This paper aims to experimentally and numerically probe fatigue behaviours and lifetimes of 3D4D(three-dimensional four-directional)braided composite I-beam under four-point flexure spectrum loading.New fatigue damage...This paper aims to experimentally and numerically probe fatigue behaviours and lifetimes of 3D4D(three-dimensional four-directional)braided composite I-beam under four-point flexure spectrum loading.New fatigue damage models of fibre yarn,matrix and fibre–matrix interface are proposed,and fatigue failure criteria and PFDA(Progressive Fatigue Damage Algorithm)are thus presented for meso-scale fatigue damage modelling of 3D4D braided composite I-beam.To validate the aforementioned model and algorithm,fatigue tests are conducted on the 3D4D braided composite I-beam under four-point flexure spectrum loading,and fatigue failure mechanisms are analyzed and discussed.Novel global–local FE(Finite Element)model based on the PFDA is generated for modelling progressive fatigue failure process and predicting fatigue life of 3D4D braided composite I-beam under four-point flexure spectrum loading.Good agreement has been achieved between experimental results and predictions,demonstrating the effective usage of new model.It is shown that matrix cracking and interfacial debonding initially initiates on top surface of top flange of I-beam,and then gradually propagates from the side surface of top flange to the intermediate web along the braiding angle,and considerable fiber breakage finally causes final fatigue failure of I-beam.展开更多
This study examines the slug-induced vibration(SIV)response and fatigue behavior of offshore risers subjected to internal slug flow.A structural model incorporating internal slug flow dynamics is developed using the A...This study examines the slug-induced vibration(SIV)response and fatigue behavior of offshore risers subjected to internal slug flow.A structural model incorporating internal slug flow dynamics is developed using the Absolute Nodal Coordinate Formulation(ANCF)and a spatial-temporal density variation equation to analyze how slug flow parameters affect the SIV response of risers.Structural displacement,stress,and fatigue responses are systematically evaluated to characterize the structural behavior under SIV conditions.Longer slugs induce more pronounced traveling wave characteristics,while shorter slugs facilitate a mixed traveling-standing wave mode.Moreover,higher slug frequencies lead to increased fatigue accumulation,especially over an extended touchdown zone,thereby compromising the structural integrity of the riser.The findings yield valuable insights into the dynamic interactions between slug flow and riser response.This research advances the understanding of SIV mechanisms and provides a theoretical foundation for fatigue assessment and structural optimization,contributing to the safe and efficient design of offshore risers in deepwater environments.展开更多
By integrating laboratory physical modeling experiments with machine learning-based analysis of dominant factors,this study explored the feasibility of pulse hydraulic fracturing(PHF)in deep coal rocks and revealed th...By integrating laboratory physical modeling experiments with machine learning-based analysis of dominant factors,this study explored the feasibility of pulse hydraulic fracturing(PHF)in deep coal rocks and revealed the fracture propagation patterns and the mechanisms of pulsating loading in the process.The results show that PHF induces fatigue damage in coal matrix,significantly reducing breakdown pressure and increasing fracture network volume.Lower vertical stress differential coefficient(less than 0.31),lower peak pressure ratio(less than 0.9),higher horizontal stress differential coefficient(greater than 0.13),higher pulse amplitude ratio(greater than or equal to 0.5)and higher pulse frequency(greater than or equal to 3 Hz)effectively decrease the breakdown pressure.Conversely,higher vertical stress differential coefficient(greater than or equal to 0.31),higher pulse amplitude ratio(greater than or equal to 0.5),lower horizontal stress differential coefficient(less than or equal to 0.13),lower peak pressure ratio(less than 0.9),and lower pulse frequency(less than 3 Hz)promote the formation of a complex fracture network.Vertical stress and peak pressure are the most critical geological and engineering parameters affecting the stimulation effectiveness of PHF.The dominant mechanism varies with coal rank due to differences in geomechanical characteristics and natural fracture development.Low-rank coal primarily exhibits matrix strength degradation.High-rank coal mainly involves the activation of natural fractures and bedding planes.Medium-rank coal shows a coexistence of matrix strength degradation and micro-fracture connectivity.The PHF forms complex fracture networks through the dual mechanism of matrix strength degradation and fracture network connectivity enhancement.展开更多
To accurately predict the fatigue properties of additively manufactured(AM)titanium alloys,it is important to understand the fatigue damage origin behavior.However,this behavior is still ambiguous.Therefore,the effect...To accurately predict the fatigue properties of additively manufactured(AM)titanium alloys,it is important to understand the fatigue damage origin behavior.However,this behavior is still ambiguous.Therefore,the effects of internal defects and microstructures on the fatigue damage origin behavior of laser direct energy deposited TC11(LDED-TC11)alloy were investigated using a fatigue origin criterion.The criterion was proposed to analyze the competing and combining effects by coupling the plasticity-corrected crack driving force,the resistance of short cracks,and the modified Kitagawa-Takahashi diagram.Three scenarios corresponding to the criterion were clarified,representing the damage mechanisms dominated by the microstructure,the combined effect of internal defect and microstructure,and the internal defect.As a result,the fatigue fracture morphology of high-cycle fatigue tests demonstrates two fatigue origin modes,i.e.microstructure and gas pore origin modes.The two fatigue modes belong to Scenario I and Scenario II,respectively,which indicates that the fatigue damage origin process of this alloy is sensitive to microstructure.Besides,it was found that the width of the primary a phase of this alloy is strongly relevant to intrinsic defect size.Finally,the fatigue origin criterion was verified in three aspects.展开更多
