components. But, they did not consider the impact of variable amplitude stresses.

108 citations


Journal ArticleDOI
TL;DR: In this article, a review of uncertainties involved in fatigue life predictions by fracture mechanics is presented with particular reference to steel structures, including uncertainties in loading, initial and critical defect sizes, material parameters, and in the uncertainty related to computation of the stress intensity factor.
Abstract: For offshore structures the fatigue limit state is governing the structural dimensions of several members and joint connections. Safety against fatigue failure is achieved through a combination of design requirements and performance of in-service inspections with repair of detected fatigue cracks. A review of uncertainties involved in fatigue life predictions by fracture mechanics is presented with particular reference to steel structures. Sources of uncertainties considered are: environmental conditions, hydrodynamic loading, global structural analysis, local stress calculation at fatigue sensitive points, and fatigue crack growth modeling by fracture mechanics. A probabilistic model using the fracture mechanics in probabilistic form is presented. This model accounts for uncertainties in loading, initial and critical defect sizes, material parameters, and in the uncertainty related to computation of the stress intensity factor. Failure probabilities are computed by first-order reliability methods and sensitivity factors are determined. Model updating based on in-service inspection results is formulated. Uncertainties with respect to detecting a crack and to correctly sizing a crack are included. Experience on application of the analysis method is presented.

71 citations


Journal ArticleDOI
TL;DR: In this paper, a bulk deformation fatigue model is used to estimate the fatigue life of a component or a structure without explicitly modeling the detailed mechanisms of the fatigue process; however, these models must reflect the physical process.
Abstract: Bulk deformation fatigue damage models assume that the stresses and strains at the critical location of the component or structure govern the fatigue life. They allow engineering estimates of fatigue life to be made without explicitly modeling the detailed mechanisms of the fatigue process. To be successful, however, these models must reflect the physical process. Observations of fatigue cracking behavior show that fatigue damage is dependent upon the loading mode, the strain amplitude and the type of material. The cracking behaviors of AISI stainless steel 304, SAE 1045 steel and Inconel 718, tested in tension and torsion, are used to identify the development of damage in these materials for various strain levels. Damage develops either on planes of maximum shear strain or on planes of maximum tensile strain. Identification of the damage in these materials then allows estimates of the lifespan to be made for complex multiaxial loading using an appropriate bulk deformation model. Multiaxial fatigue tests results, including mean stress effects, are presented and successfully correlated with the model that incorporates the dominant or controlling damage parameter.

