Crack Fatigue Life Research Articles

Bonded and prestressed fatigue crack retarders based on Fe-SMA

A bonded and prestressed retarder concept is proposed in this work. The shape memory effect of an iron-based shape memory alloy (Fe-SMA) has been exploited to realize a desirable self-prestressing mechanism, resulting in compressive stresses in the parent structure. The synergistic prestressing and added fail-safe features of bonded and prestressed Fe-SMA retarders desirably restrain the fatigue crack growth. The fatigue crack growth behaviour in metallic plates reinforced with bonded and prestressed retarders is experimentally studied in this work. A test campaign has been implemented to investigate the effects of prestressing, as well as the influence of the relative location between the Fe-SMA retarders and the initial crack tip on the crack growth behaviour and fatigue crack life extension. The experimental results show that the prestressing of retarders desirably extends the fatigue crack growth life. More extension in fatigue life can be achieved by positioning the bonded prestressed retarders from 40 to 20 mm before the initial crack tip, the desirable retardation due to beneficial compressive prestressing and added load path on the small crack is significant. The findings in this work imply that it is beneficial to proactively reinforce the fatigue-prone locations in metallic structures with bonded and prestressed Fe-SMA retarders in order to extend the service life.

Fatigue Crack Extension and Life Calculation Based on Finite Element Analysis

With compact tension specimen static stress analysis and fatigue life of crack as the research object, through the three-dimensional modeling software to establish compact tension specimen, using the finite element analysis software to sample statics analysis, get the maximum deformation and maximum stress, and the compact tensile samples prefabricated crack, using the fatigue crack propagation analysis software, The cycle times and a-N curves were obtained. This method can be used to calculate the fatigue crack propagation life and visualize the crack propagation process, which is convenient to analyze and master the fatigue mechanism.

Surrogate model building and error analysis for the damage tolerance life of penetration type fatigue crack

The penetration type cracks are often found in the components of mechanical systems and are a major threat to the operational reliability of mechanical components. There are many factors affecting the fatigue crack damage tolerance life, so the numerical calculation of 3D fatigue crack propagation is a complex process. Therefore, it is significant to improve the calculation efficiency of fatigue crack life with guaranteeing the calculation accuracy. The crack life is the result of the integration of crack propagation length and stress intensity factor(SIF). In this paper, a surrogate model for calculating the damage tolerance life of penetrating fatigue cracks is constructed using Kriging method based on the results of experimental tests and finite element analysis(FEA). The surrogate model is a four-dimensional response-value solution model, which can solve the fatigue crack life under random parameters. Finally, an error analysis is performed on the results of the surrogate model calculation. The results indicate that the error of the surrogate model calculation is relatively low, and the overall error is within 2%. Therefore, the surrogate model is characterized by high efficiency and accuracy.

Research on the road performance of self-adhesive basalt fiber geotextiles based on the background of long-life pavements

Achieving sustained asphalt pavements can minimize the structural damage brought on by minor pavement cracks, which will reduce the high repair and maintenance costs resulting from pavement distress. This study introduces a new composite geomaterial, self-adhesive basalt fiber geotextiles (SBFG) prepared by hot-melt lamination of basalt fiber cloth and modified asphalt, intended for the deterrence and control of reflection cracks in asphalt pavements. In this study, the self-adhesive geotextile was placed between the cement-stabilized macadam base and AC-20 surface layer to prepare composite samples, and the road performance was evaluated by a three-point bending test, Overlay Tester, dynamic shear rheology test, and the crack expansion time under different parameters of SBFG was simulated by ABAQUS finite element to predict the whole life cycle of the pavement structure. The results indicate that the fracture energy of the SBFG sample is the largest among all samples, and the structural design of fiber reinforcement disperses the concentrated stress at the crack tip, increases the stress area, and prolongs the time of crack expansion from the subgrade to the surface layer; Smooth and stable load loss curve of the sample in the reflection crack test, with slow crack expansion. This new geomaterial has an excellent rutting factor and maintains good resistance to permanent deformation at high temperatures; In the finite element prediction of fatigue cracking life of asphalt pavement, the structural life of the pavement with the addition of SBFG was improved by 78.3% compared to the control group. The application of basalt fibers in geosynthetics provides a new idea for achieving prolonged asphalt pavements.

