Cumulative Damage Theory Research Articles

Fretting fatigue experiment and simulation of WC-12Co coating taking into account the wear effects

WC-12Co coating can be used to improve the wear resistance of mechanical connectors, but due to the fretting behavior between the contact interfaces during service, the problem of fretting fatigue cannot be ignored. Through the fretting fatigue experiment and simulation study of the WC-12Co coating, the fretting fatigue mechanism of the coating was investigated under the premise of considering the competitive or coupling relationship between fretting wear and fretting fatigue. Based on Smith-Watson-Topper (SWT) fatigue damage parameter and Miner-Palmgren (M-P) linear cumulative fatigue damage theory, a prediction model for fretting fatigue crack initiation life of WC-12Co coating was established, and the stress redistribution caused by fretting wear was analyzed by Archard wear theory. The analysis results show that the fretting fatigue cracks of the WC-12Co coating mainly initiate at the edge of the wear pits and gradually extend to the substrate; the increase of external load and friction coefficient will accelerate the fretting fatigue process of WC-12Co coating and reduce its fretting fatigue crack initiation life; the change of fretting fatigue crack initiation life and position of WC-12Co coatings caused by fretting wear depends on the change of contact state between contact interfaces.

Research on the Residual Bearing Capacity of a Rib Beam Bridge Carriageway Slab Based on Fatigue Cumulative Damage

In order to study the residual bearing capacity of the carriageway slab of a reinforced concrete rib beam bridge after fatigue damage, a double T-beam carriageway slab model with a high degree of symmetry was designed and fatigue tests were carried out. Based on the fatigue cumulative damage theory, the fatigue residual strength equation of concrete was improved and a constitutive fatigue model of a steel bar and concrete with arbitrary loading times was established. Because the carriageway slabs are highly symmetrical, we used a ratio of length to width and a ratio of width to height to express the dimensional changes in the carriageway slabs. Abaqus general analysis program was used to create a symmetrical T-beams model and analyze the influence of the fatigue load level, the ratio of width to height of the roadway slab, and the ratio of length to width on the remaining bearing capacity of the roadway slab. Finally, the 1stOpt fitting software was employed to fit the roadway slab’s residual bearing capacity evaluation model. The fatigue test results show that the fatigue failure form of the roadway slab is punching failure, and the development law of fatigue damage can be divided into three stages, accounting for 6.25%, 56.25%, and 37.5% of the total fatigue life. The finite element analysis results showed that the length–width ratio of the roadway slab is positively correlated with its relative residual bearing capacity, and the residual bearing capacity of the two-way slab is higher than that of the one-way slab. The fatigue load level and the aspect ratio of width to height are negatively correlated with their relative residual bearing capacity.

Experimental study on the bearing capacity and fatigue life of lightning rod structure joints in high-voltage substation structures

With a 500 kV high-voltage substation structure with lightning rods taken as an engineering example, the mechanical behaviors of lightning rod joints are analyzed based on bearing capacity tests of a typical lightning rod structure and reinforced lightning rod structure. In addition, finite element models are built with ANSYS software and verified by experimental results to design an aeroelastic model based on wind tunnel tests and to calculate hot-spot stresses in the subsequent fatigue life analysis. On this basis, according to the aeroelastic model wind tunnel testing results, the fatigue lifetimes of the lightning rod structures are analyzed according to the rain-flow counting method, hot-spot stress range S-N curve and linear fatigue cumulative damage theory. The results show that the bearing capacity and fatigue properties of typical lightning rod joints cannot meet the design requirements, while reinforced lightning rod joints have a better bearing capacity and longer fatigue life because the stress concentration in the joints is significantly relieved. With the distribution of the wind speed and direction at the engineering example site, the wind-induced vibration fatigue life of the typical lightning rod structure is 11.68 years, which is far less than the mandated 50-year design period. In contrast, the fatigue life of the corresponding reinforced lightning rod structure is greatly improved and reaches 326.4 years, which indicates that the reinforcement method is efficient. Overall, the proposed fatigue life estimation method for lightning rod structure joints is feasible and workable.