The trade-off between mechanistic interpretability,operational convenience,and predictive accuracy is challenging for predicting the lifetime of lithium-ion batteries.To resolve this contradiction,we propose a damage ...The trade-off between mechanistic interpretability,operational convenience,and predictive accuracy is challenging for predicting the lifetime of lithium-ion batteries.To resolve this contradiction,we propose a damage model based on fatigue damage theory and electrochemical impedance spectroscopy.The causal relationship of“fatigue damage→resistance increase→capacity fading”is revealed to describe the underlying mechanism.Charge transfer resistance is chosen as the variable to ensure the convenience of data acquisition.To verify the accuracy of the model,the electrochemical impedance spectrum and capacity of a graphene-coated silicon electrode at two charging rates are collected and analyzed.50% and 75% of the measured data are utilized as inputs to compare the prediction capabilities of the proposed damage model and the existing empirical model.The particle filter algorithm is adopted to train the parameters of both models.The maximum prediction error of the damage model is less than 3%,showing better prediction accuracy and medium-term prediction stability than the empirical model.Our work demonstrates that the proposed damage model is an effective way to resolve contradictions in lifetime prediction.展开更多
Current fatigue damage analysis of various components(e.g.aircraft parts)focuses on effects of High-Cycle-Fatigue(HCF)loads while overlooking effects of Very-High-Cycle-Fatigue(VHCF)loads,thereby introducing a substan...Current fatigue damage analysis of various components(e.g.aircraft parts)focuses on effects of High-Cycle-Fatigue(HCF)loads while overlooking effects of Very-High-Cycle-Fatigue(VHCF)loads,thereby introducing a substantial bias.The crux of decreasing this bias lies in how to reasonably consider the threshold effect and nonlinear effect of VHCF loads'fatigue damage evolution.This problem is addressed in this paper from the perspective of Residual Fatigue Quality(RFQ,represent residual S-N^(*)curve and residual fatigue limitσ_(-1)^(*)).Fatigue tests were conducted on AA2024-T4 under various constant/variable-amplitude loads to reveal the evolution characteristics of RFQ and measure the equivalent fatigue damage of VHCF loads block loaded with various number of pre-loading HCF loads.Corresponding mechanisms were analysed in view of evolution of extrusions/intrusions along persistent slip bands.Theoretical analysis was conducted to reveal the relationship between RFQ and fatigue damage of VHCF loads block.Based on the above results,an isodamage curve-based fatigue damage analysis method was proposed,where bilinear-isodamage curves(consist of S-N^(*)curves intersecting at a point and corresponding_(σ-1)^(*))were adopted to consider the RFQ degeneration and its effect.This method reduces analysis bias to 1/3 of previous methods for typical variable-amplitude loads in HCF and HCF-VHCF regime.展开更多
Fatigue damage is a primary contributor to the failure of composite structures,underscoring the critical importance of monitoring its progression to ensure structural safety.This paper introduces an innovative approac...Fatigue damage is a primary contributor to the failure of composite structures,underscoring the critical importance of monitoring its progression to ensure structural safety.This paper introduces an innovative approach to fatigue damage monitoring in composite structures,leveraging a hybrid methodology that integrates the Whale Optimization Algorithm(WOA)-Backpropagation(BP)neural network with an ultrasonic guided wave feature selection algorithm.Initially,a network of piezoelectric ceramic sensors is employed to transmit and capture ultrasonic-guided waves,thereby establishing a signal space that correlates with the structural condition.Subsequently,the Relief-F algorithm is applied for signal feature extraction,culminating in the formation of a feature matrix.This matrix is then utilized to train the WOA-BP neural network,which optimizes the fatigue damage identification model globally.The proposed model’s efficacy in quantifying fatigue damage is tested against fatigue test datasets,with its performance benchmarked against the traditional BP neural network algorithm.The findings demonstrate that the WOA-BP neural network model not only surpasses the BP model in predictive accuracy but also exhibits enhanced global search capabilities.The effect of different sensor-receiver path signals on the model damage recognition results is also discussed.The results of the discussion found that the path directly through the damaged area is more accurate in modeling damage recognition compared to the path signals away from the damaged area.Consequently,the proposed monitoring method in the fatigue test dataset is adept at accurately tracking and recognizing the progression of fatigue damage.展开更多
In order to investigate the fatigue behavior of asphalt concrete, a new numerical approach based on a bi-linear cohesive zone model （CZM） is developed. Integrated with the CZM, a fatigue damage evolution model is es...In order to investigate the fatigue behavior of asphalt concrete, a new numerical approach based on a bi-linear cohesive zone model （CZM） is developed. Integrated with the CZM, a fatigue damage evolution model is established to indicate the gradual degradation of cohesive properties of asphalt concrete under cyclic loading. Then the model is implemented in the finite element software ABAQUS through a user-defined subroutine. Based on the proposed model, an indirect tensile fatigue test is finally simulated. The fatigue lives obtained through numerical analysis show good agreement with laboratory results. Fatigue damage accumulates in a nonlinear manner during the cyclic loading process and damage initiation phase is the major part of fatigue failure. As the stress ratio increases, the time of the steady damage growth stage decreases significantly. It is found that the proposed fatigue damage evolution model can serve as an accurate and efficient tool for the prediction of fatigue damage of asphalt concrete.展开更多
A robust experimental procedure was developed, by which the evolution of fatigue damage in AZ31 magnesium alloy was tracked online with the ultrasonic nonlinearity parameter β. β values of three sets of samples unde...A robust experimental procedure was developed, by which the evolution of fatigue damage in AZ31 magnesium alloy was tracked online with the ultrasonic nonlinearity parameter β. β values of three sets of samples under different stress levels were measured. Microstructures of specimens at different fatigue stages were observed in situ by optical microscopy. The experimental results show that there is a significant increase in β linked to the accumulation of persistent slip bands （PSBs） and micro-cracks at the early stages of fatigue life and reaches the maximum, about 55% of fatigue life. Ultrasonic attenuation coefficient increases with the expanding of micro-cracks and leads to β decrease slightly after 55% of fatigue life. The variation of β with fatigue cycles is in good agreement with the growth of PSBs and micro-cracks. In addition, it has no significant effect on the experimental results for the changes of low- and high-cycle fatigue and the fatigue mode with tension-tension and tension-compression.展开更多
