High Cycle Fatigue Failure Research Articles

The High-Cycle Tensile-Shear Fatigue Properties and Failure Mechanism of Resistance Spot-Welded Advanced High-Strength Steel with a Zn Coating.

Advanced high-strength steels (AHSSs) with Zn coatings are commonly joined by the resistance spot welding (RSW) technique. However, Zn coatings could possibly cause the formation of liquid metal embrittlement (LME) cracks during the RSW process. The role of a Zn coating in the tensile-shear fatigue properties of a welding joint has not been systematically explored. In this study, the fatigue properties of tensile-shear RSW joints for bare and Zn-coated advanced high-strength steel (AHSS) specimens were comparatively studied. In particular, more severe LME cracks were triggered by employing a tilted welding electrode because much more stress was caused in the joint. LME cracks had clearly occurred in the Zn-coated steel RSW joints, as observed via optical microscopy. On the contrary, no LME cracks could be found in the RSW joints prepared with the bare steel sheets. The fatigue test results showed that the tensile-shear fatigue properties remained nearly unchanged, regardless of whether bare or Zn-coated steel was used for the RSW joints. Furthermore, Zn mapping adjacent to the crack initiation source was obtained by an electron probe micro-analyzer (EPMA), and it showed no segregation of the Zn element. Thus, the failure of the RSW joints with the Zn coating had not initiated from the LME cracks. It was concluded that the fatigue cracks were initiated by the stress concentration in the notch position between the two bonded steel sheets.

Nondeterministic High-Cycle Fatigue Macromodel Updating and Failure Probability Analysis of Welded Joints of Long-Span Structures

Nondeterministic High-Cycle Fatigue Macromodel Updating and Failure Probability Analysis of Welded Joints of Long-Span Structures

Mechanical and Fatigue Properties of Welded Fe-Mn-Si Shape Memory Alloys.

This paper presents the experimental results of a study evaluating the mechanical and fatigue performance of welded Fe-Mn-Si SMA. For the experimental study, welded and welded-and-heat-treated Fe-Mn-Si SMA specimens were fabricated, and fatigue tests were performed at various stress amplitudes. In addition, direct tensile tests and recovery stress tests were also performed to evaluate the material properties of Fe-Mn-Si SMAs. The elastic modulus, yield strength, and tensile strength of the welded specimens were reduced by 35.4%, 12.1%, and 8.6%, respectively, compared to the values of the non-welded specimens. On the other hand, the elastic modulus, yield strength, and tensile strength of the welded-and-heat-treated Fe-Mn-Si SMA specimens were increased by 18.6%, 4.9%, and 1.3%, respectively, compared to the values of the welded specimens. Both welded and welded-and-heat-treated Fe-Mn-Si SMAs failed at lower cycles than the conventional Fe-Mn-Si SMAs at the same stress amplitude. High-cycle fatigue failure, characterized by cycles exceeding 104, typically occurs at relatively low stress levels within the elastic region, whereas low-cycle fatigue failure, generally occurring within cycles below 104, involves high stress levels that encompass both elastic and plastic deformation. Regardless of the welding condition, the stress amplitude at which Fe-Mn-Si SMA transitions from high-cycle to low-cycle failure exceeded the yield strength.

Efficient Forced Response Minimization Using a Full-Viscosity Discrete Adjoint Harmonic Balance Method

A forced response induced by inlet distortion and blade row interactions can lead to high-cycle fatigue failure, especially when the unsteady excitation frequency is close to the natural vibration frequency of a blade. This paper presents the study of forced response sensitivity analysis and minimization using a full-viscosity unsteady discrete adjoint method. The goal is to improve the aeroelastic performances of turbomachinery blades and simultaneously constrain/improve aerodynamic performances. The decoupled modal reduction method is used to compute the forced response, which is considered the objective function in adjoint-based design optimization. To analyze aeroforcing and aerodamping flow and adjoint fields efficiently, the harmonic balance method and its adjoint counterpart developed by an automatic differentiation tool are applied. Two cases—the NASA Rotor 67 with inlet distortion and a three-row configuration with multiple fundamental frequencies in the second row—are used to demonstrate the effectiveness of the aerodynamic and aeroelastic coupled design optimization system developed in this work. For the latter case, the Fourier-transform-based method that first decomposes and then matches the time and space modes at two sides of an interface is used for interface coupling. The almost-periodic Fourier transform method is used to determine the time instances for cases with multiple fundamental frequencies.