Fatigue life prediction of brake discs for high-speed trains via thermal stress.

As one of the essential components of the braking system, the high-speed train brake disc is an integral part of ensuring the safety of the train. The main objective of this study is to conduct thermal analysis and reliable life prediction on brake discs. The research was conducted by developing a programmer spectrum of brake discs with high-speed train brake discs. According to the results of numerical analysis and the S-N curve of the material, the temperature distribution on the surface of the brake disc is determined, and the fatigue life of the brake disc is predicted. The comparison with the service life of the brake disc verifies the rationality of the calculation results. In addition, a fatigue damage probability model of brake discs is established based on the theory of fatigue cumulative damage. Through the relationship between the reliability of mechanical parts and the number of load cycles, the reliable life of the brake disc under different working conditions is predicted. This work establishes a method of reliable life analysis for brake discs of high-speed trains based on the load spectrum, which could analyze the life and reliability of brake discs more systematically.

Three-dimensional nonlinear vibration model and fatigue failure mechanism of deepwater test pipe

In deepwater test condition, the riser–test pipe (tubing string) system (RTS) is subject to the vortex-induced effect on riser, flow-induced effect on test pipe and longitudinal/transverse coupling effect, which is prone to buckling deformation, fatigue fracture and friction perforation. To resolve this, the three-dimensional (3D) nonlinear vibration model of deepwater RTS is established using the micro-finite method, energy method and Hamilton variational principle. Based on the elastic–plastic contact collision theory, the nonlinear contact load calculation method between riser and test pipe is proposed. Compared with experimental measurement results, calculation results using the proposed vibration model in this study and the single tubing vibration model in our recent work, the correctness and effectiveness of the proposed vibration model of the deepwater RTS are verified. Meanwhile, the cumulative damage theory is used to establish the fatigue life prediction method of test pipe. Based on that, the influences of outflow velocity, internal flow velocity, significant wave height, as well as top tension coefficient on the fatigue life of test pipe are systematically analyzed. The results demonstrate that, first, with the increase in outflow velocity, the maximum alternating stress and the annual fatigue damage rate increased. The location where fatigue failure of the test pipe is easy to occur at the upper “one third” and the bottom of test pipe are easy to occur fatigue failure. Second, with the increase in internal flow velocity, the “one third damage effect” of the test pipe will decrease, and the “bottom damage effect” of the test pipe increased that needs the attention of field operators. Third, during field operation, it is necessary to properly configure the top tension coefficient so that there can be a certain relaxation between the riser and the test pipe, so as to cause transverse vibration and consume some axial energy and load. The study led to a theoretical method for safety evaluation and a practical approach for effectively improving the fatigue life of deepwater test pipe.

Research on Fatigue Performance of the Rib Beam Bridge Carriageway Slab Based on Cumulative Damage Theory

The purpose of this paper is to study the development law of fatigue damage of the carriageway slab of reinforced concrete ribbed girder bridge and to provide theoretical support for carriageway slab design. The fatigue test of reinforced concrete rib beam bridge carriageway slabs was conducted. Based on the material fatigue damage theory, the fatigue damage model was established by ABAQUS software. The fatigue performance, failure mechanism, and the effect of fatigue level on the fatigue performance of the carriageway slab were studied. The experimental research results show that when the slab of the rib beam bridge was fatigued, and the radial crack appeared at the bottom of the slab, which belonged to punching shear failure. The fatigue failure process was divided into three stages as follows: in the initial stage of fatigue, the deflection and reinforcement strain increased linearly with fatigue times, and in the stable development stage, the bottom deflection and reinforcement strain increased steady progression. With the increase in fatigue cycles, the fatigue accumulation damage was gradually accumulated, and the stiffness of the carriageway slab gradually decreases. In the rapid development stage, the deflection, reinforcement strain, and crack growth speed were significantly increased. According to the fatigue damage model, the simulation analysis results show that the accumulated damage to the bridge carriageway was more serious with the increase in fatigue load level. The fatigue damage degree was lower when the design fatigue load level is not greater than 0.55.