Experimental and analytical investigations on the residual strength of the stiffened LY12CZ aluminum alloy panels with widespread fatigue damage （WFD） are conducted. Nine stiffened LY12CZ aluminum alloy panels with ...Experimental and analytical investigations on the residual strength of the stiffened LY12CZ aluminum alloy panels with widespread fatigue damage （WFD） are conducted. Nine stiffened LY12CZ aluminum alloy panels with three different types of damage are tested for residual strength. Each specimen is pre-cracked at rivet holes by saw cuts and subjected to a monotonically increasing tensile load until failure is occurred and the failure load is recorded. The stress intensity factors at the tips of the lead crack and the adjacent WFD cracks of the stiffened aluminum alloy panels are calculated by compounding approach and finite element method （FEM） respectively. The residual strength of the stiffened panels with WFD is evaluated by the engineering method with plastic zone linkup criterion and the FEM with apparent fracture toughness criterion respectively. The predicted residual strength agrees well with the experiment results. It indicates that in engineering practice these methods can be used for residual strength evaluation with the acceptable accuracy. It can be seen from this research that WFD can significantly reduce the residual strength and the critical crack length of the stiffened panels with WFD. The effect of WFD crack length on residual strength is also studied.展开更多
Aiming to investigate the fatigue damage mechanism and bearing characteristics of multi-pillar system under cyclic loading,a series of axial cyclic loading tests with different cyclic amplitudes were carried out on tr...Aiming to investigate the fatigue damage mechanism and bearing characteristics of multi-pillar system under cyclic loading,a series of axial cyclic loading tests with different cyclic amplitudes were carried out on triple-pillar marble specimens.The acoustic emission(AE)and digital image correlation(DIC)were jointly applied to monitoring and recording damage evolution and failure behavior of each pillar,which reproduced the cataclysmic instability process of underground pillar groups.Experimental results indicated that the cyclic amplitude exceeding the threshold of damage initiation weakened the resistance to deformation,resulting in obvious release of dissipated energy and the reduction of bearing capacity.Conversely,after low-amplitude cyclic loading,both the pre-peak bearing capacity and the post-peak ductility of the pillar system increased due to the compaction of initial defects,indicating that the peak bearing capacity was closely related to the extent of pre-peak fatigue damage.The axial strain of each pillar was measured by DIC virtual extensometer to present the damage extent during cyclic loading phase.Meanwhile,fracture evolution of typical load drop points was also characterized by transverse strain fields(εxx),and observations showed that the damage extent of key pillar undergoing high-amplitude cyclic loads was more serious and violent,accompanied by the ejection of rock debris and loud noises.展开更多
Assessing the fatigue life of mooring systems is important for deep water structures. In this paper, a comprehensive fatigue analysis is conducted on the mooring lines applied in a semi-submersible platform with speci...Assessing the fatigue life of mooring systems is important for deep water structures. In this paper, a comprehensive fatigue analysis is conducted on the mooring lines applied in a semi-submersible platform with special focus on the low frequency(LF) fatigue damage. Several influential factors, including water depth, wave spectral parameters, and riser system, are considered. Numerical simulation of a semi-submersible platform with the mooring/riser system is executed under different conditions, and the fatigue damage of mooring lines is assessed by using the time domain analysis method as a benchmark. The effects of these factors on the mooring line tension and the fatigue damage are investigated and discussed in detail. Research results indicate that the LF fatigue damage only accounts for a very small portion of the total damage, although the LF components dominate the global motion response and the mooring line tension of the semi-submersible platform. However, it is demonstrated that the LF fatigue damage is clearly affected by the influential factors. The increase in water depth and spectral peak periods, and the existence of risers can weaken the contribution of the LF components to the mooring line fatigue damage, while the fatigue damage due to the LF components increases with the increase of significant wave height.展开更多
Individual aircraft life monitoring is required to ensure safety and economy of aircraft structure, and fatigue damage evaluation based on collected operational data of aircraft is an integral part of it. To improve t...Individual aircraft life monitoring is required to ensure safety and economy of aircraft structure, and fatigue damage evaluation based on collected operational data of aircraft is an integral part of it. To improve the accuracy and facilitate the application, this paper proposes an engineering approach to evaluate fatigue damage and predict fatigue life for critical structures in fatigue monitoring. In this approach, traditional nominal stress method is applied to back calculate the S-N curve parameters of the realistic structure details based on full-scale fatigue test data. Then the S-N curve and Miner＇s rule are adopted in damage estimation and fatigue life analysis for critical locations under individual load spectra. The relationship between relative small crack length and fatigue life can also be predicted with this approach. Specimens of 7 B04-T74 aluminum alloy and TA15 M titanium alloy are fatigue tested under two types of load spectra, and there is a good agreement between the experimental results and analysis results. Furthermore, the issue concerning scatter factor in individual aircraft damage estimation is also discussed.展开更多
Rotary bending fatigue tests were carried out for smooth specimens of a mediumcarbon steel with two different grain sizes near the fatigue limit. The process of fatigue damagewas observed by replication method, and th...Rotary bending fatigue tests were carried out for smooth specimens of a mediumcarbon steel with two different grain sizes near the fatigue limit. The process of fatigue damagewas observed by replication method, and the effects of grain size,stress level and microstructure on surface damage were studied. The effect of following cycle stress level on the coaxing effects was also discussed. The fatigue limit is the maximum stress at which the short fatigue crack initiates and becomes a non-propagating crack.. The length of non-propagating crack is related to grain sizes and stress level. The coaxing effects disappear when the following stress level is greater than the critical value.展开更多
