High Cycle Fatigue Life Research Articles

Fatigue Life Assessment of KC-1 Membrane Considering the Effects of Cryogenic Temperature and Plastic Deformation

In this study, fatigue life assessment was conducted on a KC-1 membrane, considering cryogenic operation temperature, effect of stamping, and very long service period. KC-1 membranes are produced through a process of stamping, and they make direct contact with LNG filled within a containment system at − 162 °C. The high waves that LNG carriers encounter during sailing, and even when at anchor, cause rolling motions of the hull, which result in resonant fluid motions that generate a sloshing phenomenon; such sloshing motions expose containment systems to a high level of repeated stress. To assess the very high cycle fatigue (VHCF) life of the membrane, the effects of plastic deformation and the mechanical properties of STS304L, a membrane material, were examined at cryogenic temperatures. To identify the effects of plastic deformation and cryogenic temperatures on their mechanical properties, tensile and VHCF tests were conducted at cryogenic temperatures on a sheet to which plastic strain was applied through cold-rolling. Through forming analysis, changes in the thickness and plastic strain of a membrane caused during the process of stamping were examined. The results of earlier studies that performed flow analysis and fluid–structure interaction analysis to measure the stress applied to each component of the KC-1 containment system were cited, and the VHCF life of the membrane was assessed based on the surveyed mechanical properties, and the results of forming analysis.

High cycle fatigue behavior and life prediction for additively manufactured 17-4 PH stainless steel: Effect of sub-surface porosity and surface roughness

The high potential of additive manufacturing (AM) techniques offers novel opportunities and unexplored design freedom. However, typical internal defects and poor surface quality inherent to AM process not only cause a lower fatigue resistance, but also more scatter in fatigue data; thus, hindering adoption of AM to fatigue critical applications. This study investigates the effect of surface quality and sub-surface porosity on high cycle fatigue behavior of 17-4 precipitation hardening (PH) stainless steel (SS) fabricated using laser beam powder bed fusion (LB-PBF) process. Parts were fabricated in three conditions: net-shape (NS) specimens, oversized specimens, and cylindrical rods. The oversized specimens and cylindrical rods were, respectively, further shallow machined (SM) and deep machined (DM) to the dimensions and geometry of net-shape specimens. The population of defects was investigated via optical microscopy of polished sections, X-ray micro-CT scan analysis, and fractography of fracture surfaces after fatigue tests. The fatigue crack growth (FCG) properties were generated at three stress ratios of R=-1,0.1,0.7 to determine the Kitagawa-Takahashi diagram and propagation curve. The polished sections showed the presence of large sub-surface, close-to-surface pores in the NS specimens, while SM and DM conditions had smaller and more uniformly distributed porosity. Critical defects detected on the fracture surfaces were small pores in machined specimens, and relatively large surface irregularities in NS specimens. Machining process, both in SM and DM conditions, enhanced the fatigue performance of the material as compared to that of NS condition. However, in terms of level of machining allowance, no further enhancement in fatigue performance was observed for DM specimens as compared to that of SM ones. Fatigue assessment for both net-shape and machined conditions was obtained performing FCG simulations based on the typical surface features and volumetric defects. Simulation results yielded correct estimates for both net-shape and machined specimens.

Rethinking scaling laws in the high-cycle fatigue response of nanostructured and coarse-grained metals

The high-cycle fatigue life of nanocrystalline and ultrafine-grained Ni-Fe was examined for five distinct grain sizes ranging from approximately 50–600 nm. The fatigue properties were strongly dependent on grain size, with the endurance limit changing by a factor of 4 over this narrow range of grain size. The dataset suggests a breakdown in fatigue improvement for the smallest grain sizes <100 nm, likely associated with a transition to grain coarsening as a dominant rate-limiting mechanism. The dataset also is used to explore fatigue prediction from monotonic tensile properties, suggesting that a characteristic flow strength is more meaningful than the widely-utilized ultimate tensile strength.