53 citations


Dissertation
01 Dec 1988
TL;DR: In this article, the authors used power spectral density (PSD) data for estimating the fatigue damage of structures or components subjected to random loadings, and derived a theoretical solution for the prediction of rainflow ranges using statistics computed directly from PSD plots.
Abstract: The work in this thesis outlines the use of power spectral density data for estimating the Fatigue Damage of structures or components subjected to random loading. Since rainflow cycle counting has been accepted as the best way of estimating the fatigue damage caused by random loadings, an obvious target was a method of obtaining the rainflow range distribution from the PSD. Such a solution is derived in this thesis. It forms the major part of the work presented and appears in chapter 5. The rest of the thesis deals with the following topics; Chapter 3 first presents some empirical solutions developed by other authors for the prediction of rainflow ranges from PSD's. An empirical solution developed by Dirlik in 1985 is then used to investigate the effect that stresses contained within a given frequency range have on fatigue damage when there are other frequencies present in the PSD plot. This can be thought of as 'fatigue damage potential'. Interactions between stresses in different frequency intervals are investigated and it is shown that the fatigue damage potential of one frequency interval is dependent not only on the magnitude of that interval but on the magnitudes of other frequency intervals present. This 'Interaction' effect within the PSD plot, is of specific interest because it can be used to determine the change of fatigue damage for any given structure or component when parts of the signal or PSD plot are altered. Chapter 4 is concerned with methods of regenerating a signal from a PSD in the form of a set of peaks and troughs. Work by Kowalewsld in 1963 is introduced which gives a solution for the joint distribution of peaks and troughs. This distribution can be used to generate a continuous set of adjacent peaks and troughs, of any length, using Monte-Carlo techniques. Approximations in this result are discussed, in comparison with the (distribution of times between) zero crossings problem. An improvement to this joint distribution of peak and troughs is given which uses an empirical solution for the distribution of 'ordinary ranges' (ranges between adjacent peaks and troughs). Chapter 5 forms the major part of the original work presented in this thesis and outlines a theoretical solution for the prediction of rainflow ranges using statistics computed directly from the power spectral density plot. The rainflow range mechanism is broken down into a set of logical criteria which can be analyzed using Markov process theory. The dependence between extremes in this instance is modelled using the prediction of the joint distribution of peaks and troughs proposed by Kowalewsld, and shown in chapter 4. Chapter 6 deals with the fatigue damage assessment and stress history determination of components when only limited samples of the service data are available. An investigation is carried out into the relative merits of time and frequency domain techniques. In particular, the effect of finite sample length was investigated with particular reference to the variance of fatigue predictions using both a rainflow count on a limited time sample and a rainflow count produced directly from a PSD of the same time sample. The frequency domain approach is shown to be at least as accurate as the direct time domain approach. Chapter 7 deals with one specific area where the methods presented in this thesis are applicable, namely, dynamically sensitive offshore structures. Various methods of fatigue damage assessment are highlighted, followed by a detailed description of the 'deterministic/spectral' approach. Many factors which have not previously been recognised are investigated and shown to have significant effect, for instance, tidal effects.

45 citations


Journal ArticleDOI
TL;DR: In this article, the amplitude and phase of the changes in the vibration due to a fatigue crack in a tooth was determined by an existing digital signal processing technique for calculating the amplitude of the tooth meshing vibration from the time domain average of the vibration.

45 citations


Journal ArticleDOI
TL;DR: In this paper, a simple model to handle fatigue-life length problems is discussed, which combines the Palmgren-Miner rule with time invariance, and is applied to situations with both random strength and random load.
Abstract: A simple model to handle fatigue-life length problems is discussed. The characteristic property of the model is that it combines the Palmgren-Miner rule with time invariance. The model is applied to situations with both random strength and random load. The randomness in the life is generated by the random strength and not by the random load. The only property of the random load that affects the life is its damage intensity, which is independent of the particular realization in the ergodic-load case. The damage intensity is even independent of the distribution of the random function, provided its level-crossing intensity is known. Particular attention is given to simple random strength models. In general, the exhaustion density is a random function, but in the simple models the only randomness that appears in the strength is either randomness in the time scale or randomness in the amplitude scale. The model is well-suited for comparative calculations under different load conditions, since it connects fatigue life for random loads to fatigue life for periodically oscillating loads, which is usually measured in experiments. >

20 citations


Patent
18 Oct 1988
TL;DR: In this article, the authors proposed a testing machine consisting of a substrate 2 fixed perpendicularly at the center part of a surface plate 11, a thin-film exciting mechanism part provided to the substrate 2, a thinner-film tension mechanism part, a displacement measuring instrument 9, and a controller 12.
Abstract: PURPOSE:To conduct a tension fatigue test and a vibration fatigue test by one testing machine by adding a vibration fatigue testing function to a tension testing machine. CONSTITUTION:This testing machine consists of a substrate 2 fixed perpendicularly at the center part of a surface plate 11, a thin-film exciting mechanism part provided to the substrate 2, a thin-film tension mechanism part, a displacement measuring instrument 9, and a controller 12. Further, the thin-film exciting mechanism part consists of a laminate piezoelectric element 1 as an excitation source, a joint 3, a metallic fixture 5 where one end of the thin film 4 is fitted and clamped, etc. Further, the thin-film tension mechanism part consists of a metallic fixture 7 where the other end of the thin film 4 is fitted and clamped, a load transducer 6, a linear moving device 8, etc. A displacement measuring instrument 9 measures the movement displacement of the device 8 and consists of, for example, an optical sensor to measure the displacement from the quantity of reflected light. The controller 12 performs extension- contraction driving control over the element 1, up-down movement control over the device 8, the data input processing of the load transducer 6, and the data input processing of the displacement measuring instrument 9 and are provided with respective start switches for driving the linear moving device and the laminate piezoelectric element.

