Potential Fatigue Damage Research Articles

Microstructure-based RVE modeling of the failure behavior and LCF resistance of ductile cast iron

In this work the failure behavior of ductile cast iron microstructure subjected to tensile and low-cycle fatigue loadings is simulated by a 3-D, FE Reference Volume Element approach. A fully ferritic matrix is considered as representative of the low-hardness, high-ductility material class of nodular cast irons. Plastic flow potential rule, ductile and low cycle fatigue damage models are implemented at the micro-scale for the matrix constituent in conjunction with nonlinear cyclic hardening laws, and periodic boundary conditions are imposed over the RVE at the meso-scale. Different values of triaxiality are imposed. Numerical results confirm experimental findings of the behavior at the meso-scale and correctly predict the LCF lifetime, driving the interpretation of inner strain distribution, voids interaction and triaxiality effects on failure mechanisms.

A study on the simulation method for fatigue damage behavior of reinforced concrete structures

This paper mainly focuses on developing an efficient simulation method for fatigue behavior of reinforced concrete structures (RC structures), through which the damage state and the potential fatigue damage failure pattern of the RC structures could be obtained in finite element analysis (FEA). In order to accomplish such object, fatigue behavior of RC structures is studied using the entire history of damage accumulation for both concrete and steel bars. A bi-scalar damage-plasticity constitutive model for concrete and a single-scalar damage constitutive model for reinforcement are first introduced to characterize the fatigue damage state of the structure. Then, a two-scale temporal expediting computational technique is developed for the material constitutive models, by which the original material models could be split into a micro periodic time scale portion and a macro homogenized time scale portion. Through this calculation technique, the original increment-by-increment FEA procedures could be transferred to the two-time scale calculation, which would greatly enhance the efficiency of the structural fatigue simulation. By combining the material constitutive models and the expediting calculation technique with FEA, a set of numerical examples and comparisons are performed, specifically, a column-drilled shaft connection in bridge structure is simulated, which validates the effectiveness and reliability of the current simulation method for the fatigue behavior of RC structures.

Experimental HALTs with sine-on-random synthesized profiles

In several applications, certain components must be designed to withstand the fatigue damage induced by dynamic loads due to vibrations. Highly Accelerated Life Tests (HALTs) by means of vibration qualification can be performed for the most critical ones. The proper synthesis of test profiles, which starts from the real environment vibrations and which preserves both the fatigue damage potential and the signal characteristics of the excitation, is important to obtain reliable results. A special kind of vibration excitation is the so-called Sine-on-Random (SoR), i.e. sinusoidal contributions superimposed to random vibrations, particularly significant for systems where rotating parts are present. A methodology was previously proposed to synthesize SoR test profiles for HALTs, starting from reference measured vibrations. The present paper illustrates the experimental campaign carried out to verify the effectiveness and the accuracy of the proposed method.

Fatigue Damage of Vertical Rigid Risers due to In-Line Vortex Induced Vibration in Nigeria Shallow Waters

In-line and Transverse Vortex Induced Vibrations (VIV) pose potential Fatigue damage threat to Vertical Rigid Risers (VRR) even in the less volatile Nigeria Shallow Waters. In this paper, a typical VRR of 31.031m length clamped to a fixed jacket platform in 18.29m water depth was used while relevant metOcean data were used to simulate the environmental conditions. The process was statically and dynamically simulated using different wave spectra on Orcaflex platform. The results from JONSWAP spectra showed a fatigue damage value of 102.5 x 10-5 due to in-line VIV which is greater than 29.1 x 10-5 due to transverse VIV. The results from the Ochi-Hubble spectra indicate a fatigue damage value of 96.2 x 10-5 due to in-line VIV which is greater than 7.03 x 10-5 due to transverse VIV. Also, the in-line vortex force (VF) analysis on the VRR for the JONSWAP spectra showed VF range, beginning from the touchdown point (TDP) to the unstraked region (UR), of 0.16 - 0.34kN/m; 0.01 - 0.53kN/m; and 0 - 0.85kN/m at End A (0m); 8.74m and 21.00m, respectively. Whereas, for the Ochi-Hubble spectra, VF range, from TDP to the UR, of 0.16 - 0.302kN/m; 0.018 - 0.56kN/m; 0 - 1.42kN/m at End A (0m); 8.74m and 21.00m, respectively, were obtained. The results for both spectra showed zero in-line VF on the VRR at 23.69m, 26.21m and End B (31.031m). Hence, fatigue damage and VF due to in-line VIV is important from the TDP to most parts of the UR on the VRR irrespective of the wave spectra and requires proper analysis in riser designs.