Quantitative relationship between microstructural factors and fatigue life of Ti-5Al-2Sn-2Zr-4Cr-4 Mo (Ti-17) fabricated using a 1500-ton forging simulator

The microstructures, tensile properties, and fatigue lives of the forged Ti-17 using a 1500-ton forging simulator subjected to different solution treatments and a common aging treatment under both load- and strain-controlled conditions to evaluate high cycle fatigue and low cycle fatigue lives, respectively were examined. Then, the tensile properties, microstructures, and relationships between fatigue lives and the microstructural factors were discussed. The fatigue limit under load-controlled conditions increases with increasing solution treatment temperature up to 1143 K, which is in the (α + β) region. However, it decreases with further increase in the solution treatment temperature to 1203 K in the b region. The fatigue ratio at fatigue limit is increasing with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase, and it relates well qualitatively with the volume fraction of the primary α phase when the solution treatment temperature is less than the b transus temperature. The fatigue life under strain-controlled conditions to evaluate the low cycle fatigue life increases with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase. The fatigue life under strain-controlled conditions to evaluate the low cycle fatigue life relates well quantitatively with the tensile true strain at breaking of the specimen and the volume fraction of the primary α phase for each total strain range.

A rotating gear test methodology for evaluation of high-cycle tooth bending fatigue lives under fully reversed and fully released loading conditions

Gear bending fatigue life is a primary consideration in gear design. Each gear tooth is subjected to cyclic root stresses that may cause fatigue fracture. A gear in a transmission is subjected to either fully released or fully reversed loading conditions, with different fatigue lives. This study develops an experimental methodology for evaluation of high-cycle tooth bending fatigue lives of gears under both loading conditions. Unique specimens for tooth bending fatigue and an adaptive diagnostics method for test termination are designed while root strains under high-speed conditions are quantified. Example fatigue tests are presented to demonstrate the effectiveness of the proposed methodology.

Effects of the γ″-Ni3Nb Phase on Fatigue Behavior of Nickel-Based 718 Superalloys with Different Heat Treatments.

The effects of the γ″-Ni3Nb phase on fatigue behavior of nickel-based 718 superalloys with standard heat treatment, hot isostatic pressing + solution treatment + aging, and hot isostatic pressing + direct aging were investigated by scanning electron microscope, transmission electron microscopy, and fatigue experiments. The standard heat treatment, hot isostatic pressing + solution treatment + aging, and hot isostatic pressing + direct aging resulted in the formation of more and smaller γ″ phases in the matrix in the nickel-based 718 superalloys. However, the grain boundaries of the hot isostatic pressing + direct aging sample showed many relatively coarse disk-like γ″ phases with major axes of ~80 nm and minor axes of ~40 nm. The hot isostatic pressing + direct aging sample with a stress amplitude of 380 MPa showed the longest high cycle fatigue life of 5.16 × 105 cycles. Laves phases and carbide inclusions were observed in the crack initiation zone, and the cracks propagated along the acicular δ phases in the nickel-based 718 superalloys. The precipitation of fine γ″ phases in the matrix and relatively coarse γ″ phases in the grain boundaries of the hot isostatic pressing + direct aging sample can hinder the movement of dislocation.

Generalized 3D high cycle fatigue criteria for multiscale bridging‐based progressive damage analysis of multilayer composite parts under random loads and material deterioration

AbstractTwo frameworks are employed to develop two distinct categories of multiaxial high cycle fatigue life assessment models for composite components experiencing general and random loading conditions. In this regard, the decay in the material properties with cycles is also taken into account. It is obvious that in multilayer components, the fatigue failure is a progressive process that may be accompanied by gradual or sudden changes in the material properties and, consequently, the resulting stresses. In addition to using the traditional progressive damage analyses, a new concept is proposed for tracing of the localized fatigue failures more accurately. It is postulated that generally, the stress components have distinct frequencies, phase shifts, and mean values that all vary with time in a random manner. The proposed fatigue criteria, especially, the equivalent‐stress–based ones, are capable of predicting various fatigue failure modes, such as the fibre breakage, matrix cracking, and interfacial debonding. A special and comprehensive fatigue failure tracking and cycle counting algorithms that are capable of handling the mentioned general peculiarities are proposed. The proposed HCF criteria and the relevant fatigue life assessment algorithm are then implemented on a composite multilayer mono‐leaf spring of a realistic vehicle under a random field‐measured loading condition, as a typical component, and the results are compared and the experimental results conducted by the authors, for accuracy investigations. The considered stochastic road inputs have been chosen on the basis of the consumption times and field measurements.