Effect of coating-substrate microstructure on nucleation and growth of surface microcracks in a PtAl-coated Ni-based SX superalloy with sheet specimens during HCF at 900 °C

The fatigue crack initiation process accounts for the main portion of the high-cycle fatigue (HCF) life. Although coated superalloys are well-known to be prone to surface microcracks, the influence of the coating-substrate microstructure on the damage mechanism during HCF of the coated single crystal (SX) superalloys remains unclear. In the current study, HCF failure and interrupted tests were conducted at 900 °C under a low applied maximum stress on a PtAl-coated third-generation SX superalloy using sheet specimens. The HCF crack initiation was investigated by analyzing the evolution of surface microcracks and coating-substrate microstructure. The results show that the surface microcracks nucleation and growth are controlled by the initial microstructure of the coating-substrate region and the oxidation process during the HCF crack initiation stage. The rapid nucleation and growth of the surface microcracks are promoted by grain boundaries (GBs) in the coating and the interdiffusion zone (IDZ). Comparatively, the surface microcracks are blunted by oxidation in the SX substrate due to the loss of GBs, leading to a slower microcrack growth. However, the surface microcracks can gradually grow further into the substrate by repeating the processes as follows: oxidation at the crack tip, formation of γ′-depleted region due to oxidation, recrystallization at the γ′-depleted region and cracking along the GBs in the recrystallized γ′-depleted region. Subsequently, the surface microcracks, which reach the critical size, propagate along the slip bands during the progressive propagation stage. This study will contribute to improve the HCF durability of the PtAl-coated SX superalloy.

What if fractography does not tell us anything? – Failure of a side seal retainer

Abstract A fractured transition side seal retainer, together with an intact piece for reference, was received from the client on December of 2023. The subject part fractured next to the fastening hole, liberating a long ligament that was never found but reportedly caused some damage to hot gas path components downstream of a large gas turbine engine. It is speculated that the subject side seal retainer fractured due to high-stress, not fully reversed bending high cycle fatigue failure. It is recommended to make the design sturdier by considering dampening the long free length of the part, and by specifying a larger fillet radius in the initiation area. Also, over-torquing upon assembly of the subject part should be avoided.

Development of a real-time ultrasonic monitoring tool for high-cycle thermal fatigue

Pipe networks within nuclear power plants (NPPs) are susceptible to high-cycle thermal fatigue (HCTF) failures especially in so-called mixing zones where fluids with different thermal and hydraulic properties interact. The 1998 incident at Civaux 1 NPP is a good example of such a failure and its potential consequences. Given the critical impact on safety of these NPP components, a non-invasive method for HCTF progression monitoring in real time is expected to be of great use. Previous ultrasonic monitoring work showed that it is possible to predict the through-thickness temperature distribution and its temporal evolution of a mild steel block to within ±2 °C, relative to a resistance temperature device. These predictions were achieved using time of flight measurements from an ultrasonic transducer placed on the accessible surface with the so-called inverse thermal model (ITM) to invert the data. However, experiments to date have been limited to slow (10 minute) thermal transients at low temperatures (T < 100 °C). Given that HCTF is driven by thermal gradients, the ITM method seems promising to monitor its progression. In this work the performance of the ITM method was investigated under more realistic conditions: faster (1 minute) thermal transients at higher temperatures (≈ 250-300 °C). A special high temperature electromagnetic acoustic transducer (EMAT) and a fast acquisition and inversion methodology were created to collect the data. The measurement setup and the collected data will be presented in this paper.

