Rate Of Fatigue Damage Accumulation Research Articles

Phase field modeling of fatigue crack growth retardation under single cycle overloads

A zone-based crack retardation model that responds to single cycle overloads is applied to a phase field fatigue framework. Fatigue crack growth is incorporated through the degradation of fracture toughness in the phase field fracture model where a representative loading strategy is followed instead of explicit cyclic loading. The model is demonstrated to capture Paris-Erdogan law type behavior. Crack growth retardation following an overload cycle is simulated through a zone ahead of the crack tip taking inspiration from existing plastic zone-based retardation models. The retardation zone is described through a strain energy density limit, with the overload ratio controlling the extent to which the fatigue damage accumulation rate is slowed inside the retardation zone. The model is implemented utilizing user subroutines in Abaqus with coupled-temperature displacement elements where temperature acts as a stand in for the phase field parameter. The model is found capable of reproducing experimental levels of fatigue life gains and reduction in crack growth rate for compact tension and center-cracked tension panel specimens when various overload levels are applied. Furthermore, the model is demonstrated to be able to capture complex crack paths with great accuracy.

Multiaxial Fatigue Assessment for the Hanger Deck Connection of a High-Speed Steel-Truss-Arch Railway Bridge

Steel-truss-arch bridges have been applied in high-speed railway bridges due to their excellent dynamic and static structural performance. Under the action of high-speed trains, the steel connections between hangers and decks suffer from repeated stresses, inducing potential fatigue problems or even fatigue failure. In this study, a multiaxial fatigue evaluation method was first created and established based on critical damage-plane methodology, following which the fatigue evaluation procedure was also created and recommended. The methodology was applied to real-life strain data from a high-speed railway bridge from which an assessment of fatigue damage and predicted fatigue life was estimated. The connection between the shortest hanger and deck on the downstream side was selected as the target due to its relatively high stress. A multiscale finite-element model of this bridge was created according to the design profile and monitoring results of traffic flow, where the finite-element model was calibrated and validated by comparing the calculation results with the monitoring data. Influence analysis was then carried out to investigate two factors—i.e., the total traffic flow and compositions of freight trains—having effects on the fatigue life of the steel connection. The results indicate that the applied multiaxial fatigue method is suitable for online fatigue evaluation of actual bridges. In addition, by using the multiaxial fatigue method, the fatigue-damage accumulation rate can be nearly 60 times that obtained by the uniaxial fatigue method. If freighting is taken into consideration, the fatigue damage will increase rapidly, and for the case 10% of proportion traffic as freighting, the actual fatigue life is estimated to be shorter than the design life.

High-cycle fatigue damage accumulation in paper

The mechanical durability of paper is a key consideration for applications ranging from shipping boxes to disposable medical substrates. Paper commonly experiences fatigue loading in such applications, but a high-cycle fatigue mechanism has not been identified. This research details paper’s high-cycle fatigue degradation mechanism. Paper specimens were loaded with monotonically increasing, constant, and sinusoidally varying cyclic stresses, and the resulting tensile, creep, and fatigue damage accumulation rates were compared. The difficulty in defining the size and growth of cracks in paper’s cellulosic fiber network were overcome with optically measured strain fields. We found that fatigue damage can accumulate via a fiber fracture mechanism, while ratchetting, creep, and tensile overload damage accumulation occurs due to failure of inter-fiber bonds. We also discovered the synergistic interaction between creep and high-cycle fatigue damage accumulation mechanisms, which is critical for extending the high-cycle fatigue life of paper.

Multiaxial fatigue behavior and life prediction of 7075-T651 aluminum alloy under two-step loading

Focusing on the loading sequential effects on the multiaxial fatigue damage accumulation, tests including two series of constant amplitude loadings and 12 groups of two-step loading spectra were conducted on 7075-T651 aluminum alloy. Under the same equivalent stress amplitude, the multiaxial fatigue life raises with the increase of stress amplitude ratio. Fatigue damage accumulation rate is decreased by the two-step loading interaction. Cyclic loading curves and fracture morphology analysis reveal that the loading step corresponding to lower fatigue life is dominant. Considering the stress amplitude ratio effects and loading interaction, a non-linear accumulative damage model is proposed based on the modified Basquin’s criterion. The proposed model provides a more accurate calculation of accumulative fatigue damage compared with the other four commonly used models. Fine life prediction results are obtained by the proposed model with all predicted data within a factor of three.

