Fatigue Damage Ratio Research Articles

Application of a new method for probabilistic fatigue analysis from strain measurements on bridges

Increasing loads, ageing of materials as well as environmental change make the issue of fatigue damage critical on bridges, especially in the case of old steel or iron structures. The assessment of the fatigue loads on specific elements of these assets can be carried out from on-field strain measurements with the application of classical methods involving rainflow cycle counting and the use of Palmgren-Miner's rule. However, such a fatigue assessment suffers of significant uncertainties about the real fatigue damage ratio and the consecutive residual fatigue life. A new probabilistic method for the fatigue assessment is proposed, as the result of a joint research by OSMOS Group and the Ecole des Ponts. The theoretical background of the method is described, involving a probabilistic formulation of Miner's rule and the use of a Weibull-Basquin model to describe the health of structural elements. Real field case studies are presented, on two historical iron truss road bridges in France, with a dataset of more than 18 months of continuous strain measurements used for the fitting of the probabilistic model of fatigue loads. The incidence of the quantity of data and of the number of sensors used for the analysis is discussed, along with the conclusive results concerning the probabilistic description of the residual fatigue life.

Estimation of the Ice-Induced Fatigue Damage to a Semi-Submersible Platform under Level Ice Conditions

This study presents a fatigue analysis procedure for inclined structures operated in level ice fields. Three methods for calculating the local ice load causing fatigue damage, namely the direct method, simplified method, and semi-analytical method, were introduced and compared. The direct method uses finite element analysis to simulate the continuous breaking of ice, while the simplified method and the semi-analytical method estimate the probability distribution of local ice loads based on theoretical equations and empirical data. The fatigue damage ratio at the target location was calculated by applying the ice load calculated by each method to a deformable finite element model of the structure. The results obtained from each method indicate that they provide a reasonable estimation of the local ice load causing fatigue damage in level ice fields. The direct method offers high accuracy but requires significant computational time, while the simplified method and semi-analytical method offer a faster analysis time and are more suitable for long-term time domain analysis. The semi-analytical method requires empirical data to supplement theoretical formulas due to the complex natural phenomena involving various environmental conditions that must be modeled. The findings of this study provide valuable insights into the prediction of fatigue damage in ice-going ships due to long-term ice impacts. The methods proposed in this study can aid in the design of Arctic ships exposed to various conditions and provide a more cost-effective and time-efficient approach to evaluating fatigue damage compared to field measurement. Future research in this field could investigate the application of these methods to other types of structures and further refine the methodology to improve accuracy and reduce computational costs.

Assessment of Dynamic Effects of Wave Loads in Fatigue Analysis for Fixed Steel Offshore Structures

This paper presents an algorithm and develops a formula to evaluate the dynamic effect of wave loading on fixed steel offshore structures (jacket structures) through the fatigue damage ratio. Applying the algorithm and formula proposed in this paper to evaluate the dynamic effect of wave loads in fatigue analysis for 03 Jacket structures built at increasing water depth under one specific marine condition and provide specific recommendations on the limits of application of quasi-static and dynamic methods in the fatigue analysis of the jacket structures. This research is really necessary because currently, the current standards (API, DnV) only stop at evaluating the dynamic effects of wave loads acting on the Jacket structure in the strength analysis. These standards propose a limit for quasi-static or dynamic analysis based on the "3.0 s or 2.5 s rule" (use the quasi-static method when Tmax≤ 3.0 s or ≤ 2.5 s), and it is advised that they only apply to waters within the North Sea and the Gulf of Mexico. This paper has demonstrated that it is not appropriate to use the specified standards for the North Sea and the Gulf of Mexico to select the method of fatigue analysis of the jacket structure in marine conditions outside the study area of the standard. Hoped that this paper will be a reference for engineers when choosing a fatigue analysis method for jacket structures in specific marine conditions at the location where the jacket structure has been installed. Doi: 10.28991/CEJ-2023-09-02-016 Full Text: PDF

Performance of Enhanced Problematic Soils in Roads Pavement Structure: Numerical Simulation and Laboratory Study

