Showing papers on "Vibration fatigue published in 1989"
TL;DR: In this paper, the applicability of a damage integral approach that provides a numerical accounting of accumulated fatigue damage is examined, and the fatigue damage rate is described by a phenomenological crack-growth law expressed in terms of a nominal stress-intensity factor, determined from isothermal fatigue data.
Abstract: Thermal cycling of electronic assemblies produces repeated mechanical loading of connecting solder joints through differential thermal expansion among assembly members. Such cyclic loading can lead to the fatigue failure of these solder joints. The instantaneous fatigue damage rate during this is determined by the solder stress, temperature, and environment. The applicability of a damage integral approach that provides a numerical accounting of accumulated fatigue damage is examined. The stress is calculated using state-variable constitutive relations for inelastic deformation. The fatigue damage rate is described by a phenomenological crack-growth law expressed in terms of a nominal stress-intensity factor, determined from isothermal fatigue data. Damage integral calculations are performed for solder joints fatigued to failure with either isothermal or thermomechanical cycles. The results indicate that the phenomenology of fatigue damage may be equivalent for these two loading modes. >
53 citations
TL;DR: In this paper, a two-state stochastic model for fatigue crack growth problems is presented and solutions are given which will, for the first time, provide the distribution of the random time to reach a critical crack size directly.
32 citations
TL;DR: In this article, a crack-size dependent toughness function, based on grain-localized interfacial bridging, and a hyperbolic-sine velocity function, representative of a fundamental activation process, was developed.
Abstract: Fatigue properties in the noncyclic loading of ceramics with R-curves are studied. Particular attention is directed to the potential role of R-curves in the enhancement of fatigue limits. A numerical algorithm for solving the appropriate differential equations of rate-dependent failure is developed. Our formalism specifically incorporates a crack-size dependent toughness function, based on grain-localized interfacial bridging, and a hyperbolic-sine velocity function, representative of a fundamental activation process. In a case study, dynamic fatigue (constant stressing rate) and static fatigue (constant applied stress) data for a coarse-grained alumina with a pronounced R-curve are analysed. With foreknowledge of the toughness parameters, the intrinsic crack-tip velocity function is deconvoluted. This intrinsic function is distinguished from the usual “apparent”, or “shielded”, (and demonstrably nonunique) function determined directly from the external load. It is confirmed that the R-curve, by virtue of its stabilizing influence on the crack growth, significantly enhances the fatigue limit, and confers the quality of “flaw tolerance” on fatigue lifetimes.
30 citations
01 Jan 1989
20 citations
TL;DR: In this article, a theoretical study on nonlinear response of discretely stiffened panels to random pressures and thermal loads is presented in a time-space domain and the nonlinear equations of motion are solved numerically by a Monte Carlo type approach.
8 citations
01 Dec 1989
TL;DR: In this article, the authors proposed a new partial weighted average stress range (WASR) concept to facilitate efficient fatigue fracture mechanics assessment of offshore welded structures, which can be applied in S/N analysis.
Abstract: Welded steel joints are usually susceptible to fatigue under the long-term, random service loading. Extensive investigations have shown that the load interaction effect for this type of joint under random offshore loading is negligible. The weighted average stress range (WASR) concept was therefore developed to facilitate efficient fatigue fracture mechanics assessment of offshore welded structures. Several equations have been developed to predict the WASR directly from the stress power spectra which could be the results of dynamic stress analysis or in-situ monitoring. these equations bypass the lengthy process of time history generation and cycle counting and are therefore very useful tools in the fast assessment of fatigue damage under random loading. The same WASR concept can be shown to be procedurally equivalent to the traditional stress life (S/N) and Miner's sum fatigue assessment, and so these prediction equations can be applied in S/N analysis. There are situations, however, in which the applications of these equations will give inconsistent or highly conservative predictions. The paper presents the enhancement of a previously proposed prediction equation in order to predict the partial WASR for a random fatigue history. With this new partial WASR, it has now become possible to analyse very complex fatigue and crack growth situations involving multiple exponential m values for WASR. The uses of this new procedure are further illustrated with sample calculations for fatigue crack growth and S/N analysis.
5 citations
TL;DR: In this article, the fatigue behavior of fillet welded joints with a scallop under highway and railroad loading was studied and it was verified that the fatigue life under variable amplitude loading could be estimated accurately by applying the fracture mechanics approach with the linear damage rule.