Mechanism of residual stress and surface roughness of substrate on fatigue behavior of micro-arc oxidation coated AA7075-T6 alloy

The micro-arc oxidation (MAO) coatings were produced on AA7075-T6 alloy with a surface roughness (Ra) of 0.2, 0.8, and 1.6. The effects of the Ra of substrates on the morphologies of MAO coating and fatigue behavior of the coated samples were investigated. The structural characteristics of the MAO coating were analyzed by X-ray diffraction, scanning electron microscopy, and laser scanning confocal microscopy. Moreover, the residual stress in the oxide films was measured using an X-ray stress tester. The surface and cross-section analyses of the coatings revealed the mechanism of the oxide layer growth. The phase composition and the mechanism of residual stress were further investigated according to the heat transfer in the MAO process. The relationship between the nature of residual stress in MAO coating and the surface porosity as well as the temperature of the substrate and the coating was revealed. The fatigue test results showed a significant effect of the Ra of the substrate on the high cycle fatigue life at low cyclic stress levels. The residual stress relaxation attributed to the insignificant changes in the fatigue life of the coated samples with Ra = 0.2, 0.8, and 1.6 at high cyclic stress levels. Besides, the mechanism of the residual stress affecting the fatigue performance was explored.

Residual stress relaxation and duty cycle on high cycle fatigue life of micro-arc oxidation coated AA7075-T6 alloy

Ceramic coatings were produced on AA7075-T6 alloy by micro-arc oxidation (MAO). The MAO treatment was performed at different duty cycles (8, 10, 15, and 20%). Effects of duty cycle on microstructure and fatigue behavior of the coated samples were investigated. Surface features and cross-section morphology, and fatigue fracture were observed by SEM and laser microscope. Phase structure and residual stress in the coatings were analyzed by X-ray diffraction. The nature and relaxation mechanism of the residual stress were revealed. Finally, the influence of the residual stress relaxation on the fatigue life at high and low cyclic stresses was explored.

A high-performance multiscale space-time approach to high cycle fatigue simulation based on hybrid CPU/GPU computing

A multiscale space/time computational framework for high cycle fatigue (HCF) life predictions is established by integrating the extended space-time finite element method (XTFEM) with a multiscale progressive damage model. While the robustness of the multiscale space/time method has been previously demonstrated, the associated high computational cost remains a critical barrier for practical applications. In this work, a novel hybrid iterative/direct linear system solver is first proposed with a unique preconditioner. Computational efficiency is further improved by taking advantage of the high-performance computing platform featuring hierarchy of the distributed- and the shared-memory parallelisms using CPUs and GPUs. Robustness of the accelerated framework is demonstrated through benchmark problems. It is shown that the serial version of the hybrid solver is at least 1–2 orders of magnitude faster in computing time and cheaper in memory consumption than the conventional sparse direct or iterative solver, while the parallel version efficiently handles XTFEM stiffness matrix equations with over 100 million unknowns using 64 CPU cores. Optimal speedups are achieved in the parallel implementations of the multiscale progressive damage model using either CPUs or GPUs. HCF simulations on 3D specimens are performed to quantify key effects due to mean stress and multiaxial load conditions.

Effects of process combinations of milling, grinding, and polishing on the surface integrity and fatigue life of GH4169 components

The nickel-based superalloy GH4169 is widely applied in the aviation industry due to its outstanding mechanical properties. However, many blades of GH4169 are still produced by milling and manual polishing, which is costly and unreliable. In this article, GH4169 superalloy components manufactured with combination processes of milling, grinding, and polishing were comparatively studied involving surface integrity and fatigue performance. Test results indicate that the final polishing is the most dominant process that influences the high-cycle fatigue life of GH4169 components. Samples produced via cubic boron nitride grinding and numerical control polishing with a diamond-rubber wheel exhibit fatigue limits of 150 MPa higher than the milled and manually polished samples. Cubic boron nitride grinding induces a considerable compressive residual stress profile with a magnitude of -930 MPa and a depth of 200 μm. Milling induces a typical “hook” residual stress profile with 318 MPa at the surface. Polishing affects the machined surface by two ways, the removal effect and the squeezing effect. The squeezing effect induces a shallow compressive residual stress with approximately −1000 MPa, therefore improves the surface condition. However, inevitable omissions, scratches, texture disorders, and knock marks in hand-polishing are the main causes of the unstable high-cycle fatigue life of hand-polished components.