Investigation of the heat energy and multi‐level load on subsurface fatigue damage evolution via multi‐scale method

AbstractThe relationship between heat energy and initial fatigue life of different metals under multi‐level loading stress and elevated temperature is introduced. The fatigue damage evolution model was established from the microscopic and mesoscopic perspectives to explore the fatigue damage and the crack initiation location at elevated temperature. Based on the method of continuous damage mechanics, the influence of multi‐level loads on fatigue cracking life and heat energy on strain energy of distribution were investigated. The mathematical model is verified by the experimental data. The model has important engineering significance for predicting the service life of parts at elevated temperature.

Fatigue Cracking Characteristics of Asphalt Pavement Structure under Aging and Moisture Damage

Structural characteristics influence assessment of fatigue cracking behavior. In the assessment of asphalt pavements, the asphalt structure and practical conditions must be considered. This study analyzes changes in the elastic modulus of the pavement of different asphalt mixtures amid aging and moisture damage through fatigue cracking tests. A model to predict the tensile strain at the bottom of the pavement layer is developed through a structural analysis based on the material properties. The results are comparatively analyzed using the Mechanistic-Empirical Pavement Design Guide to predict the fatigue crack life. The test results indicate that moisture damage significantly influences the material properties of asphalt pavement and can accelerate pavement damage as the asphalt ages. The coefficient values of the proposed fatigue-life prediction model can be used to predict the fatigue life depending on the age of the asphalt and its moisture damage after aging. The degree of fatigue damage can be predicted by calculating the tensile strain using the regression equation and elastic modulus according to the aging and moisture damage.

Investigation of the Fatigue Life of Bottom-Up Cracking in Asphalt Concrete Pavements

Traditionally, fatigue cracking in asphalt pavement means fatigue failure, which is the basis for controlling the design thickness of asphalt pavements. In fact, the fatigue failure of asphalt pavements includes three stages: fatigue cracking, crack expansion, and structural failure. Therefore, this paper aims to investigate the fatigue life of the bottom-up cracking of asphalt concrete (AC) pavements considering the different stages of fatigue failure. The dynamic modulus of AC of different grades was experimentally determined. The tensile stresses at the bottom of the AC layer were evaluated by embedding the tested dynamic modulus into a numerical simulation, which can be used to calculate the fatigue cracking life. Then, overlay tests (OTs) at different temperatures were conducted to obtain the fracture parameters A and n from the asphalt mixture. The crack propagation life was calculated via the Paris formula based on the fracture parameters A and n. The analysis results showed that an increase in AC thickness could effectively improve the fatigue crack life of the pavement structure, and the proportion of crack propagation life to fatigue crack life at different temperatures varied significantly. Therefore, when analyzing and calculating the fatigue life of pavement structures, besides the fatigue cracking life, the crack propagation life after cracking should also be considered, which is very important for accurately calculating the entire fatigue life of asphalt pavement structures. This will offer guidance for asphalt pavement thickness design.

Fatigue Crack Calculation of Steel Structure Based on the Improved McEvily Model

Numerous fatigue crack mechanism models have been proposed based on an in-depth study of material fatigue mechanisms and engineering requirements. However, due to many of the parameters in these models being difficult to determine, their application to engineering is limited. The fatigue crack of the steel structure was calculated based on the improved McEvily model. To begin, based on the theory of linear elastic fracture mechanics, some parameters of the McEvily fatigue crack growth model were deduced and determined by using more reasonable assumptions and empirical formulas. Second, the effectiveness of the improved McEvily fatigue crack growth model was proven by comparison to the results of the improved model with the classical Paris model. Finally, the improved McEvily model was applied to practical engineering, and the typical fatigue crack of steel structure was selected and compared with the results of the Paris model and nominal stress method to verify its feasibility in engineering. The results reveal that the application conditions of the improved McEvily model can be extended from laboratory conditions to practical engineering, and its accuracy is better than that of the Paris model, which can well evaluate the fatigue crack life of steel structures.

