Showing papers on "Vibration fatigue published in 2010"

Monitoring-Based Fatigue Reliability Assessment of Steel Bridges: Analytical Model and Application

Abstract: A fatigue reliability model which integrates the probability distribution of hot spot stress range with a continuous probabilistic formulation of Miner's damage cumulative rule is developed for fatigue life and reliability evaluation of steel bridges with long-term monitoring data. By considering both the nominal stress obtained by measurements and the corresponding stress concentration factor (SCF) as random variables, a probabilistic model of the hot spot stress is formulated with the use of the S-N curve and the Miner's rule, which is then used to evaluate the fatigue life and failure probability with the aid of structural reliability theory. The proposed method is illustrated using the long-term strain monitoring data from the instrumented Tsing Ma Bridge. A standard daily stress spectrum accounting for highway traffic, railway traffic, and typhoon effects is derived by use of the monitoring data. Then global and local finite element models (FEMs) of the bridge are developed for numerically calculating the SCFs at fatigue-susceptible locations, while the stochastic characteristics of SCF for a typical welded T-joint are obtained by full-scale model experiments of a railway beam section of the bridge. A multimodal probability density function (PDF) of the stress range is derived from the monitoring data using the finite mixed Weibull distributions in conjunction with a hybrid parameter estimation algorithm. The failure probability and reliability index versus fatigue life are achieved from the obtained joint PDF of the hot spot stress in terms of the nominal stress and SCF random variables.

Probabilistic multiscale models and measurements of self-heating under multiaxial high cycle fatigue

Abstract: Different approaches have been proposed to link high cycle fatigue properties to thermal measurements under cyclic loadings, usually referred to as “self-heating tests.” This paper focuses on two models whose parameters are tuned by resorting to self-heating tests and then used to predict high cycle fatigue properties. The first model is based upon a yield surface approach to account for stress multiaxiality at a microscopic scale, whereas the second one relies on a probabilistic modelling of microplasticity at the scale of slip-planes. Both model identifications are cost effective, relying mainly on quickly-obtained temperature data in self-heating tests. They both describe the influence of the stress heterogeneity, the volume effect and the hydrostatic stress on fatigue limits. The thermal effects and mean fatigue limit predictions are in good agreement with experimental results for in and out-of phase tension-torsion loadings. In the case of fatigue under non-proportional loading paths, the mean fatigue limit prediction error of the critical shear stress approach is three times less than with the yield surface approach.

Comparison of some selected multiaxial fatigue failure criteria dedicated for spectral method

Abstract: The paper presents the procedure of estimation of fatigue life in the high-cycle fatigue regime under a multiaxial random loading using the spectral method. The procedure consists of application of the power spectral density function of the equivalent stress in the fatigue life assessment together with the known spectral method developed for the uniaxial stress state. The model proposed by Miles and Dirlik was presented as an example. Two groups of multiaxial fatigue failure criteria have been distinguished: the criteria based on the critical plane approach and the criteria using invariants of the stress state. Two sets of experimental data were used in order to compare the calculated and experimental fatigue lives. It has been shown that under the multiaxial random loading the results of fatigue life calculated according to the considered method are well correlated with the results of experiments if the multiaxial fatigue failure criterion is properly selected for mechanical parameters of the tested material.