Fatigue damage increases with the applied loading cycles in a cumulative manner and the material deteriorates with the corrosion time. A cumulative fatigue damage rule under the alternative of corrosion or cyclic load...Fatigue damage increases with the applied loading cycles in a cumulative manner and the material deteriorates with the corrosion time. A cumulative fatigue damage rule under the alternative of corrosion or cyclic loading was proposed. The specimens of aluminum alloy LY12-CZ soaked in corrosive liquid for different times were tested under the constant amplitude cyclic loading to obtain S-N curves. The test was carried out to verify the proposed cumulative fatigue damage rule under the different combinations among corrosion time, loading level, and the cycle numbers. It was shown that the predicted residual fatigue lives showed a good agreement with the experimental results and the proposed rule was simple and can be easily adopted.展开更多
A modified nonlinear fatigue damage accumulation model based on the Manson-Halford theory was presented,and the new model was developed for fatigue life prediction under constant and variable amplitude loading, which ...A modified nonlinear fatigue damage accumulation model based on the Manson-Halford theory was presented,and the new model was developed for fatigue life prediction under constant and variable amplitude loading, which took the effects of the load interactions and the phenomenon of material's strength degradation into account. The experimental data of the 30 Cr Mn Si A and the LY-12 cz from literature were used to verify the proposed model. And from the good agreement between the experimental data and predicted results,we can see it clear that the proposed method can be applied to predicting fatigue life under different loadings.展开更多
A prediction model of the deepwater steel catenary riser VIV is proposed based on the forced oscillation test data, taking into account the riser-seafloor interaction for the cross-flow VIV-induced fatigue damage at t...A prediction model of the deepwater steel catenary riser VIV is proposed based on the forced oscillation test data, taking into account the riser-seafloor interaction for the cross-flow VIV-induced fatigue damage at touch-down point （TDP）. The model will give more reasonable simulation of SCR response near TDP than the previous pinned truncation model. In the present model, the hysteretic riser-soil interaction model is simplified as the linear spring and damper to simulate the seafloor, and the damping is obtained according to the dissipative power during one periodic riser-soil interaction. In order to validate the model, the comparison with the field measurement and the results predicted by Shear 7 program of a full-scale steel catenary riser is carried out. The main induced modes, mode frequencies and response amplitude are in a good agreement. Furthermore, the parametric studies are carried out to broaden the understanding of the fatigue damage sensitivity to the upper end in-plane offset and seabed characteristics. In addition, the fatigue stress comparison at TDP between the truncation riser model and the present full riser model shows that the existence of touch-down zones is very important for the fatigue damage assessment of steel catenary riser at TDP.展开更多
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 a...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 primaryα(α_(p))phase were examined comparatively.The results showed that both pure fatigue and dwell fatigue life decreased with increasing the volume fraction of theα_(p)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 theα_(p)-secondaryα(α_(s))combination reveal that theα_(s)phase close to theα_(p)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 theα_(s)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 theα_(s)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.展开更多
Both wave-frequency(WF) and low-frequency(LF) components of mooring tension are in principle non-Gaussian due to nonlinearities in the dynamic system.This paper conducts a comprehensive investigation of applicable pro...Both wave-frequency(WF) and low-frequency(LF) components of mooring tension are in principle non-Gaussian due to nonlinearities in the dynamic system.This paper conducts a comprehensive investigation of applicable probability density functions(PDFs) of mooring tension amplitudes used to assess mooring-line fatigue damage via the spectral method.Short-term statistical characteristics of mooring-line tension responses are firstly investigated,in which the discrepancy arising from Gaussian approximation is revealed by comparing kurtosis and skewness coefficients.Several distribution functions based on present analytical spectral methods are selected to express the statistical distribution of the mooring-line tension amplitudes.Results indicate that the Gamma-type distribution and a linear combination of Dirlik and Tovo-Benasciutti formulas are suitable for separate WF and LF mooring tension components.A novel parametric method based on nonlinear transformations and stochastic optimization is then proposed to increase the effectiveness of mooring-line fatigue assessment due to non-Gaussian bimodal tension responses.Using time domain simulation as a benchmark,its accuracy is further validated using a numerical case study of a moored semi-submersible platform.展开更多
A general method of probabilistic fatigue damage prognostics using limited and partial information is developed.Limited and partial information refers to measurable data that are not enough or cannot directly be used ...A general method of probabilistic fatigue damage prognostics using limited and partial information is developed.Limited and partial information refers to measurable data that are not enough or cannot directly be used to statistically identify model parameter using traditional regression analysis.In the proposed method, the prior probability distribution of model parameters is derived based on the principle of maximum entropy（Max Ent） using the limited and partial information as constraints.The posterior distribution is formulated using the principle of maximum relative entropy（MRE） to perform probability updating when new information is available and reduces uncertainty in prognosis results.It is shown that the posterior distribution is equivalent to a Bayesian posterior when the new information used for updating is point measurements.A numerical quadrature interpolating method is used to calculate the asymptotic approximation for the prior distribution.Once the prior is obtained, subsequent measurement data are used to perform updating using Markov chain Monte Carlo（MCMC） simulations.Fatigue crack prognosis problems with experimental data are presented for demonstration and validation.展开更多
基金supported by the National Natural Science Foundation of China(No.12472340).
