Fatigue Life Prediction Method Research Articles

Fatigue life prediction method for central hole of needled ceramic matrix composite

Based on the consideration of matrix porosity and representative volume element of needled structure, the macroscopic elastic constants of needled C/SiC ceramic matrix composite and the stress concentration factor of the hole-edge were calculated by the finite element method first. Then, based on the fatigue test data of the smooth and central hole specimens, the fatigue notch factors corresponding to different stress levels were obtained. In view of the different characteristics of the fatigue notch factor obtained under different limit lives, the relationship between the fatigue notch and stress concentration factors was established, and the influence of nominal stress on the fatigue notch factor was also considered. Based on this, a fatigue life prediction method for central hole of needled C/SiC composite was proposed. The proposed method can predict the fatigue life of central hole by using the S–N curve of smooth specimen and the stress concentration factor of central hole specimen. The comparison between predicted and experimental lives showed that the proposed method can better predict the fatigue life of central hole specimen for needled C/SiC composite.

Multiaxial fatigue life prediction based on single defect for additively manufactured 316L

A multiaxial fatigue life prediction method based on single defect for 316L stainless steel processed by laser powder bed fusion is studied. Defects are detected in the crack initiation zone of more than 95% of the specimens. A method based on the small crack propagation theory is applied to predict fatigue life under uniaxial and pure torsional loading. The fatigue parameters obtained from the above method are substituted into the Modified Wöhler Curve Method to predict multiaxial fatigue life. The result shows that the predicted fatigue lives are in good agreement with the experimental results.

An Energy-Based Method for Lifetime Assessment on High-Strength-Steel Welded Joints under Different Pre-Strain Levels.

Pre-loading on engineering materials or structures may produce pre-strain, especially plastic strain, which would change the fatigue failure mechanism during their service time. In this paper, an energy-based method for fatigue life prediction on high-strength-steel welded joints under different pre-strain levels was presented. Tensile pre-strain at three pre-strain levels of 0.2%, 0.35% and 0.5% was performed on the specimens of the material Q345, and the cyclic stress and strain responses with pre-loading were compared with those without pre-loading at the same strain level. The experimental work showed that the plastic strain energy density of pre-strained welded joints was enlarged, while the elastic strain energy density of pre-strained welded joints was reduced. Then, based on the strain energy density method, a fatigue life estimation model of the high-strength-steel welded joints in consideration of pre-straining was proposed. The predicted results agreed well with the test data. Finally, the validity of the developed model was verified by the experimental data from TWIP steel Fe-18 Mn and complex-phase steel CP800.

Fatigue life prediction of gasoline storage tank considering varying current density and weld stress

In the field of corrosion fatigue crack research, how to couple corrosion and fatigue under various conditions is a problem worthy of discussion. According to the electrochemical corrosion principles and the superposition principles, studies have been made on the interaction between corrosion and fatigue, and the relationship model between the corrosion fatigue crack size and the corrosion fatigue remaining life in the Corrosion of Hydrogen evolution (COHE) fatigue long crack growth stage is established. The feasibility of the model is verified by using the experimental data. According to the specific structure of the dislocation butt weld of large storage tank, the stress at the crack is calculated. Based on the above model and the experimental data, the corrosion fatigue residual life of large storage tank is predicted. The feasibility of the model is verified, which provides a new method for corrosion fatigue life prediction of large storage tanks.

Design of a Practical Metal-Made Cold Isostatic Pressing (CIP) Chamber Using Finite Element Analysis

The fast development of deep-ocean engineering equipment requires more deep-ocean pressure chambers (DOPCs) with a large inner diameter and ultra-high-pressure (UHP). Using the pre-stressed wire-wound (PSWW) concept, cold isostatic pressing (CIP) chambers have become a new concept of DOPCs, which can provide 100% performance of materials in theory. This paper aims to provide a comprehensive design process for a practical metal-made CIP chamber. First, the generalized design equations are derived by considering the fact that the cylinder and wire have different Young’s moduli and Poisson’s ratios. Second, to verify the theory and the reliability of the CIP chamber, the authors proposed a series of FEA models based on ANSYS Mechanical, including a two-dimensional (2D) model with the thermal strain method (TSM) and a three-dimensional (3D) model with the direct method (DM). The relative errors of the pre-stress coefficient range from 0.17% to 5%. Finally, the crack growth path is predicted by using ANSYS’s Separating Morphing and Adaptive Remeshing Technology (SMART) algorithm, and the fatigue life is evaluated by using the unified fatigue life prediction (UFLP) method developed by the authors’ group. This paper provides a more valuable basis to the design of DOPCs as well as to the similar pressure vessels than the previous work.

