High Cycle Fatigue Damage Research Articles

Rotation bending high cycle fatigue behaviors of TC21 alloy with bimodal microstructure

The TC21 alloy has been extensively utilized in the aerospace structural components, making it crucial to investigate the fatigue damage mechanism of this alloy. In this study, a comprehensive investigation was conducted into the high-cycle fatigue damage mechanism of TC21 alloy under rotation bending, considering variations in primary equiaxed α (αp) phase contents and size in bimodal microstructure (BM). Results demonstrate that the TC21 alloy exhibits optimal strength-ductility and fatigue life at approximately 25 percent of the αp phase content. The content and dimension of the αp phase play a significant role in regulating the onset of fatigue fractures. Dislocation pile-up around the αp phase promotes the formation of microvoids and microcracks. Notably, when the content of the αp phase falls below 15%, there is an increased influence from secondary α phase (αs) on crack initiation. Moreover, excessive amounts of αp coupled with decreased size lead to a reduction in fatigue life. The aforementioned factors contribute to an intensified concentration of stress, facilitate a more uniform path for crack extension, and expedite the rate of fatigue crack propagation.

Dynamic stress prediction for a Pump-Turbine in Low-Load Conditions: Experimental validation and phenomenological analysis

To meet the increasing demand for higher flexibility in hydropower, an operating range extension in an existing hydroelectric powerplant is considered. To this end, the dynamic flow and structural behavior of the low-head pump-turbine is investigated in turbine mode in partial load and deep partial load conditions, to evaluate the feasibility of this flexibilization due to the increased high cycle fatigue damage. In a first step, different numerical simulation approaches that combine fluid dynamics and structural dynamics are applied and compared to in-situ dynamic strain and pressure measurements on the impeller. As a result, the modelling requirements for a numerical workflow that leads to unmatched accuracy in predicting the broad-band dynamic stresses of deep partial load are identified. In a second step, the operating-point-dependent fatigue crack initiation spots are identified based on dynamic stresses. Herein, the emergence of an additional dominant critical spot near the blade leading edge is observed, which is unexpected for low-head pump turbines. Thanks to the detailed numerical flow and structural analyses, the root cause for the dynamic stress concentration is studied and the emergence of the new critical spot is understood. It turns out in deep partial load, that the main source of pressure oscillations on the impeller blade surfaces is the vortex-dominated flow detachment zone around the blade leading edge, which, in combination with the geometry of the investigated impeller, translates into the main stress oscillations. The results of this work were later used to extend the operating range of the hydroelectric powerplant from initially 25% to 100% power output to now 0% to 100%.

Investigation of Concrete Damage on a Prefabricated Steel Spring Floating Slab Track by Finite Element Modelling

To investigate the concrete damage of prefabricated steel spring floating slab tracks (SSFST), a three-slab prefabricated SSFST system was established using the ABAQUS finite element software. Full trainload conditions and fatigue load conditions of a train passage were successively applied to the system. Plastic damage and fatigue damage of the floating slab were simulated based on concrete damage plasticity theory and model code, respectively. For comparison, a simulation of the fatigue experiment was conducted. Parametric analyses of the concrete strength and isolator stiffness were also performed. The results show that the maximum positive and negative bending moments of the floating slab throughout the loading stage are close in value. The positive bending moment causes stress concentration on the top slab surface which leads to plastic damage and low-cycle fatigue damage, while the negative bending moment causes middle-level elastic tensile stress on the bottom slab surface which leads to high-cycle fatigue damage. Under experimental conditions, damage on the bottom surface is much more severe, while the upper part is undamaged. Improving the concrete strength can reduce both kinds of damage, while increasing the isolator stiffness can only mitigate the high-cycle fatigue damage. Accordingly, recommendations are provided for improving fatigue experiments and structural design of prefabricated floating slabs.This study can inform the design and maintenance of the prefabricated SSFST system, ultimately enhancing their safety and longevity.

