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Dwell fatigue effect is a long-standing problem threatening the long-term service reliability for fan blades and fan disks of an aircraft engine. To understand the basic mechanism of dwell fatigue damage, pure fatigue and 60 s dwell fatigue properties of bimodal Ti-6Al-4V alloys with different volume fractions of the primary α (αp) phase were examined comparatively. The results showed that both pure fatigue and dwell fatigue life decreased with increasing the volume fraction of the αp phase and the dwell fatigue life was lower than the pure fatigue one. The quasi-in-situ test results and the quantitative characterization of damage behaviors of the local microstructure units defined by the αp-secondary α (αs) combination reveal that the αs phase close to the αp phase with extensively slip activities was gradually damaged under dwell fatigue loading, while that under pure fatigue loading was undamaged, demonstrating that the dwell loading induced the damage of the αs phase, and further reduced the fatigue life. A stress relaxation-based model is proposed to describe the physical mechanism on dwell fatigue damage of the bimodal Ti-6Al-4V alloy, i.e. the elastic deformation of the αs phase caused by the strain incompatibility would be gradually transformed into plastic deformation during the dwell stage, and thus promotes fatigue damage. The model provides new insights into the microscopic process of stress/strain transfer between the soft and hard microstructure units under dwell fatigue loading.

Corrosion has a significant deteriorative effect on fatigue life of aged ship and offshore structures; hence reliable numerical fatigue life analysis of aged ship structures is crucial for safe operation. The reliability of the fatigue damage assessment techniques depends on the quality of the S-N curve which should account for corrosion degradation. In this paper, the different factors affecting the randomness of stress concentration and fatigue life of corroded specimens have been studied. It was demonstrated that the Stress Concentration, which results from the distinctive thickness variation of the corroded specimens, significantly depends on the mean and minimum thickness of the corroded plate. The equivalent thickness of a typical plate, which has the same fatigue strength of the corresponding corroded one under the same cyclic load, was investigated. A time-dependent S-N curve of corroded structures considering the deterioration of material mechanical properties was proposed. The corroded surfaces were modeled using random spatial distributions and the effect of corrosion degradation on the material mechanical properties was taken into account. The numerically estimated fatigue life and the proposed S-N curve were compared with experimental fatigue test results. The comparison showed good agreement between the experimental results and the adopted approaches for fatigue life assessment.

Fatigue damage of asphalt mixture is the amount of energy dissipated from the tested sample in cyclic fatigue tests. The fatigue cracking could be reduced by prevailing the dissipated energy that can be applied to clarify the decrease in flexural stiffness. This study investigates the effects of Reclaimed Asphalt Pavement (RAP) and strain level on the fatigue life and dissipated energy concepts of the asphalt mixtures. Thirty-six beams were prepared and tested at a constant strain loading mode with 0%, 30%, 50%, and 100% content of RAP at a temperature of 20 °C and frequency of 5 Hz at three strain levels of 750, 400, and 250 micro-strain. Results show that the plateau value (PV) criterion seemed more feasible in estimating the fatigue performance of RAP mixtures and the dissipated energy approach is useful to understand fatigue testing under load-controlled mode. Therefore, fatigue life can be projected without performing millions of load repetitions.

PurposeThe purpose of this paper is to contribute to the solution of the fatigue damage problem of reinforced concrete frames in bending.Design/methodology/approachThe problem of fatigue damage is formulated based on the rheological–dynamical analogy, including a scalar damage variable to address the reduction of stiffness in strain softening. The modal analysis is used by the finite element method for the determination of modal parameters and resonance stability of the selected frame cross-section. The objectivity of the presented method is verified by numerical examples, predicting the ductility in bending of the frame whose basic mechanical properties were obtained by non-destructive testing systems.FindingsThe modal analysis in the frame of the finite element method is suitable for the determination of modal parameters and resonance stability of the selected frame cross-section. It is recommended that the modulus of elasticity be determined by non-destructive methods, e.g. from the acoustic response.Originality/valueThe paper presents a novel method of solving the ductility in bending taking into account both the creep coefficient and the aging coefficient. The rheological-dynamical analogy (RDA) method uses the resonant method to find material properties. The characterization of the structural damping via the damping ratio is original and effective.