The deficiency of high-quality soils in Saudi Arabia’s southern and northern regions, as well as along the Arabian Gulf coasts, is regarded as one of the most common issues with the construction of roads. High compressibility, low shear strength, substantial volume change (particularly in Sabkha), and low bearing capacity are the most typical issues with these problematic soils. In this study, finite element simulations were performed using the Plaxis 3D software v20 to simulate the performance and study the critical responses (fatigue, rutting strains, and damage ratio) of an enhanced pavement structure with a geogrid reinforcement resting on the naturally problematic Sabkha subgrade. A normal asphalt concrete layer, a base layer of Sabkha soil stabilized with Foamed Sulfur Asphalt (FSA), and a sand dune subbase layer comprised the pavement structure. For each layer, the model’s input parameters were a mix of laboratory and literature data. The simulation was performed on a pavement structure without reinforcement and on another section enhanced with a geogrid positioned at various locations to determine the ideal placement for lowering the important responses such as fatigue, rutting stresses, and damage ratio. The nonlinear behavior of an FSA–Sabkha base, sand subbase layer, and Sabkha subgrade was simulated using the hardening soil model, whereas the asphaltic concrete layer and geogrid material were simulated using the linear elastic model. The findings of the simulations demonstrated that placing geogrid reinforcement at the top of the subgrade layer resulted in the greatest reduction in horizontal tensile (fatigue) and vertical compressive (rutting) strains, as well as vertical displacement (32.71%, 13.2%, and 14.2%, respectively). In addition, geogrid reinforcement greatly reduced the fatigue damage ratio (33% to 55%), although the reduction in the rutting damage ratio was slightly lower (14% to 30%). The simulation results were validated using a wheel tracking machine and it was clear that there is a reasonable agreement between the results.

Residual monotonic mechanical properties of bimetallic steel bar with fatigue damage

When a reinforced concrete structure experiences an earthquake and does not collapse, irreversible damage in the reinforcement is caused by the fatigue load, which affects the residual bearing capacity of the structure significantly. Stainless-clad bimetallic steel bars (BSBs) are a new type of coated reinforcement with effective resistance to corrosion. In this study, to accurately evaluate the residual bearing capacity of a concrete structure reinforced with BSBs following an earthquake, it is tested with different fatigue damage ratios. Thereafter, the monotonic stress–strain nonlinear performance, failure behaviour, and residual mechanical properties of BSBs with fatigue damage are explored. The evolution law of the mechanical properties of BSBs with fatigue damage is analysed. A monotonic stress–strain model of the BSB that considers the impact of fatigue damage is proposed. The test results indicate that the stainless-steel cladding of the BSB does not demonstrate apparent buckling following fatigue damage. Cracks are observed on both sides of the rib teeth. When the fatigue damage ratio is 0.6, a fracture occurs at the maximum crack caused by the fatigue damage. When the fatigue damage ratios are 0.2 and 0.4, fractures occur in the necking region of the upper or lower part of the specimen. Fatigue damage leads to the disappearance of the yield platform from the monotonic stress–strain curve of the BSB. The yield strength of the BSB decreases significantly owing to the fatigue damage ratio. The ultimate strength is barely affected by the fatigue damage ratio. Fatigue damage has an adverse effect on the deformation capacity of the BSB. With an increase in the fatigue strain amplitude and fatigue damage ratio, elongation following the fracture of the BSB gradually decreases. This study provides solid theoretical and experimental bases for the engineering application of BSBs, particularly in the post-earthquake evaluation of concrete structures reinforced with BSBs.

Mechanistic-empirical analysis of asphalt pavement fatigue cracking under vehicular dynamic loads

Vehicle-pavement interaction causes dynamic loads and accelerate pavement deterioration. The study provides a methodology to consider dynamic loads in mechanistic-empirical (M-E) pavement design and analysis. The dynamic load coefficients were found increasing as pavement roughness increased or axle loads decreased. The impulse response method was adopted to calculate tensile strains of asphalt layer under random loads. The relative ratios of fatigue life due to dynamic loads were calculated and fitted as a function of axle type, load magnitude, and international roughness index (IRI). The accumulative fatigue damage ratio between dynamic and static loads was proposed for M-E pavement analysis.

