Showing papers on "Vibration fatigue published in 2012"
TL;DR: In this article, an experimental scheme for characterizing thermal fatigue damage in composite laminates using second harmonic Lamb waves was proposed. But the results showed a monotonic increase of acoustic nonlinearity with respect to thermal fatigue cycles.
Abstract: Composite materials which are widely used in the aerospace industry, are usually subjected to frequent variation of temperature. Thermal cyclic loading may induce material degradation. Considering the long-term service of aircraft composites and the importance of safety in the aircraft industry, even a little damage that may be accumulative via thermal fatigue is often of great concern. Therefore, there is a demand to develop non-destructive approaches to evaluate thermal fatigue damage in an early stage. Due to the sensitivity of acoustic nonlinearity to micro-damage, the nonlinear ultrasonic technique has been explored as a promising tool for early detection of micro-damage. This paper investigates an experimental scheme for characterizing thermal fatigue damage in composite laminates using second harmonic Lamb waves. The present results show a monotonic increase of acoustic nonlinearity with respect to thermal fatigue cycles. The experimental observation of the correlation between the acoustic nonlinearity and thermal fatigue cycles in carbon/epoxy laminates verifies that nonlinear Lamb waves can be used to assess thermal fatigue damage rendering improved sensitivity over conventional linear feature based non-destructive evaluation techniques. Velocity and attenuation based ultrasonic studies are carried out for comparison with the nonlinear ultrasonic approach and it is found that nonlinear acoustic parameters are more promising indicators of thermal fatigue damage than linear ones.
172 citations
TL;DR: Prediction of fatigue reliability of welded multi-planar tubular joints of the support structure of a fixed jacket offshore wind turbine designed for a northern North Sea site in a water depth of 70 m is performed.
144 citations
TL;DR: In this paper, a three-dimensional finite element implementation of a continuum damage mechanics formulation for multiaxial fatigue is presented, incorporating elastic modulus reduction due to fatigue damage.
93 citations
TL;DR: In this article, a framework of fatigue reliability assessment for existing bridges in lifetime serviceability considering the random effects of vehicle speed and road-roughness condition is presented, and the revised equivalent stress-range is introduced to include fatigue damage accumulations for one truck passage.
Abstract: During the life cycle of a bridge, dynamic impacts due to random traffic loads and deteriorated road surface conditions can induce serious fatigue issues for bridge components. It is necessary, and more realistic than the deterministic approach, to use reliability methods and treat the input parameters as random variables for the vehicle-bridge dynamic system. This paper presents a framework of fatigue reliability assessment for existing bridges in lifetime serviceability considering the random effects of vehicle speed and road-roughness condition. Since each truck passage might generate multiple stress ranges, revised equivalent stress-range is introduced to include fatigue damage accumulations for one truck passage. Therefore, the two variables, i.e., the stress-range numbers and equivalent stress ranges per truck passage, are coalesced in the newly defined variable based on equivalent fatigue damage. The revised equivalent stress-range is obtained through a fully-computerized approach toward so...
73 citations
TL;DR: The simulation results show that the vibration amplitude of the lower body soft-tissue package may considerably increase (up to 20%) with muscle fatigue, while the effects of fatigue on the GRF are negligible.
Abstract: A modeling approach is used in this paper to study the effects of fatigue on the ground reaction force (GRF) and the vibrations of the lower extremity soft tissues. A recently developed multiple degrees-of-freedom mass-spring-damper model of the human body during running is used for this purpose. The model is capable of taking the muscle activity into account by using a nonlinear controller that tunes the mechanical properties of the soft-tissue package based on two physiological hypotheses, namely, “constant force” and “constant vibration.” In this study, muscle fatigue is implemented in the model as the gradual reduction of the ability of the controller to tune the mechanical properties of the lower body soft-tissue package. Simulations are carried out for various types of footwear in both pre- and post fatigue conditions. The simulation results show that the vibration amplitude of the lower body soft-tissue package may considerably increase (up to 20%) with muscle fatigue, while the effects of fatigue on the GRF are negligible. The results of this modeling study are in line with the experimental studies that found muscle fatigue does not significantly change the GRF peaks, but may increase the level of soft-tissue vibrations (particularly for hard shoes). A major contribution of the current study is the formulation of a hypothesis about how the central nervous system tunes the muscle properties after fatigue.