On the defect tolerance by fatigue spectral methods based on full-field dynamic testing

In real life production of dynamically loaded components, we might accept the risk of defects only if we can assess their position by NDT techniques, their effect by proper cumulative damage theory, the dynamic signature of the excitation and the structural dynamics of our structures in service. This work addresses the latter topic by means of experimental full-field optical techniques, which can provide accurate surface displacement distribution in a broad frequency band directly from real components, while recording the excitation, thus, with advanced numerical derivations, coming to an experiment-based full-field strain FRF characterisation, here applied on an aluminium plate. The knowledge of the material constitutive parameters is used to obtain the Von Mises equivalent stress FRFs. The signature of the excitation permits the evaluation of the Von Mises stress PSDs, which can be used in a spectral fatigue method (here the one from Dirlik), coming to a frequency-to-failure distribution. The same distribution can be scaled to a risk index and compared to the defect locations from NDT, in order to build a defect tolerance map and discriminate the product acceptance for dynamically loaded components. The smart exploitation of full-field optical techniques play a relevant role in measuring, with high spatial resolution, the manufactured components in their effective broad structural dynamics and give defect tolerance experiment-based maps, without the need of a highly tuned FE model.

Topology Optimization with Aperiodic Load Fatigue Constraints Based on Bidirectional Evolutionary Structural Optimization

Because of descriptive nonlinearity and computational inefficiency, topology optimization with fatigue life under aperiodic loads has developed slowly. A fatigue constraint topology optimization method based on bidirectional evolutionary structural optimization (BESO) under an aperiodic load is proposed in this paper. In view of the severe nonlinearity of fatigue damage with respect to design variables, effective stress cycles are extracted through transient dynamic analysis. Based on the Miner cumulative damage theory and life requirements, a fatigue constraint is first quantified and then transformed into a stress problem. Then, a normalized termination criterion is proposed by approximate maximum stress measured by global stress using a P-norm aggregation function. Finally, optimization examples show that the proposed algorithm can not only meet the requirements of fatigue life but also obtain a reasonable configuration.

Failure analysis of fatigue damage for fastening clips in the ballastless track of high-speed railway considering random track irregularities

In order to study the influence of wheel-rail random dynamic interaction on the fatigue damage for fastening clips, a three-dimensional (3-D) high-speed railway vehicle-track coupling random dynamics model is established based on the random theory of the probability density evolution method (PDEM). The number theoretic method (NTM) and stochastic harmonic functions (SHF) are employed to generate the representative random track irregularities. Furthermore, a refined finite element model of WJ-8 fastening system is established, and the stress time history results of the clips are obtained based on the co-simulation analysis. Eventually, the rain-flow counting is introduced to study the influence of random track irregularities on fatigue damage of fastening clips combined with cumulative damage theory and the S-N curve of the clips. The results show that, the dynamic characteristics and stochastic probability evolution mechanism of the vehicle-track random system considering random track irregularities, as well as the evolution characteristics of the fatigue failure probability of clips with service time are accurately reproduced based on PDEM. Significantly, the fatigue damage of fastening clips caused by one vehicle passing by follows the lognormal distribution with a mathematical expectation of 2.35 × 10-8 and a variance of 1.48 × 10-12. The 95% confidence interval of mathematical expectation is [7.05 × 10-9, 5.89 × 10-7] and the 95% confidence interval of variance is [1.37 × 10-13, 1.59 × 10-11]. Additionally, the longer the service time of the fastening system, the more serious the fatigue damage of the clips and the greater the fatigue failure probability.

