High Cycle Fatigue Loading Research Articles

Stress recovery behavior of an Fe-Mn-Si shape memory alloy

This study investigated the stress recovery behavior of an Fe-Mn-Si-Cr-Ni-VC shape memory alloy for prestressed strengthening, focusing on high-temperature activation of the alloy. The effects of different prestrain levels (1%, 2%, 4%, 6% and 8%), activation temperatures (100, 150, 200, 250, 300, 350, and 455 °C), and initial preloads (50, 100 and 150 MPa) on recovery stress were evaluated to propose an optimum activation strategy. In addition, mechanical properties of the Fe-SMA after activation, including the performance under a second high-temperature activation (up to 455 °C) and high-cycle fatigue (HCF) loadings (stress-controlled with a stress range of 57 MPa), were studied. According to the results, a prestrain level of 2% was found to be the optimum level when the activation temperature was below 200 °C. However, at higher activation temperatures, an increased prestrain resulted in an increase in the recovery stress. In this study, the specimens prestrained by 4 and 8% and activated by 350 °C led to a recovery stress of 421 and 445 MPa, respectively. According to the fatigue test results, the recovery stress decreased by 12 – 15% after two million load cycles, regardless of the activation temperature.

Experimental and Numerical Study of Combined High and Low Cycle Fatigue Performance of Low Alloy Steel and Engineering Application.

The fatigue behaviors of metals are different under different in-service environment and loading conditions. This study was devoted to investigating the combined effects of high and low cycle fatigue loads on the performance of the low alloy steel Q345. Three kinds of experiments were carried out, including the pure high cycle fatigue (HCF) tests, the pure low cycle fatigue (LCF) tests, and the combined high and low cycle fatigue (HLCF) tests. The prediction formulae were proposed for the combined high and low cycle fatigue failure. Scanning electron microscopy (SEM) and stereo microscope were used to analyze the microstructure and fracture morphology due to different fatigue loads. Case study on the combined high and low cycle fatigue damage of a steel arch bridge was carried out based on the FE method and the proposed formula. The results show that the LCF life decreases evidently due to the prior HCF damages. The HLCF fracture surface is relatively flat near the crack initiation side, and rugged at the other half part. The fatigue damages at the bridge joints increase significantly with consideration of the pre-fatigue damages caused by traffic load. In the 100th anniversary of service, the fatigue damage index without considering the HCF pre-damage is only about 50% of the coupled damage value.

Threshold damage-based fatigue life prediction of turbine blades under combined high and low cycle fatigue

Life prediction based on the damage mechanics of aero-engine turbine blades is crucial for performing their strength design and ensuring the operational reliability under combined high and low cycle fatigue (CCF) loadings. In view of this, a simple and efficient life prediction method is developed to consider the interaction of high cycle fatigue (HCF) and low cycle fatigue (LCF) without any additional material constants, and as a basis of that a new nonlinear damage accumulation model is proposed by introducing threshold damage of the component related to material type and current HCF damage. In order to validate the presented methodology, model predictions were compared with the experimental data sets of turbine blades and its alloy materials. The predicted results indicate that the simple life prediction model is capable of estimating the fatigue life quickly with an acceptable accuracy in contrast to other four existing ones. Moreover, the threshold damage-based method provides the higher prediction accuracy than others due to improved HCF damage determined by the damage threshold.

Continuum-based approach for modelling the flexural behaviour of plain concrete beam under high-cycle fatigue loads

In this study, a continuum-based model was proposed to characterise the flexural performance and damage evolution process of a plain concrete beam under high-cycle fatigue loads. The plain concrete beam under three-point bending load was modelled by combining the damaged constitutive model of concrete and the Euler–Bernoulli beam theory with varied stiffness. The dynamic stiffness matrix method, in conjunction with the discretization technique, was adopted to solve the nonlinear governing equations of motion. A global damage index corresponding to natural frequencies was introduced to quantify the performance degradation of the beam. To improve the analysis efficiency of the high-cycle fatigue problems, the accelerated algorithm, namely the jump-in-cycle method, was employed in this model. It is demonstrated that the numerical results agree well with the experimental data under fatigue harmonic loads. Performance degradation under fatigue bending loads only occurs at the midspan of the beam. Adopting the jump-in-cycle methods significantly improves the analysis efficiency of the high-cycle fatigue problem, and the calculation time is reduced by approximately 90% compared with the cycle-by-cycle method. This model is capable of rationally predicting damage evolutions, stiffness degradation processes, stress redistributions, and loading level-fatigue life (S–N) curves and can provide a basis for simulating the flexural behaviours of reinforced concrete (RC) beams under fatigue bending loads.

