Showing papers on "Vibration fatigue published in 1990"

Improved Spectral Method for Variable Amplitude Fatigue Prediction

Abstract: The dependence of fatigue damage accumulation on power spectral density (psd) is investigated for several types of random processes relevant to the stresses in offshore structures. Representative data have been obtained from rain‐flow analysis of time histories simulated from both unimodal and bimodal psd functions. These data are used to test the accuracy of spectral approximation methods in which the damage predictions are made from fairly simple calculational operations on the psd function. Primary emphasis is placed on the commonly used Rayleigh approximation method and a new method that involves calculation of only one spectral moment (i.e., one integral of the psd). The new method is shown to be substantially more accurate than the Rayleigh approximation for some situations.

Fatigue damage properties of asphaltic concrete pavements

Abstract: The development of material property relations for the two fatigue damage properties, K sub 1 and K sub 2, which can be used to predict the fatigue life of asphaltic concrete pavements, is described. The fatigue damage properties developed are based on the theory of fracture mechanics along with regression analysis on published beam fatigue data and, thus, can take into account crack initiation, propagation, and material properties that are not accounted for with the conventional strain-based fatigue equation. The approach provides more insight into how these fatigue damage properties reflect the fatigue behavior of asphaltic concrete pavement while producing acceptable estimates of field fatigue life. Derivations have shown that the fatigue damage property K sub 1 is dependent on the asphalt mixture and pavement properties, such as the parameters of the Paris crack growth law, elastic stiffness, and thickness of the asphaltic concrete layer and that the fatigue damage property K sub 2 varies with the initial asphalt cement properties, such as asphalt content, viscosity, penetration, and temperature. Two significant functions of the fatigue damage properties developed are (a) the prediction of fatigue life allows for the application of loading with single or dual tires on single, tandem, or triple axles, and (b) they provide for the calculation of load equivalence factors for fatigue life as affected by multiple-axle loads. A shift factor that can be used to adjust the laboratory (or calculated) fatigue damage properties to that measured in the field is also described. This factor takes into account healing and residual stresses between applications of traffic loads that are responsible for the difference in fatigue life between laboratory test results and those measured in the field.

Fatigue of Concrete under Random Loadings

Abstract: A fatigue model is presented for plain concrete subjected to random loadings in compression. Hysteretic nonlinear behavior of concrete is incorporated to express the cumulative fatigue damage in terms of the residual plastic strain. A dual-coordinate system is used to model the envelope curve in compression and the hysteresis loops within the envelope curve. The equivalent linearization technique is utilized to obtain the root-mean-square (RMS) response statistics of hysteretic nonlinear behavior of concrete. Available fatigue test data are analyzed to obtain an optimal form of damage function and calibrate the model. Constant amplitude and random loading tests are used for this purpose. A practical formulation is presented to evaluate fatigue failure probability based on the assumption that the loadings are narrow-banded Gaussian processes. The variabilities both in loading and capacity are incorporated in the formulation. The method can be used to evaluate the fatigue damage and failure probability of c...

Prediction of bending fatigue behaviour by the reference stress approach

Abstract: — A technique is presented for prediction of low-cycle fatigue behaviour under bending conditions from the knowledge of uniaxial fatigue data. The technique utilizes the reference stress approach used in the analysis of creeping components. The results enable determination of nominal elastic bending stress in terms of the observed saturation stress amplitude in an uniaxial fatigue test conducted at a reference value of strain amplitude. The reference parameters are determined for beams with both rectangular and circular cross-sections. The predictions of fatigue bending behaviour are in excellent agreement with closed form solutions reported recently. The merits of this alternative approach lie in its potential applicability to other structural situations once their reference uniaxial parameters are determined. Since the reference parameters are nearly the same for both creep and fatigue, the approach can be a useful experimental tool for relating creep-fatigue interaction effects in structural components with uniaxial creep-fatigue tests conducted under the reference conditions.

Fatigue of steel-reinforced elastomeric bearings

Abstract: Fatigue is an important design criterion for elastomeric bearings, but it is not well understood. This paper examines the design methods currently in use for controlling fatigue. Twenty‐six fatigue tests were performed to evaluate the design methods, and the results are described here. The bearings were tested in cyclic shear or compression. Fatigue cracks formed in the rubber near the steel reinforcement, and they sometimes grew to a significant depth. The important parameters affecting fatigue life are described. Rates of crack growth and location of cracking are presented, and they are correlated with load rate, mean loading, load range, and the material properties. A design method for improving fatigue behavior is then proposed.