Abstract: Fatigue behavior of fillet welded joints with a scallop under highway and railroad loading was studied. Variable amplitude stress fluctuations were generated by computer simulations of highway and railroad live loads. Fatigue failure occurred even if the equivalent stress range was less than the constant amplitude fatigue limit. Therefore, fatigue life evaluation assuming that stress ranges below the fatigue limit did no damage was unconservative. It was verified that the fatigue life under variable amplitude loading could be estimated accurately by applying the fracture mechanics approach with the linear damage rule.
4 citations
TL;DR: In this article, a non-Gaussian stochastic field simulation method is used to estimate the probability distribution of fatigue crack growth life and reliability assessment of structures by simulating material resistance to fatigue crack formation along a crack path.
Abstract: A method is proposed for estimation of the probability distribution of fatigue crack growth life and reliability assessment of structures by simulating material resistance to fatigue crack growth along a crack path. The data for the simulation can be obtained from a few fatigue tests. The material resistance is treated as a spatial non-Gaussian (eventually Weibull, in this report) stochastic process. Therefore, a non-Gaussian stochastic fields simulation method proposed by Shinozuka, et al. is applied with statistical data obtained experimentally. The statistical analysis of the material resistance is performed with the data obtained by stress intensity factor control tests. The main results obtained are : (1) This method is useful to estimate the probability distribution of fatigue crack growth life ; (2) the material resistance seems to follow a 3-parameter-Weibull distribution ; (3) this method is useful for simulation of rather long fatigue crack ; (4) using this method, the probability distribution of fatigue crack growth life can be estimated from very few fatigue tests ; (5) the smallest life can be determined ; and (6) stress intensity factor control test is preferable for the statistical analysis.
3 citations
TL;DR: In this article, a Monte Carlo simulation is used to estimate the fatigue strength of constructional steel weldments and its expected uncertainty at long-life applications, where several different kinds of fatigue variables are considered: applied or induced bending stresses, notch severity, notch root residual stresses and notch root mechanical properties.
3 citations
24 Jan 1989
TL;DR: In this paper, simple closed-form analytical expressions are derived to accurately predict the durability of avionic equipment structural elements as part of the US Air Force Avionics Integrity Program (AVIP) requirements.
Abstract: Simple closed-form analytical expressions are derived to accurately predict the durability (i.e. failure-free operating period or fatigue life) of avionic equipment structural elements as part of the US Air Force Avionics Integrity Program (AVIP) requirements. These expressions are functions of both the quantity of like-structural elements per assembly and quantity of identical assemblies per system for thermal cycling and random vibration environments. Analytical predictions are compared with empirical results for cantilever beams for solder joints on multilayer assemblies containing leadless chip carriers (LCCs). >
2 citations
12 Dec 1989
TL;DR: In this article, a software package was developed to perform estimates of life to fatigue crack initiation in metals under random loading using cycle-by-cycle local stress strain analysis, which involves simulation of notch root stress-strain history under arbitrary, axial, elastic nominal stress excursions.
Abstract: A software package was developed to perform estimates of life to fatigue crack initiation in metals under random loading using cycle-by-cycle local stress strain analysis. This involves simulation of notch root stress-strain history under arbitrary, axial, elastic nominal stress excursions. Low cycle fatigue constants for the material and notch stress concentration factor are used as inputs for the analysis. The scftware provides a choice of five different graphical outputs. It was implemented on a PDP 11/73 using Fortran'77 and graphical output was obtained using data transfer to AutoCAD on an IBM PC compatible.
TL;DR: In this paper, the vibrational characteristics of the machines and components to be tested were investigated analytically, numerically and experimentally to determine the safe region of structural fatigue testing frequencies.
Abstract: Structural fatigue tests are required in engineering practice for safety and reliability. Structural bending and torsional fatigue testing machines were developed. The vibrational characteristics of the machines and components to be tested were investigated analytically, numerically and experimentally to determine the safe region of structural fatigue testing frequencies.
TL;DR: In this paper, the service life of aircraft structural components undergoing random stress cycling was analyzed by the application of fracture mechanics, and the initial crack sizes at the critical stress points for the fatigue crack growth analysis were established through proof load tests.
Abstract: The service life of aircraft structural components undergoing random stress cycling was analyzed by the application of fracture mechanics. The initial crack sizes at the critical stress points for the fatigue crack growth analysis were established through proof load tests. The fatigue crack growth rates for random stress cycles were calculated using the half-cycle method. A new equation was developed for calculating the number of remaining flights for the structural components. The number of remaining flights predicted by the new equation is much lower than that predicted by the conventional equation.