A new cyclical generative adversarial network based data augmentation method for multiaxial fatigue life prediction

To meet the requirement of large experimental data for machine learning (ML) methods on multiaxial life prediction, a cyclical Generative Adversarial Network (named cGAN) integrating Fourier transformation and other semi-empirical equations, was proposed to augment data following physical knowledge. Two samples of each loading path can be augmented into hundreds of good quality samples. Consequently, the accuracy of ML methods for multiaxial fatigue life of 316L stainless steel can been improved by 35%-91%. The new method can definitely balance time cost of bigger sample size and prediction accuracy well.

Reliability Prediction Method for Low-Cycle Fatigue Life of Compressor Disks Based on the Fusion of Simulation and Zero-Failure Data

Targeting reliability assessment problems with a small sample size and large amount of zero-failure data which appear in the life assessment tests of aero-engine compressor disks, a reliability assessment method and simulation test method were developed by fusing numerical simulation and zero-failure data based on the life reliability assessment method for zero-failure data. The developed method was verified by numerical examples, and further applied in the reliability analysis of compressor disks by combining the test and simulation results. The results indicated that fusing the test data with the simulation data increased the amount of information, improved the life prediction accuracy, and increased the lower confidence limit of the reliable life by 6.02% compared with the case where the test data alone were used.

Fatigue Life Prediction of Structures With Interval Uncertainty

Abstract A new method for reliable fatigue life prediction in metal structural components is developed, which quantifies uncertainties using interval variables. Using this crack-initiation-based method, first, the uncertainties in laboratory test data for the fatigue failure of a structural detail are enumerated. This uncertainty quantification is performed through an interval-based enveloping procedure that relates the interval stress ranges to the number of cycles to failure. This will lead to the construction of an interval S–N relationship. Next, the uncertainties in field test data are enumerated in the extremum values of each stress range, as intervals, leading to the construction of interval stress ranges. For both the laboratory and field data uncertainty analyses, the mean stress effects are considered. Next, the interval damage accumulated over the duration of the field data is determined using the constructed interval S–N relationship and the obtained interval stress ranges. Then, the interval existing damage and interval remaining life are determined. Finally, as a conservative measure, the minimum remaining fatigue life is obtained in which all uncertainties are considered. A numerical example illustrating the developed method is presented, and the results are compared with results obtained by both Monte Carlo simulation and optimization. Using this method, for the numerical example considered, it is shown that the results for bounds on the existing damage and the remaining fatigue life are sharp. Moreover, due to its set-based approach, the method is significantly more computationally efficient when compared with iterative procedures.

Research on Fatigue Life Prediction Method of Key Component of Turning Mechanism Based on Improved TCD

The main objective of this paper is to accurately obtain fatigue life prediction for the key components of a turning mechanism using the improved theory of critical distances (TCD). The irregularly shaped rotating arm is the central stressed part of the turning mechanism, which contains notches. It has been found that TCD achieves good results in predicting the fatigue strength or fatigue life of notched components with regular shape but is less commonly used for notched components with irregular shape. Therefore, TCD was improved and applied broadly to predict the fatigue life of an irregularly shaped rotating arm. Firstly, the notch depth and structure net width parameters were introduced into the low-order and low-accuracy classical TCD function to obtain a novel stress function with high computational efficiency and high accuracy, whereas the stress concentration factor was introduced to modify the length of critical distance. Secondly, the improved TCD was used to predict the fatigue strength of notched components with regular shape, and its accuracy was demonstrated by a fatigue experiment. Finally, the improved TCD was applied to predict the fatigue life of an irregularly shaped rotating arm. The deviation between prediction results and experimental results is less than 18%. The results demonstrate that the improved TCD can be applied effectively and accurately to predict the fatigue life of key components of turning mechanisms.