Equi-biaxial loading effect on austenitic stainless steel fatigue life

Fatigue lifetime assessment is essential in the design of structures. Under-estimated predictions may result in unnecessary in service inspections. Conversely, over-estimated predictions may have serious consequences on the integrity of structures. In some nuclear power plant components, the fatigue loading may be equibiaxial because of thermal fatigue. So the potential impact of multiaxial loading on the fatigue life of components is a major concern. Meanwhile, few experimental data are available on austenitic stainless steels. It is essential to improve the fatigue assessment methodologies to take into account the potential equi-biaxial fatigue damage. Hence this requires obtaining experimental data on the considered material with a strain tensor in equibiaxial tension. Two calibration tests (with strain gauges and image correlation) were used to obtain the relationship between the imposed deflection and the radial strain on the FABIME2 specimen. A numerical study has confirmed this relationship. Biaxial fatigue tests are carried out on two austenitic stainless steels for different values of the maximum deflection, and with a load ratio equal to -1. The interpretation of the experimental results requires the use of an appropriate definition of strain equivalent. In nuclear industry, two kinds of definition are used: von Mises and TRESCA strain equivalent. These results have permitted to estimate the impact of the equibiaxiality on the fatigue life of components.

Steady and unsteady calculations on thermal striping phenomena in triple-parallel jet

The phenomenon of thermal striping is encountered in liquid metal cooled fast reactors (LMFR), in which temperature fluctuation due to convective mixing between hot and cold fluids can lead to a possibility of crack initiation and propagation in the structure due to high cycle thermal fatigue. Using sodium experiments of parallel triple jets configuration performed by Japan Atomic Energy Agency (JAEA) as benchmark, numerical simulations were carried out to evaluate the temperature fluctuation characteristics in fluid and the transfer characteristics of temperature fluctuation from fluid to structure, which is important to assess the potential thermal fatigue damage. In this study, both steady (RANS) and unsteady (URANS, LES) methods were applied to predict the temperature fluctuations of thermal striping. The parametric studies on the effects of mesh density and boundary conditions on the accuracy of the overall solutions were also conducted. The velocity, temperature and temperature fluctuation intensity distribution were compared with the experimental data. As expected, steady calculation has limited success in predicting the thermal–hydraulic characteristics of the thermal striping, highlighting the limitations of the RANS approach in unsteady heat transfer simulations. The unsteady results exhibited reasonably good agreement with experimental results for temperature fluctuation intensity, as well as the average temperature and velocity components at the measurement locations.

Wind-Induced Vibrations of the Stay Cables of a Roundabout Flyover: Assessment, Repair, and Countermeasures

AbstractThis paper presents the results of a multifaceted investigation into the vortex-induced vibrations of the stay cables of a roundabout flyover. Large cable vibrations were spotted during moderate wind speed conditions immediately after the completion of the structure, and after three weeks, because of concerns about the structural integrity of the cable system, temporary restrainers were applied. An investigation was conducted to assess the potential fatigue damage that occurred during that time, combining experimental measurements and a finite-element model of the cable system. As a result, the cable sockets were replaced, causing delays in the opening of the flyover and additional costs. Wind-induced vibration occurred as a result of the very low damping of the cables. Therefore, after the repair, to suppress the phenomenon two differently tuned mass dampers of the Stockbridge type were installed on each cable. The article describes the results of the investigation and presents the methodology us...

Fatigue management of the Midland Links, UK steel box girder decks

The Midland Links motorway viaducts, carrying the M5 and M6 around Birmingham, UK have been subject to a regular programme of assessment, repair and strengthening since 1989, after corrosion problems, primarily due to chloride contamination, were first detected in 1979. A number of the longer spans comprise multiple steel and concrete composite box girders and some of these superstructures are supported by steel box girder cross-beams. Assessment showed areas of very high overstress in the web plate at the locations of internal bracings. These overstresses affected ultimate, serviceability and fatigue limit states and arose because of poor detailing of the cross-braces and stiffeners. Acoustic emission sensors were installed to determine if the predicted fatigue activity was actually occurring and elastic shell finite-element (FE) modelling was undertaken for an improved determination of stresses. Plastic redistribution was considered to demonstrate adequate ultimate limit state (ULS) performance and an analysis was undertaken with potential fatigue damage modelled to prove the structure would not collapse with such damage at the ULS. In situ strain monitoring was undertaken to calibrate the FE results, improve the predicted fatigue life and allow preparation of a long-term strategy for managing and monitoring fatigue activity using a damage tolerant approach.