Pre-Calculation of Wind Turbine Blade Fatigue Damage by Machine Learning

Blade fatigue failure poses a great threat to the safe and stable operation of wind turbines. To solve the problem that the existing fatigue damage calculation methods are difficult to balance the calculation accuracy and calculation speed, a LightGBM machine learning fatigue damage calculation method is proposed. The method mainly analyses the blade 3D model by finite element software to determine the blade fatigue dangerous nodes and the stress magnitude corresponding to the unit load at the nodes, then uses Von Mises yield criterion to convert the load time series data into equivalent force time series data, and applies the rain-flow counting method and linear fatigue cumulative damage theory to calculate the blade fatigue damage amount. Finally, on the basis of the obtained minute-level blade fatigue damage amount, LightGBM machine learning algorithm is applied to train the fatigue damage calculation model, inputting wind speed, air density, turbulence intensity, wind shear and other wind parameters as well as the inflow angle and other wind turbine operation conditions, which can output the blade fatigue damage amount correspondingly. The proposed fatigue damage calculation method is evaluated to be highly accurate and feasible.

Thermal fatigue life predication of thermal barrier coatings by 3D hill-like model and GA

In previous studies, the coating interface was simplified to a 2D axisymmetric model in order to solve the thermal stress of thermal barrier coatings (TBCs). But the 2D TBCs model ignored the circumferential roughness, which influenced the accuracy of thermal fatigue life predication. To solve the problem, a 3D hill-like TBCs model is established by cylindrical coordinate equation, and solved by finite element method (FEM). A life prediction method of the 3D TBCs is proposed by combining Manson-Coffin equation, linear cumulative damage theory and Genetic Algorithm (GA). The life prediction results of 3D hill-like TBCs model are compared with the 2D TBCs model. The result shows that the thermal stress distribution of the 3D hill-like TBCs model is similar to that of the 2D TBCs model. However, the circumferential positive stress is greater than the axial positive stress, which is hardly obtained by classical 2D TBCs model. The analysis of thermal stress in TC layer with 4 μm TGO thickness at different time shows that the thermal stress reaches 255.8 MPa (maximum value) at 1050 °C (maximum temperature in one cycle). Moreover, the maximum value of thermal stress is located at circumferential direction near the peak of the 3D hill-like TBCs model, and this phenomenon indicates that the risk point will appear in this area. The maximum fatigue life prediction error of 3D hill-like TBCs model is reduced by 153% compared with the 2D TBCs model, and all predicted fatigue results are located in ±1.66 scattering zone. The efforts of this study provide a framework for the thermal fatigue life prediction of TBCs.

Effects of Wheel-Rail Impact on the Fatigue Performance of Fastening Clips in Rail Joint Area of High-Speed Railway

In order to study the effects of wheel-rail impacts on the fatigue damage of the fastening clips at the rail joints of a high-speed railway, field tests were carried out on the wheel-rail impacts at the rail joints of a high-speed railway in China. On the basis of the track irregularities at the rail joints obtained from field measurements, a nonlinear vehicle-track coupling dynamics three-dimensional (3D) model with consideration of Timoshenko beam elements and a refined finite element model of WJ-8 fastening system were constructed. And combined with the theory of cumulative damage and the method of fatigue analysis, the effects of wheel-rail impact at the rail joints on the fatigue life of fastening clips were analyzed. The results showed that the impacts of the wheel-rail in the joint area caused high-frequency fluctuations in the stress-time curves of the clips, which significantly increased the amplitude of stress cycle and increased a lot of stress cycles, of which the amplitudes were reached at a large level; the clips in the area where a rail joint was located suffered the most serious fatigue damage and had the shortest fatigue life; in the actual operation line, besides the clips in the rail joint area, it is also necessary to be concerned about the fatigue performance of fastening clips near the rail joint area.

Towards the Functional Ageing of Electrically Conductive and Sensing Textiles: A Review.

