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In this contribution, it was suggested an extension of Gurson model for cyclic application, regarding the prediction of fretting fatigue life and the study of the influence of the plastic strain field on fretting fatigue for an aluminum alloy 7050-T7451. In this setting, a modification in the defects growth mechanism was done, including a variable that distinguishes the evolution rate of Gurson damage in tension-compressive loads and, the coupling of the Xue shear mechanism to the extension of the model to low range of stress triaxiality. Initial simulations were performed for traditional fatigue tests and the suggested model has worked in good agreement with experimental data. After that, experimental fretting fatigue tests were proposed and carried out in order to observe the influence of the contact pressure of the fretting pad on the fretting specimen and in the system life. Numerical simulations were performed, considering now the modeling of the fretting fatigue problem by Finite Elements Method and life predictions were calculated, applying the suggested Gurson-based continuum damage formulation, by an analysis in a Gauss point. The calculated and observed life diagram has shown a robustness performance of formulation, predicting lives within a band factor of 2. It was also verified that the plastic strain field introduced, due to the increase in contact pressure on the fretting pad, benefits the specimen life, since the plastic strain was induced by the appearance of dislocations, which causes a hardening and an increase of the macroscopic material properties, as well as a negative mean stress into the specimen.

Fatigue cracking of rib-to-deck welded joints is the major fatigue problem of the orthotropic steel deck (OSD). It is important to evaluate the fatigue performance improvement of rib-to-deck double-side welded joints in an OSD when compared with single-side welded joints. In this study, the software ABAQUS and FRANC3D were used to set up a multiscale finite element model for segments of an OSD. Under vehicle load, the mode I stress intensity factor (SIF) of a fatigue crack at the rib-to-deck single-side and double-side welded details without or with the effect of welding residual stress was computed. The relationship between the mode I SIF of the fatigue crack and the key parameters was analyzed, including welded penetration, thickness of deck plate and the initial crack surface length and depth. The results showed that the welding residual stress can significantly influence the SIF values of the rib-to-deck welded joints in the OSD. The maximum SIF of the crack in the rib-to-deck double-side welded joints was 29.6% less than that of the single-side welded joints, which can effectively improve the fatigue performance of the rib-to-deck welded joints. The effect of the welded penetration rate on the fatigue performance of rib-to-deck double-side welded joints was only slight. By increasing the thickness of the deck, reducing the initial crack surface length and depth, the SIF of cracks in the rib-to-deck double-side welded joints can be significantly decreased, and this approach improves fatigue performance.

The objective of this study is to develop a Driving Fatigue Strain Index using fuzzy logic to analyze the risk levels of driving activity among road users. Driving fatigue is always related to the driving activity and has been identified as one of the vital contributors to the road accidents and fatalities in Malaysia. Therefore, the present paper introduces the use of fuzzy logic for the development of strain index to provide the systematic analysis and propose an appropriate solution in minimizing the number of road accidents and fatalities. The development of strain index is based on the six risk factors associated with driving fatigue; muscle activity, heart rate, hand grip pressure force, seat pressure distribution, whole-body vibration, and driving duration. The data is collected for all the risk factors and consequently, the three conditions or risk levels are defined as “safe”, “slightly unsafe”, and “unsafe”. A membership function is defined for each fuzzy conditions. IF-THEN rules were used to define the input and output variables which correspond to physical measures. This index is a reliable advisory tool for providing analysis and solutions to driving fatigue problem, which constitutes the first effort toward the minimization of road accidents and fatalities.

This perspective paper describes the building elements for realizing a precise patient monitoring algorithm to fundamentally address the alarm fatigue problem. Alarm fatigue is well recognized but no solution has been widely successful. Physiologic patient monitors are responsible for the lion’s share of alarms at the bedside, most of which are either false or non-actionable. Algorithms on patient monitors lack precision because they fail to leverage multivariate relationship among variables monitored, to integrate rich patient clinical information from electronic health record system, and to utilize temporal patterns in data streams. Therefore, a solution to patient monitor alarm fatigue is to open the black-box of patient monitors to integrate physiologic data with clinical data from EHR under a four-element algorithm strategy to be described in this paper. This strategy will be presented in this paper in the context of its current status as described in our prior publications.

