Fatigue Damage Evolution Process Research Articles

Full-scale resonant bending fatigue testing of casing joints under bending moment load

The quality and reliability of oil casings play a pivotal role in the safety and efficiency of offshore oil and gas exploration. This study conducted research on resonant bending fatigue of 9-5/8-inch casing joints and established a systematic theoretical model for resonant bending fatigue based on the Euler–Bernoulli beam equation. The relationships between parameters affected by frequency and mode shape functions were deduced and solved to analyze the influence of wall thicknesses, length and weights at both ends of the specimen on the natural frequency of the resonant bending fatigue system. A full-scale fatigue test was then designed and conducted to investigate the circumferential stress distribution, reveal the stress amplitude–frequency response characteristics of the specimen, and explore resonance response behaviors under different excitation forces. This was done to establish a method for evaluating the oil casing life and obtain fatigue life characteristic curves of the specimen. A finite element model was employed to analyze the internal stress distribution of the coupling under bending moment load, considering the influence of material properties, thread lead angle and non-linear contact on casing joints. Finally, the fatigue life algorithm was summarized and compared by integrating the stress simulation results with the material properties of the specimen, elucidating the fatigue damage evolution process of casing joints. This research provides a significant engineering reference value for structural design optimization, fatigue testing and life analysis of oil casing threaded joints.

Fatigue damage evaluation of welded joints in steel bridge based on meso-damage mechanics

Welding is a rapid and flexible connection that facilitates the use of a broad range of steel bridge. However, fatigue cracks initiating from various welded connection details are common problems in steel bridges. Therefore, it is vital to accurately evaluate the fatigue damage evolution and fatigue life of welded joints in steel bridge. In this study, a fatigue damage evolution model based on the meso-damage mechanics was proposed to evaluate the fatigue damage of welded joints in steel bridge. The number density of micro-cracks was adopted as the damage variable in the fatigue evolution model. Finite element modelling and user material subroutine (UMAT) in ABAQUS were combined to simulate fatigue damage evolution of welded joints in steel bridge. The fatigue damage evolution model was embedded in UMAT while the UMAT was coupled with the finite element model of the welded joints under cyclic loading. Then, the proposed model was validated by fatigue tests. The fatigue damage evolution model was also used to investigate the fatigue damage evolution process, and fatigue life prediction of the typical welded joints specimens in orthotropic steel decks (OSDs) of steel bridge. The results indicate that the fatigue strengths of nominal stress method were estimated to be 65.7 MPa for typical welded joints. The fatigue cracks mainly initiating at the weld toe and propagating along the weld toe line. The simulation results indicate that the fatigue damage evolution model provides superior ability in evaluating fatigue damage process and fatigue life of welded joints in steel bridge.

Analysis on damage evolution and corrosion fatigue performance of high-strength steel wire for bridge cable: Experiments and numerical simulation

Corrosion fatigue (CF) failure is one of the typical failure modes of high-strength steel wires for bridge cables because the cables are subjected to the long-term cyclic loads and exposed to the heavy polluted environment at the same time. In this paper, the damage evolution process and CF performance were investigated, and the service life was predicted for steel wire with machine-cut notch via experiments and numerical simulation. Firstly, a novel experimental device was constructed to apply fatigue load and corrosive medium on multiple specimens simultaneously. With the constructed device, two groups of experiments were conducted to analysis the fatigue performance and CF performance of surface notched wire specimens, and the fatigue life and CF life of steel wire were obtained under fatigue load and the coupling effect of corrosive medium and fatigue load (CCF) respectively. Additionally, in order to study the fatigue damage evolution process and CF damage evolution process of surface notched steel wire under fatigue load and CCF respectively, a fatigue damage constitutive equation and a CF damage constitutive equation were proposed respectively according to continuum damage mechanics, and experimental data were used to determine the value of each parameter in these two equations. With the proposed model, damage evolution process in steel wire was simulated under fatigue loads and CCF respectively. The effect of corrosive medium on wire life was discussed. The results show that the fatigue life and CF life of surface notched wire obtained from simulation are consistent well with the experimental results, which shows that the simulation method can achieve the expected goal, and has high reliability in predicting the fatigue life and CF life, and simulating the fatigue damage evolution and CF damage evolution of surface notched wire. For the fatigue damage evolution process and CF damage evolution process, damage evolves gradually, and the damage evolution rate gradually increases. There are more and more damage elements at the bottom of machine-cut notch, and some elements inside the steel wire are also damaged. Comparing the damage distribution of steel wire subjected to fatigue load only and CCF, it can be found that corrosive medium will cause the damaged elements to appear earlier. Under the same stress range, the fatigue life and CF life of steel wire with machine-cut notch are significantly different, but the fatigue damage evolution rate and CF damage evolution rate are similar. It can be concluded that the difference in service life is mainly due to the corrosive medium that causes the damaged elements near the surface notch appear earlier, especially under higher stress ranges.