Misalignment effect on the fatigue failure behavior of load-carrying cruciform welded joints

This paper presents an analytical model based on the Strain Energy Density (SED) method to predict the high cycle fatigue failure behavior of load-carrying cruciform welded joints (LCWJ) weakened by axial and angular misalignments. Compared with the Hot Spot Stress (HSS) and Effective Notch Stress (ENS) methods recommended in standard codes, the SED values at weld toe and weld root were carried out systematically considering the welded details and the types of misalignments. Moreover, the analytical model was applied to estimate the magnitudes of fatigue indicators and illustrated the effects of misalignment on the fatigue failure transition region in LCWJ. It is validated effectively as a supplementary analysis method for fatigue life prediction and fatigue design of welded joints compared with the experimental data and published reports.

Multiaxial fatigue life prediction method considering notch effect and non-proportional hardening

Engineering components with geometric discontinuous structures generally appear notch effect, which might eventually induce fatigue failure. In this study, a novel multiaxial fatigue prediction model is established for notched components by incorporating the notch effect and non-proportional hardening. Firstly, according to the notch effect, a computational procure of damage parameters is presented by combining the notion of stress intensity with finite element simulations based on the critical plane method. Secondly, considering the non-proportional hardening effect of path modes and material properties, a new modified non-proportional hardening factor is proposed. Particularly, the relationship between the relative stress gradient and the fatigue life is investigated under different stress concentration factors. Finally, with the help of the Manson-Coffin equation, a multiaxial fatigue life prediction model is developed subjected to multiaxial proportional/non-proportional loadings. Experimental data of medium steel En8 and GH4169 alloys are utilized to evaluate and validate the proposed model as well as four other classical models (FS model, MSWT model, Yu model and CXH model). The result indicates that the proposed model yields a higher accuracy on multiaxial fatigue life than other four models, and the majority of prediction results are within the ±2 life factor.

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.

Fatigue life prediction method for subsea wellhead welds based on the nonlinear fatigue accumulation model

In drilling and completion conditions, subsea wellheads are exposed to enormous alternating bending moment loads from the riser due to complex environmental conditions, causing fatigue damage. The joint weld between the high-pressure (HP) wellhead and the casing is especially vulnerable to fatigue, creating the risk of operational failure and accidents. Although fatigue analysis is vital, the traditional S–N curve method is often not accurate enough. This paper proposed an analytical technique to examine subsea wellhead fatigue by combining subsea wellhead fatigue decoupled analysis with a nonlinear fatigue accumulation theoretical model. This method was used to assess subsea wellhead weld fatigue in a gas field in China's Bohai Sea during drilling and completion. The bending moment load spectrum at the top of the HP wellhead was obtained via global dynamic analysis. The bending moment-stress and bending moment-strain response curves of the welds were extracted using local quasi-static analysis. Finally, the theoretical nonlinear fatigue accumulation model and traditional S–N curve method were used to evaluate subsea wellhead weld fatigue, respectively. The results indicated that the fatigue damage caused by drilling was more significant than completion, while the fatigue damage at the weld between the HP wellhead and the 16″ casing exceeded that of the weld between the low-pressure (LP) housing and the 30″ conductor. Furthermore, the technique proposed in this paper could be used to assess more extensive fatigue damage than when employing the S–N curve method, indicating that the results were more conservative and more suitable for practical engineering applications.

Fatigue life prediction for power supporting frame of electric-driven seismic vibrator under random load

Developing electric-driven seismic vibrator is a promising way to realize green exploration. To ensure the service life of the power supporting frame under long-term operation, a method of predicting fatigue life under random load is proposed. First, stress history of the maximum stress node is obtained through dynamic analysis. Second, based on the rainflow counting method, the stress history at the maximum stress node was statistically analyzed, the distribution of amplitude and the distribution of mean are studied, and the load spectrum is compiled. Third, considering structural parameters and the stress below the fatigue limit, the P-S-N curve of the power supporting frame is achieved through two-steps corrections, and combined with the Miner’s rule, the fatigue life of the power supporting frame is predicted. The results show that under the condition of the significance level of 0.05, the amplitude and the mean of the stress are independent of each other. The amplitude of stress obeys the Weibull distribution with a shape parameter of 1.0362 and a scale parameter of 10.5108, and the mean of stress obeys a normal distribution with a mean value of 40.253 and a standard deviation of 10.1803. Under 95% reliability, considering the structural parameters and the stress below the fatigue limit, a more accurate P-S-N curve of the power supporting frame is obtained, and then with Miner’s rule the fatigue life of the power supporting frame is predicted to be 8.5 years. Based on this study, the power supporting frame was successfully manufactured. This research also provides method and case reference for structural fatigue life prediction under random loads.