Size effects on crack growth are of paramount importance on the fatigue problem. Paris’ and Wohler’s fatigue curves exhibit scale effects, which can be explained in the framework of incomplete self-similarity and fractal geometry concepts. In particular, scaling laws are found for the main fatigue parameters, that is, the fatigue threshold ΔKth and the fatigue limit Δσfl. The fatigue threshold increases with the crack length, whereas the fatigue limit decreases with the specimen size. Eventually, the proposed models are positively compared to experimental data available in the literature.

The fatigue problem of concrete is still a challenging topic in the researches and applications of concrete engineering. This paper aims to develop a fatigue damage evolution law based model for concrete motivated by the analysis of physical mechanism. In this model, the fatigue energy dissipation process at microscale is investigated with rate process theory. The concept of self-similarity is employed to bridge the scale gap between microscale cracking and mesoscale dissipative element. With the stochastic fracture model, the crack avalanches and macro-crack nucleation processes from mesoscale to macroscale are simulated to obtain the behaviors of macroscope damage evolution of concrete. In conjunction with continuum damage mechanics framework, the fatigue damage constitutive model for concrete is then proposed. Numerical simulations are carried out to verify the model, revealing that the proposed model accommodates well with physical mechanism of fatigue damage evolution of concrete whereby the fatigue life of concrete structures under different stress ranges can be predicted.

The fatigue problem induced by wave loads and floater movements of dynamic umbilicals in deepwater is studied. The prediction method of the fatigue life is investigated by considering no-linear local stress due to contact and friction between components of the umbilical. A case study of a dynamic umbilical for 1500 meters depth in South China Sea was presented. The results showed that the more accurate result of the fatigue life was calculated by considering non-linear local stress. The fatigue life by considering local stress with the no-slip assumption was conservative. An obviously longer fatigue life was obtained by considering local stress with the full-slip assumption.

Sustained loads have for some Ni-based superalloys been shown to give rise to increased crack growth rate at elevated temperature. Such loads generate a history dependent fatigue problem due to weakening and cracking of grain boundaries during dwell times, later broken apart during subsequent load cycles. So far most studies have focused on the interaction of load cycles, overloads, and temperature. However, vibrations of different kinds are to some extent always present in engine components, and an investigation of how such loads affect the dwell time cracking, and how to incorporate them in a modelling context, is therefore of importance. In this paper a study of the most frequently used gas turbine material, Inconel 718, has been carried out. Mechanical crack propagation testing has been conducted at 550 °C for surface cracks with and without the interaction of superimposed vibrational loads. Subsequent investigation of the fracture behaviour was performed by scanning electron microscopy and the modelling work has been conducted by incorporating the vibration load description within a history dependent crack growth law. The obtained results show reasonable accuracy with respect to the mechanical test results. Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through the Swedish research programme TURBO POWER

Ultra-high cycle fatigue problem has received more and more attention with the continuous improvement of the reliability and life index of modern equipment, and has become a hot spot in fatigue research. As the non-metallic material with the most application potential in the modern aviation industry, the ultra-high cycle fatigue problem of carbon fiber reinforced plastic (CFRP) is the most prominent. In this paper, the research progress of ultra-high cycle fatigue research of CFRP has been systematically sorted out and summarized from three dimensions of test method, fatigue fracture macro-micro characteristics and fatigue damage model construction, including the adopted technical methods, the mechanism of fatigue crack initiation, the characteristics of S-N curve, Goodman diagram and the influence of humidity and other influence factors. The mechanism, evolution and model of CFRP ultra-high cycle fatigue damage are expounded, and the problems existing in the ultra-high cycle fatigue research of CFRP are presented.