Specificity of Crack Initiation under Equibiaxial Fatigue: Development of a New Experimental Device

Fatigue lifetime assessment is essential in the design of structures. Under-estimated predictions may result in unnecessary in-service inspections. Conversely, over-estimated predictions may have serious consequences on the integrity of structures. In some nuclear power plant components, the fatigue loading may be equibiaxial because of thermal fatigue. So the potential impact of multiaxial loading on the fatigue life of components is a major concern. Meanwhile, few experimental data are available on austenitic stainless steels. It is essential to improve the fatigue assessment methodologies to take into account the potential equibiaxial fatigue damage. Hence this requires obtaining experimental data on the considered material and with a strain tensor in equibiaxial tension. This paper describes an experimental program on austenitic stainless steel carried out on the new experimental fatigue device FABIME2 developed in the LISN in collaboration with EDF and AREVA. This new device allows accurate quantification of the effects of both equibiaxial strain state as well as structural parameters (such as mean stress) on the fatigue life. It also allows studying the complexity of combinations between potential detrimental effects like surface roughness, mean stress and equibiaxial loading. Different load ratios can be tested by adjusting the loading conditions. A Finite Element Modeling is performed in order to obtain a precise description of the strain state in the specimen. The results of the on-going test campaign will be presented.

New Method in Suppressing Vortex-Induced Vibration of Marine Riser

Marine risers are key apparatus in connecting the subsea wells to the oil production platform. When the ocean current flow past a riser, the vortex shedding behind riser may induce vibration. If the frequency of vortex shedding is approaching or equal to the natural frequency of riser, the resonance will be generated. Such phenomenon leads to the potential fatigue damage of riser. Therefore, the safety and assurance of marine risers are widely arousing the interest of offshore engineering. In present paper, previous apparatus or methods in suppressing vortex-induced vibration (VIV) of risers used in marine engineering are firstly analyzed, and correspondingly the conditions in design of VIV suppressors are proposed. Based on the Bernoulli equation, the disturbance in flow around a bluff body and the relationship of vortex shedding in span-wise direction, a new method of VIV suppression is proposed. The numerical results have shown that the vibration of risers could be reduced by such disturbance.

Large-eddy simulation of thermal striping in unsteady non-isothermal triple jet

Unsteady temperature fluctuations of non-isothermal turbulent jets are encountered in many engineering applications including liquid metal cooled fast reactors (LMFR), and can cause thermal stresses on solid boundaries. An accurate prediction of the temperature fluctuations is important to assess potential thermal fatigue damage to components, and traditionally this has been done by RANS turbulence modelling calculations with limited success. In this study, a large eddy simulation (LES) technique was applied to predict the temperature fluctuations of thermal striping observed in a triple jet. The triple jet model was used as a mock-up of the outlet of fuel subassemblies in a nuclear fast reactor. The results show that LES predicted the highly oscillatory nature of unsteady thermal mixing of the triple jet. The LES results were in good agreement with the available experimental data in terms of mean, RMS, skewness and kurtosis. The large amplitude of the temperature fluctuations associated with the thermal striping was captured correctly, demonstrating that LES can be used to analyse unsteady characteristics of thermal striping. Instantaneous and time mean thermal fields were further analysed to assess the capability and accuracy of LES in the thermal striping study. The Spalart–Allmaras and realisable k − ε turbulence models were also considered along with LES. It is found that these turbulence models produced a very small amplitude of fluctuations, and failed to predict the correct magnitude of unsteady thermal fluctuations, highlighting the limitations of the RANS approach in unsteady heat transfer simulations.