This paper investigates the fatigue damage of the wellbore cement sheath under different cyclic loading conditions. According to the irreversible principle of thermodynamics, a damage evolution model considering both tension and compression fatigue damage is established. With acoustic emission monitoring, uniaxial compression and Brazilian disc splitting cyclic loading failure tests were performed. Based on the test results, the damage theory is verified using the cumulative strain, Young’s modulus and acoustic emission characteristics. The research gives a numerical algorithm of the fatigue damage theory to develop as a constitutive equation. With reference to the structural and operating parameters of a gas storage salt cavern in Jintan, a casing-cement sheath-stratum numerical model is established. By inserting the damage constitutive equation into the numerical model calculation, the damage characteristics of the cement sheath are shown. Finally, the gas storage operating parameters that meet the requirements of high injection-production efficiency and long service life are given.

The corrosion environment of a steel truss bridge significantly shortens its service life, particularly the chemical pollution in the air. A linear corrosion prediction model is proposed based on Miner’s linear cumulative damage concept to solve the difficulty of implementing accelerated corrosion tests. Moreover, an equivalent fatigue test is designed in combination with the corrosion prediction model. The results indicate that the bridge’s fatigue resistance can meet the design requirements when the corrosion environment is not considered. When the corrosion effects are jointly considered, the fatigue durability of the bridge is insufficient. With the increase in fatigue cycles, stiffness degradation presents a three-stage trend. The intermediate stage is a gentle development stage from the fatigue test results, accounting for approximately 80% of the total life cycles. Finally, a fatigue damage prediction model considering corrosion factors is established, and the law of fatigue damage and stiffness degradation of the structure under a corrosive environment is determined.

The fatigue damage behavior of the nanocrystalline Au films on polyimide substrates was investigated. It was found that the very high-cycle fatigue damage resistance of the Au film was significantly enhanced by at least a factor of ∼2 in supported loading through adding an ultrathin Ti interlayer at the Au film/polyimide interface. Such a better fatigue damage resistance is mainly ascribed to the effective suppression of voiding at the Au film/polyimide interface through modulation of the Au/Ti interface, and thus the propensity of the cyclic strain localization and grain boundary cracking is reduced. The finding may provide a potential strategy for the design of flexible devices with ultra-long fatigue life.

Adoption of heavy haul traffic on many railroads, comprising Russian railways, has highlighted the relevance of assessing the effect of increased axial loads on the contact fatigue life of rails.The article describes a set of theoretical studies carried out to create a scientifically substantiated method for predicting the contact fatigue life of rails depending on the values of axial loads. The stress-strain state of the contact area has been determined using the finite element model of wheel rolling on a rail. It has been found that the wheel-rail rolling contact area undergoes complex multiaxial loading with the simultaneous action of normal and shear strains. Based on the analysis of models describing multiaxial fatigue damage, the Brown–Miller model was chosen, which considers the simultaneous action of normal strains at the contact area and of maximum shear strains, which most fully describes the stress-strain state of the wheel-rail rolling contact area. To apply the Brown–Miller model, fatigue stress-strain curves for rail steel have been identified. Based on the analysis of methods for determining the parameters of stress-strain curves carried out by V. A. Troschenko, a modified Roessle– Fatemi hardness method has been applied. Based on the experimentally determined values of hardness on the rolling surface, the parameters of the curves of elastic and plastic fatigue have been revealed by calculation and experiment. To establish the damaging effect of the load from wheel rolling on a rail, the concept of relative damage per rolling cycle had been assumed which is the value inverse to the number of cycles preceding formation of a contact-fatigue crack at a given value of the axial load.Calculations of the relative damage rate of the rolling surface of rails caused by contact fatigue defects were carried out with the Fatigue software package considering mean values of the indicators of the degree of fatigue strength and plasticity of rail steel and the calculated stresses in the wheel-rail contact area, as well as the plasticity correction using Neuber method. The polynomial dependence of relative damageability of the rolling surface of rails is obtained. The established functional dependence of relative damageability of the rolling surface of rails on the values of vertical forces can be used as the basis for the developed methodology for predicting the contact fatigue life of rails.