3D modelling of fatigue crack growth and life predictions using ANSYS

This study uses ANSYS mechanical APDL 19.2 to predict crack propagation trajectories and fatigue crack growth at constant amplitude loading. Mixed-mode fatigue life assessment is implemented by the Paris law model for different configuration of modified compact tension specimen (MCTS) in linear elastic fracture mechanics (LEFM). The methodology includes: evaluating stress intensity factors (SIFs), a direction of crack propagation and estimating fatigue life via incremental crack growth process. Predicted crack growth path in the present analysis revealed a change in orientation of the hole proportionately affected fatigue crack life cycles. The propagation of fatigue crack is mostly attracted to the hole and the crack could either curve its path and grow towards it, or bypass the hole and propagate. The mixed-mode fatigue crack path and fatigue crack growth from this study were validated by several crack growth experimental and numerical results in literature.

Study into the laboratory simulation of asphalt mixtures ageing: the influence of temperature, time and pressure

This article studies the phenomenon of ageing in asphalt mixtures, considering the impact of temperature, time and pressure via laboratory techniques, compared with roadway samples. In particular, the ageing of two mixtures was analysed, manufactured with a high voids content and with two different modified binders (SBS polymer and crumb rubber), while comparing results with those obtained for cores from a highway using similar mixtures in surface layer . The stiffness and fatigue cracking life of the mixtures were assessed, after different ageing periods at diverse temperature and pressure levels. Results demonstrated that the laboratory ageing simulation of asphalt mixtures strongly depended on the studied parameters. Long ageing periods (in this study 9 days) at a high temperature (135°C for the cases analysed in this paper) was required in order to reproduce a marked ageing impact, while providing the ability to differentiate the susceptibility of ageing of different materials.

Numerical Simulation and Parametric Analysis of Fatigue Crack in UIC60 Rail Thermite Welded Joint

The mechanism of rail-wheel contact is the most essential field of study in railway engineering since it requires extensive application expertise, diagnostic skills, and a trustworthy analysis technique. In this research the fatigue life of a UIC60 rail AT weld under vertical load and its parametric effect has been studied, and for that a three-dimensional elastic-plastic finite element model is created using ANSYS space-claim software, and then finite element method is employed to analyse the full-scale model of wheel-track and weld system with realistic three-dimensional solution. Model assembly components include axle, wheel, and thermite-welded rail. Simulation of contact between wheel and UIC60 rail weld with crack on weld at angles of 30 and 60 degrees with different coefficients of friction between the weld wheel contact and between crack surfaces was carried out under vertical loadings. In general, the Hertz contact theory assumptions are taken into consideration throughout the analysis, and the impacts on fatigue life are given by using damage mechanics method. The results of the wheel/weld fatigue crack analysis have been displayed to demonstrate the influence of different parameters on the fatigue life of cracks. The purpose of this study is to identify and safeguard the rail against failure, as well as to ensure the safety of passengers and to reduce the cost of maintaining the rail system.

Influence of shape of weld toe and hardness of weld metal on fatigue properties in GMA welded fillet lap joint of UHSS sheet

ABSTRACT This study aims to clarify the influence of shape around weld toe and hardness of weld metal on fatigue crack life in fillet lap joints for automotive chassis elements. Gas metal arc (GMA) welding was performed using 980 MPa class hot rolled steel sheet as the test material. The shape around weld toe and hardness of weld metal were changed by the combination of the shield gas composition and the welding wire. The smoothing of the weld toe significantly improved the fatigue life compared to the hardened weld metal. The total fatigue life was separated into crack initiation life and crack propagation life by measuring the decreasing ratio in the stiffness of the specimen during the fatigue test. Then, the effect of smoothing the weld toe and hardening the weld metal on each life was examined. The changes in the propagating crack front shape and the propagation rate during fatigue test were examined by the beach mark technique. As a result, it was suggested that the smoothing of weld toe improves not only the crack initiation life but also the propagation life by delaying the crack propagation rate in the early stage of crack propagation. The mechanism of retardation of crack propagation rate due to smoothing of weld toe was discussed from the viewpoint of crack shape and aspect ratio.

Uncertainty Modeling of Fatigue Crack Growth and Probabilistic Life Prediction for Welded Joints of Nuclear Stainless Steel.