Analysing the mechanism of fracture in drive pins used in magnetically controlled growth rods

The MAGnetic Expansion Control (MAGEC) spinal implant has transformed the treatment of early-onset scoliosis (i.e. abnormal curvature of the spine in children). Despite the innovative solution, the MAGEC device has encountered various performance issues. One component that has been frequently reported amongst the failure issues is the drive pin and the cause of these reoccurring fractures may be associated with multiple factors including over-loading, fatigue, and corrosion. This study aimed to examine the failure of eight broken drive pins from explanted MAGEC rods through fractography analysis, to better understand the factors leading to their fracture. The fracture surface of the drive pins was examined using Scanning Electron Microscopy (SEM). The clinical data were compared against observed failure modes. The fracture surfaces of four drive pins showed low cycle (high stress) or high cycle (low stress) fatigue failure mechanisms. The other four drive pins displayed environment assisted stress corrosion cracking. Almost all samples had evidence of corrosion after fracture with the amount of corrosion implying fracture occurred a relatively long time before explantation. Since multiple failure mechanisms of low cycle fatigue, high cycle fatigue or simultaneous effect of tension and corrosive environment have been observed, the fracture mechanisms illustrate the complexity of loading in these spinal growing rods. Evidence of corrosion after the failure recognises that the pins have snapped long before the device was explanted.

Comprehensive investigation on linear friction welding a dissimilar material joint between Ti17(α+β) and Ti17(β): Microstructure evolution, failure mechanisms, with simultaneous optimization of tensile and fatigue properties

In order to advance the use of Ti17 (α+β)-Ti17(β) dissimilar material blisks produced with linear friction welding (LFW) for advanced aeroengines, detailed studies of failure mechanisms and performance enhancements of such joints were conducted. The changes in microstructure including phase transformations and dynamic recrystallization were investigated. Also, the tensile failure mechanism of the joint was investigated by in-situ tensile test using scanning electron microscopy, while the high-cycle fatigue failure mechanism was studied using quasi-in-situ electron back-scattering diffraction observations combined with transmission electron microscopy characterization. A post-weld annealing heat treatment (PWAHT) was applied for optimizing tensile and fatigue strength. Results shows that α dissolution and β continuous dynamic recrystallization (CDRX) are controlling microstructure changes during welding. Tensile loading failure is related to local dislocation slip concentration on the Ti17(β) side of the thermo-mechanically affected zone with limited α strengthening phase and low degree β CDRX; while fracture under high-cycle fatigue loading is related to equiaxed α/metastable β boundary microcracks on the Ti17 (α+β) side of the heat-affected zone, which was produced by unequal deformation between the two phases. Following PWAHT for 630 °C at 3 h, re-precipitation of secondary α occurred, which increased dislocation movement resistance in the weak areas, producing tensile and high-cycle fatigue strengths of 1196.4 MPa and 550.2 MPa, respectively, higher than those of BM-(β). In addition, an adequate plasticity of the joint with elongation of 8.7 % (82.1 % of Ti17(β)) was reached.

Numerical Investigation of the Excitation Characteristics of Contaminated Nozzle Rings

The deposition of combustion residues in the nozzle ring (NR) of a turbocharger turbine stage changes the NR geometry significantly in a random manner. The resultant complex and highly asymmetric geometry induces low engine order (LEO) excitation, which may lead to resonance excitation of rotor blades and high cycle fatigue (HCF) failure. Therefore, a suitable prediction workflow is of great importance for the design and validation phases. The prediction of LEO excitation is, however, computationally expensive as high-fidelity, full annulus CFD models are required. Previous investigations showed that a steady-state computational model consisting of the volute, the NR, and a radial extension is suitable to reduce the computational costs massively and to qualitatively predict the level of LEO forced response. In the current paper, the aerodynamic excitation of 69 real contaminated NRs is analyzed using this simplified approach. The results obtained by the simplified simulation model are used to select 13 contaminated NR geometries, which are then simulated with a model of the entire turbine stage, including the rotor, in a transient time-marching manner to provide high-fidelity simulation results for the verification of the simplified approach. Furthermore, two contamination patterns are analyzed in a more detailed manner regarding their aerodynamic excitation. It is found that the simplified model can be used to identify and classify contamination patterns that lead to high blade vibration amplitudes. In cases where transient effects occurring in the rotor alter the harmonic pressure field significantly, the ability of the simplified approach to predict the LEO excitation is not sufficient.