文摘This paper aims to experimentally and numerically probe fatigue behaviours and lifetimes of 3D4D(three-dimensional four-directional)braided composite I-beam under four-point flexure spectrum loading.New fatigue damage models of fibre yarn,matrix and fibre–matrix interface are proposed,and fatigue failure criteria and PFDA(Progressive Fatigue Damage Algorithm)are thus presented for meso-scale fatigue damage modelling of 3D4D braided composite I-beam.To validate the aforementioned model and algorithm,fatigue tests are conducted on the 3D4D braided composite I-beam under four-point flexure spectrum loading,and fatigue failure mechanisms are analyzed and discussed.Novel global–local FE(Finite Element)model based on the PFDA is generated for modelling progressive fatigue failure process and predicting fatigue life of 3D4D braided composite I-beam under four-point flexure spectrum loading.Good agreement has been achieved between experimental results and predictions,demonstrating the effective usage of new model.It is shown that matrix cracking and interfacial debonding initially initiates on top surface of top flange of I-beam,and then gradually propagates from the side surface of top flange to the intermediate web along the braiding angle,and considerable fiber breakage finally causes final fatigue failure of I-beam.
基金financially supported by the National Natural Science Foundation of China(Grant No.52222111)the Science Foundation of China University of Petroleum,Beijing(Grant No.2462025SZBH002)。
文摘This study examines the slug-induced vibration(SIV)response and fatigue behavior of offshore risers subjected to internal slug flow.A structural model incorporating internal slug flow dynamics is developed using the Absolute Nodal Coordinate Formulation(ANCF)and a spatial-temporal density variation equation to analyze how slug flow parameters affect the SIV response of risers.Structural displacement,stress,and fatigue responses are systematically evaluated to characterize the structural behavior under SIV conditions.Longer slugs induce more pronounced traveling wave characteristics,while shorter slugs facilitate a mixed traveling-standing wave mode.Moreover,higher slug frequencies lead to increased fatigue accumulation,especially over an extended touchdown zone,thereby compromising the structural integrity of the riser.The findings yield valuable insights into the dynamic interactions between slug flow and riser response.This research advances the understanding of SIV mechanisms and provides a theoretical foundation for fatigue assessment and structural optimization,contributing to the safe and efficient design of offshore risers in deepwater environments.
基金Supported by the National Natural Science Foundation of China(52274014,52421002).
文摘By integrating laboratory physical modeling experiments with machine learning-based analysis of dominant factors,this study explored the feasibility of pulse hydraulic fracturing(PHF)in deep coal rocks and revealed the fracture propagation patterns and the mechanisms of pulsating loading in the process.The results show that PHF induces fatigue damage in coal matrix,significantly reducing breakdown pressure and increasing fracture network volume.Lower vertical stress differential coefficient(less than 0.31),lower peak pressure ratio(less than 0.9),higher horizontal stress differential coefficient(greater than 0.13),higher pulse amplitude ratio(greater than or equal to 0.5)and higher pulse frequency(greater than or equal to 3 Hz)effectively decrease the breakdown pressure.Conversely,higher vertical stress differential coefficient(greater than or equal to 0.31),higher pulse amplitude ratio(greater than or equal to 0.5),lower horizontal stress differential coefficient(less than or equal to 0.13),lower peak pressure ratio(less than 0.9),and lower pulse frequency(less than 3 Hz)promote the formation of a complex fracture network.Vertical stress and peak pressure are the most critical geological and engineering parameters affecting the stimulation effectiveness of PHF.The dominant mechanism varies with coal rank due to differences in geomechanical characteristics and natural fracture development.Low-rank coal primarily exhibits matrix strength degradation.High-rank coal mainly involves the activation of natural fractures and bedding planes.Medium-rank coal shows a coexistence of matrix strength degradation and micro-fracture connectivity.The PHF forms complex fracture networks through the dual mechanism of matrix strength degradation and fracture network connectivity enhancement.
基金supported by the National Natural Science Foundation of China(Nos.5175018,52090044)the 2025 Science and Technology Innovation Program of Ningbo,China(No.2022Z014)。
文摘To accurately predict the fatigue properties of additively manufactured(AM)titanium alloys,it is important to understand the fatigue damage origin behavior.However,this behavior is still ambiguous.Therefore,the effects of internal defects and microstructures on the fatigue damage origin behavior of laser direct energy deposited TC11(LDED-TC11)alloy were investigated using a fatigue origin criterion.The criterion was proposed to analyze the competing and combining effects by coupling the plasticity-corrected crack driving force,the resistance of short cracks,and the modified Kitagawa-Takahashi diagram.Three scenarios corresponding to the criterion were clarified,representing the damage mechanisms dominated by the microstructure,the combined effect of internal defect and microstructure,and the internal defect.As a result,the fatigue fracture morphology of high-cycle fatigue tests demonstrates two fatigue origin modes,i.e.microstructure and gas pore origin modes.The two fatigue modes belong to Scenario I and Scenario II,respectively,which indicates that the fatigue damage origin process of this alloy is sensitive to microstructure.Besides,it was found that the width of the primary a phase of this alloy is strongly relevant to intrinsic defect size.Finally,the fatigue origin criterion was verified in three aspects.