Welded joints are widely used in the pipeline connection of nuclear power plants. Defects in these joints are an important factor leading to the failure of welded joints. It is critical to study the fatigue crack growth and life prediction methods for the welded joints with defects, to reduce their likelihood. In this paper, we present our study of the uncertainty of fatigue crack propagation and probabilistic life prediction for welded joints of nuclear stainless steel. The standard compact tension (CT) specimens were fabricated according to the American Society for Testing and Materials (ASTM) standard. Fatigue crack propagation tests with different stress ratios were performed on CT specimens, using the Mei Te Si (MTS) fatigue test system. A fatigue crack propagation rate model considering the uncertainty of material parameters, and based on the Paris formula and crack propagation experimental data, was established. A probabilistic life prediction method based on Monte Carlo simulation was developed. The fatigue crack propagation prediction result of a CT specimen was compared with the actual tested result, to verify the effectiveness of the proposed method. Finally, the method was applied to an embedded elliptical crack in welded joints of nuclear stainless steel, to predict the fatigue crack growth life and evaluate the reliability.

Fatigue cracking checking of cement stabilized macadam based on measurement uncertainty and interval analysis

The discreteness of fatigue test results of inorganic bonded stabilized materials is very voluminous. In this study, the fatigue crack checking process of cement stabilized macadam is analyzed by using measurement uncertainty and interval analysis theory in order to improve the efficiency of fatigue test data. Firstly, the measurement uncertainty of the bending strength and fatigue life of cement stabilized macadam is evaluated based on the measurement uncertainty theory. Secondly, the regression analysis of the fatigue life interval of different stress ratio conditions is realized, following which the regression model of the fatigue life interval of cement stabilized macadam is derived. Finally, the calculation model of fatigue cracking life interval is deduced, and the fatigue cracking life interval of cement stabilized macadam is then obtained by interval algorithm. Meanwhile an evaluation method of interval comparison results is proposed in order to undertake a comparative analysis of the fatigue cracking life interval of cement stabilized macadam. According to the findings, the non-uniformity of the specimen is determined as the root cause of the large discreteness of fatigue test results. A fatigue interval model with 95% guarantee rate can be obtained based on the regression analysis method of fatigue life interval, which is proved to be effective in improving the efficiency of fatigue test data. There is a case of interval expansion in calculating the equation of fatigue cracking life interval. It is verified that the extended interval result has engineering applicability. Therefore, it can be surmised that the interval result comparison method proposed in this paper can achieve both quantitative and qualitative evaluation, which is particularly suitable for the engineering field of interval analysis.

Assessment of Mechanical Crack Fault Dependent on Wavelet Finite Element Model

Given that cracks in the forging and heat treatment process of switch actuator rod can affect its service life, damage mechanics is combined with the finite element analysis method to calculate the fatigue crack propagation life by using the Paris equation. The wavelet finite element model is used to establish the GM (1,1) grey differential equation. The identification parameter of the model is determined by experimental data calculation to assess the fatigue crack life of the switch actuator rod and compare it with the measured data in the experiment. The results show that the application of the wavelet finite element model to assess the fault of switch actuator rod is simple, feasible, and highly accurate, with excellent application value.

Effect of Alternate Corrosion and Fatigue on Fatigue Crack Growth Characterization of 2024-T4 Aluminum Alloy

To investigate the effect of alternate corrosion and fatigue on fatigue crack growth characterization of 2024-T4 aluminum alloy, the pure fatigue test, “corrosion + fatigue” test (commonly known as pre-corrosion fatigue), and the “fatigue + corrosion + fatigue” alternating test of single-sided notched specimen of 2024-T4 aluminum alloy were carried out. The fatigue crack life of alternate corrosion and fatigue is longer than that of the pre-corrosion fatigue when the corrosion time is the same. And the more the times of alternating, the longer the crack growth life will be. This is mainly because the fatigue crack growth rate will change suddenly, which will have a certain hysteresis effect on the fatigue crack growth. The corrosion and fracture morphology characteristics of the alternate test were examined by scanning electron microscopy (SEM), and the composition of corrosion products was examined by the energy dispersion spectrum (EDS). The prediction model of fatigue crack growth rate considering the alternating hysteresis effect of corrosion and fatigue based on the Paris formula was established, and the parameters and precision of the model were calculated and verified. The results show that the model has certain engineering application value.