64 citations
TL;DR: In this paper, the origin of fatigue failure that occurs on the air ventilation holes of a newly designed heavy commercial vehicle steel wheel in dynamic radial fatigue tests is studied via finite element analysis.
64 citations
TL;DR: In this paper, an improved fatigue-testing methodology based on the dynamic response of the test specimen to the harmonic excitation in the near-resonant area with simultaneous monitoring of the modal parameters is presented.
63 citations
TL;DR: In this paper, a model for notch fatigue damage evaluation in the case of an arbitrary multiaxial loading history is proposed by using an endurance function which quantifies the damage accumulation in the material up to the final failure.
56 citations
TL;DR: In this paper, a fatigue life assessment model for materials and structures under triaxial random stress state in time and frequency domains developed over 25 years in Opole University of Technology is presented.
53 citations
TL;DR: In this article, different approaches are applied to the fatigue strength assessment of ship structures, including nominal, structural hot-spot as well as the effective notch stress approach have been applied.
50 citations
TL;DR: In this paper, a model for fatigue damage evaluation in the case of an arbitrary multiaxial loading history is proposed by using an endurance function which allows us to determine the damage accumulation up to the final failure of the material.
Abstract: In order to assess the fatigue behaviour of structural components under a complex (cyclic or random) multiaxial stress history, methods based on damage mechanics concepts can be employed. In this paper, a model for fatigue damage evaluation in the case of an arbitrary multiaxial loading history is proposed by using an endurance function which allows us to determine the damage accumulation up to the final failure of the material. By introducing an evolution equation for the endurance function, the final collapse can be assumed to occur when the damage D is complete, that is when D reaches the unity. The parameters of this model, which adopts the stress invariants and the deviatoric stress invariants to quantify the damage phenomenon, are determined through a Genetic Algorithm once experimental data on the fatigue behaviour of the material being examined are known for some complex stress histories. With respect to traditional approaches to multiaxial fatigue assessment, the proposed model presents the following advantages: (1) the evaluation of a critical plane is not necessary; (2) no cycle counting algorithm to determine the fatigue life is required, because it considers the progressive damage process during the fatigue load history; (3) the model can be applied to any kind of stress history (uniaxial cyclic loading, multiaxial in-phase or out-of-phase cyclic loading, uniaxial or multiaxial random loading).
TL;DR: The reliability of fatigue prone structures is improved by maintenance scheduling and the optimum is a trade off between the inspection, repair and failure costs.
Book•
11 May 2012
TL;DR: In this article, the application of the advanced life assessment methods using the finite element method studied in this thesis produces more accurate stress results, including stress raising effects at welded details that are prone to fatigue.