基金supported by the National Natural Science Foundation of China(12021002,12472183,and 12041201).
文摘The trade-off between mechanistic interpretability,operational convenience,and predictive accuracy is challenging for predicting the lifetime of lithium-ion batteries.To resolve this contradiction,we propose a damage model based on fatigue damage theory and electrochemical impedance spectroscopy.The causal relationship of“fatigue damage→resistance increase→capacity fading”is revealed to describe the underlying mechanism.Charge transfer resistance is chosen as the variable to ensure the convenience of data acquisition.To verify the accuracy of the model,the electrochemical impedance spectrum and capacity of a graphene-coated silicon electrode at two charging rates are collected and analyzed.50% and 75% of the measured data are utilized as inputs to compare the prediction capabilities of the proposed damage model and the existing empirical model.The particle filter algorithm is adopted to train the parameters of both models.The maximum prediction error of the damage model is less than 3%,showing better prediction accuracy and medium-term prediction stability than the empirical model.Our work demonstrates that the proposed damage model is an effective way to resolve contradictions in lifetime prediction.
基金the support from National Key Laboratory of Strength and Structural Integrity independent research project“Failure law and fatigue life prediction method of Metal Materials based on Material property degradation”。
文摘Current fatigue damage analysis of various components(e.g.aircraft parts)focuses on effects of High-Cycle-Fatigue(HCF)loads while overlooking effects of Very-High-Cycle-Fatigue(VHCF)loads,thereby introducing a substantial bias.The crux of decreasing this bias lies in how to reasonably consider the threshold effect and nonlinear effect of VHCF loads'fatigue damage evolution.This problem is addressed in this paper from the perspective of Residual Fatigue Quality(RFQ,represent residual S-N^(*)curve and residual fatigue limitσ_(-1)^(*)).Fatigue tests were conducted on AA2024-T4 under various constant/variable-amplitude loads to reveal the evolution characteristics of RFQ and measure the equivalent fatigue damage of VHCF loads block loaded with various number of pre-loading HCF loads.Corresponding mechanisms were analysed in view of evolution of extrusions/intrusions along persistent slip bands.Theoretical analysis was conducted to reveal the relationship between RFQ and fatigue damage of VHCF loads block.Based on the above results,an isodamage curve-based fatigue damage analysis method was proposed,where bilinear-isodamage curves(consist of S-N^(*)curves intersecting at a point and corresponding_(σ-1)^(*))were adopted to consider the RFQ degeneration and its effect.This method reduces analysis bias to 1/3 of previous methods for typical variable-amplitude loads in HCF and HCF-VHCF regime.
基金funded by the Key Program of the National Natural Science Foundation of China(U2341235)Youth Fund for Basic Research Program of Jiangnan University(JUSRP123003)+2 种基金Postgraduate Research&Practice Innovation Program of Jiangsu Province(SJCX23_1237)the National Key R&D Program of China(2018YFA0702800)Key Technologies R&D Program of CNBM(2023SJYL01).
文摘Fatigue damage is a primary contributor to the failure of composite structures,underscoring the critical importance of monitoring its progression to ensure structural safety.This paper introduces an innovative approach to fatigue damage monitoring in composite structures,leveraging a hybrid methodology that integrates the Whale Optimization Algorithm(WOA)-Backpropagation(BP)neural network with an ultrasonic guided wave feature selection algorithm.Initially,a network of piezoelectric ceramic sensors is employed to transmit and capture ultrasonic-guided waves,thereby establishing a signal space that correlates with the structural condition.Subsequently,the Relief-F algorithm is applied for signal feature extraction,culminating in the formation of a feature matrix.This matrix is then utilized to train the WOA-BP neural network,which optimizes the fatigue damage identification model globally.The proposed model’s efficacy in quantifying fatigue damage is tested against fatigue test datasets,with its performance benchmarked against the traditional BP neural network algorithm.The findings demonstrate that the WOA-BP neural network model not only surpasses the BP model in predictive accuracy but also exhibits enhanced global search capabilities.The effect of different sensor-receiver path signals on the model damage recognition results is also discussed.The results of the discussion found that the path directly through the damaged area is more accurate in modeling damage recognition compared to the path signals away from the damaged area.Consequently,the proposed monitoring method in the fatigue test dataset is adept at accurately tracking and recognizing the progression of fatigue damage.
基金The Open Research Fund of Key Laboratory of Highway Engineering of Sichuan Province of Southw est Jiaotong University (No.LHTE002201102)
文摘In order to investigate the fatigue behavior of asphalt concrete, a new numerical approach based on a bi-linear cohesive zone model （CZM） is developed. Integrated with the CZM, a fatigue damage evolution model is established to indicate the gradual degradation of cohesive properties of asphalt concrete under cyclic loading. Then the model is implemented in the finite element software ABAQUS through a user-defined subroutine. Based on the proposed model, an indirect tensile fatigue test is finally simulated. The fatigue lives obtained through numerical analysis show good agreement with laboratory results. Fatigue damage accumulates in a nonlinear manner during the cyclic loading process and damage initiation phase is the major part of fatigue failure. As the stress ratio increases, the time of the steady damage growth stage decreases significantly. It is found that the proposed fatigue damage evolution model can serve as an accurate and efficient tool for the prediction of fatigue damage of asphalt concrete.