9 citations


01 Jan 1988
TL;DR: In this article, a pile platform was installed in 1982 approximately 60km offshore the Hook of Holland, at the entrance of the Rotterdam harbor channel, in 32m water depth.
Abstract: A simple pile platform was installed in 1982 approximately 60km offshore Hook of Holland, at the entrance of the Rotterdam harbour channel, in 32m water depth. The platform is being used for the continuous measurement of oceanographic and meteorological data and is normally unmanned. In the autumn of 1986 a long term measuring program of the structure was carried out in order to determine horizontal accelerations at deck level. Analysis of the data showed a strong relation between the magnitude of the horizontal accelerations and tidal variations, in particular when tidal current coincided with the direction of wave propagation. The obvious explanation of this phenomenon is that the change on frequency of encounter of the waves due to tidal current leads to an appreciable increase in wave energy input at the natural frequency of the platform. As a consequence, the fatigue life of the platform may be affected. Calculation of the fatigue life of the platform by means of a simplified spectral fatigue analysis confirmed the findings. The paper describes the relevant results of the in-situ measurements (including the estimate of the total damping), the simplified spectral calculation procedure (stress transfer function determined in the time domain in regular waves, linearisation, combination with scatter diagram) and the resulting fatigue life estimate. The effects of current are illustrated and discussed.

7 citations


Journal ArticleDOI
TL;DR: In this paper, the fatigue design curves of steel highway bridges were analyzed parametrically under computer simulated variable amplitude stresses, and the fatigue limit for each joint was defined by using estimated fatigue life curves and Miner's rule.
Abstract: Fatigue design curves of steel highway bridges were analyzed parametrically under computer simulated variable amplitude stresses. Crack propagation life of 4 types of welded joints was estimated by applying the constant amplitude da/dN-ΔK relationship and the liner cumulative damage rule. The configuration of fatigue life curves under variable amplitude stresses varied with the traffic constitution and the beam span particularly in the longer life region. The fatigue limit under variable amplitude stresses for each joint could be defined by using estimated fatigue life curves and Miner's rule.

3 citations


Book ChapterDOI
TL;DR: In this article, the authors present the current state in the development of a new three-dimensional elastic-plastic FEM-based fatigue analysis concept, FEMFAT, using a material model according to MrOz's proposal, and the fatigue damage is calculated on the basis of the plastic work as performed at the fatigue critical locations of components.
Abstract: In order to minimize the expenses of the development of engineering components and to reduce the risk of their operation, reliable fatigue life prediction methods have to be available in the design stage. Presently two groups of methods can be distinguished which explicitly account for the local stresses/strains in the fatigue critical areas: the so-called notch analysis concepts or "local approaches," and new developments which are based on finite element methods (FEM). In the first part of the paper typical areas in application of the notch analysis methods and some aspects of their further development are described. The significance of the short crack stage is briefly characterized from a physical and an engineering point of view. In the second part the present state in the development of a new three-dimensional elastic-plastic FEM-based fatigue analysis concept, FEMFAT, is described. FEMFAT uses a material model according to MrOz's proposal, and the fatigue damage is calculated on the basis of the plastic work as performed at the fatigue critical locations of components. A calculation scheme for the damage increments under arbitrary out-of-phase loading based on uniaxial data is proposed. Two examples of the application of FEMFAT are given.