Development and validation of an acceptance criteria and damage index for buckling-restrained braces (BRB)

This paper focuses on introducing two methodologies related to buckling-restrained braces (BRBs): one for determining the acceptance criteria generally used in performance-based seismic design (PBSD), and another for assessing a damage index (DI) when BRBs are subjected to seismic actions . Both methodologies are established from the results of experimental test conducted on a series of full-scale BRB specimens. In total 19 full-scale BRB specimens were manufactured with local industry and workforce. 14 BRB specimens were tested using a low-cycle loading protocol, and five more BRB specimens were tested using a high-cycle fatigue loading protocol. The specimens were designed having differential deformation and energy dissipation capacities. For the low-cycle protocol, the axial strain in the BRB core was continuously increased until failure, while for the fatigue protocol, the axial strain in the core was increased from zero to 1.5%, and continued at 1.5% strain until core failure occurred. This paper also describes the results of a series of nonlinear dynamic analyses carried out on a sample building in order to validate the proposed methodologies when subjecting the building to ground motions. The results provided sufficient arguments to conclude that: (1) the proposed acceptance criteria is capable of considering the effect of (i) core plastic length, (ii) cumulative plastic deformation , (iii) and brace failure type (depending on the loading history). (2) The proposed damage index is shown to be capable of considering the effect of the maximum core strain attained as well as the cumulative plastic deformation effect. Moreover, a qualification scale was assigned to the proposed damage index as a tool for evaluating whether the BRB element should be replaced or left on site. Finally, the results suggest that the proposed methodologies can be useful in structural design practice. • The proposed damage index for BRBs is a potential tool for post-quake evaluation. • The acceptance criteria of ASCE 41-17 for BRBs should be redefined. • The proposed acceptance criteria scheme for BRBs is a potential tool for designers.

A modification of Matake criterion for considering the effect of mean shear stress under high cycle fatigue loading

AbstractIn the present paper, a brief review for some existing critical plane‐based life prediction models is presented, and limitations of these models in reflecting the influence of mean stress on fatigue life are discussed. It is found that the effect of mean normal stress on fatigue damage has been well taken into account for most of the critical plane‐based fatigue life prediction models, while mean shear stress effect is not well considered in these models. Therefore, a new critical plane‐based multiaxial high cycle fatigue life prediction model is proposed in this paper to account for the effects of both mean shear and normal stresses. The shear Walker factor and mean normal stress sensitivity index are introduced in the developed criterion to consider the effects of mean shear and normal stresses, respectively. Procedures to determine the damage parameters acting on the critical plane and to calculate the material constants contained in the proposed model are all presented. Experimental validations by using six different materials show that most of the predictions are within a factor of 3 in fatigue life.

Fatigue crack arrest in steel beams using FRP composites

Previous studies have demonstrated the effectiveness of strengthening with pre-stressed carbon-fiber reinforced polymer (CFRP) composites to increase the lifetime of cracked steel members. In some cases, complete crack arrest has been observed. This study aims to present a method that can estimate the minimum required prestressing that would result in a complete crack arrest in steel I-beams. Analytical and numerical models based on linear elastic fracture mechanics (LEFM) were developed and verified using a set of experimental results. Three steel I-beams with different crack lengths were strengthened with pre-stressed CFRP composites and later tested under a high-cycle fatigue loading regime. It was shown that the pre-stressed CFRP composites could result in a crack closure mechanism, in which the crack surfaces remained closed even under large external loads. Furthermore, it was shown that by considering the stiffness of the CFRP in the analytical formulation, the amount of prestressing required to arrest the fatigue crack growth can be reduced.

Residual bearing capacity of steel-concrete composite beams under fatigue loading

This study was conducted to investigate the residual bearing capacity of steel-concrete composite beams under highcycle fatigue loading through experiments and theoretical analysis. Six test beams with stud connectors were designed and fabricated for static, complete fatigue, and partial fatigue tests. The failure modes and the degradation of several mechanical performance indicators of the composite beams under high-cycle fatigue loading were analyzed. A calculation method for the residual bearing capacity of the composite beams after certain quantities of cyclic loading cycles was established by introducing nonlinear fatigue damage models for concrete, steel beam, and shear connectors beginning with the material residual strength attenuation process. The results show that the failure mode of the composite beams under the given fatigue load appears to be primarily affected by the number of cycles. As the number of fatigue loadings increases, the failure mode transforms from midspan concrete crushing to stud cutting. The bearing capacity of a 3.0-m span composite beam after two million fatigue cycles is degraded by 30.7% due to premature failure of the stud. The calculated values of the residual bearing capacity method of the composite beam established in this paper agree well with the test values, which indicates that the model is feasibly applicable.