High cycle fatigue life prediction of laser additive manufactured stainless steel: A machine learning approach

Variations in the high cycle fatigue response of laser powder bed fusion materials can be caused by the choice of processing and post-processing strategies. The numerous influencing factors arising from the process demand an effective and unified approach to fatigue property assessment. This work examines the use of a neuro-fuzzy-based machine learning method for predicting the high cycle fatigue life of laser powder bed fusion stainless steel 316L. A dataset, consisting of fatigue life data for samples subjected to varying processing conditions (laser power, scan speed and layer thickness), post-processing treatments (annealing and hot isostatic pressing) and cyclic stresses, was constructed for simulating a complex nonlinear input-output environment. The associated fracture mechanisms, including the modes of crack initiation and deformation, were characterised. Two models, by employing the processing/post-processing parameters and the static tensile properties respectively as the inputs, were developed from the training data. Despite the diverse fatigue and fracture properties, the models demonstrated good prediction accuracy when checked against the test data, and the computationally-derived fuzzy rules agree well with understanding of the fracture mechanisms. Direct application of the model to literature results, however, yielded a range of prediction accuracies because of the variability in the reported data. Retraining the model by incorporating the literature results into the dataset led to improved modelling performance.

Effects of thermal exposure on high-cycle-fatigue behaviours in Ni-based superalloy GH4169

ABSTRACTEffects of thermal exposure (TE) on high cycle fatigue (HCF) behaviours in Ni-based superalloy GH4169 have been investigated in this study. GH4169 specimens were thermally exposed at 650°C for 1, 2, 7, 14 and 21 days before fatigue test. These TEs produced eruptions, bulge-like features and pits at surface due to oxidation of carbides/nitrides. Fatigue life was not reduced evidently by TE as compared to the specimens in virgin conditions, indicating the insignificant influence of TE on HCF life. Fracture morphology analysis showed fatigue crack mainly initiated from oxides, crystallographic facets and subsurface inclusions. Although long TE is not necessarily related to crack initiation from oxides, crack initiation from oxides is generally associated with a shorter fatigue life.

Mechanisms driving high-cycle fatigue life of as-built Inconel 718 processed by laser powder bed fusion

This study investigates the relationships among the high-cycle fatigue life, surface roughness, and additive manufacturing processing parameters in laser powder bed fusion Inconel 718 in the as-built condition. Standardized fatigue specimens were manufactured using 25 different sets of processing parameters by varying laser power, scan speed, layer thickness, and build orientation, with three repeat specimens per parameter set. Surface roughness measurements were conducted using white light interferometry; high-cycle fatigue life was measured; and fractography analysis was performed using scanning electron microscopy. Two processing-parameter metrics were observed to dominate high-cycle fatigue life: build orientation and laser-energy density. Build orientation affected fatigue life due to the relationship between build orientation and surface roughness. Increasing surface roughness decreased the fatigue life due to increasing number of surface-crack initiation sites. For a fixed build orientation, the laser-energy density, outside of the optimal range, decreased the fatigue life due to sub-surface defects. Specifically, fractography analysis showed that sub-surface defects consisted of lack-of-fusion pores at low laser-energy densities and secondary cracking and pores (possibly related to keyholing) at high laser-energy densities. While variability in residual stresses among the specimens could also play a role, this work focuses on geometrical surface and sub-surface defects caused by different processing parameters and their corresponding impact on total fatigue life. Based on these findings, guidelines are offered to improve fatigue life of additively manufactured Inconel 718 in the as-built, non-heat-treated condition.

Enhanced fatigue performance of modified plasma electrolytic oxidation coated Ti-6Al-4V alloy: Effect of residual stress and gradient nanostructure

Abstract Plasma electrolytic oxidation (PEO) has a negative effect on the fatigue performance of titanium alloys. To reduce/eliminate this influence, the effect of an ultrasonic surface rolling process (USRP)-induced compressive residual stress and gradient nanostructure on the PEO coating growth and fatigue behavior of a PEO-coated Ti-6Al-4V alloy was investigated. The PEO process yielded a severe decrease in the fatigue life of the substrate. Owing to the USRP pretreatment, the low cycle fatigue life and high cycle fatigue life of the PEO-coated sample improved to similar values and considerably higher values, respectively, compared with those of the substrate. This is attributed to the synergistic effect of the gradient nanostructure and compressive residual stress, which retarded crack initiation and propagation, although the residual stress played the major role in the aforementioned improvement. Additionally, the nanostructure promoted nucleation and growth of the PEO coating, as surface nanocrystallization improves the chemical activity of the titanium alloy surface. The PEO treatment influenced the residual stress mainly at the top surface of the substrate, but had almost no influence on the stress distributed in the interior.