This paper studies the flexural fatigue performance of damaged steel beams strengthened by carbon fiber reinforced plastic-optical fiber bragg grating (CFRP-OFBG) plates. By analyzing the test beam’s failure mechanism under cyclic loading and the strain data monitored by the CFRP-OFBG panel in real-time, a life prediction model based on cumulative fatigue damage is proposed. The test results show that CFRP-OFBG plate reinforcement effectively reduces the fatigue crack growth rate of damaged steel beams and increases the fatigue life of damaged steel beams by 22.46%. The analysis and test results show that the minimum error between the calculated value of the life prediction model and the test value is −24.13%, and the maximum error is −5.61%. This study provides some suggestions for improving the service life of existing fatigue-damaged steel beams and establishing a simple fatigue life evaluation model.

In order to investigate the fatigue damage property of permeable friction courses (PFC) under the coupling action of water, temperature and load, the PFC with length of 2.93 m, width of 1.10 m and thickness of 0.04 m was prepare in the laboratory and tested by the accelerated loading testing system MMLS3. The profilometer and the portable seismic properties analyzer (PSPA) was utilized to measured the rutting depth and modulus of the whole asphalt pavement, respectively. It is found that the PFC is compaction-type rutting. In the position 200 mm, the modulus first increases and then decreases. The excess pore water pressure is not measured in pavement. The results can provide beneficial references for the design, construction and fatigue damage analysis of PFC.

Based on the stress-strain relationship under cyclic loading by large dynamic triaxial test, the cumulative strain distribution law of CSG materials was studied, and a dynamic damage model of CSG m...

The naturally fractured rock in the open pit slope is susceptible to irreversible damage caused by fatigue loads related to freeze-thaw weathering, blasting vibration, earthquakes and tramcar traffic. To ensure the safety of rock mass and reveal how natural fracture affects the damage modelling characteristics is of great concern. Hence, this work aims at investigating the fatigue damage evolution of rock from volumetric deformation caused by F-T and cyclic loads. The rock structural deterioration and damage accumulation were investigated as well as the stimulated natural fracture pattern. Results show the frost heaving force acted on natural fracture results in the rock volumetric changes. The damage variable expressed by volumetric strain presents a linear relationship with freeze-thaw cycles. In addition, the axial, lateral and volumetric strain of marble exposed to cyclic loads present a two-stage pattern, they first increase quickly and then get to steady and last for a long time. A new fatigue damage model was established by considering the freeze-thaw damage and mechanical damage simultaneously. The proposed coupling damage model can well describe rock damage accumulation. Moreover, the CT images further reveal the influence of the natural fracture on rock volumetric deformation and the final damage accumulation. It is suggested that the opening-mode natural fractures contribute a lot to rock freeze-thaw deformation and fatigue deformation.

In this work, a new fatigue damage model considering the additive manufacturing (AM) effects is established. We first present the elastoplastic constitutive model with the newly established fatigue damage model considering AM effects. The method to calibrate the material parameters is put forward, and the numerical solution of the theoretical model is implemented. Second, the fatigue lives of two AM metal materials are predicted, and the applicability of the theoretical model is verified by the test results. Finally, the influence of the volume energy density ratio on the fatigue life of AM metal materials is analyzed, and the results show that the volume energy density ratio has a great influence on the fatigue behavior of AM metal materials. When the ratio is less than 1.0, the fatigue life increases rapidly with the increase of the ratio. The fatigue life increases with the stress ratio when the volume density ratio keeps as a constant. The research work in this paper provides a feasible method to predict the fatigue life of AM metal materials by continuum damage mechanics in engineering.