Расчетный анализ усталостной долговечности и скорости выработки ресурса на различных стадиях жизненного цикла СПБУ

This paper gives modal and structural calculations of jack-up rigs at operational and transportation stages, as well as more accurate structural calculations for jack-up supports, as well as effective stress ranges at hot points. Based on these results, the paper gives a simplified fatigue strength calculation for jack-up support, by means of Weibull bi-parametric distribution. It also compares fatigue damage accumulation rates of jack-up at different stages of their life cycles, as well as predicts its residual lifetime.

Fatigue life prediction of composite material's adhesive joints in automotive applications

Composite and adhesive joints are used increasingly in the automotive industry, not only because of the government policy but also their advantages in mechanical properties over traditional materials and joints. An active research area is the fatigue analysis of adhesive joints. In this paper, a methodology to predict the fatigue life of adhesive joint is proposed and implemented into LS-DYNA with the joint modelled using a user-defined cohesive material. Fatigue crack growth rate is used to obtain the fatigue damage accumulation rate in cohesive zone model. Our method is verified by numerical simulations of two commonly used adhesive joints in the automotive industry: single-lap joint and stepped-lap joint. The predicted S-N curve fits well with the experimental data.

Evaluating the heat energy dissipated in a small volume surrounding the tip of a fatigue crack

Fatigue crack initiation and propagation involve plastic strains that require some work to be done on the material. Most part of this irreversible energy is dissipated as heat and consequently the material temperature increases. The heat being an indicator of the intense plastic strains occurring at the tip of a propagating fatigue crack, the hypothesis is formed that it can be used to assess the fatigue damage accumulation rate of cracked components. Moreover, the heat energy at the crack tip is averaged according to Neuber’s finite particle concept. The aim of the present paper is to present the theoretical framework and the corresponding experimental technique to evaluate the heat energy dissipated in a structural volume surrounding the crack tip. The shape and size of the structural volume have been assumed according to the literature, even though the definition of the structural volume size of the analysed material in a fatigue sense is not the scope of the present paper. The proposed experimental technique to evaluate the averaged heat energy is based on the radial temperature profiles measured around the crack tip by means of an infrared camera. The temperature fields measured within few millimetres from the crack tip have been compared successfully with existing analytical solutions.

Experimental estimation of the heat energy dissipated in a volume surrounding the tip of a fatigue crack

Fatigue crack initiation and propagation involve plastic strains that require some work to be done on the material. Most of this irreversible energy is dissipated as heat and consequently the material temperature increases. The heat being an indicator of the intense plastic strains occurring at the tip of a propagating fatigue crack, when combined with the Neuber’s structural volume concept, it might be used as an experimentally measurable parameter to assess the fatigue damage accumulation rate of cracked components. On the basis of a theoretical model published previously, in this work the heat energy dissipated in a volume surrounding the crack tip is estimated experimentally on the basis of the radial temperature profiles measured by means of an infrared camera. The definition of the structural volume in a fatigue sense is beyond the scope of the present paper. The experimental crack propagation tests were carried out on hot-rolled, 6-mm-thick AISI 304L stainless steel specimens subject to completely reversed axial fatigue loading.

Microstructure-sensitive accumulation of plastic strain due to ratcheting in bearing steels subject to Rolling Contact Fatigue

It is well known that the empirical parameters correlated to Rolling Contact Fatigue (RCF) bench tests are sensitive to the microstructural attributes of the bearing material. The key driver for this sensitivity is the accumulated deformation accentuated by the difference in the mechanical properties of the carbide precipitate, matrix, and interface. This manuscript studies the accumulation of deformation/micro-plastic strain during RCF due to ratcheting behavior in the microstructure of bearing steels. The objective of this study is to understand the contribution of carbide particles towards ratcheting. Homogeneous elastic–plastic finite element (FE) simulations of the ball-on-rod RCF test using a ‘global–local’ approach is used, and is applicable when the drivers for fatigue degradation are controlled primarily by the heterogeneous field represented by the carbides. The global model simulates the overall ball-on-rod RCF test considering homogeneous material, while the local model accounts for the influence of the carbide particles in the microstructure. The results from finite element simulations reveal that carbide particles act as stress concentrators and introduce a shear stress cycle with a non-zero mean stress at the scale of the carbide microstructure, which promotes strain accumulation via ratcheting. A study on the spatial variation of ratcheting behavior in the vicinity of the carbide particle is also presented. The results presented translate to other through and case-hardened bearing steels subject to RCF and highlight the important role played by the carbide microstructure in controlling the spatial and temporal rate of fatigue damage accumulation via localized ratcheting. The approach presented has general applicability to heterogeneous materials with other forms of heterogeneity such as inclusions, pores and grain boundaries, subject to multiaxial fatigue.