Fatigue lifetime assessment on a high-pressure heater in supercritical coal-fired power plants during transient processes of operational flexibility regulation

The operational flexibility of coal-fired power plants has become a priority objective; however, the lifetime of main devices is reduced due to thermomechanical fatigue during transient processes. This study focuses on the safety of high-pressure heaters at operational flexibility measures. The dynamic characteristics of thermal parameters in the 1# HP heater were obtained and analyzed based on transient models of a coal-fired power plant. The change trends of pressure/temperature on the steam/feedwater side of the 1# HP heater at three throttling the extraction steam measures were different with that at the feedwater bypass measure. Subsequently, finite element analysis method was used, and the thermomechanical stresses under the four measures were calculated and analyzed. The time to reach the maximum mechanical stresses was shorter than that of thermal stresses. Finally, the fatigue lifetimes of the heater were estimated. The maximum fatigue damage ratio at the per load cycle was 0.0069%, and the minimal allowable number of cycle was 14413 in the upper region of the tube sheet when the extraction steams of #1, #2, and 3# HP heaters are regulated simultaneously. The study could offer data guidance to the safety and maintenance of coal-fired power plants during operational flexibility regulations.

Influence of Linear Springing on the Fatigue Damage of Ultra Large Ore Carriers

Springing occurs more frequently to ultra large ships, as their natural frequencies are relatively low and approaches the spectral peak of the wave energy spectrum in certain sea states. Springing is a resonance phenomenon between the waves and the ship hull, and this high frequency vibration has a significant influence on the fatigue damage of hull structures. This paper deals with the influence of springing on the fatigue damage of ultra large ore carriers. The springing responses of ultra large ore carriers are calculated by a three-dimensional linear hydroelasticity method in the frequency domain. A fatigue damage calculation method accounting for the springing effect is applied that is based on the fatigue spectrum analysis method and the approximation method of joint narrowband. The fatigue damage of the deck and bottom longitudinals in the deck and bottom of ultra large ore carriers of various sizes has been calculated by this method. The influences of ship size, structural damping, sea state, wave heading, navigational speed, and loading condition on the structure fatigue damage ratio of ultra large ore carrier are analyzed.

Welded joint fatigue reliability analysis on bogie frame of high-speed electric multiple unit

A new method for welded joint fatigue reliability analysis on bogie frame of high-speed electric multiple unit (EMU) is proposed according to the International Union of Railways (UIC) standard, the Britain Standard Institute (BSI) standard and the Miner rule. Firstly, the fatigue calculation condition is loaded according to the UIC standard. The welded joint damage ratio is calculated by the BSI standard. Fatigue reliability analysis is conducted for a typical welded joint based on probabilistic design system (PDS) module in software ANSYS 14.0. In the system, the automatic program is prepared by ANSYS parametric design language (APDL) to calculate the welded joint fatigue damage ratio. Meantime, the relationship between the input variables and the output response is fitted by the response surface (RS) method. Then, the RS method is improved by the orthogonal design. Specifically, the selecting process optimization for the RS method based on the orthogonal design is conducted to improve the fitting efficiency of the RS method. Finally, a program of the automatic analysis documents is generated by Microsoft foundation class (MFC) technique. Through the self-defined interface, the researchers can easily import the automatic generation of the orthogonal table into the PDS module and analyze the fatigue reliability. Results show that the improved RS method can better fit the RS which covers the sample area, and the distribution law agrees well with the actual situation. At the same time, the improved RS method reduces the calculation time.

Research on the Connection Type between Evaporating Tube Bundle and a Steam Drum Shell on a Natural Circulation Marine Supercharged Boiler

The research work, Ascertaining the connection type between evaporating tube bundle and a steam drum shell on a Natural Circulation marine supercharged boiler, is important. For this reason the method, calculating the low-cyle fatigue life of supercharged boiler steam drums put forward by Xin-wei Zheng, et al., was put to use; Based on the relevant basic data from design department and two typical running conditions of one supercharged boiler, the cumulative fatigue damage ratio of welding technique was calculated. The calculated result proves that it exceeds the maximum value of 1.0 and the upper limit value of 0.75 in fossil-fuel power plants, respectively. So welding technique can’t guarantee the low-cycle fatigue life of this steam drum, the only connection type is expanded joint, and the connection type has been put into practice.