This research focusing on fatigue crack growth experiment and assessments of fatigue crack growth model. Fatigue has been considered as the most important phenomena in the engineering problems. It has been found to occur in every engineering field. Many methods were introduced to overcome fatigue problem. One of it is fatigue crack growth prediction models. Fatigue crack growth model prediction can determine the residual life of the mechanical component. Fatigue crack growth is an important parameter in engineering. It may begin from undamaged area and propagate afterwards. In this case, a mechanical component condition before an unstable crack still can be used until fatigue. With the study of fatigue crack growth, it can predict the crack life of the component and can reduce cost to repair the component. In this thesis, primary objective is to develop, test and provide computational fracture mechanics model that emphasized an uncertainties quantification for surface crack. Fracture and failure study that has been promoted by S-version finite element method is focus on the analysis of the surface-crack problem. In this project, a few limitations of the study have been implemented as to present a specific scope of the investigation. Both fatigue crack growth model is considered; Paris law model and modified Forman model. The specimen in this analysis is aluminium al 2024 T3. The effect of load on the fatigue crack growth rate is investigated on aluminium 2024 T3. It is concluded that modified Forman has a low exponent compared to the Paris law. Further the crack growth prediction based on modified Forman is lower than Paris law. Paris law only can predict the crack in the region II while modified Forman can predict the crack in region II and III. After finish setup the project based on the instruction, the project is proceeded and the data is collected. The result is analysed based on the objective by using data collected from the project. After that, conclusion is made based on the result of the project.

Crankshaft fatigue problem has long been a headache and frequent phenomenon in combustion engine which attracts various efforts especially including fundamental fatigue experimental data. In this paper, the rational experimental method is employed to study the crankshaft fatigue phenomenon based on a customized experiment platform, mimicking the real-world crankshaft working condition physically. Then, based on the experiment data, the statistical regression analysis of eight commonly used hypothesis distributions is conducted. The degrees of fitting effects of the chosen statistical model are evaluated individually. Results show that the three-parameter Weibull distribution model fits the data best which may be used as the fundamental model in future analysis. This study provides a solid foundation for better understanding the mechanism of crankshaft fatigue phenomenon.

As vibrations from vortex-shedding occur at moderate wind speeds, structures undergo a considerable number of stress variations. So risk of fatigue is to be taken into account at the design stage itself. Even if a fatigue analysis is not demanded in the code to be applied, risk of fatigue is to be considered, especially with regard to slender steel chimneys due to larger volumes of material subjected to high stresses. Thus, risk of fatigue which has not been addressed in the Indian context, has been taken care in the present paper. It is envisaged that this formulation will be appropriate for inclusion in Indian codes and standards. As part of the case study, a chimney from an industry having Diesel Power Plant has been undertaken. Fatigue analysis of this chimney has been done and measures to reduce fatigue problem have been suggested.

Hammers are most typical of impact machines and are widely used in the mechanical manufacture industry. It is important to predict the effects of the damage growth on the fatigue process of the hammer foundation especially when subjected to long-term repeated impact loading. Although there have been many articles about damage model of soils, few of them have studied the problem of soil failure under cyclic loading as the fatigue damage of soils failure. In this paper, a damage fatigue problem of a hammer foundation system considered with fatigue damage growth and vibration on the machine foundation due to the impact of hammer blows is discussed by numerical results using the concept of damage mechanics based on the interaction between hammer foundation and soil ground. It has been found that the influence of damage due to hammer blows on the responses of the ground soil near the foundation is significantly increased with damage development both in the hammer foundation and the surrounding soil. Therefore, in order to protect the environment from damage due to the blows of a hammer, the design for actively vibration absorbing control and damage control in the hammer foundation system needs to be taken into account.

As the general features of fretting fatigue, initiation of fretting fatigue crack is in the very early stage of the fretting fatigue life and there are small non-propagating cracks in the test specimen that doesn't fracture at the fretting fatigue limit. In accordance with these experimental facts, fretting fatigue problem can be considered as a propagation problem of small crack. Thus, a pre-cracked specimen was used in the fretting fatigue test in this study. The objective was to consider the determinant factors of fretting fatigue strength. In the fretting fatigue test, the fretting fatigue limit of the pre-cracked specimen was once reduced and after increased with increase of the contact pressure. The reason was understood by the stress intensity factor of the pre-crack obtained by a finite element analysis. In this study, the fretting fatigue limit can be predicted by the comparison of ΔK of the pre-crack and the propagation threshold of the pre-crack ΔKth. The effect of the relative location of the pre-crack to the contact edge on the fretting fatigue strength was also discussed by both fretting fatigue test and FEM analysis.