A New Stress-Range Distribution Model For Fatigue Analysis Under Wave Loading

Abstract: For fatigue analysis under wave loading the long-term probability distribution of stress range needs to be known The work described in this paper shows that, for any given sea-state, the short-term distribution of stress range can be closely approximated by a linear combination of two Weibull distributions A semi-theoretical technique has been devised to derive the parameters of these distributions as functions of the spectral irregularity factor The probability density function so obtained is shown to provide a close fit to the histograms of stress range obtained by simulation and rainflow counting In addition, the equivalent stress ranges obtained from this model compare very favourably with those obtained by simulation, in comparison with other empirical models, thus providing an accurate method for the prediction of fatigue damage under random loading, with minimal computational effort

Changes in modal parameters of a bridge during fatigue testing

Abstract: The effects of high-cycle fatigue on the dynamic modal properties of a full-scale bridge test section are examined in this study. A span 30.5 m (100 ft) in length was salvaged from an interstate bridge for experimental testing to establish the fatigue performance of the retrofit procedures which could be used for future field repairs of the fatigue cracks. Horizontal cracks had formed in the webs of the twin bridge girders in the vicinity of the web-flange weld at or near the connections of the girders to the floor beams. An electrohydraulic vibration shaker was used to excite the test span in the torsional and bending modes to promote fatigue crack growth. In addition to the experimental evaluation of the retrofit procedures, the dynamic response characteristics of the test span during the high-cycle fatigue test were monitored. Experimental data have been used to establish mode shapes and modal damping ratios during the four-million-cycle fatigue test. Damping ratios ranged from 1.09 percent to 0.53 percent. Modal stiffnesses were calculated based on the experimental mode shapes. There is a modest correlation between the changes in stiffness and the observed cracking of the steel girders and the subsequent repairs.

Analysis of dual control vibration testing

Abstract: Analysis of dual control vibration testing is conducted using a two-degree-of-freedom system to represent the interaction between a vibration mode of a test item and a mode of a mounting structure. The results indicate that exact dual control based on specification of the source free acceleration and blocked force is strictly valid only if phase is taken into account. However, extremal dual control without phase alleviates overtesting without risk of undertesting, when the limit acceleration and force specifications are chosen to envelope the coupled system results. Several approaches to deriving appropriate force specifications are explored. Random vibration parametric results from the literature are used to estimate the limit force between coupled oscillators with different source and load masses.

Vibrations, Dynamics and Structural Systems

Abstract: Introduction Free vibration of single degree of freedom system Forced vibration of single degree of freedom system Numerical methods in structural analysis: Applied to SDF systems Vibration of two degrees of freedom system Free vibration of multiple degrees of freedom system Free vibration analysis of continuous systems Forced vibration of continuous systems Dynamic direct stiffness method Vibration of ship and aircraft as a beam Finite element method in vibration analysis Finite difference method for the vibration analysis of beams and plates Nonlinear vibration Random vibration Computer program in vibration analysis The stiffness matrix Table of spring stiffness Index.

Testing method of vibration fatigue of stranded wire

Abstract: PURPOSE: To conduct a fatigue test of a stranded wire easily by using a vibrator for vibrating the stranded wire. CONSTITUTION: A vibrator 7 is suspended from a stranded wire 3, as a device for vibrating the stranded wire 3. When the vibrator 7 is made to vibrate in this state, the vibration is transmitted to the stranded wire 3 and the same vibration as obtained by using an exciter is obtained. When the one of an eccentric weight type is used as the vibrator 7, in this case, a force of vibration can be adjusted with ease only by moving an eccentric weight, and the amplitude and the vibration fatigue strain of the stranded wire 3 can be adjusted simply. When an inverter is used for a power source of the vibrator 7, besides, a frequency can be varied also with ease. According to this constitution, limitation on a testing place is removed and a fatigue test of the stranded wire can be executed with ease. COPYRIGHT: (C)1992,JPO&Japio

Variable amplitude load fatigue, task A - literature review; volume 3: variable amplitude fatigue behaviour

Abstract: This volume (a) reviews present fatigue design methods, (b) summarizes variable amplitude fatigue data, and (c) discusses the major parameters influencing variable amplitude fatigue behavior.

Fatigue Crack Closure Under Random Loading

Abstract: The goals of the research are to determine fatigue crack growth rates for stationary random amplitude loadings with arbitrary mean stress. Fatigue crack closure theory is applied to justify an equivalent constant amplitude R-ratio and stress range approach. The definition of the equivalent R-ratio is based on consideration of the shape of the plastic wake formed by the crack. The equivalent stress range is determined by two methods: local stress range pair counting and rainflow cycle counting.