Abstract: Fatigue design and analysis of steel and composite bridges is generally based on the notion of the nominal stress using the classified S-N curves with corresponding fatigue classes for typical details. Such an approach can yield unrealistic the estimation of the load effects for structure components because of an ever increasing number of structural details and loading situations resulting in a limited number of possible treatable design cases. The hot spot stress method has been developed to enable an accurate estimation of the load effects for the fatigue strength of welded steel structures, in cases where the nominal stress is hard to estimate because of geometric and loading complexities or in cases where there is no classified detail that is suitable to be compared with. Although this method has been used in fatigue design and analysis in tubular structures for several decades, the method has not been applied on a larger scale on steel and composite bridges. The essential of adopting the finite element method for determining the design stresses for fatigue life calculations has been increased recently especially when utilizing the advanced fatigue assessment methods for welded steel structures. However, the result from finite element analysis can be highly sensitive to modelling technique since the stresses obtaining from these advanced methods such as the structural hot spot stress method and the effective notch stress method are often in an area of high strain gradients, i.e. stress singularities. The resulting stresses may differ substantially depending on the type and size of elements. In this study, this was recognized by evaluating the hot spot and effective notch stresses obtained from the finite element analyses with the fatigue test data collected from the literature. Orthotropic steel bridges have both complex geometry and loading conditions producing complex bridge deck behaviour which is hard to estimate and analyse using the traditional fatigue assessment methods. The effects of the loading and geometrical conditions, i.e. decks components which are working in a group, need to be considered accurately in the stress calculations. Assuming overall elastic behaviour in such complex structure systems, in which the stress raising sources that have decisive effects on the fatigue strength capacity are partly included, can yield over/underestimated stress values to be evaluated in fatigue design. The application of the advanced life assessment methods using the finite element method studied in this thesis produce more accurate stress results, including stress raising effects at welded details that are prone to fatigue.
TL;DR: In this article, a study of the fatigue strength of friction stir welds in AA6082-T6 under constant and variable amplitude loadings under the stress ratio R = −1 and R =−−1, respectively, was carried out in a servo-hydraulic testing machine using typified Gassner amplitude spectra.
TL;DR: In this article, a bilinear S-N approach is integrated into a probabilistic framework that can model the uncertainties associated with the fatigue deterioration process, and the equivalent stress range is computed by using two SN slopes and several probability density functions associated with stress ranges.
Abstract: This paper focuses on estimating the fatigue life below the constant amplitude fatigue threshold (CAFT) of steel bridges by using a probabilistic approach on the basis of a bilinear stress life (i.e., the S-N approach). The current AASHTO S-N approach uses a single S-N line for predicting the fatigue life. However, because of the variation of actual applied live-load stress cycles, this approach very often results in a severe underestimation of the useful life of structures. It implies that fatigue damage in respective structural steel details may be overestimated. To improve fatigue life estimation, a bilinear S-N approach is integrated into a probabilistic framework that can model the uncertainties associated with the fatigue deterioration process. In this approach, the equivalent stress range is computed by using two S-N slopes and several probability density functions associated with stress ranges. These probabilistic functions are determined on the basis of stress-range bin histograms from long-term ...
TL;DR: In this article, the fracture energy density obtained from indirect tension (IDT) test was employed in the fatigue model to consider the resisting energy of the asphalt mixtures against fracture damage.
TL;DR: In this paper, an extension of the UniGrow model is proposed to derive probabilistic fatigue crack propagation data, in particular the derivation of the P-da/dN-ΔK-R fields.
Abstract: Purpose – Recently, a new class of fatigue crack growth models based on elastoplastic stress‐strain histories at the crack tip region and strain‐life fatigue damage models have been proposed. The fatigue crack propagation is understood as a process of continuous crack initializations, over elementary material blocks, which may be governed by strain‐life data of the plain material. The residual stresses developed at the crack tip play a central role in these models, since they are used to assess the actual crack driving force, taking into account mean stresses and loading sequential effects. The UniGrow model fits this particular class of fatigue crack propagation models. The purpose of this paper is to propose an extension of the UniGrow model to derive probabilistic fatigue crack propagation data, in particular the derivation of the P–da/dN–ΔK–R fields.Design/methodology/approach – An existing deterministic fatigue crack propagation model, based on local strain‐life data is first assessed. In particular,...
TL;DR: In this paper, a numerical model for predicting the probability of subsurface initiated rolling contact fatigue failure in railway wheels subjected to operational loading is presented, where the loading is evaluated through simulations of dynamic train-track interaction incorporating the influence of, e.g., corrugation.
TL;DR: The results obtained suggest that the friction between layers and the annulus conditions strongly influences the fatigue life of flexible pipes.