A multi-scale corrosion fatigue damage model of high-strength bridge wires

Cables are the most sensitive components in cable-supported bridges, and the failure of cables is usually caused by the degradation of mechanical properties of internal wires. Based on Faraday's law and the rates of microcrack initiation and propagation, a multi-scale corrosion fatigue damage model was developed to describe the damage evolution in the stages of pit growth and microcrack propagation. The accuracy and effectiveness of this damage model were also verified through the experimental data of corrosive fatigue life of high-strength bridge wires. The result shows that this damage model can describe the multi-scale corrosion fatigue damage evolution process of high-strength bridge wires reasonably and effectively, which provides a new way to better understand the trans-scale damage evolution mechanism during the corrosion fatigue process of high-strength bridge wires.

Multiscale Damage Evolution Analysis of Aluminum Alloy Based on Defect Visualization

The evaluation of fatigue life through the mechanism of fatigue damage accumulation is still a challenging task in engineering structure failure analysis. A multiscale fatigue damage evolution model was proposed for describing both the mesoscopic voids propagation in the mesoscopic-scale and fatigue damage evolution process, reflecting the progressive degradation of metal components in the macro-scale. An effective method of defect classification was used to implement 3D reconstruction technology based on the MCT (micro-computed tomography) scanning damage data with ABAQUS subroutine. The effectiveness was validated through the comparison with the experimental data of fatigue damage accumulation. Our results indicated that the multiscale fatigue damage evolution model built a bridge between mesoscopic damage and macroscopic fracture, which not only used the damage variable in the macro-scale to characterize the mesoscopic damage evolution indirectly but also understood macroscopic material degradation behavior from mesoscale with sufficient precision. Furthermore, the multiscale fatigue damage evolution model could offer a new reasonable explanation of the effect of load sequence on fatigue life, and also could predict the fatigue life based on damage data by nondestructive testing techniques.

Research on the Damage Evolution Process of Steel Wire with Pre-Corroded Defects in Cable-Stayed Bridges

A numerical simulation method is presented in this paper to study the damage evolution and failure process of high-strength steel wires with pre-corrosion defects in cable-stayed bridges under fatigue loads. This method was based on the mechanism of crack nucleation accelerated by corrosion pits, in which cellular automata (CA) and finite element (FE) simulation methods were used. First, based on the continuum damage mechanics (CDM) theory, a fatigue damage model suitable for steel wire with pre-corroded defects was established to describe the evolution process of the microscopic damage of steel wires, and a user-defined material subroutine (UMAT) was written using formula translator (FORTRAN) language. Then, in MATLAB, the shape and position of random pitting defects on the steel wire surface were generated using 3D CA technology. Afterwards, a pitting defect model was successively inputted into AutoCAD, Rhino and ABAQUS software to obtain the FE model of steel wire with initial pitting defects or initial damage. Finally, the life-and-death element method and the UMAT program were used to simulate the fatigue damage evolution process of the steel wire with initial defects in ABAQUS software, and the fatigue life of the steel wire was obtained. The results show that the proposed strategy and algorithm can effectively describe the fatigue damage evolution process of the steel wire with initial pitting defects under the action of a fatigue load, and the simulated fatigue life is in good agreement with the experimental results. The obtained stress-life (S-N) curves of the steel wire with different corrosion degrees show that the influence of pit corrosion on fatigue life is much greater than that of the mass loss caused by corrosion. By comparing the irregular pit model with regular pit models, it can be found that the irregular shape angle is the main reason for the smaller fatigue life and the larger stress concentration in the irregular pit model than in the regular pit model.