Effect of loading frequency and cycle asymmetry on the fatigue resistance of alloy AMg, 6N

Abstract: Results are given for experimental determination of the fatigue resistance characteristics of alloy AMg6N with symmetrical and asymmetrical loading in the frequency range 35–10,000 Hz. Dependences are suggested for describing fatigue curves and limiting amplitude diagrams taking account of structural and operating factors making it possible to predict cyclic strength characteristics for the material at low loading frequencies from data for high-frequency fatigue tests.

Analysis of Fatigue Crack Propagation Under Random Loading by Markov Chain

Abstract: Fatigue crack propagation is simulated in terms of a discrete Markov process considering both the randomness of crack propagation resistance and the randomness of external loading, which are the major sources of variability of fatigue crack propagation. This stochastic simulation for fatigue crack propagation is such that the characteristics of residual life distribution and the distribution of a crack length at an arbitrary time are obtained when the initial distribution of crack length and the transition of its central tendency are given. This research is considered as the foothold to establish the appropriate stochastic model on fatigue crack propagation with more wide applications to the practical design of machines and structures.

Method for estimating occurring time of fatigue damage

Abstract: PURPOSE: To make it possible to estimate the time of occurrence of fatigue damage readily and in high evaluating accuracy by obtaining the fluctuating width of the strain of an object structure based on the time of breakdown of a thin wire. CONSTITUTION: The thin wire of a material 2, whose fatigue strength is lower than the fatigue strength of an object structure and has the known fatigue strength, is attached to the structure. The time of the breakdown of the thin wire is detected. The fluctuating width of the strain of the object structure is obtained based on the time of breakdown of the thin wire. The time of the occurrence of a crack in the object structure is further obtained from the fluctuating width of the strain. The attached material 2 indicates the lower fatigue strength in comparison with the material 2 used in the actual structure. Therefore, breakdown occurs in the attached material 2 before the occurrence of fatigue damage in the actual structure. The time of the occurrence of the fatigue damage can be estimated based on the time of breakdown, i.e. the life when fatigue occurs. When the kinds of the estimating wires (material 2) are changed and a plurality of the lines are used, the estimation of the fatigue damage can be performed in high accuracy. COPYRIGHT: (C)1992,JPO&Japio

Spectral Analysis and Fatigue Reliability Assessment for Offshore Structures

Abstract: This paper presents a cumulative fatigue damage formulation in stochastic variable space using bilinear SN model and the Palmgren-Miner's rule for evaluating the fatigue reliability of offshore structures. Statistical stress characteristics are determined from a spectral analysis procedure based on a modified modal analysis technique which ensures an exact result in the quasi-static part of the response. Uncertainties arising from different origins are characterized by representative stochastic variables in the analysis. The reliability index is calculated employing the Level II Approximate-Full Distribution method. An example is also presented to demonstrate the calculation results and sensitivities of design variables.

Testing method for vibration fatigue of stranded wire

Abstract: PURPOSE:To accurately and easily detect the fatigue rupture of element wires constituting the stranded wire by fixing an extremely thin insulated conductor which is connected to a power source to the outer periphery of the stranded wire and detecting electrically the breaking of the extremely thin insulated conductor which is caused by the rupture of the stranded wire. CONSTITUTION:The wire 1 which is held by a metallic fixture 2 by applying a specific tensile force axially is vibrated by an exciter 3 as specified and a vibration fatigue test is conducted. Then the enamel coated conductor 4 is wound around the outer periphery of the wire nearby the holding part and connected to an applied vibration controller 5. Then the wire 1 is vibrated by the exciter 3 as specified and the applied vibration controller 5 detects electrically the breaking of the enamel coated conductor 4 which is fed with electricity according to the fatigue rupture of an element wire constituting the wire 1, thereby stopping the exciter 3. Consequently, the fatigue rupture of the element wire is accurately detected and the repetitive vibration frequency up to the fatigue rupture is accurately grasped.

Propagation of physically short fatigue cracks and the life of structural elements. Report 1

Abstract: A relationship for describing the kinetics of short fatigue cracks is proposed and experimenteally confirmed on the basis of the energy two-parameter criterion of fracture. It is established that with use of this relationship it is possible to quantitatively describe the influence of the concentration and asymmetry of the stress cycle and the role of the compressive portion of the cycle and the surface layer on the kinetics of a crack and the threshold values ΔKth.

Large deflection random response of a pipe containing fluid flow subjected to random loading

Abstract: An analytic approach is developed for beam type pipes undergoing large deflections subjected to random loadings. The influence of fluid velocity on the random response is investigated. The root-mean-square (rms) deflections and frequencies for different sound spectrum level values are determined for pipes with both ends either simply supported or clamped. The required number of modes to achieve accurate rms deflections and strains is also studied. The prediction of fatigue life is then based on obtained rms maximum stress. This analytical investigation will help to broaden the basic understanding of the role of fluid flow within structures subjected to acoustic loading.