Fatigue of Solder Interconnects in Microelectronic Assemblies under Random Vibration

This study investigates vibration fatigue durability of solder interconnects of surface mount electronic IC packages under harmonic and random excitation, through accelerated stress testing and physics-of-failure (PoF) simulations. The solder material of interest is Sn3.0Ag0.5Cu. The test vehicle consists of several HVQFN (Heat-sink Very-thin Quad Flat-pack No-leads) components soldered onto a Printed Wiring Board (PWB). The fatigue damage accumulation rates under ED random vibration excitation is found to be much higher than under harmonic vibration excitation, for equivalent RMS responses of PWB. To understand the reasons for such discrepancy we use FEA-based modeling. For simplicity of modeling we use a simple PWB with a simple Leadless Ceramic Resistor (LCR) component. We use a multiscale FEA modeling approach where the global analysis provides insights into the PWB modal response under the given excitation and can be conducted in the frequency-domain or in the time-domain. The local FEA model allows us to establish a transfer function between PWB curvature (flexural strain) in the vicinity of the critical component and equivalent strain in the critical region of the critical solder joint. al analysis is conducted to investigate the PWB mode shapes and natural frequencies, and they are compared with the measured strain time history, to understand the modal participation factors under both harmonic and ED random vibration excitation. The failure data is found to correlate well with the modal participations. Multiscale finite-element (FE) simulations are conducted to assess the dynamic response of the critical interconnects. This is done with two steps, first using a FE global analysis in the frequency domain for the global response consisting of all participating modes. Participation factors for individual modes are estimated from the global response, using numerical filtering methods. Inverse FFT is used to convert the frequency-domain response into the time-domain response histories for each dominant mode. In the second step, dynamic FE local analysis is conducted to obtain the transfer function between the PWB flexure and the strain in the critical solder interconnect for each dominant mode. Finally, rainflow cycle counting and Coffin-Manson fatigue model are used to estimate durability model constants and to compare fatigue damage accumulation rates under harmonic versus ED random vibration excitation.

Investigation of Load Control Errors for Spectrum Fatigue Testing at High Frequencies

Abstract Ultra-high cycle fatigue (gigacycle) tests have shown that a true fatigue endurance limit does not exist for most metallic materials used in high cycle applications. These findings have significant implications for rotorcraft dynamic structural components that have traditionally been designed using endurance limit, stress-life methods. Unfortunately, the gigacycle fatigue test results generated to date cannot be easily applied to rotorcraft component design, because the interaction of different crack nucleating mechanisms under variable amplitude loading is not well understood, and must be studied using spectrum fatigue tests carried out to very long lives. To quantify the effect of spectrum load control errors on the rate of fatigue damage accumulation for a standard servo-hydraulic fatigue test machine, a damage ratio parameter for crack initiation is calculated using the high cycle fatigue portion of the Coffin-Manson strain-life curve with rainflow cycle counting. The fatigue damage parameter allows the level of controller error to be assessed as a function of test frequency, peak load levels, and test spectrum complexity. Also, different command feedback compensation schemes are tested to determine the range of control error that can be expected for a given set of test parameters. A sensitivity study was performed on the command signal response errors as a function of changes in the slope of the mean damage curve beyond 106 cycles. The test results demonstrate that rotorcraft spectrum fatigue tests can be performed at frequencies up to 150 Hz with a level of nominal damage accumulation error less that 1 % under most conditions. When electrical measurement system error is accounted for, the damage accumulation error is less than 2 % under most conditions. The results also show that it is important to consider the shape of the stress-life curves in the gigacycle fatigue range when performing spectrum tests out to long fatigue lives.