Electronic textiles (e-textiles) have become more and more important in daily life and attracted increased attention of the scientific community over the last decade. This interdisciplinary field of interest ranges from material science, over chemistry, physics, electrical engineering, information technology to textile design. Numerous applications can already be found in sports, safety, healthcare, etc. Throughout the life of service, e-textiles undergo several exposures, e.g., mechanical stress, chemical corrosion, etc., that cause aging and functional losses in the materials. The review provides a broad and critical overview on the functional ageing of electronic textiles on different levels from fibres to fabrics. The main objective is to review possible aging mechanisms and elaborate the effect of aging on (electrical) performances of e-textiles. The review also provides an overview on different laboratory methods for the investigation on accelerated functional ageing. Finally, we try to build a model of cumulative fatigue damage theory for modelling the change of e-textile properties in their lifetime.

Fatigue analysis of all-electric shale gas fracturing truck frame

Fracturing truck is the core equipment in shale oil and gas exploitation. The operation environment is harsh. As the main bearing structure of the fracturing truck, the frame should have high efficiency and reliability to ensure the stable operation of the fracturing truck. Therefore, a frame model of the all-electric fracturing vehicle was established in this paper, and the load spectrum of the frame was simulated with white noise load when the fracturing vehicle was running on uneven road surface, and the finite element transient analysis of the frame was carried out. Then, a five-block diagram of fatigue analysis was established by using ncode Design-Life software, and the fatigue analysis results of the fracking truck frame were calculated according to the linear cumulative damage theory and S-N material characteristic curve. The research provides an effective reference for the detection of the fracking truck frame, so as to ensure the running stability of the fracturing truck.

Evaluation of the collapse mode of isolated structures subjected to multi-directional dynamic coupling excitation based on reliability theory

The identification of the structural collapse mode is an important foundation of structural anti-collapse design and safety evaluation. The collapse mode evaluation method based on probability reliability is widely used in theoretical research and engineering applications. However, studies on the collapse mode of isolated structures have rarely been reported. For the initial damage, the main control excitation and the remaining system constraints of isolated structures all being different from that of traditional fixed-base structures, the collapse mode and the collapse mechanical behaviors of the isolated structure are disparate from the traditional fixed-base structures. The most likely collapse mode of isolated structures subjected to multi-directional dynamic coupling excitation is evaluated based on reliability theory in the presented research work. First, multi-directional dynamic coupling analysis on the isolated structure is performed. Then, a reliability analysis method suitable for isolated structures is proposed, which takes the damage index as the state parameter, and calculates the failure probability based on the quadratic fourth-order moment theory method. The structural collapse probabilities under different collapse modes are calculated, in order to evaluate the most likely collapse mode of the isolated structure. Finally, the identification method is applied to one prototype isolated structure designed in accordance with the Chinese design code. The results indicate that the identification method based on cumulative damage and reliability theory could effectively be used for evaluation of the most likely collapse mode of the isolated structure.

Fatigue Design of Steel Bridge Deck Asphalt Pavement Based on Nonlinear Damage Accumulation Theory

Based on the nonlinear damage theory, this paper aims to explore the fatigue performance of steel bridge deck asphalt pavement under multistage fatigue load. Manson–Halford cumulative damage model and the modified model were introduced to describe loading sequence effects, and interactions between multiple loads were represented in stress ratio. The fatigue life prediction method of steel bridge deck asphalt pavement was put forward, considering loading sequence effects and load interactions. The fatigue design of steel bridge deck asphalt pavement was investigated with the fatigue life prediction model. The effects of different load levels and loading sequence on the fatigue design parameters stress ratio of steel bridge deck asphalt pavement were studied. The design results were compared with experimental results, and the prediction results were based on traditional Miner’s theory. The analysis results showed that the fatigue life prediction method based on the nonlinear cumulative damage theory can effectively design and analyze the fatigue characteristics of asphalt pavement of steel bridge deck with high accuracy and reliability. The fatigue life prediction model of steel bridge deck asphalt pavement can well reflect loading sequence effects and load interactions. In addition, the design model has relatively few parameters; therefore, it can be applied to practical engineering design.