Axial and bending very high cycle fatigue of completion string

Preventing or mitigating very high cycle fatigue (VHCF) damage and failure of completion string is essential for ensuring their long-term stable operation. Therefore, a comprehensive understanding of the string's fatigue performance in tension, compression, and bending over an extended service life is necessary. This study investigated the evolution, microscopic mechanisms, fracture behavior, and life prediction of VHCF damage in completion string under axial and bending conditions. It was found that the intragranular twin structures on the critical interface of VHCF source directly participate in lattice reconstruction, enhancing the grain's strain coordination ability, and increasing the proportion of facet area on the fatigue fracture surface. Based on the fracture characteristics of VHCF, the Mayer empirical formula was improved, and a novel convolutional neural network (CNN) based VHCF life prediction model was proposed. Utilizing the CNN's powerful fracture feature extraction and nonlinear modeling capabilities, the VHCF fatigue life prediction accuracy was significantly enhanced, with prediction errors all within 2 times the experimental results' error range. Based on the axial and bending VHCF fracture mechanisms of completion string and CNN, a more advanced method for predicting axial and bending VHCF life is provided, offering theoretical supports for the engineering safety service and life assessment of completion string.

Experimental and numerical study on fatigue damage evolution of Q690D welding details

Steel structures are widely used in various types of structures, and welding details, which are fatigue-prone constructions, are typically utilized in steel constructions. In this study, regarding the high cycle fatigue performance and fatigue damage evolution behaviors of high strength steel welding details, experimental and numerical studies have been carried out on two typical types of Q690D high strength steel welding details, including butt-weld connections and cruciform load-carrying fillet weld (CLFW) connections. High cycle fatigue tests have been conducted, SN curves based on effective notch stress have been established and compared with the suggested curves in IIW specification, showing that FAT200 is more suitable for fatigue evaluation of high strength steel welding details. Fatigue damage evolution model and numerical simulation methods for Q690D welding details based on effective notch stress and continuum damage mechanic have been established and validated. Damage evolution analysis of welding details has been conducted based on the proposed numerical simulation method. The simulation method enables accurate characterization of fatigue damage locations.

An efficient phase-field model for fatigue fracture in viscoelastic solids using cyclic load decomposition and damage superposition

Accurate and efficient evaluations of fatigue fracture is of great importance for the design and evaluation of viscoelastic materials in critical applications subject to cyclic load. In this study, an efficiency-enhanced phase-field model for viscoelastic fatigue fracture is proposed, allowing for fast evaluations of high-cycle fatigue damage. Based on the Boltzmann superposition principle, the cyclic fatigue load is decomposed into a mean load and a zero-mean cyclic load. The response of the mean load is solved numerically, while the response of the zero-mean cyclic load is solved analytically. The phase-field driving force is obtained analytically by combining the responses of the two independent parts, and the phase-field evolution is calculated numerically. In addition, both the dissipated energy and the elastic energy are decomposed using the volumetric-deviatoric decomposition to avoid unrealistic damage under the compression portion of the cyclic load. The proposed efficiency-enhanced model satisfies the energy conservation law as it does not require the fracture toughness degradation or additional fatigue energy treatments. The computational efficiency of the overall fatigue fracture can be greatly improved by leveraging the analytical solution for the response associated with the cyclic load. Numerical investigations are performed, and comparisons with the conventional cycle-by-cycle computation method are made. The results show that the proposed method can reduce the exponential computational demand to a constant or a linear one while achieving an accuracy comparable to that of the conventional method. The effectiveness of the proposed method is further demonstrated using an actual rubber component with testing data.

A nonlinear cumulative fatigue damage life prediction model under combined cycle fatigue loading considering load interaction

In the present work, combined high and low cycle fatigue (CCF) tests were performed on GH4169 nickel-based alloy under stress-controlled conditions. The interaction between high cycle fatigue (HCF) and low cycle fatigue (LCF) results in a complex process of fatigue damage evolution under CCF loading. Based on the fatigue damage curve and the theory of equivalent damage, considering the interaction between HCF and LCF loading, a nonlinear cumulative damage model is proposed under CCF loading. The proposed model is deduced from the fatigue damage curve under CCF loading, which establishes a connection between the LCF and HCF damage curve. Three materials, including the other two materials, namely TC11 and Al 2024-T3, published in the relevant literature, are used to verify the proposed model. The experimental results demonstrate that the proposed model has better prediction results than those for Miner’s rule and the Trufyakov-Kovalchuk (T-K) model. The validation of the proposed model shows its superior performance.