Fatigue life prediction of horizontally curved thin walled box girder steel bridges

The fatigue damage accumulation rates of horizontally curved thin walled box-girder bridge have been estimated from vehicle-induced dynamic stress history using rain flow cycle counting method in the time domain approach. The curved box-girder bridge has been numerically modeled using computationally efficient thin walled box-beam finite elements, which take into account the important structural actions like torsional warping, distortion and distortional warping in addition to the conventional displacement and rotational degrees of freedom. Vehicle model includes heave-pitch-roll degrees of freedom with longitudinal and transverse input to the wheels. The bridge deck unevenness, which is taken as inputs to the vehicle wheels, has been assumed to be a realization of homogeneous random process specified by a power spectral density (PSD) function. The linear damage accumulation theory has been applied to calculate fatigue life. The fatigue life estimated by cycle counting method in time domain has been compared with those found by estimating the PSD of response in frequency domain. The frequency domain method uses an analytical expression involving spectral moment characteristics of stress process. The effects of some of the important parameters on fatigue life of the curved box bridge have been studied.

Notch Root Oxide Formation During Fatigue of Polycrystalline Silicon Structural Films

This paper investigates the fatigue behavior of n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -type 2-mum- thick polycrystalline silicon films that exhibit an initially thin (~2-3 nm) native oxide layer. The testing of kilohertz-frequency resonators provided accurate stress-life fatigue data at 30 and 50% relative humidity (RH) in the low (< 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> )and high (up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> ) cycle regimes. Long fatigue life specimens were associated with larger decreases in the natural frequency of the resonator and very smooth failure origins (at the notch) that encompassed several grains. Additional testing at various humidity levels highlighted the critical influence of humidity on the fatigue damage accumulation rate, which was measured via changes in the natural frequency. Finally, Auger electron spectroscopy (AES) characterized the formation of a nanometer-scale oxygen-rich reaction layer during cyclic loading. Although AES revealed a thin 2-3-nm initial oxide layer on a control specimen, measurements on a long-life fatigued specimen revealed an increased oxygen concentration over the first 10 nm of the material at the notch root. These findings demonstrate that the reaction-layer fatigue mechanism for silicon structural films operates even when reaction layers are initially very thin.

Scatter in the fatigue characteristics of steels and its analysis with allowance for cyclic inelastic strains

The regularities of the scatter in the characteristics of fatigue and inelasticity of steels 45 and 1Kh13 have been studied under steady-state, step, and block loading. It is shown that the use of the inelastic strain per cycle as a measure of the fatigue damage accumulation rate makes it possible to take into account the scatter in the number of cycles to fracture and in the fatigue limits and to substantiate the cumulative fatigue damage rule.

Effects of interfacial debonding on fatigue damage of cemented hip prostheses

Clinical studies on retrieved cement mantles have pointed out that the cemented hip prostheses failed after long‐term use due to debonding at the cement‐stem interface and local fractures in the cement mantles. These were linked to fatigue damages of cement mantles proved by fatigue experiments. In this paper, a numerical approach based on finite element analysis and continuum damage mechanics is proposed to investigate the fatigue behavior of cement mantles during gait cycles. Results reveal that the major sites for failure initiation are at the proximal medial regions and at the distal prostheses tip. Such fatigue failures not only result in the corruption of cementstem interfaces, but also greatly affect the stress distribution and damage rate of the proximal cement mantles in subsequent loading cycles. The interfacial debonding rate increases from 2.5% to 15% with gait loadings from five to twenty million cycles. Meanwhile, owing to the partial debonding of interface, the cement stresses on the remaining regions increase by 91% to 871% when compared with those generated with a fully bonded interface, which in turn accelerates the fatigue damage accumulation rate of the cement mantle from 5.99 % to 21.5%.

Stochastic fatigue damage accumulation in a T-welded joint accounting for the residual stress fields

The residual stresses that occur as a result of nonhomogeneous heating and cooling during welding may have a significant effect on the accumulation of fatigue damage in a welded joint. The problem is complicated not because of the complex spatial distribution of the residual stress fields, but because those fields typically change under an applied load. The present study considers the effect of residual stresses on fatigue damage accumulation in a welded joint subjected to stochastic loading. The influence of residual stresses on stochastic fatigue damage accumulation is accounted for by a simple approach based on an elastic–perfectly-plastic material model and the Gerber correction factor. The model assumes that the residual stress remaining at the critical location depends on the largest nominal stress ever endured by a welded joint. The model predicts that the residual stresses during stochastic loading randomly decay to zero. The effect of material yielding is additionally investigated by considering an elastic–plastic material model with linear kinematic hardening. The residual stresses in this case are computed through Monte Carlo simulations. It is demonstrated that the effect of material hardening is to reduce the rate of residual stress decay and thus to accelerate the rate of fatigue damage accumulation.