A Two-point Method for Multiaxial Fatigue Life Prediction

A Two-point Method for Multiaxial Fatigue Life Prediction

Gaussian process regression based remaining fatigue life prediction for metallic materials under two-step loading

Remaining fatigue life prediction is vital for engineering structures to ensure safety and reliability. It can be more challenging when the structures suffer variable amplitude loadings because of the complex, non-uniform of the fatigue damage accumulation and inherent noise, uncertainty in the data. To further tackle the problem, the Gaussian process regression (GPR) is introduced, which can simultaneously estimate the output value and quantify the associated uncertainty. Therefore, a GPR-based remaining fatigue life prediction method is proposed to predict the remaining fatigue life for metallic materials under two-step loading in this paper. The proposed method is comprehensively evaluated on the dataset containing 12 materials, 328 samples in total. The proposed method achieves the lowest mean square error (MSE), mean absolute percentage error (MAPE), residual standard deviation (RSD) values and the highest correlation coefficient (CC) values among the six machine learning methods and the two model-driven methods. Those results indicate that the proposed method can achieve greater accuracy and reliability in remaining life prediction under two-step loading, which illustrate the effectiveness of the proposed method as a data-driven method in the field of remaining life prediction.

Proposal of an Interlaminar Fatigue Life Evaluation Method for CFRP Based on Inelastic Two-Scale Analysis

In this paper, a prediction method for interlaminar fatigue life of carbon fiber-reinforced plastic (CFRP) is proposed based on an inelastic two-scale analysis method combined with the Coffin-Manson law. For this, the flatwise tension test of a CFRP is simulated using the two-scale analysis method, and the distributions of microscopic viscoplastic strain occurring at resin parts in micro-structures (unit cells) are examined. Then, the maximum value of microscopic viscoplastic strain is applied to the Coffin-Manson law for the resin to predict interlaminar fatigue life of the CFRP.

Research on low cycle fatigue life prediction considering average strain

To address the difficult problems in the study of the effect of average strain on fatigue life under low-cycle fatigue loads, the effect of average strain on the low-cycle fatigue life of materials under different strain cycle ratios was discussed based on the framework of damage mechanics and its irreversible thermodynamics. By introducing the Ramberg-Osgood cyclic constitutive equation, a new low-cycle fatigue life prediction method based on the intrinsic damage dissipation theory considering average strain was proposed, which revealed the correlation between low-cycle fatigue strain life , material properties, and average strain. Through the analysis of the low-cycle fatigue test data of five different metal materials, the model parameters of the corresponding materials were obtained. The calculation results indicate that the proposed life prediction method is in good agreement with the test, and a reasonable characterization of the low-cycle fatigue life under the influence of average strain is realized. Comparing calculations with three typical low-cycle fatigue life prediction models, the new method is within two times the error band, and the prediction effect is significantly better than the existing models, which is more suitable for low-cycle fatigue life prediction. The low-cycle fatigue life prediction of different cyclic strain ratios based on the critical region intrinsic damage dissipation power method provides a new idea for the research of low-cycle fatigue life prediction of metallic materials.

A new fatigue life prediction method based on nonlinear fatigue cumulative damage generalized expression

A new fatigue life prediction method based on nonlinear fatigue cumulative damage generalized expression

Improved accuracy of low cycle fatigue life prediction of elbow

Elbow piping is characterized by complicated stress conditions and easy wall thinning. Therefore, a highly accurate fatigue life prediction method is required to accurately evaluate the soundness of elbow piping. In previous studies, the revised universal slope method was proposed as a life prediction formula for elbow pipes, and the relationship between strain range and fatigue life was obtained. However, with the conventional analysis method, the strain range is overestimated compared to the actual behavior, resulting in a significantly conservative prediction result. In this study, we will improve the prediction accuracy of the strain range by using a more detailed stress-strain diagram than before in the finite element analysis and examine the further improvement of the fatigue life prediction.