광대역 이봉형 응력 범위 스펙트럼에 대한 주파수 영역 피로 손상 평가 모델에 대한 연구

The offshore plants such as FPSO are subjected to combination loading of environmental conditions (swell, wave, wind and current). Therefore the fatigue damage is occurred in the operation time because the units encounter the environmental phenomena and the structural configurations are complicated. This paper is a research for frequency domain fatigue analysis of wide-band random loading focused on accuracy of fatigue damage estimation regarding the proposed methods. We selected ideal bi-modal spectrum. And comparison between time-domain fatigue analysis and frequency-domain fatigue analyses are conducted through the fatigue damage ratio. Fatigue damage ratios according to Vanmarcke's bandwidth parameter are founded for wide-band. Considering safety, we recommend that Jiao-Moan and Tovo-Benasciutti methods are optimal way at the fatigue design for wide-band response. But, it is important that these methods based on frequency-domain unstably change the accuracy according to the material parameter of S-N curve. This study will be background and guidance for the new frequency-domain fatigue analysis development in the future.

Detecting fatigue damage in 2.25Cr–1Mo steel with scanning SQUID gradiometry

In order to develop a new method for detecting fatigue damage nondestructively in 2.25Cr–1Mo steel, which is used in high temperature steam piping of fossil power plants and petroleum chemical facilities, fractured and interrupted samples in low-cycle fatigue (LCF) tests were investigated using scanning superconducting quantum interference device (SQUID) gradiometer. High temperature LCF experiments on 2.25Cr–1Mo steel were conducted to obtain various fatigue damage ratio, D f . Simultaneously, we also examined the fatigued samples by optical microscopy, electron back scatter diffraction pattern, magnetic force microscopy and hardness measurements to analyze the damage level. Except for a couple of samples, SQUID integrated intensity decreased with increasing D f , suggesting the potential of SQUID to evaluate fatigue damage in 2.25Cr–1Mo steel.

Corrosion behaviour of nitrided low alloy steel in chloride solution

PurposeThe corrosion behaviour of low alloy steel type AISI 4130 (before and after nitriding) and austenitic stainless steel type AISI 304L were studied in tap water +3.5 per cent NaCl. A liquid nitriding process had been applied on the low alloy steel.Design/methodology/approachThe tests that were carried out in this study were anodic polarization, rotating bending fatigue and axial fatigue using compact tension (CT). For determining the corrosion potential and pitting potential (breakdown potential) for the alloys, anodic polarization curves were established using the potentiodynamic technique. Rotating bending fatigue tests were used to calculate the fatigue strength and damage ratio. Using linear elastic fracture mechanics, the CT specimens were prepared for determining the threshold stress intensity factor, fatigue crack growth rate and fracture toughness in air and in the solution.FindingsThe results showed that nitrided specimens showed higher fatigue strength in air compared to stainless steel. However, the corrosion fatigue limit for both these samples were approximately equal, while this limit for non‐nitrided sample was less. Moreover, the non‐nitrided steel had lower corrosion and pitting potentials than did the stainless steel. In addition, the CT tests showed that the nitrided specimens had a lower resistance to crack initiation in air and the solution compared to the non‐nitrided sample and the stainless steel.Practical implicationsThese results can be attributed to the chemical and mechanical behaviour of the nitrided layer constituents, mainly FeN and CrN, which were recognized by X‐ray diffraction. Since, these components consist of very hard particles, they act to increase the hardness and fatigue limit. Moreover, due to the low conductivity of these nitrides, the corrosion and pitting potential of the nitrided steel becomes very high. However, the high breakdown potential does not help to increase the corrosion fatigue or damage ratio values due to the porous nature of the nitrided layer.Originality/valueAlthough the nitrided steel had very high fatigue strength and pitting potential, this did not reflect in its corrosion fatigue and/or damage ratio improvement because of its surface roughness and the porous nature of the nitrided layer.

Biomechanical analysis of differing pedicle screw insertion angles

Pedicle screw fixation to stabilize lumbar spinal fusion has become the gold standard for posterior stabilization. A significant percentage of surgical candidates are classified as obese or morbidly obese. For these patients, the depth of the incisions and soft tissue makes it extremely difficult to insert pedicle screws along the pedicle axis. As such, the pedicle screws can only be inserted in a much more sagittal axis. However, biomechanical stability of the angled screw insertion has been controversial. We hypothesized that the straight or parallel screw was a more stable construct compared to the angled or axially inserted screw when subjected to caudal cyclic loading. We obtained 12 fresh frozen lumbar vertebrae from L3 to L5 from five cadavers. Schantz screws (6.0 mm) were inserted into each pedicle, one angled and along the axis of the pedicle and the other parallel to the spinous process. Fluoroscopic imaging was used to guide insertion. Each screw was then subjected to caudal cyclic loads of 50 N for 2000 cycles at 2 Hz. Analysis of initial damage, initial rate of damage, and total damage during cyclic loading was undertaken. Average total fatigue damage for straight screws measured 0.398+/-0.38 mm, and 0.689+/-0.96 mm for angled screws. Statistical analysis for total fatigue damage ratio of angled to straight screws revealed that a significant stability was achieved in straight-screw construct (P<0.03). This study showed that straight screw insertion results in a more stable pedicle-screw construct. The angled screw insertion technique resulted in more scattered values of damage indicating that the outcome from the angled screw fixation is less predictable. This validates the use of this technique to implant pedicle screws across the axis of the pedicle (parallel to the mid sagittal line) rather than along the axis, and has broad implications in instrumented posterior lumbar spinal surgery.