基金Project (KZ200810005001) supported by the Beijing Municipal Natural Science Foundation, ChinaProject (10772008) supported by the National Natural Science Foundation of China
文摘A robust experimental procedure was developed, by which the evolution of fatigue damage in AZ31 magnesium alloy was tracked online with the ultrasonic nonlinearity parameter β. β values of three sets of samples under different stress levels were measured. Microstructures of specimens at different fatigue stages were observed in situ by optical microscopy. The experimental results show that there is a significant increase in β linked to the accumulation of persistent slip bands （PSBs） and micro-cracks at the early stages of fatigue life and reaches the maximum, about 55% of fatigue life. Ultrasonic attenuation coefficient increases with the expanding of micro-cracks and leads to β decrease slightly after 55% of fatigue life. The variation of β with fatigue cycles is in good agreement with the growth of PSBs and micro-cracks. In addition, it has no significant effect on the experimental results for the changes of low- and high-cycle fatigue and the fatigue mode with tension-tension and tension-compression.
文摘Experimental and analytical investigations on the residual strength of the stiffened LY12CZ aluminum alloy panels with widespread fatigue damage （WFD） are conducted. Nine stiffened LY12CZ aluminum alloy panels with three different types of damage are tested for residual strength. Each specimen is pre-cracked at rivet holes by saw cuts and subjected to a monotonically increasing tensile load until failure is occurred and the failure load is recorded. The stress intensity factors at the tips of the lead crack and the adjacent WFD cracks of the stiffened aluminum alloy panels are calculated by compounding approach and finite element method （FEM） respectively. The residual strength of the stiffened panels with WFD is evaluated by the engineering method with plastic zone linkup criterion and the FEM with apparent fracture toughness criterion respectively. The predicted residual strength agrees well with the experiment results. It indicates that in engineering practice these methods can be used for residual strength evaluation with the acceptable accuracy. It can be seen from this research that WFD can significantly reduce the residual strength and the critical crack length of the stiffened panels with WFD. The effect of WFD crack length on residual strength is also studied.
基金Project(2015CB060200)supported by the National Basic Research Program of ChinaProject(41772313)supported by the National Natural Science Foundation of ChinaProject(2017zzts185)supported by the Fundamental Research Funds for the Central Universities,China
文摘Aiming to investigate the fatigue damage mechanism and bearing characteristics of multi-pillar system under cyclic loading,a series of axial cyclic loading tests with different cyclic amplitudes were carried out on triple-pillar marble specimens.The acoustic emission(AE)and digital image correlation(DIC)were jointly applied to monitoring and recording damage evolution and failure behavior of each pillar,which reproduced the cataclysmic instability process of underground pillar groups.Experimental results indicated that the cyclic amplitude exceeding the threshold of damage initiation weakened the resistance to deformation,resulting in obvious release of dissipated energy and the reduction of bearing capacity.Conversely,after low-amplitude cyclic loading,both the pre-peak bearing capacity and the post-peak ductility of the pillar system increased due to the compaction of initial defects,indicating that the peak bearing capacity was closely related to the extent of pre-peak fatigue damage.The axial strain of each pillar was measured by DIC virtual extensometer to present the damage extent during cyclic loading phase.Meanwhile,fracture evolution of typical load drop points was also characterized by transverse strain fields(εxx),and observations showed that the damage extent of key pillar undergoing high-amplitude cyclic loads was more serious and violent,accompanied by the ejection of rock debris and loud noises.
基金financial support by the National Basic Research Program of China (Grant No. 2011CB013704)the major program of the National Natural Science Foundation of China (Grant No. 51490675)+1 种基金the Shandong Provincial Science & Technology Development Project (Grant No. 2013GHY11503)the Taishan Scholars Program of Shandong Province
文摘Assessing the fatigue life of mooring systems is important for deep water structures. In this paper, a comprehensive fatigue analysis is conducted on the mooring lines applied in a semi-submersible platform with special focus on the low frequency(LF) fatigue damage. Several influential factors, including water depth, wave spectral parameters, and riser system, are considered. Numerical simulation of a semi-submersible platform with the mooring/riser system is executed under different conditions, and the fatigue damage of mooring lines is assessed by using the time domain analysis method as a benchmark. The effects of these factors on the mooring line tension and the fatigue damage are investigated and discussed in detail. Research results indicate that the LF fatigue damage only accounts for a very small portion of the total damage, although the LF components dominate the global motion response and the mooring line tension of the semi-submersible platform. However, it is demonstrated that the LF fatigue damage is clearly affected by the influential factors. The increase in water depth and spectral peak periods, and the existence of risers can weaken the contribution of the LF components to the mooring line fatigue damage, while the fatigue damage due to the LF components increases with the increase of significant wave height.
基金support from National Natural Science Foundation of China (No. 11772027)National Key Research and Development Program of China (No. 2017YFB1104003)Aeronautical Science Foundation of China (No. 28163701002)
文摘Individual aircraft life monitoring is required to ensure safety and economy of aircraft structure, and fatigue damage evaluation based on collected operational data of aircraft is an integral part of it. To improve the accuracy and facilitate the application, this paper proposes an engineering approach to evaluate fatigue damage and predict fatigue life for critical structures in fatigue monitoring. In this approach, traditional nominal stress method is applied to back calculate the S-N curve parameters of the realistic structure details based on full-scale fatigue test data. Then the S-N curve and Miner＇s rule are adopted in damage estimation and fatigue life analysis for critical locations under individual load spectra. The relationship between relative small crack length and fatigue life can also be predicted with this approach. Specimens of 7 B04-T74 aluminum alloy and TA15 M titanium alloy are fatigue tested under two types of load spectra, and there is a good agreement between the experimental results and analysis results. Furthermore, the issue concerning scatter factor in individual aircraft damage estimation is also discussed.