Numerical Analysis of Ship-Generated Waves Action on a Vertical Cylinder

In this paper, the action of ship-generated waves on a nearby vertical cylinder is considered in pure theory. Intensive demands of modern sea transportation result in larger and larger ships. These ships generate high waves as they move in calm water. The ship-generated waves can travel long distances without much attenuation. They are so strong that they might cause damage to nearby marine structures (e.g., platforms, river banks, breakwaters, etc.). Therefore, it is necessary to evaluate the forces of ship-generated waves acting on nearby marine structures. The problem turns out to be composed of two problems: evaluation of waves generated by a moving ship (ship-wave problem) and evaluation of the action of ship waves on a cylinder (wave-action problem). Here the wave-action problem is computed in detail with a boundary element method in time domain. And the ship-wave problem is evaluated in the well-known Michell thin-ship theory. Thus, the problem posed in this paper is finally solved using numerical methods by combining the ship-wave and wave-action problems. The numerical analyses of the result are: The resultant forces and moments acting on the cylinder are surprisingly large, characterized by being highly oscillatory. The periods of the oscillations are proportional to ship speed. The actions of ship-generated waves on nearby structures are not negligible. This is a new factor necessary to be considered for design of both marine structures and ships. Meanwhile, the potential fatigue damage resulting from oscillations of the forces and moments should be considered, too.

Method for identification of fluid mixing zones subject to thermal fatigue damage

High cycle thermal fatigue due to the mixing of hot and cold fluids may initiate cracking in pipes of safety related circuits. A method has been developed to identify such fluid mixing zones subjected to potential thermal fatigue damage. This method is based on a loading model and a mechanical model that depend on the main characteristics of the mixing zone and on the material properties. It is supported by a large experimental program. This method has been applied to all the mixing zones of safety related circuits of the EDF pressurised water reactors, allowing to identify sensitive zones and to apply an appropriate inspection program that ensures the control of the risk due to this damage mechanism.

Fatigue Damage Evaluation of Railway Truss Bridges from Field Strain Measurement

This paper is concerned with fatigue damage evaluation of railway truss bridges in Thailand, which have been in service for more than 60 years by using the deterministic approach. The dynamic strain measuring system was installed on selected bridge members to record the actual strain histories induced by the passing trains. The fatigue damages of all bridge members are evaluated based on Palmgren-Miner damage rule and the S-N curves of the stress ranges from field strain measurement of daily train traffic. For the members that their field strains were directly not monitored, the finite element analysis has been employed to estimate their stress ranges. The finite element models of the bridges are verified with the stress data obtained from the field load test of a locomotive. It is found that the vertical and diagonal members of the railway bridges appear to have the most fatigue damage risk whereas the lower chord and floor beams have the lowest estimated fatigue damage potential.

Quantification of Pavement Damage Caused by Dual and Wide-Base Tires

A study conducted in 2001 on the heavily instrumented Virginia Smart Road measured pavement responses to a new generation of single wide-base tire (445/50R22.5) and to dual tires (275/80R22.5). The new single wide-base tire has a wider tread and a greater load-carrying capacity than conventional wide-base tires. The potential fatigue damage resulting from different tire configurations was evaluated. After successful field testing, a finite element (FE) parametric study was conducted to investigate different failure mechanisms that were not evaluated in the field. In this study, dual tires and two new generations of wide-base tires (445/50R22.5 and 455/55R22.5) were evaluated. The main difference between the two generations of wide-base tires is that the 455/55R22.5 is wider than the 445/50R22.5; hence, it further reduces the contact stress at the pavement surface under the same nominal tire pressure. In the developed FE models, geometry and dimensions were selected to simulate accurately the axle configurations typically used in North America; actual tire tread sizes and applicable contact pressure for each tread were considered; laboratory-measured pavement material properties were incorporated; and models were calibrated and properly validated against stress and strain measurements obtained from the experimental program. Four failure mechanisms were considered: fatigue cracking, primary rutting, secondary rutting, and top-down cracking. Results indicated that the new generations of wide-base tire would cause the same or relatively greater pavement damage than conventional dual tires. Because overall truck weight is reduced by approximately 450 kg when wide-base tires are used, it is reasonable to implement the load limits currently applied to the dual-tire assembly on the 455/55R22.5 wide-base tire.