To examine the reliability and validity of the Japanese-language version of the PedsQL™ Multidimensional Fatigue Scale and to investigate the agreement between child self-reported fatigue and parent proxy-reported fatigue. The Japanese-language version of the PedsQL™ Multidimensional Fatigue Scale was administered to 652 preschoolers and schoolchildren aged 5–12 and their parents, and to 91 parents of preschool children aged 1–4. Internal consistency reliability was 0.62–0.87 for children and 0.81–0.93 for parents. Known-group validity was examined between a group of healthy samples (n = 530) and chronic condition sample (n = 102); the chronically ill group reported a significantly higher perceived fatigue problem. Correlations between child self- and parent proxy reports ranged from poor to fair. In subgroups identified by cluster analysis based on child self-reported scores, the greatest agreement between child and parent reports was seen in the good HRQOL group, while the least occurred in the poor HRQOL group. The parents overestimated their child’s fatigue more when the child’s HRQOL was low. The Japanese-language version of the PedsQL™ Multidimensional Fatigue Scale demonstrated good reliability and validity and could be useful in evaluating Japanese children in school and health care settings.

In the statistics of stress-strain cyclic response involved with cyclic-loading, rain-flow counting method has always been thought the most reasonable way to proceed cycle counting, based on which researchers could conduct fatigue test or calculate the damage extent according to e一N(or S一N) curve. That is the main reason why this method is widely used. This article will minutely discuss the principle, developing status, computer-based realization and application of rain-flow counting method, after which briefly discuss its application in fatigue problem in road and bridge.

A new multiaxial fatigue damage model named characteristic plane approach is proposed in this paper, in which the strain components are used to correlate with the fatigue damage. The characteristic plane is defined as a material plane on which the complex three-dimensional (3D) fatigue problem can be approximated using the plane strain components. Compared with most available critical plane-based models for multiaxial fatigue problem, the physical basis of the characteristic plane does not rely on the observations of the fatigue crack in the proposed model. The cracking information is not required for multiaxial fatigue analysis, and the proposed model can automatically adapt for different failure modes, such as shear or tensile-dominated failure. Mean stress effect is also included in the proposed model by a correction factor. The life predictions of the proposed fatigue damage model under constant amplitude loading are compared with a wide range of metal fatigue results in the literature.

load. Abstract:The mechanical properties of rubber materials are complex, and the strength problem is getting more and more attention. This paper summarizes the research status of mechanics experiment of rubber materials under dynamic and static load, commented recent years domestic and foreign the progress on the field of rubber uniaxial and multiaxial fatigue. Introduced strength problem research under quasi static load of commonly used constitutive model, selection of constitutive model and determination of parameters status, pointed out the exist problems in experimental study of rubber materials strength.

In this paper, a comprehensive approach is developed to integrate computational reliability methods and nondestructive inspection (NDI) for fatigue reliability evaluation. Uncertainties existing in the performance and outcome of NDI are considered through numerical statistical measures, and the mathematical relationships among these measures are derived. A new method is proposed to estimate the probability of detection (POD) and confidence interval using these relationships. Also, a new method of using the NDI results to update the reliability estimation is presented, which accounts for POD, measurement accuracy, false call probability, and the probability that a very large flaw may not be detected. The application of the proposed methods is illustrated through an example fatigue problem and inspection techniques with different POD characteristics are compared.

As a room temperature multi-ferroic with coexisting anti-ferromagnetic, ferroelectric and ferroelastic orders, BiFeO 3 has been extensively studied to realize magnetoelectric devices that enable manipulation of magnetic ordering by an electric field. Moreover, BiFeO 3 is a promising candidate for ferroelectric memory devices because it has the largest remanent polarization ( P r >100 μC cm −2 ) of all ferroelectric materials. For these applications, controlling polarization switching by an electric field plays a crucial role. However, BiFeO 3 has a complex switching behaviour owing to the rhombohedral symmetry: ferroelastic (71 ° , 109 ° ) and ferroelectric (180 ° ) switching. Furthermore, the polarization is switched through a multi-step process: 180 ° switching occurs through three sequential 71 ° switching steps. By using monodomain BiFeO 3 thin-film heterostructures, we correlated such multi-step switching to the macroscopically observed reliability issues of potential devices such as retention and fatigue. We overcame the retention problem (i.e. elastic back-switching of the 71 ° switched area) using monodomain BiFeO 3 islands. Furthermore, we suppressed the fatigue problem of 180 ° switching, i.e. loss of switchable polarization with switching cycles, using a single 71 ° switching path. Our results provide a framework for exploring a route to reliably control multiple-order parameters coupled to ferroelastic order in other rhombohedral and lower-symmetry materials.