文摘Rotary bending fatigue tests were carried out for smooth specimens of a mediumcarbon steel with two different grain sizes near the fatigue limit. The process of fatigue damagewas observed by replication method, and the effects of grain size,stress level and microstructure on surface damage were studied. The effect of following cycle stress level on the coaxing effects was also discussed. The fatigue limit is the maximum stress at which the short fatigue crack initiates and becomes a non-propagating crack.. The length of non-propagating crack is related to grain sizes and stress level. The coaxing effects disappear when the following stress level is greater than the critical value.
基金supported by the National Natural Science Foundation of China(No.10377007)
文摘Fatigue damage increases with the applied loading cycles in a cumulative manner and the material deteriorates with the corrosion time. A cumulative fatigue damage rule under the alternative of corrosion or cyclic loading was proposed. The specimens of aluminum alloy LY12-CZ soaked in corrosive liquid for different times were tested under the constant amplitude cyclic loading to obtain S-N curves. The test was carried out to verify the proposed cumulative fatigue damage rule under the different combinations among corrosion time, loading level, and the cycle numbers. It was shown that the predicted residual fatigue lives showed a good agreement with the experimental results and the proposed rule was simple and can be easily adopted.
基金National Natural Science Foundation of China(No.11272082)Fundamental Research Funds for the Central Universities(No.E022050205)the Open Research Fund of Key Laboratory of Fluid and Power Machinery of Xi Hua University,China(No.szjj2013-03)
文摘A modified nonlinear fatigue damage accumulation model based on the Manson-Halford theory was presented,and the new model was developed for fatigue life prediction under constant and variable amplitude loading, which took the effects of the load interactions and the phenomenon of material's strength degradation into account. The experimental data of the 30 Cr Mn Si A and the LY-12 cz from literature were used to verify the proposed model. And from the good agreement between the experimental data and predicted results,we can see it clear that the proposed method can be applied to predicting fatigue life under different loadings.
基金supported by the National Natural Science Foundation of China(Grant No.51009089)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20100073120017)
文摘A prediction model of the deepwater steel catenary riser VIV is proposed based on the forced oscillation test data, taking into account the riser-seafloor interaction for the cross-flow VIV-induced fatigue damage at touch-down point （TDP）. The model will give more reasonable simulation of SCR response near TDP than the previous pinned truncation model. In the present model, the hysteretic riser-soil interaction model is simplified as the linear spring and damper to simulate the seafloor, and the damping is obtained according to the dissipative power during one periodic riser-soil interaction. In order to validate the model, the comparison with the field measurement and the results predicted by Shear 7 program of a full-scale steel catenary riser is carried out. The main induced modes, mode frequencies and response amplitude are in a good agreement. Furthermore, the parametric studies are carried out to broaden the understanding of the fatigue damage sensitivity to the upper end in-plane offset and seabed characteristics. In addition, the fatigue stress comparison at TDP between the truncation riser model and the present full riser model shows that the existence of touch-down zones is very important for the fatigue damage assessment of steel catenary riser at TDP.
基金financially supported by the National Natural Science Foundation of China(Nos.51771207 and 52171128)the Fundamental Research Project of Shenyang National Laboratory for Materials Science(No.L2019R18)。
文摘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 primaryα(α_(p))phase were examined comparatively.The results showed that both pure fatigue and dwell fatigue life decreased with increasing the volume fraction of theα_(p)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 theα_(p)-secondaryα(α_(s))combination reveal that theα_(s)phase close to theα_(p)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 theα_(s)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 theα_(s)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.
基金the financial support of the Major Program of the National Natural Science Foundation of China(No.51490675)the National Science Fund for Distinguished Young Scholars(No.51625902)+1 种基金the Taishan Scholars Program of Shandong Provincethe Fundamental Research Funds for the Central Universities(No.841713035)
文摘Both wave-frequency(WF) and low-frequency(LF) components of mooring tension are in principle non-Gaussian due to nonlinearities in the dynamic system.This paper conducts a comprehensive investigation of applicable probability density functions(PDFs) of mooring tension amplitudes used to assess mooring-line fatigue damage via the spectral method.Short-term statistical characteristics of mooring-line tension responses are firstly investigated,in which the discrepancy arising from Gaussian approximation is revealed by comparing kurtosis and skewness coefficients.Several distribution functions based on present analytical spectral methods are selected to express the statistical distribution of the mooring-line tension amplitudes.Results indicate that the Gamma-type distribution and a linear combination of Dirlik and Tovo-Benasciutti formulas are suitable for separate WF and LF mooring tension components.A novel parametric method based on nonlinear transformations and stochastic optimization is then proposed to increase the effectiveness of mooring-line fatigue assessment due to non-Gaussian bimodal tension responses.Using time domain simulation as a benchmark,its accuracy is further validated using a numerical case study of a moored semi-submersible platform.
文摘A general method of probabilistic fatigue damage prognostics using limited and partial information is developed.Limited and partial information refers to measurable data that are not enough or cannot directly be used to statistically identify model parameter using traditional regression analysis.In the proposed method, the prior probability distribution of model parameters is derived based on the principle of maximum entropy（Max Ent） using the limited and partial information as constraints.The posterior distribution is formulated using the principle of maximum relative entropy（MRE） to perform probability updating when new information is available and reduces uncertainty in prognosis results.It is shown that the posterior distribution is equivalent to a Bayesian posterior when the new information used for updating is point measurements.A numerical quadrature interpolating method is used to calculate the asymptotic approximation for the prior distribution.Once the prior is obtained, subsequent measurement data are used to perform updating using Markov chain Monte Carlo（MCMC） simulations.Fatigue crack prognosis problems with experimental data are presented for demonstration and validation.