TL;DR: In this article, the fatigue life distributions of single-spot joints and the distribution properties of the loads assigned to the respective spots were theoretically derived for both single and multi-spot joint.
01 Jan 1989
TL;DR: In this article, a fatigue analysis is carried out for the critical column-pontoon intersection of a four column tension leg platform, where both a simplified method for fatigue estimation and a more sophisticated approach involving the spectral technique for response prediction are presented.
Abstract: A fatigue analysis is carried out for the critical column-pontoon intersection of a four column tension leg platform. The study includes both a simplified method for fatigue estimation and a more sophisticated approach involving the spectral technique for response prediction. For the actual structure the present study indicates that the deterministic method yields very conservative results when standard recommendations are used for shape parameters. The main reason for this is that directionality is not properly accounted for by the standard deterministic approach. Directionality refers in this context both to the main wave directions and short crested spreading around this direction. However, even when results from comparable formulations of the two methods are compared, the simplified method typically yields much lower fatigue life. For the actual response quantity yields much lower fatigue life. For the actual response quantity a factor of about two is indicated.
TL;DR: In this paper, the effect of high cycle random loading at 330°C and at 550°C on the fatigue resistance of austenitic stainless steels Type 316LN has been investigated.
Patent•
04 Feb 1989
TL;DR: In this article, the authors use Hill Hilbert transform processing to detect the amplitude envelope and instantaneous frequency of the displacement signal generated by the proximity sensor, with the cumulative fatigue usage to be monitored constantly changing and the vibration displacement in the static stress.
Abstract: Displacement of an object such online vibration fatigue monitor measures as turbine rotor blades, to issue a displacement signal generated by the proximity sensor, and calculating means of the displacement signal accumulated fatigue in the object, the signal is digitized, and by using Hill Hilbert transform processing, in order to detect the amplitude envelope and instantaneous frequency of the displacement. The combination of amplitude and frequency determine fatigue usage and static stress on the object, with the cumulative fatigue usage to be monitored constantly changing and the vibration displacement in the static stress.
02 Oct 1989
TL;DR: In this paper, a probabilistic approach for assessing the fatigue life of a component containing defects is presented. Butts et al. proposed a method that incorporates the aspect ratio of the initial defect, the proportional coefficient of the fatigue crack growth law, and the threshold stress intensity range into the CEGB two-criteria method.
Abstract: A method of assessing the fatigue life of a component containing defects is presented. The method incorporates a probabilistic approach into the CEGB two-criteria method. The aspect ratio of the initial defect, the proportional coefficient of the fatigue crack growth law, and the threshold stress intensity range are assumed to be treated as random variables in the method. Examples are given to illustrate the method's application to the reliability analysis of the conduit for an internally cooled cabled superconductor (ICCS) subjected to cyclic quench pressure. The possible failure mode and mechanical properties contributing to the fatigue life of the thin conduit are discussed using analytical and experimental results. >
01 Jan 1989
TL;DR: In this article, a criterion of vibration fatigue failure is received by the assumption of material volume unit failure energy equality under static loading failure energy under harmonic vibration failure, which coincides with the experimental criterion by Manson-Koffin and also explains an experimentally observed fact of durability dissipation increase while a level of cyclic vibration stresses is decreased.
Abstract: The criterion of vibration fatigue failure is received by the assumption of material volume unit failure energy equality under static loading failure energy under harmonic vibration failure. The criterion coincides with the experimental criterion by Manson-Koffin, and also explains an experimentally observed fact of durability dissipation increase while a level of cyclic vibration stresses is decreased. The experimental relationships of material durability on mean and amplitude values of stresses of asymetric cycle at asymetric cycle of vibration loading are confirmed. The preliminary vibration loading is shown to decrease mechanical performances of the material (strength limit) at static tension tests. The criterion allows to estimate the cyclic strength of the material according to the results of static failure tests.
01 Jan 1989
TL;DR: In this article, the many engineering decisions necessary before a useful variable amplitude test can be carried out are explained in detail, such as measuring of the stress time history in service, which couting procedure to use and why.
Abstract: Fatigue life prediction by experiment, that is variable amplitude testing, is becoming more and more widespread in industry. The many engineering decisions necessary before a useful variable amplitude test can be carried out are explained in detail, such as
measurement of the stress time history in service
which couting procedure to use and why
scatter of measured stress spectra
manipulation of measured stress spectra
reconstitution (synthesis) of the test spectrum as a basis for a realistic variable amplitude test sequence
predicted fatigue life under this sequence etc.