A micromechanical cyclic damage model for high cycle fatigue failure of short fiber reinforced composites

This paper presents a micromechanical high cycle fatigue damage model for short fiber reinforced composite materials. Because the damage processes within such materials are influenced strongly by their microstructure, we use a mean field homogenization framework to compute the macroscopic behavior of the composite as well as the microscopic stresses and strains in the constituent phases. This allows us to account for damage phenomena related to both the fiber phase as well as in the matrix material. Fiber and fiber-interface damage is modeled using a Tsai–Wu and Weibull-based approach and the progressive damage due to cyclic loading is described by a progressive matrix damage model. The latter includes a novel coupling term in which the matrix damage progression is linked to the damage state of the reinforcing fibers. A cycle-based numerical formulation is used to overcome the computational limits of such load cases in the time domain. While the approaches are in principle applicable to different types of fiber–matrix composite, a short glass fiber reinforced polyamide 6.6 is used as an example material, for which microstructural analyses as well as tensile and fatigue tests are reported. The model’s capabilities with regard to complex fiber orientations and different fiber fractions are studied using different grades of this material class. Furthermore, the model is analyzed via benchmarks of the numerical schemes and by parameter sensitivity studies. The results show that the approach is capable of modeling the complex and microstructure-dependent fatigue damage and fatigue limits for the different material grades with limitations only becoming visible at very high fiber fractions.

Performance evolution of self-compacting concrete for ballastless track based on high-cycle fatigue damage constitutive model

Performance evolution of self-compacting concrete for ballastless track based on high-cycle fatigue damage constitutive model

On the consideration of loading interaction in combined high and low cycle fatigue life prediction

AbstractBased on the analysis of the test data and Miner's rule, a combined high and low cycle fatigue (CCF) life prediction model considering the loading interaction is established by introducing coupled damage. The coupled damage is determined by multiplying the high cycle fatigue damage and the low cycle fatigue damage by a coupled damage coefficient . According to the analysis of the test data, the coupled damage coefficient is positively correlated with the high cycle stress ratio . In addition, an interaction factor, which reflects the loading interaction effect, is introduced to correct the coefficient . The CCF experimental data of four materials are employed for model verification and comparison among the proposed model, Miner's rule, and Trufyakov–Kovalchuk model (T–K model). The proposed model exhibits a relatively higher prediction accuracy and is more suitable for predicting the fatigue life of CCF.

Life prediction model based on toughness exhaustion under combined high and low cycle fatigue loading

It is very important to establish a life prediction model that evaluates the combined high and low cycle fatigue (CCF) damage of materials. Based on the toughness exhaustion, this paper develops a CCF life prediction model considering loading interaction effect. The loading interaction factor is proposed to reflect the interaction effect between high cycle fatigue and low cycle fatigue. The proposed model does not require any additional material parameters and is convenient for application. The experimental data of four materials including GH4033 Ni-basis alloy, TC11 titanium alloy, LY12-CZ aluminum alloy, and 45 steel are applied to verify the proposed model. Comparing the prediction results of the proposed model with the Miner’s rule and the T-K model, the results show that the predicted results of the proposed model are more satisfactory.

Study on fatigue performance of double cover plate through-core bolted joint of rectangular concrete-filled steel tube bundle wind turbine towers

Rectangular steel tube concrete bundle wind turbine towers is a new type of tower structure with high prefabrication, convenient installation, convenient transportation and good integrity.Based on the uniaxial tensile test and fatigue loading test of the double cover plate through-core bolted joint, the stress condition of the key connection parts of the structure is analyzed, the S-N curve of the joint under parameter expansion is summarized, and the Weibull distribution test is carried out for the fatigue life of the concrete inside the joint. Finally, the fatigue damage of the joint are analyzed. The results show that the failure mode of the double cover plate through-core bolted joint under fatigue loading is bolt shear; Through S-N curve fitting, the S-N curve expression and fatigue limit value of different types of joints are obtained. It is found that under the shear failure mode, the fatigue limit of different types of joints is higher than the limit value specified in GB50017–2017, EC3 and AISC-360; The fatigue life of concrete at different loading factors conforms to the two parameter Weibull distribution.The damage analysis of the joint through the high cycle fatigue damage model shows that the trend of a sharp increase in the damage rate of the joints in the late loading period can better explain the phenomenon of instantaneous fracture. The research results of this paper can provide reference for the analysis, research and application of wind turbine towers.