The fatigue damage process of SiC coated needled C/SiC composite specimen was monitored by acoustic emission (AE) under tension-tension cyclic loading. By analyzing the collected AE parameters of the composite, it is found that Kaiser effect enhances with the increase of stable cycles in the fatigue process. Moreover, multivariate K-means cluster analysis of AE parameters was carried out after the standardization of energy, amplitude, peak frequency and duration of AE signal. By comparing the objective function values of different number of clusters, and referring to the intra group variance and the variance between groups, the damage modes of the needled C/SiC composite are finally divided into four clusters, and the characteristics of AE parameters with different damage modes can be obtained. Furthermore, by referring to the microstructure characteristics of needled C/SiC composite, various damage modes at different fatigue stages were analyzed. In addition, the fracture morphology of the specimen was also observed by scanning electron microscope after fatigue fracture.

The multiaxial character of high-speed railway brake disc thermomechanical fatigue damage is studied in this work. Although the amplitudes and distributions of temperature, strain and stress are similar with uniform and rotating loading methods, the multiaxial behavior and out-of-phase failure status can only be revealed by the latter one. With the help of a multiaxial fatigue model, fatigue damage evaluation and fatigue life prediction are implemented, the contribution of a uniaxial fatigue parameter, multiaxial fatigue parameter and out-of-phase failure parameter to the total damage is discussed, and it is found that using the amplitude and distribution of temperature, stress and strain for fatigue evaluation will lead to an underestimation of brake disc thermomechanical fatigue damage. The results indicate that the brake disc thermomechanical fatigue damage belongs to a type of multiaxial fatigue. Using a uniaxial fatigue parameter causes around 14% underestimation of fatigue damage, while employing a multiaxial fatigue parameter without the consideration of out-of-phase failure will lead to an underestimation of about 5%. This work explains the importance of studying the thermomechanical fatigue damage of the brake disc from the perspective of multiaxial fatigue.

The core of structural health monitoring is to provide a real-time monitoring, inspection, and damage detection of structures. As one of the most promising technology to structural health monitoring, the Lamb wave method has attracted interest because it is sensitive to small-scale damage with a long detection range. However, in many real-world structural health monitoring applications, the nature of the problem implies structures work under normal condition in most of its operating phases; therefore, classes of data collected are not equally represented. The predictive capability of damage detection algorithms may significantly be impaired by class imbalance. This article presents a damage detection method using imbalanced inspection data which is collected through Lamb wave detection. Aiming at maximizing detection accuracy, an improved synthetic minority over-sampling technique using three-point triangle (triangle synthetic minority over-sampling technique) is proposed to conduct the over-sampling procedure and increase the number of minority samples. The iterative-partitioning filter is employed to remove the noisy examples which may be introduced by triangle synthetic minority over-sampling technique. Three conventional classification methods, namely, support vector machine, decision tree, and k-nearest neighbor, are used to perform the damage detection. A fatigue crack detection test using Lamb wave is performed to demonstrate the overall procedure of the proposed method. Three damage sensitive features, namely, normalized amplitude, correlation coefficient, and normalized energy, are extracted from signals as datasets. A cross-validation is performed to verify the performance of the proposed method for crack size identification.

Fatigue damage accumulation is a critical factor resulting in the failure of prestressed concrete (PC) bridges. The fatigue damage is usually caused by the coupled effect of cyclic vehicle loading and environmental corrosion. This study investigated probabilistic fatigue damage on aging PC bridges considering both stochastic traffic loading and corrosion. A stochastic traffic model was derived based on long-term monitoring data aiming to simulate fatigue stress spectra of critical rebar. The effect of cracks on the fatigue stress spectra was investigated in order to model the fatigue stress state more realistically. A three-stage traffic growth model was established based on traffic volume histories of three highways in China. A fatigue limit state function considering traffic growth and corrosion effect was deduced for fatigue reliability assessment of PC bridges. Numerical results show that the stress amplitude of rebar considering cracks is 1.53 times greater than the rebar with no-cracks, resulting in a decrease of fatigue life by 68 years. In addition, the three-stage traffic growth models lead to 25 years shorter fatigue life than the one considering a linear traffic growth model. Finally, the corrosion effect results in a fatigue life of 44 years. The numerical results provide a theoretical basis for fatigue life estimation and maintenance of aging PC bridges.