Finite element modeling of mode I fatigue delamination growth in composites under large-scale fiber bridging

In this study, the Turon et al. and Kawashita-Hallett fatigue damage models are extended with a trilinear cohesive law to simulate mode I fatigue delamination in the composites undergoing large-scale fiber bridging. The trilinear cohesive zone model (CZM) is constructed by superposition of two bilinear CZMs. In order to implement the developed models, a user defined element (UEL) subroutine is prepared in the Abaqus software and finite element analyses are conducted based on the envelope loading technique to simulate the 3D double cantilever beam (DCB) specimens under high-cycle fatigue loading. The finite element models are assessed through the experimental data from the literature and also five available fatigue damage models based on the bilinear CZM. It is concluded that the trilinear CZMs has more accuracy than the bilinear ones in prediction of fatigue delamination with fiber bridging effects. A parametric study is performed on the two extended models and sensitivity of models to the fitting parameters and quasi-static CZM parameters are comprehensively investigated.

Dynamic crack mechanism model place in the designing of the buildings

The materials that we use always have some defects. Under static, cycling or dynamic load the materials as a function of the crack size and load environment can initiate a fracture. The crack mechanism depends on several factors, like material properties, crack type and the stress kind. The traditional fracture mechanics theories suggest several solutions to predict the crack-grow and the fracture. The fracture mechanism theories are well known in the case of the elastic-plastic behaviour materials and also for the brittle materials under different strain like a high cycle and low cycle fatigue load. These theories are supported by test results. Several researchers evaluated different test methods for determining the fracture toughness on the base of crack-grow behaviour by dynamic tests and determining dynamic fracture toughness. The paper brings the results of the brick blast resistance under the blast load. Damage level was detected as a function of the test setup parameters. The bricks were pre-cracked before the test. The results show that the fracture can be guided by the pre-cracking and decrease the blast affected damage.

Influence of reversible and non-reversible fatigue on the microstructure and mechanical property evolution of 7075-T6 aluminum alloy

Evolution of microstructural features and defects caused by high cycle fatigue loading have the potential to affect post-fatigue global behavior in different ways depending on the material, fatigue loading parameters, and subsequent loading strain rate. This work focuses on the influence of reversible and non-reversible, macroscopic elastic fatigue on the microstructure and subsequent mechanical properties of 7075-T6 aluminum alloy. Subsurface material obtained from interrupted fatigue experiments is used for both microstructural characterization and post-fatigue mechanical property evolution. Crystal plasticity modeling, in conjunction with machine learning, is used to help determine mechanisms contributing to the mechanical property evolution.It was found that the subsequent mechanical behavior was dependent on both the fatigue stress ratio and subsequent loading strain rate. There was a 7% decrease in quasi-static strength after being fatigued with a stress ratio of zero. However, quasi-static strength remained unchanged after being fatigued at other stress ratios. In addition, dynamic tension experiments did not reveal any decreases in strength due to prior fatigue loading. Fatigue-induced voids potentially developed in grains where slip transmission across the grain boundary was less likely to occur. Iron-rich inclusion cracking took place throughout the bulk fatigued material and was mainly limited to larger sized inclusion particles, but there was no evidence it contributed to significant mechanical property changes. Results from this work show how different stress ratios and degrees of dislocation reversibility during high cycle fatigue loading influence the microstructure and post-fatigue global behavior of 7075-T6 aluminum alloy.

A computational multi-scale model for the stiffness degradation of short-fiber reinforced plastics subjected to fatigue loading

In this work, we investigate a model for the anisotropic and loading-direction dependent stiffness degradation of short-fiber reinforced thermoplastics subjected to high-cycle fatigue loading. Based upon the variational setting of generalized standard materials, we model the stiffness degradation of the matrix in cycle space by a simple isotropic fatigue-damage model with minimum number of model parameters, and consider the fibers to be linear elastic. The stiffness degradation upon cyclic loading is determined, for fixed damage state, by standard linear elastic homogenization. We thoroughly investigate the influence of the involved numerical and material parameters on the effective stiffness degradation of short-fiber reinforced volume elements, and also pay close attention on the dependence on geometric parameters of the composite like fiber-volume fraction and the fiber-orientation state.To enable component-scale simulations, we use a model-order reduction strategy for identifying a suitable macroscopic model. This reduction is possible because our free energy involves polynomial powers in the fields not exceeding two, and our dissipation potential is assumed quadratic. For resolving the balance of linear momentum on the microscopic scale, we rely upon a fast Fourier transform based non-local micromechanics solver.We investigate the clever identification of the modes and demonstrate the capabilities of our model on the microscopic and on the component scale by pertinent numerical examples.