Numerical method for estimating fatigue crack initiation size using elastic–plastic fracture mechanics method

• Calculation method of crack initiation size is improved by basic model of fatigue crack initiation size. • The elastic–plastic fracture mechanics (EPFM) method is used to study the short crack fatigue life. • The calculation model of fatigue crack initiation size is established by symmetric cyclic torsional alternating stress. • The feasibility of EPFM method is verified by comparing with the crack initiation size. To solve the fatigue crack initiation problem, it is necessary to calculate the fatigue crack initiation size. According to the aspect of macroscopic crack development, the calculation method of crack initiation size is determined by the critical dimension of fatigue crack initiation. Simultaneously, the elastic–plastic fracture mechanics (EPFM) method is used to study short crack fatigue life by considering the cumulative damage rule of crack initiation life, and the calculation model of fatigue crack initiation size caused by symmetric cyclic torsional alternating stress is established under low strain. The crack initiation dimension of component is estimated, which lays a foundation for the study of fatigue life. Then the feasibility of this method is verified by comparing with the crack initiation size, which is determined by predicting the non-propagating crack size (NPCS).

A numerical study of crack shielding/anti-shielding in layered architectures

Previous research has indicated the potential effectiveness of adopting micro-scale layered architectures to improve the fatigue damage resistance of coatings. However, the optimisation of these coatings is difficult due to the existence of many different factors affecting fatigue performance in such micro-scale layered architectures. In particular, the interaction of successive shielding and anti-shielding processes on crack growth resistance is therefore addressed in this paper by numerical simulation analysis. The crack tip fields in a series of layered architectures were simulated based on varying assumed constitutive materials properties to reveal the interaction of shielding/anti-shielding characteristics in complex architectures in a simple exemplar system. The evolution of crack driving force (CDF) with crack length was calculated and linked to fatigue crack life under relatively simple conditions, including straight crack path and Paris law assumptions, to investigate the effect of the ordering of shielding/anti-shielding characteristics on the crack tip field and hence on fatigue crack life. Layered architectures with different numbers, ordering and placing of layers, were assessed and parametric studies of 4 layered architectures were carried out. This allows analysis of the effect of these individual factors on shielding and their interactive effect with anti-shielding in multi-layered architectures. Understanding the combined effect on crack growth performance and overall fatigue life controlled by crack propagation provides insight into the generic design of micro-scale layered architectures.

Lamb Wave-Minimum Sampling Variance Particle Filter-Based Fatigue Crack Prognosis.

Fatigue cracks are one of the common failure types of key aircraft components, and they are the focus of prognostics and health management (PHM) systems. Monitoring and prediction of fatigue cracks show great application potential and economic benefit in shortening aircraft downtime, prolonging service life, and enhancing maintenance. However, the fatigue crack growth process is a non-linear non-Gaussian dynamic stochastic process, which involves a variety of uncertainties. Actual crack initiation and growth sometimes deviate from the results of fracture mechanics analysis. The Lamb wave-particle filter (LW-PF) fatigue-crack-life prediction based on piezoelectric transducer (PZT) sensors has the advantages of simple modeling and on-line prediction, making it suitable for engineering applications. Although the resampling algorithm of the standard particle filter (PF) can solve the degradation problem, the discretization error still exists. To alleviate the accuracy decrease caused by the discretization error, a Lamb wave-minimum sampling variance particle filter (LW-MSVPF)-based fatigue crack life prediction method is proposed and validated by fatigue test of the attachment lug in this paper. Sampling variance (SV) is used as a quantitative index to analyze the difference of particle distribution before and after resampling. Compared with the LW-PF method, LW-MSVPF can increase the prediction accuracy with the same computational cost. By using the minimum sampling variance (MSV) resampling method, the original particle distribution is retained to a maximum degree, and the discretization error is significantly reduced. Furthermore, LW-MSVPF maintains the characteristic of dimensional freedom, which means a broader application in on-line prognosis for more complex structures.

Enhanced model for thermally induced transverse cracking of asphalt pavements

Thermal cracking is a non-load associated distress mode of asphalt pavements. Finite element models (FEM) were first introduced in this study to determine the thermally induced J-integral at the tip of thermal crack. After extensive runs of the FEM, artificial neural network models were constructed to predict the J-integral, which was used in the Paris’ law to calculate the cumulative thermal crack growth over time and thermal cracking fatigue life. Additionally, Long-term pavement performance data was collected to characterize the thermal cracking in different climatic zones. The calculated fatigue life was well correlated with the observed transverse cracking field performance.