Fatigue analysis of roof cladding under simulated wind loading

Several damage mitigation studies have concluded that wind-induced fatigue may be responsible for the extensive damage to roof cladding. This paper presents the application of the recently proposed novel simulation methodology, capable of generating both Gaussian and non-Gaussian wind pressure fluctuations, in the fatigue analysis of roof cladding. After establishing the simulated fatigue characteristics of roof pressures, the total fatigue loading has been estimated by integrating the long-term wind climate with the simulated fatigue characteristics of roof pressures. Simulated results are compared with predictions made by Rayleigh, Gaussian and Weibull models as well as German and British recommendations. The study indicates that non-normality can significantly increase the rate of fatigue damage accumulation, and, if neglected, it can result in non-conservative fatigue life estimates.

Resilient Properties and Fatigue Damage in Stabilized Recycled Aggregate Base Course Material

A stabilized fiber-reinforced base course material composed largely of recycled concrete aggregate with small amounts of portland cement and fly ash was subjected to repeated flexural loading to evaluate its resilient properties and progressive accumulation of fatigue damage. Cyclic load-deformation data were recorded continuously during the entire fatigue life until fracture to determine ( a) the magnitude and variation of cumulative plastic strain and dynamic elastic modulus as a function of the number of loading cycles, ( b) a range for the resilient modulus, and ( c) the effect of fiber inclusions on the dynamic material properties and rate of damage accumulation. The extent of fatigue damage was calculated as a fatigue damage index, which is based on the cumulative energy dissipated (absorbed) during cyclic loading. All beam specimens used in this experimental program contained (by weight) 4 percent cement, 4 percent fly ash, and 92 percent recycled aggregate; the fiber-reinforced specimens contained an additional 4 percent (by weight) hooked-end steel fibers. Results show that the resilient modulus in flexure varies between about 2.75 GPa (400,000 lbf/in2.) and 10.4 GPa (1.5 million lbf/in.2) and the degradation of the dynamic elastic modulus does not exceed 25 percent of the initial modulus. Miner’s Rule of linear summation of damage is applicable to unreinforced material but not to fiber-reinforced material. In general, a modest amount of reinforcing fibers was very effective in retarding the rate of fatigue damage accumulation in this lean cementitious composite.

Fatigue of welded steel joints under wideband loadings

Fatigue tests were conducted on high-strength welded steel cruciform-shaped specimens subjected to random loadings to investigate the effects of loading intensity, nonnormality and frequency bandwidth on the rate of fatigue damage accumulation. The test result are compared with predictions made using the Rayleigh approximation and rainflow analysis in terms of cycles and times to failure. Results indicate that nonnormality can significantly increase the rate of fatigue damage accumulation and result in nonconservative fatigue life estimates if it is effect is not accounted for properly. Likewise, frequency content was also found to influence the rate of fatigue damage accumulation, but to a lesser extent than nonnormality.

Stochastic fatigue damage accumulation under broadband loadings

Fatigue tests were conducted on 72 high-strength welded steel cruciform-shaped specimens subjected to stochastic loadings. Results of these tests are used to investigate experimentally the effects of loading non-normality and frequency bandwidth and truncation on the rate of fatigue damage accumulation. Test results are compared with predictions made using Rayleigh approximation and rainflow analysis in terms of cycles and time to failure. Results indicate that non-normality can significantly increase the rate of fatigue damage accumulation, and can result in non-conservative fatigue life estimates if its effect is not accounted for, regardless of frequency content. Likewise, frequency content was also found to influence the rate of fatigue damage accumulation, but to a lesser extent than non-normality. When higher-frequency components were included, shorter fatigue lives were observed. Fatigue life predictions using rainflow analysis produced good agreement with experimental results; predictions made using Rayleigh approximation produced non-conservative fatigue life estimates.