Quantification of Pavement Damage Caused by Dual and Wide-Base Tires

A study conducted in 2001 on the heavily instrumented Virginia Smart Road measured pavement responses to a new generation of single wide-base tire (445/50R22.5) and to dual tires (275/80R22.5). The new single wide-base tire has a wider tread and a greater load-carrying capacity than conventional wide-base tires. The potential fatigue damage resulting from different tire configurations was evaluated. After successful field testing, a finite element (FE) parametric study was conducted to investigate different failure mechanisms that were not evaluated in the field. In this study, dual tires and two new generations of wide-base tires (445/50R22.5 and 455/55R22.5) were evaluated. The main difference between the two generations of wide-base tires is that the 455/55R22.5 is wider than the 445/50R22.5; hence, it further reduces the contact stress at the pavement surface under the same nominal tire pressure. In the developed FE models, geometry and dimensions were selected to simulate accurately the axle configurations typically used in North America; actual tire tread sizes and applicable contact pressure for each tread were considered; laboratory-measured pavement material properties were incorporated; and models were calibrated and properly validated against stress and strain measurements obtained from the experimental program. Four failure mechanisms were considered: fatigue cracking, primary rutting, secondary rutting, and top-down cracking. Results indicated that the new generations of wide-base tire would cause the same or relatively greater pavement damage than conventional dual tires. Because overall truck weight is reduced by approximately 450 kg when wide-base tires are used, it is reasonable to implement the load limits currently applied to the dual-tire assembly on the 455/55R22.5 wide-base tire.

Highway Network Bridge Fatigue Damage Potential of Special Truck Configurations

A study of the fatigue damage potential of special truck configurations was conducted to facilitate informed decisions by state transportation agencies in considering various truck size and weight and permit policies as well as to provide relative damage information that will be useful in ongoing network damage evaluations. The primary objective was to evaluate 78 existing common and FHWA-proposed truck configurations for relative fatigue damage potential. To accomplish this objective, an analytical fatigue evaluation tool was developed to determine the relative fatigue damage induced in highway network bridges by simulation of a highway fleet mix database crossing actual bridges modeled analytically. Additional objectives were to evaluate the influence of impact values and endurance limits used for a fatigue analysis. The semicontinuum analysis method, the Palmgren-Miner hypothesis, and the rain-flow cycle counting algorithm are incorporated. A 39-bridge database statistically selected as representative of bridges in the United States allowed a network level fatigue analysis of several hundred fatigue-prone details. Seventy-eight special truck configurations were studied, 25 of which were developed by FHWA as part of the comprehensive truck size and weight study. The remaining 53 vehicles were taken from the Turner proposal, Michigan, Pennsylvania, Canada, military, AASHTO, and other sources. It was found that fatigue damage potential is primarily a function of axle weight, spacing, and vehicle length instead of gross vehicle weight.

Strength of Glued-In Bolts after Full-Scale Loading

In 1993 after 9 years of use, one of the wooden blades of a windmill was struck by lightning. After demounting, the damaged blade was handed over to the Technical University of Denmark, Lyngby, for the investigation of potential fatigue damage. This paper presents an experimental determination of the residual strength of the glued-in bolts that served as the blade to rotor hub connection in the windmill. The load history of the bolts, the test method, the observed fracture modes, and the force displacement curves are presented along with the recorded residual strength of the bolts. The bolts with a length of 500 mm had a special hollow tapering giving them a higher load-bearing capacity than solid bolts of equal dimensions. An FEM analysis confirms the higher load-bearing capacity. The mean residual stength was found to be 362 kN with a standard deviation of 37 kN, which is 95% of the predicted strength based on short-term tests on similar bolts. At fracture, a displacement between 0.4 and 1.0 mm was observed. In the majority of failures, the bolts were pulled out like a cork from a bottle.

Bridge Fatigue Life Estimation from Field Data

This paper presents the application of field data to condition assessment and prediction of service life of highway bridges. The study examined fifteen bridges located in Illinois for damage evaluation purposes. The example bridges are all composed of steel girders with reinforced concrete deck slabs. Only the superstructure was investigated for potential fatigue damage to the critical structural details of the main steel girders. The current condition of each bridge was assessed based on fatigue damage induced in the critical components of the bridge and the bridge fatigue life. The critical components investigated are steel girders with welded cover plates. The field stress range data compiled for each bridge was used along with a probabilistic method to estimate fatigue life. The results were then used to investigate the significance of truck weight increase and traffic growth on fatigue life.

A law of large numbers for upcrossing measures

We present a mathematical treatment of the so called RFC-counting which is applied to functions from subsets of R to R and which essentially counts upcrossings for each pair of levels. In mechanical engineering it is applied to stress or strain histories to assess their potential fatigue damage. We associate three measures on R 2 with RFC-counting and study their properties. Using the subadditive ergodic theorem of Kingman (1975) we prove a law of large numbers for these measures when they are applied to the paths of a stationary process. We compute the limit μ̃ explicitly e.g. for one-dimensional stationary diffusion processes. μ̃ may be compared with the spectral measure.