Degradation analysis on high-cycle bending fatigue for woven SiC/SiC composites based on Wiener process model

A comprehensive investigation of degradation analysis under high-cycle bending fatigue (HCBF) loading for composite materials was conducted based on the Wiener process model. Degradation data are generated by conducting the probabilistic progressive damage analysis of composite materials considering the variability of material properties including mechanical properties and strength. Based on the degradation data, the Wiener process model is established with the power time transformation function and linear time-scale functions. The HCBF tests of composite cantilever beam specimen (CBS) and turbine guide vane (TGV) are conducted to evaluate the degradation process of composite materials. Compared with the experimental data and Monte Carlo simulation (MCS) method, the proposed methodology has the promising potentials to improve computational efficiency with acceptable computational accuracy for the CBSs. As for the TGV, the maximum relative errors for mean fatigue life are within 17.89%, while the degradation tendency from experiments is similar to the simulated degradation curves, verifying the rationality of the proposed method based on Wiener process model. Moreover, reliability analysis is conducted based on the stochastic degradation process, which can be used to determine whether the performance of the structure meets the design requirement.

Ductile damage assessment of Ti6Al4V, 17-4PH and AlSi10Mg for additive manufacturing

A great research effort has been spent during the latest years in the characterization of additive manufacturing (AM) alloys, mostly focused on the analysis of microstructure and on the assessment of mechanical strength, especially under high cycle fatigue loads. Post-process treatments have been also investigated, as methods to further improve the AM materials performance. On the contrary, still fewer data are available on AM materials ultimate static strength. The present paper is intended to present a comprehensive experimental and numerical static characterization of Ti6Al4V, 17-4PH, and AlSi10Mg alloys processed via selective laser melting (SLM). A dedicated set of specimen geometries was devised to induce desired multiaxial stress state, and experiments were carried out both on as built and machined AM samples. The results were employed to identify the constitutive behavior of the materials and to calibrate four different ductile damage models. The failure prediction capabilities of the tuned models were thoroughly analyzed and discussed. The overall mechanical properties and the ductility of the investigated alloys were estimated based on the experimental results and on the information provided by the tuned models. Additionally, a comparison with data collected on the corresponding wrought materials, performing the same experiments, was carried out. The results showed a limited reduction of yield and failure strength and a significant reduction in the ductility of AM materials with respect to their wrought counterparts. Moreover, for the less ductile alloys, a weaker dependence of the strain to fracture from the stress state was observed.

Impacts of reinforcement ratio and fatigue load level on the chloride ingress and service life estimating of fatigue loaded reinforced concrete (RC) beams

High-cycle fatigue loading combined with chloride exposure was studied with a close investigation of reinforcement ratio (1.06%, 1.59%, 2.91%) and fatigue load level (0.2–0.5). This study conducts both, experimentally and service life modeling based on the Monte-Carlo simulation. Results show that: (1) high-value fatigue loads expedite the chloride ingress of compressive concrete; (2) at the load level of ≥ 0.4, chloride ingress of tensile concrete significantly increases and service life decreases ≥ 93%; (3) although reinforcement ratio of 1.59% decreases the chloride ingress of tensile concrete, varying the reinforcement ratio rarely affects the service life.

Microcrack initiation mechanism of a duplex stainless steel under very high cycle fatigue loading condition: The significance of load partitioning and micro residual stresses

Investigation on the cyclic response of metallic materials in very high cycle fatigue (VHCF) is a challenging problem, which hinders the development of fatigue theories. To overcome this difficulty, we initially applied several sensible techniques, e.g., High-energy X-ray diffraction (HEXRD), confocal laser scanning microscope (CLSM), nanoindentation and transmission electron microscope (TEM) to investigate the cyclic response of a duplex stainless steel (DSS) in the VHCF regime. In-situ XRD and in-situ digital image correlation (DIC) experiments were subsequently performed at observed changing stages, intending to explore the underlying mechanism of microcrack initiation. The first-hand results obtained revealed that the austenite phase exhibits cyclic softening-hardening-softening behavior during the VHCF process. The in-situ investigations performed at the cyclic softening and hardening stages showed a load partitioning and a load transfer between the two phases, implying the cyclic response can significantly affect the distribution of the applied load. Residual strain obtained by DIC technique after unloading exhibited strong variations at phase boundaries, suggesting micro residual stresses have developed pronouncedly. Based on all the experimental findings, a unified crack initiation mechanism for the investigated DSS during VHCF loading was proposed.