Fatigue failure mechanism of 3D tubing strings used in high-pressure, high-temperature and high-yield curved gas wells

In view of the fatigue failure of tubing strings by flow-induced nonlinear vibration (FINV) in high-temperature, high-pressure and high-yield (3H) curved gas wells, a three-dimensional (3D) FINV model of the tubing string is established using the micro-finite method, energy method and Hamilton variational principle, and verified by a similar experiment of tubing vibration. Meanwhile, the cumulative damage theory is used to establish the fatigue life prediction method of tubing string combined with the stress response which was determined by the proposed FINV model and the S-N curve of the tubing material (13Cr-L80) which was measured by fatigue test. Thus, the influences of production rate, well trajectory parameters (inclination angle and well section length), as well as the installation position of downhole tools (packer and centralizer) on the fatigue life of the tubing string are systematically analyzed. The results obtained demonstrate that, first, with the increase of production rate, the fatigue life of the tubing string decreases, and the field production allocation should be far away from the sudden production rate which can be determined using the proposed analysis method. Second, in the well trajectory design, the vertical section length should be reduced, while that of build-up section and the angle of stable inclined section should be increased. Third, the packer and centralizer should be placed in the optimal position, which depends on the well structure, downhole tool size, etc. and can be determined using the proposed analysis method. The research results provide a theoretically sound guidance for designing and practically sound approach for effectively improving the fatigue life of tubing string in 3H curved gas wells.

Vibrational fatigue failure prediction of a brake caliper used for railway vehicles based on frequency domain method

A brake caliper used for railway vehicles was introduced in this paper. In order to predict the fatigue failure under random vibration condition, firstly a dynamic model was established and proved by comparing the results of modal simulation and modal test. The weak points of the structure were identified by taking random response analysis, and the corresponding PSD (power spectral density) spectrums of stress were obtained. Furthermore three different PDF (probability density function) models of stress amplitude distribution were employed to describe the distributions of stress at weak points, then the fatigue damages were calculated based on Miner’s linear cumulative damage theory and the fatigue failures were predicted. Finally, an accelerated failure test was designed and carried out to verify the validity of the predictions proposed by three models. The result shows that, the Dirlik’s model and Steinberg’s model can provide more exact results and be suitable for vibration fatigue failure prediction of brake caliper.

Fatigue strength analysis of desilting platform structure

In order to ensure the fatigue reliability of the dredging platform and key equipment structure, the fatigue of the platform is analyzed by using the analysis method based on S-N curve and fatigue cumulative damage criterion. Firstly, according to the wave characteristics of the Pearl River Basin, the periodic load of the dredger is calculated by using hydrodynamic analysis tools. Then, the fatigue life of dangerous parts is analyzed by using cumulative damage theory and S-N characteristic curve. The results show that the joint of desilting equipment and conveying device is easy to suffer fatigue damage, and the fatigue life limit is 2328h, and the other equipment and structure meet the fatigue requirements.

Fatigue Life Analysis of Bus Body based on User Target Load Spectrum‎

In this article, fatigue life of a bus body is analyzed based on the user target load spectrum. A finite element model of the bus body is built with characteristics. The static analysis result is obtained by using the inertia release method and a multi-body dynamic model is established by using the rigid flexible coupling method. According to user investigation, the user load spectrum is obtained through dynamic simulation. The average value and amplitude of each level of stress are extracted from the load spectrum information. With the fatigue properties of the material, the damage value of the bus body is determined by using the S-N curve method and Miner linear cumulative damage theory. The simulation gives the fatigue life and damage values of the most dangerous position of the body structure. Calculation shows that the fatigue life of the bus body meets durability requirements.