Abstract: This paper focuses on a theoretical approach to access the fatigue life of flexible pipes. This methodology employs functions that convert forces and moments obtained in time-domain global analyses into stresses in their tensile armors. The stresses are then processed by well-known cycle counting methods, and S-N curves are used to evaluate the fatigue damage at several points in the pipe’s cross-section. Finally, Palmgren-Miner linear damage hypothesis is assumed in order to calculate the accumulated fatigue damage. A study on the fatigue life of a flexible pipe employing this methodology is presented. The main points addressed in the study are the influence of friction between layers, the effect of the annulus conditions, the importance of evaluating the fatigue life in various points of the pipe’s cross-section, and the effect of mean stresses. The results obtained suggest that the friction between layers and the annulus conditions strongly influences the fatigue life of flexible pipes. Moreover, mean stress effects are also significant, and at least half of the wires in each analyzed section of the pipe must be considered in a typical fatigue analysis.
TL;DR: In this article, an evaluation of the fatigue characteristics of a knuckle using multibody simulation (MBS) techniques is used for stress analysis and an actual road profile of road bumps is used as the input to MBS.
Abstract: Suspension is part of automotive systems, providing both vehicle control and passenger comfort. The knuckle is an important part within the suspension system, constantly
encountering the cyclic loads subjecting it to fatigue failure. This paper presents an evaluation of the fatigue characteristics of a knuckle using multibody simulation (MBS) techniques. Load time history extracted from the MBS is used for stress analysis. An actual road profile of road bumps was used as the input to MBS. The stress fluctuations
for fatigue simulations are considered with the road profile. The strain-life method is utilized to assess the fatigue life. The instantaneous stress distributions and maximum principal stress are used for fatigue life predictions. Mesh sensitivity analysis has been performed. The results show that the steering link in the knuckle is found to be the most susceptible region for fatigue failure. The number of times the knuckle can manage a
road bump at 40 km/hr is determined to be approximately 371 times with a 50% certainty of survival. The proposed method of using the loading time history extracted from MBS simulation for fatigue life estimation is found to be very promising for the accurate evaluation of the performance of suspension system components.
TL;DR: In this article, a generalised step-by-step procedure for fatigue crack growth analysis of structural components subjected to variable amplitude loading spectra has been presented, illustrated by analyzing fatigue growth of planar corner crack in an attachment lug made of Al7050-T7451 alloy.
TL;DR: In this paper, an improved method for analyzing the variance of the damage for any narrowband Gaussian process was presented, which involves a single summation for arbitrary processes, and closed form solutions for special cases (linear oscillator and bandpass process).
15 Mar 2012-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the equivalent uniaxial stress has been chosen as the approach useful for this purpose by combining it with a strength curve for the material (i.e. S-N curve) and damage evaluation (Damaged Stress Model (DMS) and Miner's rule).
Abstract: Fatigue life estimation or fatigue damage evaluation of mechanical components under a multiaxial state of stress time-history has an important role in virtual design phases, but this evaluation is a real problem to resolve, because this goal is not reached by classical fatigue criteria. In this context, the equivalent uniaxial stress has been chosen as the approach useful for this purpose by combining it with a strength curve for the material (i.e. S – N curve) and damage evaluation (Damaged Stress Model (DMS) and Miner's rule). So the authors have taken equivalent stresses based on a multiaxial criterion that can be used as a uniaxial stress time history for the application of damage evaluation methods to predict the fatigue life, under multiaxial random loading. The cycles were counted with the Rain Flow algorithm, using equivalent stress as a variable counting. In the case of “asymmetric” histories, the algorithm of transformation of the stress history (because of its global expected value different from zero) is required. In the case of 10HNAP steel, stress amplitude transformation according to the Goodman relationship gives good results. The proposed algorithm was verified during fatigue tests of cruciform specimens made of 10HNAP steel, subjected to biaxial non-proportional random tension-compression.
