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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.

This article explores the evolution of the nonlinear reduced-order modeling concept and its application to the acoustic fatigue problem as guided by a course of experiments. Since the advent of the jet engine, military aircraft have been plagued by acoustic fatigue. For decades, the resulting cracking has been a nuisance affecting mostly secondary structure, which can be routinely replaced. These thin aircraft panels are excited by ever increasing acoustic energy, causing the vibration to become nonlinear. The nonlinear response had been attributed to nonlinear damping but has been shown to be caused by geometric nonlinearity which results in nonlinear stiffness. Regardless of the cause of the nonlinearity, acoustic fatigue in conventional military aircraft can be controlled via damping treatments. However for high speed vehicles, the availability of high temperature damping treatments is practically non-existent. Furthermore, fatigue cracking in any part of the outer mold line can have catastrophic effects on the aerodynamic heating of these vehicles. Research into the prediction of the nonlinear vibration with reduced-order models has become popular in the past decade to address these concerns. This paper will document some experiences with these concepts through experimental investigations.

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.

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

The study of near-threshold fatigue crack growth has long remained an empirical field due principally to the highly microstructure-sensitive nature thereof. The primary challenges have been to forward physical model(s) informed by the governing micromechanism(s), which would be able to predict the experimental behaviors devoid of empiricism. Today, we have sophisticated experimental techniques (e.g. digital image correlation, electron microscopy) as well as atomistic simulation tools (e.g. molecular dynamics) at our disposal to finally revisit the century old fatigue problem in the light of physical phenomena therein. This paper is geared towards achieving such a feat with a very special type of materials, nano-twinned alloys, as the candidate materials, which are of great recent interest due to their reportedly superior damage properties. Specifically, we investigate how the microstructural features (e.g. slip transfer mechanism at coherent twin boundaries, twin thickness/spacing, frictional stress, pre-existent near-tip slip density) can be modulated to improve the damage resistance. The results suggest that these parameters considerably affect the crack propagation impedance (as quantified in terms of Δ K eff th ). A thorough discussion of the current findings and the most recent literature developments in this regard are provided.

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.

A complicated 3D model was established to solve the problem of the lifetime of an engine support. With the finite element analysis software ANSYS, we analyzed the fatigue problem for an engine support and derived the numerical values of the lifetime of a typical engine support. Our work provides the fundamental guidance to optimize the structure of the engine support.

Many mechanical components are subjected to multiaxial fatigue. These conditions are typically coming from external loads, the geometry of the component and/or residual stresses. However the majority of experimental data available in the literature are focused on the simpler uni-axial fatigue problem. The present work describes a series of experimental tests conducted to characterise in a comprehensive way the multiaxial behaviour of a ST52-3N structural steel. First, the monotonic properties of the steel were obtained experimentally. Then cyclic properties were also measured both in the longitudinal and torsional axes. Finally another series of tests were carried out to study the multiaxial response of the material. Both in-phase (proportional) and out-of-phase (non proportional) loadings were employed, thus providing a complete database for improving current models which describe the multiaxial behaviour of materials.

This paper shows the fatigue properties and fracture mechanism of modified 2.25Cr–1Mo steel. In refineries or chemical plants, modified 2.25Cr–1Mo steel is used in hot and high-pressure environments. Recently, a new fatigue problem concerning these facilities has become important, because number of cycles to failure that should be taken into consideration for maintenance has increased to over 107 cycles. For ultra-high-cycle fatigue, interior inclusions in the material are the dominant factor in a fatigue life, but the fracture mechanism for this has not been clearly elucidated. The results of ultra-high-cycle fatigue properties at elevated temperatures are presented. Interior fracture takes place at an ultra-high-cycle region, although many cases show no inclusions in the origins of an interior fracture. Crack growth life is predicted using fracture mechanics, so that life prediction for modified 2.25Cr–1Mo steel is possible.

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.

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.

This paper is aimed at developing a methodology and strategy for fatigue damage assessment and life prediction of bridge-deck sections of existing bridges with online structural health monitoring data. A fatigue damage model based on the continuum damage mechanics (CDM) is developed for evaluating accumulative fatigue damage of existing bridges. A structural model for the fatigue stress analysis of bridge-deck structures is proposed, in which structures are modeled by elastic members and welded connections with possible accumulative damage. Based on the proposed model, an analytical approach for evaluating the fatigue damage and service life of bridge-deck sections based on strain history data from an online structural health monitoring system and the CDM fatigue model are suggested. The updating of the representative block of cycles of the local stress by online monitoring data in the future is included in the computational approach. In order to compare results of fatigue damage and service life prediction evaluated by the CDM fatigue damage model, a modified Palmgren–Miner rule is developed for the same fatigue problem.

Aircraft structures are susceptible to fatigue and corrosion damage, notably at joints. There may be interactions between fatigue and corrosion, especially as aircraft age. Longitudinal lap splices from several types of transport aircraft pressure cabins were disassembled and investigated for Multiple Site Damage (MSD) fatigue cracking and corrosion. The results are compared with NASA data for a full-scale fatigue test. Broadly speaking, pressure cabin lap splices have either a fatigue problem or a corrosion problem: MSD fatigue cracking is not initiated by corrosion. The results are discussed with respect to lap splice MSD fatigue modelling, testing and analysis.

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.

In significantly underexpanded jets, screech inherently ceases to exist. This paper studies screech cessation in a supersonic rectangular jet and provides an explanation for its occurrence. Experimental data are presented for fully expanded Mach numbers, Mj, ranging from 1.1 to 1.9. Screech becomes unsteady beyond Mj=1.65 and ceases to exist beyond Mj=1.75. The reason for this cessation has remained a mystery, and this paper examines three suspects: (i) the theory of a frequency mismatch between screech tones and the band of the most-amplified jet instability waves, (ii) the notion that Mach disk formation disrupts the shock-cell structure and weakens the screech-producing shocks, and (iii) the idea that acoustic feedback and receptivity diminish at high levels of underexpansion. A thorough interrogation of experimental data shows that (i) is not the main cause of screech cessation here, (ii) plays an insignificant role, and (iii) appears to have been largely responsible for screech cessation. Cessation occurs because feedback to the jet lip is diminished due to excessive expansion of the jet boundary. Further, since the jet lip now reflects and scatters low intensity sound, the end result is poor receptivity at the initial shear layer. This theory is substantiated by the re-activation of screech when the nozzle lip thickness is made larger than the expanded jet boundary. Finally, increasing lip thickness is seen to produce a systematic shift (to higher Mj) of the onset of cessation. The results of this study are of direct relevance to the sonic fatigue problem in aircraft structures, because understanding screech helps prevent such damage.

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.

Cracking of cast iron cylinder liners in some large railway diesel engines is identified as a high strain fatigue problem. A series of low-cycle fatigue tests on three cast irons is reported. An improved material, in which the cooling rate in the critical region of the cylinder liner is slower than normal, has been produced and is shown to be clearly superior to two cast irons used extensively in service. This superiority is due to an improved resistance to both fatigue crack initiation and propagation.