Very High Cycle Fatigue Behavior of Austenitic Stainless Steel in Annealed and Predeformed Condition

Abstract Engineering components in service nowadays are designed for a large number of loading cycles (∼109), which makes fatigue behavior in this cycle range (designated as very high cycle fatigue [VHCF]) a topic of significant interest. The present study aims to investigate the high cycle fatigue (HCF) and VHCF behavior in type 304 stainless steel in two different conditions (annealed and with a martensite volume fraction of ∼45 %) through low cycle fatigue predeformation at a subzero temperature. A fatigue diagram in the form of an S–N curve extending up to the VHCF range is generated, which shows different HCF and VHCF behaviors for the annealed and predeformed conditions. Further tests are carried out at different R ratios to generate constant-life Haigh diagrams for both conditions. Although no failure is observed in the VHCF range under the annealed condition, an internal crack initiation mode is observed under the predeformed condition (Type II behavior), which is attributed to the enhanced notch sensitivity under VHCF cycling induced by a significant extent of strain-induced martensite formed during predeformation. To address the influence of varying load history under service, specimens were prefatigued in HCF, followed by VHCF cycling. The HCF–VHCF boundary is found to be significantly impacted by the prior HCF damage, with lowering of the fatigue limit under VHCF.

Very High Cycle Fatigue Damage of TC21 Titanium Alloy under High/Low Two-Step Stress Loading

Very high cycle fatigue (VHCF) tests were carried out under variable amplitude loading for TC21 titanium alloy. The first level of high amplitude loading was set as 950 MPa close to yield strength, and the second level of low amplitude loading was determined between 435 MPa and 500 MPa where fatigue cracks initiated at the specimen subsurface under constant amplitude. The results indicate that the high/low stress block significantly reduced the cumulative fatigue life of low stress amplitude, and the fatigue crack initiation site changed from the specimen subsurface under constant loading to the specimen surface under stress block. Based on continuum damage mechanics, the fatigue damage model of two-step stress block was established to estimate the fatigue damage process. The prediction of cumulative fatigue life generally agreed with the experimental data. The cumulative fatigue damage of the stress block was related to the stress amplitude and the cycle ratio, which determined the stress fatigue damage and its interaction damage. The surface crack initiation in the stress block accelerated fatigue damage of low stress amplitude, reducing the cumulative life.

An experimental validation of unified mechanics theory for predicting stainless steel low and high cycle fatigue damage initiation.

An experimental campaign of stainless-steel specimen tests has been completed. Three different types of tests have been performed: UTS (Ultimate Tensile Strength), LCF (Low Cycle Fatigue) and HCF (High Cycle Fatigue). This experimental campaign has been conceived and performed to validate the fatigue damage initiation prediction capabilities of UMT (Unified Mechanics Theory). Two different formulations have been used for LCF and HCF. For the latter, a modification to the existing approach is proposed in this paper. Good agreement has been found between UMT predictions and experimental results.

Numerical fatigue life prediction of corroded and non-corroded clinched joints

Mechanical clinching is used to create lightweight hybrid structures. In order to estimate the service life of clinched components, its fatigue properties need to be known under different mechanical loading conditions. In addition to fatigue, corrosion is another factor that affects the fatigue life of clinched joints. In the literature, many corrosion and high-cycle fatigue damage models exist. However, little is known about how both phenomena interact in clinched joints. In this article, the influence of galvanic corrosion on clinched EN AW-6014/HCT590X + Z sheets on the fatigue life is investigated by means of numerical simulations and experimental results. An accurate prediction of the Wöhler lines of non-corroded and pre-corroded clinched specimens is shown.