Modelling of flexural fatigue behaviours of hybrid engineered cementitious composite link slabs using cycle-driven analysis

Link slabs are designed and expected to be serviced under high-cycle traffic loadings. Although their high-cycle fatigue performance is critical in their practical applications, very few experimental and numerical studies have been conducted to study high-cycle fatigue failure of link slabs due to the huge amount of time and resources needed for fatigue tests and the lack of efficient modelling method for high-cycle fatigue failure. Recently, as a newly developed material with superior mechanical properties, the hybrid fibre reinforced engineered cementitious composite (hybrid ECC) has been recommended for link slab application. In this study, a novel and efficient cycle-driven analysis (CDA) procedure was developed to model the structural behaviour of ECC link slabs made of the hybrid ECC under high-cycle fatigue loadings, which is the first attempt for CDA to be applied in high-cycle fatigue structural modelling of a hybrid ECC link slab with reinforcement bars. In the proposed CDA, fatigue damages of both hybrid ECC and reinforcement bars were taken into account. The accuracy and reliability of the new CDA procedure were validated by comparing the modelling predictions with the experimental results on two quarter-scaled hybrid ECC link slabs. It was found that the proposed CDA procedure could predict the overall fatigue behaviours including the deflection histories, crack patterns, fatigue life, fatigue failure mode and the residual static strength of the hybrid ECC link slabs after fatigue damage with good accuracy.

Developing a Robust Process for Design Margin Calculation Through Modal Scaling and Harmonic Analysis of Engine Mounted After Treatment System

The last few years have seen an increase in the complexity of emission standards. This has caused OEMs to start using Exhaust Gas Processors (EGP) or Exhaust After Treatment Systems (EATS)in complex integration. These systems are usually mounted on vehicle chassis or engine body with the help of mounting straps or brackets. The arrangement of the system leads to road loads and/or engine vibrations being transferred and causing damage to its components. New BS VI engines need some AT (After treatment) components to be mounted directly on the engine and others to chassis. The components that are directly mounted on engine are called close couple AT system which are subjected to engine harmonic vibrations which falls under forced vibration criteria. Most of the AT system are subjected to random vibrations and industry has a well-defined procedure to address the problem, but for harmonic vibrations there is no specific approach. In order to optimize the structural durability of close couple AT system against HCF (high cycle fatigue) fatigue harmonic vibration, there is a need for well-defined test analysis correlation procedure. The objective of this work is defining and documenting a robust process for design margin through calculation modal scaling and harmonic analysis of close couple AT system through test analysis correlation activity. Analytical, numerical and testing data were compared and conclusions are drawn. More case studies can be added to this work in order to validate the test analysis correlation activity and boost the degree of confidence. Future study may include recording additional failure modes in addition to the harmonic HCF failure mode.

Guidelines to use input contact parameters for nonlinear dynamic analysis of jointed structures: Results of a round robin test

Turbomachinery and other jointed structures are carefully designed to optimise their dynamic response and prevent unwanted high-cycle fatigue failures due to vibration. Advanced numerical models are employed to predict the often nonlinear dynamic responses, but their reliability is partially limited by the lack of understanding of the friction mechanisms between the vibrating contact interfaces. Although several high-frequency friction rigs have been developed at different institutions to measure contact parameters such as friction coefficient and contact stiffness, a lack of direct comparisons prevents a throughout understanding. To address this issue, a comparison of these contact parameters has been performed by employing the high-frequency friction rigs of Imperial College London and Politecnico di Torino. A test plan was designed to cover a wide experimental space by testing the friction rigs to their limits and measuring hysteresis loops under a range of normal loads and displacement amplitudes at room temperature. Measurements from the two very different experimental setups are compared, showing a good level of agreement for the friction coefficient, but also highlighting some differences, especially for the contact stiffness. New insights are provided into the physics of these contact parameters and specific guidelines are given to improve contact models used for nonlinear dynamic analysis.

Dynamic Stress Test of Aero-engine Compressor Rotor Blade

To evaluate the effect of the compressor rotor blade on compressor blade fatigue, a non-contact dynamic stress measurement scheme of one aero-engine eighth stage compressor rotor blade was designed, and the dynamic stress test was carried out. Meanwhile, modal analysis of the eighth stage compressor rotor blade was done by finite element analysis software. Results show that between the range of the idle speed and the highest speed, there is no resonance for the eighth stage compressor rotor blade and the maximum vibration amplitude is less than 65 μm, which cannot result in high cycle fatigue failure.

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.