Fatigue Analysis for Void Repair of Cement Concrete Pavement with Under Slab by Polymer Grouting

After the appearing of voids beneath cement concrete slabs, the pavement loses a continuous and uniform lower support structure, and the stress state of the road panel is extremely unfavorable. The polymer grouting repair is timesaving, efficient and pollution-free. In order to verify the performance improvement and fatigue damage evolution of cement concrete pavement before and after grouting repair, a material damage constitutive model was established. The UMAT subprogram was introduced into the finite element software ABAQUS to analyze the structure under the action of moving cyclic loading, stress response and fatigue damage evolution process before and after regional grouting repair. The results show that the Mises stress and vertical displacement of the grouting repairing slab are very close to the normal state, which indicates that the grouting repair has a prominent influence on the bottom void of the slab. With the rise of loading time, the fatigue damage of the pavement structure is increasing, but the trend is gradually reduced, and the number of load times and the degree of fatigue damage are nonlinear. From the long-term cyclic loading and comprehensive analysis of the construction period, the polymer grouting repair is better than cementitious grout.

Assessment of fatigue damage in asphalt mixture using an acoustic emission approach

Fatigue failure is the main damage forms of asphalt mixture. Acoustic emission (AE) is an effective technique for continuously monitoring the development of fatigue damage in asphalt mixture. Firstly, the AE characteristic and mechanical behaviour of asphalt mixture and their relationship were investigated by performing four-point bending fatigue test and AE test. Furthermore, the parameters of continuum damage mechanics model that describes the deterioration process of asphalt mixture were calibrated in according with the AE technique. Finally, simulation analysis on the four-point bending fatigue test of asphalt mixture is performed. The results indicated that the AE parameters could reflect the changes of mechanical characteristic. The variation of AE energy and dissipated energy had a similar tendency. There is a strong correlation between the result of continuum damage mechanics model and mechanical test. The numerical results show that the definition of damage variable based on AE energy is reliable and reasonable. This research would provide a new idea for the application of AE technique on diagnosing the fatigue damage evolution process of asphalt mixture.

Simulation of Damage Evolution and Study of Multi-Fatigue Source Fracture of Steel Wire in Bridge Cables Under the Action of Pre-Corrosion and Fatigue

A numerical simulation method for the damage evolution of high-strength steel wire in a bridge cable under the action of pre-corrosion and fatigue is presented in this paper. Based on pitting accelerated crack nucleation theory in combination with continuum mechanics, cellular automata technology (CA) and finite element (FE) analysis, the damage evolution process of steel wire under pre-corrosion and fatigue is simulated. This method automatically generates a high-strength steel wire model with initial random pitting defects, and on the basis of this model, the fatigue damage evolution process is simulated; thus, the fatigue life and fatigue performance of the corroded steel wire can be evaluated. A comparison of the numerical simulation results with the experimental results shows that this method has strong reliability and practicability in predicting the fatigue life of corroded steel wire and simulating the damage evolution process. Based on the method proposed in this paper, the fatigue life of steel wires with different degrees of corrosion under the action of different stress levels is predicted. The results show that as the degree of corrosion increases, the fatigue properties of steel wire gradually decrease, and the influence of existing pitting corrosion on fatigue life is far greater than that on mass loss.Stress concentration is the main cause of fatigue life of corroded steel wire in advance attenuation. In addition, the fracture process of steel wire with multi-fatigue sources and the effect of the number and distribution of pits on the fatigue life of steel wire are studied. The results show that, compared with a stepped pitting distribution, a planar pitting distribution has a greater impact on the damage evolution process. The fatigue life of steel wire is positively correlated with the number of pits and the angle and distance between pits.