Harmonic and Random Vibration Durability of SAC305 and Sn37Pb Solder Alloys

Abstract: In this paper, durability tests were conducted on both SAC305 and Sn37Pb solder interconnects using both harmonic and random vibration. The test specimens consist of daisy-chained printed wiring boards (PWBs) with several different surface-mount component styles. Modal testing was first conducted on a test PWB to determine the natural frequencies and mode shapes. The PWB was then subjected to narrow-band excitation at its first natural frequency. Electrical continuity of the daisy-chain nets was monitored to measure the time-to-failure (and hence cycles-to-failure) of the interconnects. The response history of the PWB was recorded with strain gages located near the components of interest. Finite element analysis (FEA) was conducted for each component type, to estimate the transfer function between the flexural strain of the PWB and the strain in the critical solder joint. The predicted strain transfer function was then combined with the measured PWB strain response history to estimate the strain history in the critical solder joints. The solder strain history was used, in conjunction with the failure history, to estimate lower bounds for the fatigue durability (S-N curves) of the solder interconnects. In the first part of this paper, the results show that the SAC305 interconnects are marginally less durable than Sn37Pb interconnects for the harmonic excitation range used in this paper. The durability model constants are found to be very sensitive to the solder stress-strain curve assumed in the FEA. Since the stress-strain properties reported in the literature for these solder alloys vary significantly, the solder stress-strain curves were parametrically varied in the FEA, to assess the resulting effect on the estimated S-N curves. In the second part of this paper, random-vibration tests were conducted to assess durability under step-stress, broad-band excitation. Conventional cycle counting techniques were used to quantify the random excitation histories in terms of range distribution functions. Using the same time-domain vibration fatigue analysis used earlier for narrow-band excitation, the durability trend for the corresponding SAC305 and Sn37Pb solder interconnects under broad-band excitation was found to be similar to that found earlier under harmonic vibration excitation. Comparison between the durability prediction and test results provides a good understanding of the effect of stress-strain behavior on the fatigue constants of these solder materials. The best set of material properties was then used to verify the durability of leadless chip resistor interconnects under quasi-static mechanical cycling.

Development of a fatigue model useful in ship routing design

Abstract: In this paper, a simple fatigue estimation model, only using encountered significant wave height, is used for predicting fatigue accumulation of a vessel during a voyage. The formulation of the model is developed based on the narrow-band approximation. It is assumed that the significant response range, hs, has a linear relationship with encountered significant wave height, Hs. The mean stress up-crossing frequency, fz, is represented by the corresponding encountered wave frequency and it is expressed as a function of Hs. The capacity and accuracy of the model is illustrated by application on one container vessel’s fatigue damage accumulation in an amidships detail, operating in the North Atlantic during 2008. For this vessel, all the necessary data needed in the fatigue model, and for verification of it, was obtained by measurements. The results from the proposed fatigue model are compared with the well-known and accurate rainflow analysis. Influence of nonlinearities, e.g. whipping, on fatigue damage predictions and extreme responses is also discussed.

Finite element based fatigue life prediction for electronic components under random vibration loading

Abstract: This work develops an assessment methodology based on experiments and finite element analysis (FEA) to determine the solder joint fatigue life of electronic components under random vibration loading. Specially designed PCB with Ball Grid Array (BGA) packages attached was mounted to the Electro dynamic shaker and was applied to different random vibration excitations at the supports. Meanwhile, an event detector monitored the resistance of the daisy chained circuits and recorded the failure time of the electronic components. In addition accelerometers and dynamic signal analyzer were utilized to record the time history data of both the shaker input and the PCB's response, and to obtain the transmissibility function of the test vehicles. This finite element based fatigue life prediction approach consists of two steps: The first step aims at characterizing fatigue properties of the solder joint by generating its own S-N (stress-life) curve. A sinusoidal vibration over a limited frequency band centered at the test vehicle's 1st natural frequency was applied and the time to failure was recorded. The resulting stress was obtained from the FE model through harmonic analysis in ANSYS. Spectrum analysis specified for random vibration, as the second step, was performed numerically in ANSYS to obtain the response Power Spectral Density (PSD) of the critical solder ball. The volume averaged Von Mises stress PSD was calculated out of the FEA results and then was transformed into time history data through inverse Fourier transform. Rainflow cycle counting was used to estimate cumulative damage of the critical solder joint. The calculated fatigue life based on the Rainflow cycle counting results, the S-N curve, and the modified Miner's rule agreed with actual testing results.

A new device for fretting fatigue testing

Abstract: Fretting fatigue damage occurs in contacting parts when they are subjected to fluctuating loads and sliding movements at the same time. Fretting fatigue can reduce the fatigue life of materials by half or even more. Fretting fatigue tests are usually performed using universal hydraulic testing devices. The contact pressure is produced by a fixture, typically designed and manufactured by researchers. In this investigation, a new device is introduced in which the fluctuating loading is supplied by a variable crank system (VCSD). The device called VCSD for abbreviation is basically a position control machine in which displacements can be imposed with an accuracy of 0.01 mm. The axial and contact loads are measured by load cells. The friction load is also measured by using foil strain gauges using a Wheatstone bridge configuration. The functionality of the device is examined by making a comparison between fretting fatigue lives of a number of Al7075-T6 specimens tested on a universal testing machine and VCSD. The results show a very close agreement between the functionality of the two testing rigs. The main advantages of VCSD are its higher frequency with respect to universal devices, simplicity, and cheapness. It can be developed further for high and low temperature tests in future.