This paper presents an Acoustic Emission characterisation of the damage behaviour of asphalt concrete subjected to bending fatigue loading. An experimental campaign is carried out on an old asphalt...

In this paper, a micromechanical fatigue life prediction method for fiber-reinforced ceramic-matrix composites subjected to stochastic overloading at room temperature is developed. Fatigue damage mechanisms in the matrix, interfaces, and fibers are characterized using different damage models. Relationships between the fatigue life and related degradation rate, stochastic overloading stress, and breakage of intact fibers are established. Experimental fatigue life of different C/SiC composites subjected to different stochastic overloading is predicted. For the same stochastic overloading condition, the degradation rate of fatigue life is the highest for cross-ply C/SiC composite, and the lowest for 2.5D C/SiC composite.

It is a widely known fact that the stiffness of polymer composite materials decreases with the accumulation of fatigue damage under cyclic loading. The purpose of this article is to develop a method and obtain experimental data on decrease of the elastic characteristics of a fiber-reinforced laminate, as a result of progressive fatigue damage. The developed technique consists of two stages. At the first one, the natural frequencies and eigenmodes of the samples during their fatigue testing are experimentally obtained. The dependences of the natural frequencies of the samples on the number of loading cycles are found. At the second stage, the four elasticity parameters of the laminate monolayer (two Young modules, the shear module and Poisson's ratio) are identified via the natural frequencies. The inverse numerical/experimental technique for material properties identification is applied. The dependences of the natural frequencies and mentioned elastic characteristics on the relative fatigue life are obtained as experimental results of both modal and fatigue tests. The results can be useful to study the fatigue behavior of the investigated materials and to create methods for calculating fatigue life.

Based on the modulus mortification rule of continuum internal variable theory of thermodynamics connected to concrete materials under frazzle loading, a simple, reliable, better and computational efficient theoretical fatigue damage model due to formation of microvoids, microcracks, microdefects and fractal is proposed. The prescribed new theory is linked with strain-based approach where “strain” is the main domain and is capable for prediction of fatigue life of concrete as well as cementitious and brittle material. Investigational data from fatigue test were employed to validate the model, and results show that the model can describe the fatigue damage progression of concrete materials under different frazzle loadings by verifying the predicted fatigue life. Mortification of elastic modulus, damage enlargement corresponding to the normalized life, degradation of stress level from elastic to plastic and its accumulation subjected to variable frazzle loading including its verifications are well discussed.

One of the important aspects of mechanical design is improving fatigue life.; In this work, the effect of Ultrasonic impact treatment (UIP) and shot peening (SP)on constant cumulative fatigue life and fatigue strength of AA7075-T6 were studied; The sample group was machined and primed, and some specimens were treated using ultrasonic impact therapy (UIT) with one line of peening. Fatigue experiments were conducted under constant and variable amplitude (R=-1) at ambient temperature to determine the fatigue life of the S-N curve and fatigue strength during treatment 3.46% and 8.57% at 107 cycles for (UIT) and (SP). Cumulative fatigue damage testing was carried out for two steps loading it is observed that the fatigue life for SP and UIP treated specimens was improved compared to the unpeeled results. The fatigue endurance limit was enhanced by 35% for UIT and 54% for SP. The fatigue life for both treatments was much improved compared to as-received metal. These results also show a strong tendency of increasing fatigue strength after application of (UIT) and (SP) with an increase in mechanical properties of the material used. Conclusion The constant fatigue properties are considerably enhanced by (UIT) and (SP) techniques. The fatigue strength at 107 cycles is improved by 3.46% and 8.57% for UIT and SP respectively. Cumulative fatigue life was increased by 13.9 percent and 12.6 percent for low-high and high-low loading by UIT, respectively, while 36.6 percent and 22.3 percent were increased for low-high and high-low loading by SP, respectively, and fatigue life was improved by 36 percent and 54 percent for UIT and SP. The (UIT) and (SP) techniques are a suitable method for hardening the surface of metals due to the formation of a hard layer by increasing compressive residual stresses. The Miner theory does not follow the conservative and detailed prediction of the life of certain fatigue specimens