Effect of shot peening on fatigue performance of Ti2AlNb intermetallic alloy

The effect of shot peening on Ti2AlNb fatigue performance was investigated. Glass fine shot peening was used and residual stresses were measured by XRD technology and electropolishing method. Rotating bending fatigue test was performed. The results show compressive residual stress is introduced and the maximum is 322 MPa, and fatigue property is significantly improved. The high cycle fatigue life is prolonged more than 25 times and fatigue endurance limit is increased from 170 MPa to 360 MPa. Moreover, fatigue cracks initiate beneath surface enhanced layer for SP specimens, while for referenced specimens they are located at surface.

A rate independent inelasticity model with smooth transition for unifying low-cycle to high-cycle fatigue life prediction

A three-dimensional rate independent inelastic constitutive model has been developed to predict the fatigue behavior of metals spanning low to high cycles, based solely on the monotonic stress strain curve and a cyclic test for a few cycles ( < 1000). The key to the development of the model is that the “microplastic response” before full yield is accounted for by a new approach to inelastic modeling while retaining a rate independent response. A numerical algorithm based on the one-dimensional version of the constitutive theory has also been implemented into a computer code to model fatigue loading under simple tension/compression i.e. uniaxial loading conditions. The material parameters in the constitutive model were calibrated through fitting the constitutive model to the monotonic stress–strain curve obtained from a simple compression test experiment. By adopting the total inelastic work dissipation (which is related to the configurational entropy created due to damage) as the failure criteria and integrating the rate of entropy generation (under isothermal conditions) over a typical stabilized hysteresis cycle (including the small scale effects due to microplasticity), a close-formed expression for stress-fatigue life prediction is also derived for zero mean stress. Finally, it is shown that the model and numerical algorithm are able to predict the experimental stress-life and strain-life (with and without mean stress) responses quite well.

Combined high and low cycle fatigue life prediction model based on damage mechanics and its application in determining the aluminized location of turbine blade

A new combined high and low cycle fatigue (CCF) life prediction model based on the damage mechanics theory is proposed in this paper. The model parameters are fitted based on the material data and blade data respectively. Verification tests are carried out to evaluate predicted results in combination with the experimental data. Results illustrate that the new model based on the blade data can predict the blade life with relatively higher accuracy (within 2.2 times of scatter band), which is much better than that based on the material data (within 178.2 times of scatter band). Afterward, in comparison with typical existing models, the newly proposed model can predict the turbine blade life more accurately. What’s more, based on the newly proposed model, a novel determination method for permitted aluminized location in the turbine blade is put forward. Then, combined with aluminized blade tests, correlated model parameters are determined and the permitted aluminized location distribution is given by using the novel method. The presented life model and the determination method may have a great value for potential engineering applications.

Investigation on very high cycle fatigue of PA66-GF30 GFRP based on fiber orientation

The purpose of this study is to evaluate the effects of glass fiber (GF) of PA66-GF30 orientation on very high cycle fatigue (HVCF) life and also to develop an optimized test apparatus such as measurement of dynamic elastic modulus and design of test specimens. Dynamic elastic modulus, tensile strength and fatigue strength tests were conducted at room temperature based on GF orientation (0°, 45°, 90°). Conventional fatigue (3 Hz) and ultrasonic fatigue (20 kHz) tests were performed at the same stress ratio (R = −1). Fracture surface observation showed that GF 0° exhibited a higher fatigue strength in comparison with GF 45 and 90°. Various defects such as voids and microcracks to the load direction around the GF end or debonding in glass fiber reinforced plastic (GFRP) and the slope change in very long life regime of S–N diagram.

Influence of pre-straining path on high cycle fatigue performance of DP 600 steel

An evaluation of tensile and fatigue performances of dual phase steel subjected to change in the pre-strain path are presented in this work. Initially material is loaded up to a certain amount of pre-strain in the rolling or transverse direction, and after that specimen for tensile and fatigue tests are fabricated in the parallel or orthogonal to the pre-straining directions. Irrespective of pre-straining direction, all the pre-strained specimens show an increase in yield stress and simultaneous reduction in uniform elongation of the material, as well as improvement of high cycle fatigue life. The material exhibits better fatigue resistance for those specimens where fatigue testing is done orthogonal to the initial pre-straining direction.