Cyclic elastoplasticity and XFEM based fatigue life assessment of out-of-plane gusset welded joints

Conventional design methods for high-cycle fatigue failure of engineering components often assume a linear-elastic material behaviour. The different driving forces of crack initiation and propagation fail to be considered, resulting in less accurate predictions of fatigue life. To address this issue, the present study proposes a novel method to predict the fatigue life of out-of-plane gusset welded joints based on cyclic elastoplasticity and extended finite element method (XFEM). Incorporating the welding residual stress simulated by thermal–mechanical analysis, the cyclic stress–strain response of out-of-plane gusset welded joints was assessed by Fatigue SS (FSS) constitutive model. The crack initiation life was therefore predicted by the local strain approach considering the mean stress correction. Based on the converged cyclic stress–strain response, the crack propagation behaviour and life were predicted by XFEM in combination with Virtual Crack Closure Technique (VCCT). The influence of mean stress, mixed-mode crack and residual stress on crack initiation and propagation life was also investigated. The results show that the proposed method can predict the fatigue life of out-of-plane gusset welded joints under the pure tension loading with high accuracy against experimental results.

A two-level machine learning approach for predicting thermal striping in T-junctions with upstream elbow

Thermal striping is a phenomenon characterized by oscillatory mixing of non-isothermal streams, which is commonly seen in industrial processes such as nuclear coolant piping, petrochemical plants and liquefied natural gas transportation. The oscillatory mixing of hot and cold fluid can produce thermal field fluctuations and pose a potential risk of high-cycle thermal fatigue failures. Predicting and evaluating spatiotemporal fluctuations in thermal striping often requires high resolution and massive computational power. Although there have been extensive studies using machine learning algorithms on surrogate modeling, research focused on spatiotemporal fluctuation predictions is very limited. Due to the high dimensionality, it often requires complex algorithms with a large amount of high-fidelity training data, which limits the adoption of such methods for industrial applications. In this research, a two-level machine learning framework based on turbulence coherent structures is proposed and its application to a practical problem is demonstrated. The two-level design leverages vortex identification and local bias correction techniques, efficiently reducing the number of full-order simulations required for training. In the first level, well-organized coherent structures are extracted by performing Proper Orthogonal Decomposition on local parameters and then a tree-based machine-learning model is used to down-select the reference structures for the field reconstruction. In the second level, a parameterized convolution neural network is trained to predict the bias introduced by reference structures approximation. The demonstration of the methodology shows that the method can accurately capture the fluctuation frequencies and amplitudes of the spatiotemporal fields in a highly variational setting. Based on the vortex identification method, the methodology is expected to be applicable to general phenomenon driven by large coherent structures.

Simulation study of crack parameters’ effects on the vibration characteristics of a bladed disk system

As a key component of the turbo machine rotor in harsh operating conditions, high cycle fatigue failure and even cracks are common in bladed disks. In this paper, modal analysis was carried out for a single cracked bladed disk system, the effects of crack depth, crack height and rotating speed on its vibration characteristics were studied by the method of both numerical simulation and orthogonal test, and the effects of crack distribution on the vibration characteristics of multi-crack bladed disk systems were also studied. Finally, some conclusions have been drawn, they provide a fundamental understanding of blade health monitoring and fault prediction, and are important to improve the reliability and safety of turbine operation.

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.

Fatigue failure criterion of materials with static constitutive curve as the limit value

The fatigue failure problem actually can be explained by fatigue stress–strain envelope, and the fatigue evaluation based on fatigue stress–strain can avoid the uncertainty of selecting fatigue criteria in engineering applications. However, the application of experimental fatigue envelope criterion based on stress–strain curve is limited to concrete and rocks, and it also can not predict the fatigue failure time. To further develop the availability of fatigue stress–strain envelope criterion, the fatigue failure criterion of materials with static constitutive curve as the limit value is proposed to describe high-cycle and low-cycle fatigue failure through theoretical deduction of classic fatigue criteria and analysis of experimental results. The proposed criterion reveals the constraints mechanism that the fatigue life is dominated by fatigue failure stress–strain in the fatigue envelope surface. Finally, the comparison between calculated and experimental fatigue life indicates that the proposed criterion is suitable to.describe the fatigue failure well and has the comprehensive application prospect.