New insight into the microstructural evolution and the correlative damage mechanisms near fatigue crack tip in a TiB2/Al composite was conducted by transmission kikuchi diffraction and transmission electron microscopy. It was found that the micro deformation band formed from the crack tip and ran along slip planes. Ultrafine grains were induced in deformation band, where the fatigue crack preferring to grow along these deformation-induced boundaries was first demonstrated as the essential process of crack across parent grains and grain boundaries. Ahead of crack tip, the TiB2 particles can affect crack growth by impeding the successive propagation of deformation band.

The fatigue characteristics of rock materials are usually studied by cyclic load–unload tests, and the deformation and damage development reflect their weakening characteristics. In this paper, according to the mechanical characteristics of rock materials during load/unload cycles, the total strain can be separated into three types, that is, elastic strain, viscoelastic strain, and viscoplastic strain. The elastic strain is linear with stress, and viscoelastic strain exhibits a special behavior after unloading, the viscoplastic strain also displays its own unique features and reflects the damage in rocks. Based on their unique characteristics, we establish elastic, viscoelastic, and viscoplastic submodels, then an elastic-visco-plastic model can be obtained by connecting three submodels in series, which can reflect the development of the law of different strains. In order to verify the reliability of the model, red sandstone samples are selected for cyclic load/unload tests. The results show that the collected strain–time data are well fitted by the model. In addition, the characteristics of strain–time curves imply the deformation and damage development of rocks during load/unload cycles.

This paper investigates the fatigue performance of CFRP (carbon fiber-reinforced polymer) cables using a bond-extrusion anchorage system in which the variable stiffness of the bonding medium in the steel sleeve is adopted. A group of cyclic loading experiments under a maximum stress of 0.45 f u and a stress range from 500 MPa to 900 MPa were carried out to determine the fatigue damage evolution of the cable anchorage assemblies. In addition, the fatigue failure mechanism and the influence of cyclic loading on the mechanical performance, such as the stress and stiffness of the cable, the relative displacement of the anchorage assemblies and the stress of the steel sleeve, were also investigated. The results indicated that the stress range primarily affected the fatigue life of the cable anchorage assemblies. The damage of the anchorage assemblies was generated in the cable at the outer-layer tendons, which first forms longitudinal cracks, then splits and finally results in rupture. The axial strain of the cable was still linear, and the axial stiffness decreased by 8% compared with the initial stiffness after 1.2 million cycles under a stress range of 500 MPa. The stress variation in the steel sleeve was not obvious with cyclic loading. The fatigue performance for the anchorage assemblies was obtained and it could realize 2 million cycles below the design stress range of 470 MPa based on the trend analysis from the fatigue experiment.

In an earlier research, experimental evidence was given on the ability to use Piezo Wafer Active Sensors and acousto-ultrasonics to monitor the accumulation of fatigue damage in a thick composite structure. As a next step, numerical models are investigated as they aid in the further understanding of the governing phenomena and a quantification of the accumulated damage. However, they suffer from high computational demands, due to a high mesh density, the stochastic nature of crack initiation and the combination of initiation and propagation of cracks. The Polynomial Chaos Expansion (PCE) method is employed to efficiently make meta models and, with these models, account for the stochastic behaviour of crack initiation and formation of delaminations. The meta models thus allow predicting the overall effect of damage accumulations within certain bounds of uncertainty. This aids in the quantification of damage accumulation, hence allowing for a damage severity estimation based on the experimental results. The input for the PCE method is a 2D Finite Element (FE) model. Cracks and delaminations are generated using Random Variables (RV) describing the geometrical position and length and orientation. Moreover, the number of cracks and delaminations is randomized as well. The necessary remeshing is done automatically, allowing for a completely automated simulation for a large number of FE simulations to feed the PCE model. Several Quantities of Interests (QoI) are defined and tested against their sensitivity to the increasing amount of damage accumulation. A global sensitivity analysis is used to identify the importance of each of the Random Variables. Random variables with a low sensitivity can be eliminated from the analysis, improving the efficiency.