Fatigue Characteristics of Limestone under Triaxial Compression with Cyclic Loading

This paper presents an experimental investigation of the fatigue properties of limestone subjected to triaxial compression with axial cyclic loading. Tests were conducted on intact limestone samples with a loading frequency of 0.5 Hz and a confining pressure of 10 MPa. The test results show the following five points. (1) Under triaxial conditions, the axial and circumferential deformations at the failure point induced by cyclic loading are slightly larger than the corresponding deformations at the peak stress achieved by conventional compression tests. (2) The first level cyclic loading process has a strong influence on rock deformation in the primary phase during subsequent level cyclic loading. A smaller difference in stress amplitude between the two loading stress levels leads to less deformation during the latter. (3) Circumferential and volumetric changes are more sensitive to fatigue failure in terms of deformation and strain rate than axial changes. (4) The three phases of dissipated energy evolution are consistent with a sample’s deformation such that the energy dissipation characteristics reflect the fatigue damage evolution process. (5) A new damage formula is proposed that can concisely describe a rock’s zero-cycle damage and damage evolution.

Fatigue life prediction of welded joints with artificial corrosion pits based on continuum damage mechanics

An approach based on continuum damage mechanics (CDM) is applied to predict the fatigue life of welded joints with artificial corrosion pits. Full penetration load-carrying fillet cruciform welded joints with a 45° inclined angle were constructed, and artificial corrosion tests and fatigue tests of the welded joints were carried out. A new damage variable based on the crack size was defined to assess the stiffness degradation. Material parameters in the damage evolution equations were obtained from the fatigue experimental data. The CDM model combined with numerical simulations was used to describe the fatigue damage evolution process. A comparison between the fatigue life predicted results and the test results was made. The results show that fatigue life decreases with the increase of pit depth, decreasing by approximately 50% from d = 0 mm to 2 mm at the same stress range. The fatigue damage curves can be divided into three stages: the crack initial growth stage (D < 0.3), the crack slow growth stage (0.3 ≤ D ≤ 0.8), and the crack rapid fracture stage (D > 0.8). The fatigue damage curves for different stress ranges are nearly the same under the same pit depth. In addition to the material and loading conditions, the corrosive environment also has an effect on the material parameters in the fatigue damage evolution process. The fatigue life predicted results agree well with the test results, and the maximum relative error is 10.6%. The crack size can be used to describe the fatigue damage evolution of welded joints with artificial corrosion pits.

Meso-scale progressive damage modeling and life prediction of 3D braided composites under fatigue tension loading

3D braided composites have broad potential applications in the high-tech industries because of their superior mechanical properties. Fatigue is an essential design factor for their use in those engineering applications. The fatigue damage accumulation during cyclic loading should be involved in the numerical models in order to predict the fatigue life accurately. In this paper, a unit-cell based finite element model in conjunction with continuum damage mechanics (CDM) is developed for simulating the fatigue damage evolution process and predicting the fatigue life of 3D braided composites under fatigue tension loading. This meso-scale fatigue modeling, including stress analysis, failure criteria and material property degradation scheme, is implemented via a user-material subroutine UMAT based on ABAQUS/Standard platform with FORTRAN code. The fatigue damage initiation and propagation processes of 3D braided composites with typical braiding angles on the unit-cell model as a function of number of cycles are presented in detail. The fatigue life of 3D braided composites is predicted from the computed S-N curve and the stiffness degradation process is also investigated. The obtained numerical results indicate that the present model can provide a suitable reference to the numerical study of the fatigue issues in other textile composites.

A continuum model for damage evolution simulation of the high strength bridge wires due to corrosion fatigue

Continuum damage model and simulation algorithm are developed to simulate the corrosion fatigue process of high strength bridge cable steel wires. The developed model can be used to predict the damage curves during the corrosion fatigue process based on the concept of continuum damage mechanics (CDM). The algorithm can be used to simulate the corrosion fatigue damage evolution process of bridge wires from local damage to failure. As case study, the developed model and algorithm have been applied to simulate corrosion fatigue damage evolution of bridge wires under cyclic tensile in 3.5 wt% NaCl solution at 6 Hz, and the numerical prediction results are compared with experimental results. It shows that the developed model and algorithm are reasonable and can be used to study and describe corrosion fatigue damage evolution of bridge wires.