A fatigue life prediction procedure was discussed from the viewpoint of the constraint effect of notches. In this report, fatigue crack initiation lives were used to avoid the fatigue crack propagation process and the prediction procedure was examined experimentally. It was fouud that fatigue crack initiation lives depend on the local strain amplitude at the notch root, and the constraint effect of notches to fatigue crack initiation lives may be considered as the multiaxial effect at the notch root and might be evaluated through the equivalent stress concept as used in the multiaxial fatigue problem. The experimental results showed good agreement with the proposed fatigue life prediction procedure.

Bridges are ageing and traffic is growing, which creates a demand for accurate fatigue life assessment. The Europabrucke — a well known Austrian steel bridge near Innsbruck, opened in 1963 - is one of the main alpine north-south routes for urban and freight traffic. A long-term preoccupation of VCE with BRIMOS® (BRIdge MOnitoring System) on the Europabrucke (since 1997) and the assessed prevailing vibration intensities with regard to fatigue problems and possible damage led to the installation of a permanent measuring system in 2003. Today’s monitoring abilities enable us to measure performance precisely. High-precision sensor data of accelerations and displacements in dependence of separately registered wind and temperature data and their implementation into analytical calculation provide the possibility to realize lifetime considerations, which are of eminent importance for bridge operators.

Sonic fatigue problem is one of the important terms of civil aircraft airworthiness examination. In this paper, two different engineering analysis methods are employed to study the sonic response characteristics of a kind of typical commercial aircraft structure (skin-string-frame structure). Whereafter the sonic response experiment for this structure is carried out, and the resonance frequency and root mean square (RMS) stress are measured. According to the comparison of engineering analysis results and experimental results, the analysis error and effectiveness of these two methods are studied. The resonance frequency analysis results for both methods are in good agreement with experimental results, and the prediction results of RMS stress are also acceptable in engineering.

A two-dimensional fretting fatigue problem involving normal and tangential loading of dissimilar elastic bodies in contact is analyzed. The bodies are brought into contact by a monotonic normal load and then a cyclic tangential load is superimposed with the normal load held constant. The Hertz half plane assumption is retained for each body and the region of contact is divided into a central zone of stick and two external regions of micro-slip in each of which the Amontons-Coulomb law of sliding friction is assumed to apply. The effect of the interaction between the normal and shear stresses due to the mismatch in elastic constants is quantified by comparing the present rigid-elastic numerical solution (extreme case) to the Cattaneo-Mindlin closed form solution for elastically identical materials.

There are a number of ad hoc regression models for the statistical analysis of lifetime data, but only a few examples exist in which physical considerations are used to characterize the model. In the present paper a complete characterization of a regression model is given by solving a functional equation recurring in the literature for the case of a fatigue problem. The result is that, if the lifetime for given values of the regressor variable and the regressor variable for a given lifetime are both Weibull variables (assumptions which are well founded, at least as approximations, from extreme-value theory in some concrete applications), there are only three families of (conditional) distribution for the lifetime (or for the regressor variable). This model is then applied to a practical problem for illustration.

The analysis and application of repeated load test results of soils are approached from the point of view of improving the design of subgrades. The soils dealt with are unsaturated sandy loam and sandy clay loam. First, the characteristics of soils under repeated load are investigated by performing a simple repeated load test on the soils; next, the fatigue problem of soils are studied; thirdly, several instances of introducing the test results to the design problems of subgrades are described. Consequently, the results are found applicable to the design and construction of the subgrade.

The effect of the irradiation environment on the microstructure of materials is studied. A major part of the initial activity in this area will be aimed toward evaluating the importance of pulse effects on microstructural development. The development effort that is necessary to cope with the high cycle loading of the first wall structure is studied. The loading pulses are expected to range from 1 to 20 per second (3 x 10/sup 7/ to 6 x 10/sup 8//year), thus creating a high cycle fatigue problem for any long-lived first wall structure. The interrelationship between specimen and component testing is a major issue in this section. Static mechanical property requirements are also considered here. Lithium compatibility is treated. The final section integrates the conclusions reached in the body of the report into a unified strategy that suggests a particular effort level to support major program milestones.