An experimental investigation has been undertaken to determine the effects of fatigue on the high strain-rate material properties of high-performance steel used in modern naval vessel structures. A novel methodology to conduct tensile testing at low and high strain-rates on fatigued specimens was developed. A bespoke Split Hopkinson’s Tension Bar clamping arrangement was designed to undertake the necessary high strain-rate testing of flat dog-bone specimens. Analysis of the microstructure of the specimens was performed alongside a comparison on the strain-rate sensitivity of the tested DH36 steel against other literature sources. Testing revealed no statistically significant effect of high cycle fatigue at high strain-rate as determined by a two-sample t-test, but revealed a possible effect on quasi-static material properties. The findings of this novel comparison between fatigued and virgin material properties of shipbuilding steel provides decision-makers and researchers with an understanding on the effect of fatigue on high strain-rate material properties.

Vortex-Induced Vibration (VIV) is a major contributor to the fatigue damage of marine risers which are often arranged in an array configuration. In addition to helical strakes and fairings, studies have been strived in searching for possible VIV suppression techniques. Inspired by giant Saguaro Cacti, flexible cylinders of different cactus-shaped cross sections were tested in a water tunnel facility, and test results showed that cactus-like body shapes reduced VIV responses of a cylinder at no cost of significant increase of drag. A series of experiments were conducted on a pair of two tandem-arranged flexible cylinders and an array of four cylinders in a square configuration to investigate the effects of wake on the dynamic responses of cylinders and the VIV mitigation effectiveness of the cactus-like body shape. Results showed that the cylinders in a square configuration, either at the upstream or downstream positions, might have larger dynamic responses than those of a single cylinder. The cactus-like body shape could mitigate VIV responses of cylinders at upstream positions in an array configuration; however, similar to helical strakes, the mitigation efficiency was reduced on downstream cylinders. Note that the cactus-like cross-sectional shape investigated was not optimized for VIV suppression. The present study indicates that the modification of the cross-sectional shape of a cylinder to a well-designed cactus-like shape may be used as an alternative technique to mitigate the VIV of marine risers.

The novel destructive method, which is based on enlarging of initial cold-expanded hole diameter, is developed for quantitative assessment of fatigue damage accumulation. The secondary hole diameter increments in principal strain directions are measured at different stages of low-cycle fatigue. These data offer construction of normalized dependencies of principal residual strains, related to the secondary hole diameter, against of lifetime percentage, thus providing a explicit form of the damage accumulation function. These functions are obtained for mandrel entrance and exit side. Obtained information reveals peculiarities of damage accumulation depending on residual stress level. The results also demonstrate how stress ratio influences on the damage accumulation process under low-cycle fatigue conditions.

This study presents the fatigue response of 304 stainless steel foil, cold-rolled to a thickness of 3.2 μm with 87 percent cold work at orientations of 0, 45, and 90 degrees to the direction of rolling. Fatigue specimens were fabricated by laminating a supportive layer of 20-μm polyimide film to one side of the foil and patterning 242 crack initiation features by photolithographic process. Progression of fatigue damage was determined through electrical resistance measurement. The fatigue response was demonstrated to be largely affected by anisotropy existing between the rolling direction and the off-axis orientations. Fatigue cracks that traveled in a direction parallel to the elongated grains (cyclic loads applied at 90-degree orientation to foil rolling direction) had the most fatigue response (undesirable characteristic). The construction of the specimens with thin foil supported by a film backing contributed to high fatigue threshold.