2 citations


Patent
05 Dec 1988
TL;DR: In this paper, a relative amplitude detecting means 40 calculates the peak value of relative amplitude deltaR within a range of measurement time T from the amplitudes delta1 and delta2 and vibration frequency (f) of the piping 1 detected by a vibration detecting meter 31 and a vibration meter 32 for comparison detection and a reference amplitude deltaS is calculated 50 from an equation II based upon the vibration frequency, external diameter, distance, Young's modulus E, service life, and safety factor S; and a display means 34 displays danger, caution, or safety according to the result of
Abstract: PURPOSE:To miniaturize a device and to automatize an operation by performing security evaluation corresponding to a wide vibration frequency region and the frequency of vibrations and further corresponding to the external diameter and length of piping. CONSTITUTION:When the security of the piping 1 is evaluated, evaluation conditions are set on a console panel 20 by using respective dials 52A, 51A, and 45A for external diameter setting, distance setting, and measurement time setting. Then a relative amplitude detecting means 40 calculates the peak value of a relative amplitude deltaR within a range of measurement time T from the amplitudes delta1 and delta2 and vibration frequency (f) of the piping 1 detected by a vibration detecting meter 31 and a vibration meter 32 for comparison detection and a reference amplitude deltaS is calculated 50 from an equation II based upon the vibration frequency (f), external diameter (d), distance (l), Young's modulus E, service life, and safety factor S; and a display means 34 displays danger, caution, or safety according to the result of comparison 33 between the amplitude deltaS and deltaR.

Book ChapterDOI
01 Jan 1988
TL;DR: In this paper, it is shown that sequence effects can lead to significant accelerations of the fatigue damage process, not only for metallic materials but also for other types of materials, such as the damage tolerant hybrid composite ARALL and fibre reinforced plastics.
Abstract: The fatigue damage accumulation under variable amplitude loading conditions is significantly influenced by load sequence effects. It is shown that sequence effects can lead to significant accelerations of the fatigue damage process, not only for metallic materials but also for other types of materials, as the damage tolerant hybrid composite ARALL and fibre reinforced plastics. The parameters which are commonly used for fatigue life analysis methods are briefly described. It is then discussed that the actual physical damage phenomena, as they occur at the different types of materials, exhibit significant similarities after the influences of the presently known mechanics contributions are eliminated, despite of the fact that the microstructures are very different. In the last part of the study engineering fatigue life prediction methods are discussed.

Journal ArticleDOI
TL;DR: In this article, a method for estimating the residual fatigue life of three dimensional crack body under cycle loadings with varying amplitude is provided, where the boundary element method is employed to calculate the weighted function.

Book ChapterDOI
01 Jan 1988
TL;DR: In this article, the two-parameter Weibull distribution and the Basquin-equation were used to define a scatter band function to predict the fatigue behavior of other components as tested.
Abstract: The two-parameter Weibull-distribution and the Basquin-equation was used to define a scatter band function. This function enables to predict the fatigue behavior of other components as tested. To apply the theory, the following assumptions must be true for all components under consideration: The fatigue crack must nucleate from the surface, the material, the state of the surface and the stress history (stress-time dependence) must be the same.

Journal Article
TL;DR: In this paper, the effect of amplitude variability of the loading process on the fatigue life of steel specimens has been investigated under variable amplitude loadings to determine the extent to which fatigue life is affected by the rate of variation of loadings.
Abstract: Welded steel specimens have been tested under variable amplitude loadings to determine the extent to which fatigue life is affected by the rate of amplitude variability of the loading process. It appears that the rate of variation can significantly change the rate of fatigue damage. Comparisons have been made between the experimental results and commonly used analytical techniques such as the Rayleigh approximation and the rainflow analysis.

Journal Article
TL;DR: In this paper, the authors deal with some basic aspects of the randomloading process and point out certain changes occurring within a wide range of stress intensities, such as are observed during fatigue of large structures, for example, pressure vessels, ships, oil platforms, and bridges.
Abstract: Constant amplitude fatigue tests have been used in practical engineering for many years; they are well developed and satisfactory. However, under random loading a number of factors may have an unexpected and often significant effect on the crack growth response. Hence these factors require a detailed consideration. This paper deals with some basic aspects of the random loading process and points out certain changes occurring within a wide range of stress intensities, such as are observed during fatigue of large structures, for example, pressure vessels, ships, oil platforms and bridges.