Finite element procedures for the numerical simulation of fatigue crack propagation under mixed mode loading

Abstract: This paper addresses the numerical simulation of fatigue crack growth in arbitrary 2D geometries under constant amplitude loading by the using a new finite element software. The purpose of this software is on the determination of 2D crack paths and surfaces as well as on the evaluation of components Lifetimes as a part of the damage tolerant assessment. Throughout the simulation of fatigue crack propagation an automatic adaptive mesh is carried out in the vicinity of the crack front nodes and in the elements which represent the higher stresses distribution. The fatigue crack direction and the corresponding stress-intensity factors are estimated at each small crack increment by employing the displacement extrapolation technique under facilitation of singular crack tip elements. The propagation is modeled by successive linear extensions, which are determined by the stress intensity factors under linear elastic fracture mechanics (LEFM) assumption. The stress intensity factors range history must be recorded along the small crack increments. Upon completion of the stress intensity factors range history recording, fatigue crack propagation life of the examined specimen is predicted. A consistent transfer algorithm and a crack relaxation method are proposed and implemented for this purpose. Verification of the predicted fatigue life is validated with relevant experimental data and numerical results obtained by other researchers. The comparisons show that the program is capable of demonstrating the fatigue life prediction results as well as the fatigue crack path satisfactorily.

Vibration element coupled with non-linear force to improve non-resonant frequency response

Abstract: Embodiments of the invention couple a non-linear force to a vibration element such as a piezoelectric cantilever to introduce chaotic, i.e., non-resonant vibration in the vibration element and thereby improve the non-resonant response of the vibration element. By doing so, the vibration element is responsive to a wider frequency range of vibrations and thus may be more efficient in scavenging energy in environments where the vibration frequency is not constant, e.g., in environment subject to multi-mode or random vibration sources.

A Parametric Study on Effects of Environmental Loadings on Fatigue Life of Steel Catenary Risers (Using a Nonlinear Cyclic Riser-Soil Interaction Model)

Abstract: Steel catenary risers (SCRs) are often the preferred option for subsea tie-back to floating platforms in deep water due to their conceptual simplicity, ease of construction and installation and simple interface with the flowlines Fatigue design of SCRs, particularly in the touch down area (TDA), has always been one of the major engineering challenges Traditionally, fatigue assessment of SCRs has usually been highly conservative, because of lack of precise understanding of the non-linear soil-riser-interaction in the TDA Most fatigue studies are based on assumed linear stiffness for the seabed, partly because of the lack of robust non-linear riser-seabed interaction models and partly because the linear response simplifies the fatigue study The recent availability of non-linear seabed response models provides an opportunity to improve fatigue assessment, but it is first necessary to evaluate how best to conduct fatigue studies for such nonlinear systems which can be sensitive to wide range of input parameters This paper outlines a new advanced numerical model, considering nonlinear cyclic riser-soil interaction behavior, used to determine the contribution of different loading parameters on fatigue damage of SCRs in the TDA in deep water soft sediments The main loading parameters considered are: different motions of floating vessels, wave heights, wave periods and wave packs ordering Numerical modeling has shown that over 95% of the fatigue damage corresponds to floating vessel motion parallel to the riser axis at the connection point to the vessel It is also shown that riser response at TDA is highly influenced with amplitude and period of the environmental loadingsCopyright © 2010 by ASME

New Multiaxial HCF Criteria Based on Instantaneous Fatigue Damage Tracing in Components with Complicated Geometries and Random Non-Proportional Loading Conditions

Abstract: Majority of the available high-cycle fatigue (HCF) criteria have been proposed based on definition of an equivalent stress. Although these criteria have shown good agreements with results of the fa...

Analysis of Fatigue Damage at Wheel under Variable Load

Abstract: The variable fatigue load is simulated in this study. The stability and the life of the material are analyzed theoretically by Ansys program. These results are successfully applied to the practical wheel to predict the prevention of fracture and the endurance. The life and the damage on the every part of the fatigue specimen can be predicted. As the available lives are compared for every loading variation, the rain flow and damage matrix results can be helpful in determining the effects of small stress cycles in any loading history. The rainbow and damage matrices illustrate the possible effects of infinite life. The safety and stability of wheel and the other practical structures according to the variable load can be estimated by using the results of this study.