Determination of Cyclic-Tension Fatigue of Al-4Cu-1Mg Alloy Using Ultrasonic Shear Waves

Cyclic-tension fatigue of aluminum alloy, Al-4Cu-1Mg, was determined by an analysis of diffracted SH and SV waves, passing through the surface and reflecting the bottom of the specimen, respectively. The propagation time of SH waves and the internal friction of SV waves begins to decrease and increase from fatigue damage ratio (¼ N=Nf ) of 0.5, respectively, suggesting noticeable increase of movable dislocation. From the analysis of SH waves along the direction to the loading axis, the damping ratio decreases and the phase advances with increasing of the degree of fatigue. Assumed from SH wave flux model, the former behavior correlates well with increasing of the residual stress by cyclic tension. The latter may be characterized by viscoelasticity. These results show that ultrasonic transmission method is useful probe for evaluation of fatigue in aluminum alloy. [doi:10.2320/matertrans.48.550]

Residual Deformation and Cumulative Fatigue Damage Ratio of Breasting Dolphin by Single Pile Structures

Currently, breasting dolphins of deepwater terminals are designed so as ship's berthingenergy shall be absorbed mainly by fenders. As for a singel pile structure (SPS) whichconsists of high-tensile steel, ship's berthing energy shall be absorbed mainly by piles.Major subjects to be cleared for design ofSPS are the lateral load-deflection characteristicsof piles against large deformation, estimatation of residual deformation underrepeated loads and evaluation the safety for fatigue. In this report, both residual deformationand cumulative fatigue damage ratio within a lifetime are computed with considerationof ship's berthing and mooring forces. The lateral load-deflection characteristicsof SPS against large lateral repeated loads which are obtained from the field tests andmodel experiments are taken into consideration in this study.

鉄筋コンクリート柱の低サイクル疲労に関する実験的研究

Prediction of damage is important in estimating the dynamic response analysis for reinforced concrete structures subjected to earthquake excitations. Damage prediction is usually measured in term of ductility factor, however, a combination of maximum displacement response and cumulative fatigue damage may cause to fail. In order to investigate low-cycle fatigue damage in RC columns, 7 reinforced concrete frames with rigid beams were tested by using a dynamic actuator. From the results of the test reported in this work, it is concluded that : 1) All specimens collapsed due to considerable degradation of axial load carrying capacity which occured after the shear compression failure at the head or knee of specimen and buckling of compressive longitudinal reinforcing bars. 2) The collapse of concrete structures with axial load is defined explicitly as sudden increase of cumulative axial displacement. 3) The rate of cumulative axial displacement dδ_v/dn can be expressed in the form dδ_v/dn=C △δ^α_T, where C and α are member constants, as shown in Fig.19. The Wohler curve can be obtained from this differential equation. 4) The Wohler curve for the lateral displacement amplitude △δ_T and average area △E of hysteresis loops can be shown as Eq. (3) and Eq. (6), respectively. The latter has a high correlation to experimental results. 5) The linear cumulative fatigue damage hypothesis is not true for low-cycle fatigue of reinforced concrete columns. 6) The non-linear cumulative fatigue damage ratio for reinforced concrete columns can be expressed in the form of Eq. (17) and (18).

A Concept of Fatigue Damage

Abstract An experimental investigation was conducted to study the effects of cumulative fatigue damage on endurance life. Stepwise-varying stress sequences were applied to rotating-cantilever-beam specimens. Typical curves of fatigue damage versus cycle ratio were deduced. The effect of scatter in the test results was evaluated.