18 Apr 2012
TL;DR: In this article, the fatigue strength of turbine blades is considered in the design of the turbine blades of a turbine and it is expected that fatigue strength will be a major consideration in their design.
Abstract: Tidal turbine blades experience significant fatigue cycles during operation and it is expected that fatigue strength will be a major consideration in their design. Glass fibre reinforced polymers a...
TL;DR: A multi-axial fatigue model for fiber-reinforced composite laminates based on Puck's criterion is proposed in this paper, where fatigue master curves from the ATM are used to construct the fatigue master curve.
Abstract: A new multi-axial fatigue model for fiber-reinforced composite laminates based on Puck’s criterion is proposed in this article. In the fatigue model, fatigue master curves from the ATM are used to ...
TL;DR: Based on the cycle counting method of Wang and Brown and on the linear accumulation damage rule of Miner, four multiaxial fatigue damage models without any weight factors proposed by Pan et al., Varvani-Farahani, Shang and Wang, and Shang et al. are used to compute fatigue damage.
Abstract: Based on the cycle counting method of Wang and Brown and on the linear accumulation damage rule of Miner, four multiaxial fatigue damage models without any weight factors proposed by Pan et al., Varvani-Farahani, Shang and Wang, and Shang et al. are used to compute fatigue damage. The procedure is evaluated using the low cycle fatigue experimental data of 7050-T7451 aluminum alloy and En15R steel under tension/torsion variable amplitude loading. The results reveal that the procedure is convenient for engineering design and application, and that the four multiaxial fatigue damage models provide good life estimates.
TL;DR: In this article, the effect of multiple-axle loadings is simplified and taken into account via load equivalency factors using Miner's Law, and a method for the computation of the fatigue life of bituminous mixtures under multipleaxle configurations that couples a structural approach and a material-based approach is presented.
Abstract: The fatigue damage caused by multiple-axle configurations is a key issue for pavement design. The standard fatigue test consists of the application of a continuous sinusoidal signal on a specimen, which enables the fatigue life to be described as a function of the strain level. For more complex loading signals, additional parameters were found to have an influence on the fatigue life of bituminous mixtures. In the French design method, the effect of multiple-axle loadings is simplified and taken into account via load equivalency factors using Miner's Law. In this article, we present a method for the computation of the fatigue life of bituminous mixtures under multiple-axle configurations that couples a structural approach and a material-based approach. The structural approach consists of a parametric study of real loading signals that enables the computation of the independent shape parameters characterising a loading signal. An experimental plan whose variables are the independent shape parameters was th...
TL;DR: In this paper, a linear damage rule was used to estimate the fatigue life of an air- craft engine by considering the load spectrum difference factor, and a good agreement was found between the estimated results and real life data.
Abstract: Aircraft engine components are subjected to variable amplitude load conditions usually they tend to ex- perience fatigue damage. Many fatigue damage accumula- tion theories have been put forward to predict the fatigue lives of structure components. Under different load spectra, the aircraft engine has different working life. In this paper, based on the linear damage rule, the fatigue life of an air- craft engine was estimated by considering the load spectrum difference factor. According to one aircraft engine used for different load spectrums, the relationship between the load spectrum and the life is discussed. Moreover, the fatigue life of this engine used in A-type bomber is estimated based on the different load spectrum of the B-type bomber. A good agreement is found between the estimated results and real life data.
TL;DR: In this article, an advanced model of alongwind-induced fatigue damage and using a probabilistic assessment of the parameters involved are discussed and propagated the uncertainties inherent in the input parameters over the fatigue damage prediction.
TL;DR: In this article, a fatigue life analysis method combined with experiment and simulation is presented to accurately predict location of cracks and fatigue life of this component and find the reasons, a rigid and flexible hybrid model of whole truck is built to get the stress situation based on modal stress recovery method, taking flexible body of A-type frame into account.