Response spectrum method for fatigue damage assessment of mechanical systems

In this paper, a new response spectrum method is proposed for high-cycle fatigue damage assessment of a linear multi-degree-of-freedom system subjected to random base acceleration. Mode damage response can be accessed by separating the modal participation factor and stress mode from the contribution of a mode to the total damage, assessed by the Single Moment method. The fatigue damage response spectrum is defined as the family of curves formed by the mode damage response with the variation of the frequency and modal damping ratio, which is irrelevant to the spatial characteristics of the load and structure. Three calculation formats of the response spectrum method are formed by considering different cross-correlation hypotheses of each mode (i.e. the Complete Quadratic Combination format, the Square Root of the Sum of Squares format, and the Modified Square Root of the Sum of Squares format). The proposed method has higher computational efficiency than other frequency-domain methods because of avoiding the calculation of power spectral density function and spectral moment of stress responses. The spatial and frequency information of the structure are decoupled from each other in the implementation, which can effectively reduce the computational cost of reanalysis. Compared to the result of the Dirlik method (self-compiled program and MSC.Patran/Nastran) and the Single Moment method, the correctness and efficiency of the proposed method are verified, and the influences of the material and load spectrum form on the response spectrum method are investigated.

Novel quantification of porosity defects on fatigue behavior for cast aluminum-silicon alloys by X-ray micro-tomography

Casting pores, as inevitable microscopic defects in castings, usually have a significant influence on the mechanical properties of materials, especially the fatigue properties. In this study, high cycle fatigue (HCF) tests for smooth specimens made of cast AlSi7Mg1 alloy (close to ASTM A357) with casting pores are performed. X-ray micro-tomography is used to obtain the 3D information of pores and cracks. The experimental logarithmic fatigue life is found to have a linear relation with the equivalent size and relative location of the critical pore. In addition, locally concave or convex areas on crack surfaces are discovered and the formation mechanism is identified. Based on a continuum damage mechanics (CDM) based HCF damage evolution equation, a pore-sensitive fatigue model is proposed by considering the size and location of pores in 3D. The test results and calculation results show that the developed pore-sensitive fatigue model can accurately predict the fatigue life.

Fatigue Evaluation of Bridges Based on Strain Influence Line Loaded by Elaborate Stochastic Traffic Flow

Stochastic traffic flow, as a type of repeated load, can cause serious high-cycle fatigue damage to bridges. In addition, the rough simulation of stochastic traffic flow and inappropriate analysis method of fatigue stresses cause the fatigue evaluation results to deviate from reality. To overcome this challenge, a probabilistic fatigue valuation method is proposed based on an elaborate simulation of the stochastic traffic flow and field-measured strain influence line. By selecting vehicle load features affecting the bridge structural fatigue as clustering parameters, the two-step clustering (TSC) method is applied to distinguish the different traffic states with the clustering numbers to be determined objectively. On this basis, the elaborate stochastic traffic flow is simulated by random sampling of vehicle feature probabilistic models for each traffic state. Subsequently, the bridge strain influence line, which is identified through synchronous monitoring of strain and vehicle positions, is loaded by the simulated traffic loads to obtain the stress history instead of the traditional finite-element model (FEM). Finally, the structural fatigue life can be probabilistically predicted through a Monte Carlo simulation. The proposed method was verified to be effective through a case study of a long-span suspension bridge. It can be concluded that distinguishing the different traffic states can improve the rationality of stochastic vehicle load simulation, and a more reasonable prediction of the vehicle-induced bridge fatigue damage can be obtained through the influence line loaded by stochastic vehicle loads.

Feasibility of early fatigue damage evaluation using the Neutron diffraction method

One of the most successful applications of the Neutron Diffraction (ND) method is the evaluation of residual stress, specifically in welded structures, and many examples exists in the literature. The present study explores the feasibility of applying the ND method to the evaluation of early high-cycle fatigue damage (i.e. the damage prior to formation of fatigue micro- or macro-cracks). In metals and advanced alloys early fatigue damage is normally associated with the accumulation of irreversible and highly localised micro-plastic strains. These strains change the micro-strain/stress field on various scale levels. In this study we attempt to measure these changes applying the ND method to G350 steel fatigue samples, which have been relieved from residual stress and subjected to various degrees of high-cycle fatigue damage. Multiple measurements of the strain/stress field in each sample have been undertaken using the ND method with an incoming beam of 0.5×0.5 mm2. The outcomes demonstrate that it is feasible to evaluate severe fatigue damage using the ND method, and, in general, the severity of the fatigue damage correlates relatively well with the averaged hydrostatic component of the residual stresses measured by the ND. However, more accurate evaluation may require higher spatial resolution (smaller gauge length) and, possibly, a larger number of measurement points to improve the quality of the experimental data.