Synergistic effects of temperature, oxidation, and stress level on fatigue hysteresis behavior of cross-ply ceramic-matrix composites at room and elevated temperatures under cyclic loading

In this paper, the synergistic effects of temperature, oxidation, and stress level on the fatigue hysteresis behavior of cross-ply SiC/CAS ceramic-matrix composites (CMCs) at room temperature and 700 and 850 °C in air atmosphere has been investigated. The relationships between the fatigue hysteresis loops, fatigue hysteresis-dissipated energy, fatigue hysteresis modulus, and the fiber/matrix interface shear stress have been established using the hysteresis loop models considering different matrix cracking modes. The fatigue damage evolution process of SiC/CAS composite under tension–tension fatigue loading has been analyzed using the hysteresis loops. By comparing the experimental fatigue hysteresis-dissipated energy with theoretical computational values, the interface shear stress of SiC/CAS composite were obtained for different cycle numbers and fatigue peak stress. It was found that at elevated temperature in air, the interface shear stress degradation rate is much more affected by the fatigue peak stress than that at room temperature due to interface oxidation. The comparisons of interface shear stress evolution between unidirectional SiC/MAS and SiC/CAS, 2D SiC/SiC, and cross-ply SiC/CAS composites have been analyzed.

Monitoring and Failure Analysis of Corroded Bridge Cables under Fatigue Loading Using Acoustic Emission Sensors

Cables play an important role in cable-stayed systems, but are vulnerable to corrosion and fatigue damage. There is a dearth of studies on the fatigue damage evolution of corroded cable. In the present study, the acoustic emission (AE) technology is adopted to monitor the fatigue damage evolution process. First, the relationship between stress and strain is determined through a tensile test for corroded and non-corroded steel wires. Results show that the mechanical performance of corroded cables is changed considerably. The AE characteristic parameters for fatigue damage are then established. AE energy cumulative parameters can accurately describe the fatigue damage evolution of corroded cables. The failure modes in each phase as well as the type of acoustic emission source are determined based on the results of scanning electron microscopy. The waveform characteristics, damage types, and frequency distribution of the corroded cable at different damage phases are collected. Finally, the number of broken wires and breakage time of the cables are determined according to the variation in the margin index.

Prediction of Fatigue Damage Development in Undirectional Long fibre Composites

Cyclic damage development in polymer matrix composites reinforced with long fibres may be modelled by a two stage process. The first stage involves transverse and shear cracking of the matrix which is particularly significant in cross-ply laminates. Its development may be described using a two-parameter Weibull model. The damage rate continuously decreases until saturation is reached. This stage also occurs in unidirectional glass’ polyester rods pultruded under industrial conditions. The second stage exhibits an increasing rate of damage development resulting from longitudinal splitting, delamination, fibre pull-out and fracture. This may be described by applying continuum damage mechanics. The summation of the two expressions results in a comprehensive description of the fatigue damage evolution process. Using this approach it is possible to predict complete damage accumulation in undirectional long fibre composites.

Prediction of Fatigue Damage Development in Undirectional Long fibre Composites

Cyclic damage development in polymer matrix composites reinforced with long fibres may be modelled by a two stage process. The first stage involves transverse and shear cracking of the matrix which is particularly significant in cross-ply laminates. Its development may be described using a two-parameter Weibull model. The damage rate continuously decreases until saturation is reached. This stage also occurs in unidirectional glass’ polyester rods pultruded under industrial conditions. The second stage exhibits an increasing rate of damage development resulting from longitudinal splitting, delamination, fibre pull-out and fracture. This may be described by applying continuum damage mechanics. The summation of the two expressions results in a comprehensive description of the fatigue damage evolution process. Using this approach it is possible to predict complete damage accumulation in undirectional long fibre composites.