For structural health of mechanical structures, non-destructive detection and material defect characterization represent the main useful tools for mechanical decay prediction caused by local composite damage phenomena. In this work, internal delamination due to alternate bending were characterized in flat specimens, performing fatigue and static tests, coupled with thermographic, optical, and ultrasonic analysis for damage detection and evolution purposes. Damage to rupture behavior of CFRP material through mechanical tensile tests is performed on several samples and non-destructive inspection procedures are optimized during successive HCF tests to detect in real time local compliance variations and damage initiation. Thermographic continuous monitoring and occasional ultrasonic analysis are implemented to analyze composite anomalies during fatigue life and to elaborate a procedure for identification of delamination induced damage before failure. IRT and UT results are computed with MATLAB analysis for damage evaluation with strain and compliance data acquired during tests.

The effect of martensitic transformation on the fatigue damage of AISI 321 stainless steel is investigated. After low-cycle fatigue testing five batches of AISI 321 steel, several specimens were selected, which significantly differed in the amount of α'-martensite measured by the eddy current method. The influence of the variations in chemical composition on the maximum amount of strain-induced α'-martensite is discussed. With an increase in amount of α'-martensite, an increase in shear bands intersections was observed on the optical micrographs. The material density measurements were carried out by hydrostatic weighing. The density reduction resulting from fatigue was quantified. It is shown that a decrease in density linearly depends on the amount of strain-induced α'-martensite formed in the fatigue-damaged material. It is concluded that the effects of damage accumulation and martensitic transformation on the density reduction are inseparable, since both are caused by the same mechanism – the slip of dislocations and the increase in the density of dislocations.

Рассматривается влияние остаточных напряжений, формирующихся при различных видах поверхностной обработки элементов пар трения, на скорость накопления контактно-усталостных повреждений, возникающих при циклическом нагружении поверхностей взаимодействующих тел в условиях трения качения при наличии поверхностного изнашивания. Исследовано влияние относительного проскальзывания, коэффициента трения скольжения, величины остаточных напряжений на распределение амплитудных значений максимальных касательных напряжений. Полученные результаты использованы для анализа влияния поля остаточных напряжений и скорости поверхностного изнашивания на процесс накопления контактно-усталостных повреждений. Residual stresses are formed during various types of surface treatment of elements of friction pairs. The effect of the residual stresses on the rate of fatigue damage accumulation is considered for the case of cyclic rolling contact in the presence of surface wear. The effect of relative slippage, friction coefficient, and residual stresses on the distribution of the amplitude values of the principal shear stress is studied. The results are used to analyze the effect of the residual stresses and the surface wear rate on the fatigue damage accumulation.

Failure of the cables can cause a bridge to collapse. Fatigue damage of steel wire is one of the causes of cable failure. In this paper, we study the relationship between the fatigue damage and the group speed of guided waves in the steel wire. The relationship between cyclic loading times and group speed of steel wire is obtained by applying tension to steel wire. The results show that the group speed of guided waves increases linearly before the 6.02 million cyclic-loading times, increases exponentially from 6.02 to 6.97 million times. The curve of the relationship between the group speed of the guided waves and the number of cyclic loading times can be fitted to an exponential function, and this curve can be used as a calibration curve to evaluate the fatigue damage of steel wire.

The contact fatigue of aviation gears has become more prominent with greater demands for heavy-duty and high-power density gears. Meanwhile, the coexistence of tooth contact fatigue damage and tooth profile wear leads to a complicated competitive mechanism between surface-initiated failure and subsurface-initiated contact fatigue failures. To address this issue, a fatigue-wear coupling model of an aviation gear pair was developed based on the elastic-plastic finite element method. The tooth profile surface roughness was considered, and its evolution during repeated meshing was simulated using the Archard wear formula. The fatigue damage accumulation of material points on and underneath the contact surface was captured using the Brown-Miller-Morrow multiaxial fatigue criterion. The elastic-plastic constitutive behavior of damaged material points was updated by incorporating the damage variable. Variations in the wear depth and fatigue damage around the pitch point are described, and the effect of surface roughness on the fatigue life is addressed. The results reveal that whether fatigue failure occurs initially on the surface or sub-surface depends on the level of surface roughness. Mild wear on the asperity level alleviates the local stress concentration and leads to a longer surface fatigue life compared with the result without wear.