Very High Cycle Fatigue Behavior of Additively Manufactured 316L Stainless Steel.

The present paper is focused on an experimental study of the damage-to-failure mechanism of additively manufactured 316L stainless steel specimens subjected to very high cycle fatigue (VHCF) loading. Ultrasonic axial tension-compression tests were carried out on specimens for up to 109 cycles, and fracture surface analysis was performed. A fine granular area (FGA) surrounding internal defects was observed and formed a “fish-eye” fracture type. Nonmetallic inclusions and the lack of fusion within the fracture surfaces that were observed with SEM were assumed to be sources of damage initiation and growth of the FGAs. The characteristic diameter of the FGAs was ≈500 μm on the fracture surface and were induced by nonmetallic inclusions; this characteristic diameter was the same as that for the fracture surface induced by a lack of fusion. Fracture surfaces corresponding to the high cycle fatigue (HCF) regime were discussed as well to emphasize damage features related to the VHCF regime.

Microcrack Initiation Mechanism of a Duplex Stainless Steel Under Very High Cycle Fatigue Loading Condition: The Significance of Load Partitioning and Micro Residual Stresses

Investigation on the cyclic response of metallic materials in very high cycle fatigue (VHCF) is a challenging problem, which hinders the development of fatigue theories. To overcome this difficulty, we initially applied several sensible techniques, e.g., High-energy X-ray diffraction (HEXRD), confocal laser scanning microscope (CLSM), nanoindentation and transmission electron microscope (TEM) to investigate the cyclic response of a duplex stainless steel (DSS) in the VHCF regime. In-situ XRD and in-situ digital image correlation (DIC) experiments were subsequently performed at observed changing stages, intending to explore the underlying mechanism of microcrack initiation. The first-hand results obtained revealed that the austenite phase exhibits cyclic softening-hardening-softening behavior during the VHCF process. The in-situ investigations performed at the cyclic softening and hardening stages showed a load partitioning and a load transfer between the two phases, implying the cyclic response can significantly affect the distribution of the applied load. Residual strain obtained by the DIC technique after unloading exhibited strong variations at phase boundaries, suggesting micro residual stresses have developed pronouncedly. Based on all the experimental findings, a unified crack initiation mechanism for the investigated DSS during VHCF loading was proposed.

A Damage Criterion to Predict the Fatigue Life of Steel Pipelines Based on Indentation Measurements

Abstract A study was conducted to investigate the effects of surface microhardness on different phases of fatigue damage. This helps to estimate the evolution of the material resistance from microplastic distortions and gives pertinent data about cumulated fatigue damage. The objective of this work is to propose a damage criterion, associated with microstructural changes, to predict the fatigue life of steel structures submitted to cyclic loads before macroscopic cracking. Instrumented indentation tests (IIT) were conducted on test samples submitted to high cycle fatigue (HCF) loads. To evaluate the role of the microstructure initial state, the material was considered in two different conditions: as-received and annealed. It was observed that significant changes in the microhardness values happened at the surface and subsurface of the material, up to 2 µm of indentation depth, and around 21% and 7% of the fatigue life for as-received and annealed conditions, respectively. These percentages were identified as a critical period for microstructural changes, which was taken as a reference in a damage criterion to predict the number of cycles to fatigue failure (Nf) of a steel structure.

A fatigue damage accumulation model for reliability analysis of engine components under combined cycle loadings

AbstractRotor components of an aircraft engine in service are usually subjected to combined high and low cycle fatigue (CCF) loadings. In this work, combining with the load spectrum of CCF, a modified damage accumulation model for CCF life prediction of turbine blades is first put forward to take into account the effects of load consequence and load interaction caused by high‐cycle fatigue (HCF) loads and low‐cycle fatigue (LCF) loads under CCF loading conditions. The predicted results demonstrate that the proposed model presents a higher prediction accuracy than Miner, Manson‐Halford model does. Moreover, to evaluate the fatigue reliability of rotor components, reliability model with the failure mode of CCF is proposed on the basis of the stress‐strength interference method when considering the strength degeneration, and its results show that the reliability model with CCF is more suitable for aero‐engine components than that with the failure mode of single fatigue.