CERES :: Browsing by Author "Castelluccio, Gustavo M."

Browsing by Author "Castelluccio, Gustavo M."

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Open Access
Abnormal grain growth in ultrafine grained Ni under high-cycle loading
(Elsevier, 2022-03-01) Barrios, Alejandro; Zhang, Yin; Maeder, Xavier; Castelluccio, Gustavo M.; Pierron, Olivier; Zhu, Ting
Abnormal grain growth can occur in polycrystalline materials with only a fraction of grains growing drastically to consume other grains. Here we report abnormal grain growth in ultrafine grained metal in a rarely explored high-cycle loading regime at ambient temperature. Abnormal grain growth is observed in electroplated Ni microbeams with average initial grain sizes less than 640 nm under a large number of loading cycles (up to 109) with low strain amplitudes (< 0.3%). Such abnormal grain growth occurs predominantly in the family of grains whose <100> orientation is along the tensile/compressive loading direction. Micromechanics analysis suggests that the elastic anisotropy of grains dictates the thermodynamic driving force of abnormal grain growth, such that the lowest strain energy density of the <100> oriented grain family dominates grain growth. This work unveils a unique type of abnormal grain growth that may be harnessed to tailor grain microstructures in materials.
Open Access
Advancing the synergy between models and experiments to investigate environmentally and mechanically driven crack propagation
(Cranfield University, 2023-09) Elsherkisi, Mustafa; Castelluccio, Gustavo M.; Gray, Simon
Aero-gas turbine running temperatures are rapidly increasing in order to improve their efficiency, and as a consequence components are subjected to more extreme environ- ments. With higher operational temperatures and improved reliability, there is an in- creased chance of both corrosion and mechanical degradation. In addition to operational temperatures, the environment in which an aircraft flies has a significant effect on the material life. Many contaminants are ingested by the engine and deposited on the turbine blades, which often leads to surface degradation. Depending on the ingested contami- nants, temperature, and applied stresses, cracking can be initiated and propagated rapidly. This is particularly evident in the lower-shank regions of single-crystal nickel-based su- peralloy blades, which have recently experienced significant cracking. This study aims to understand the mechanisms behind crack propagation in single- crystal nickel alloys exposed to intermediate temperatures, and when this propagation is either mechanically or chemically driven. This research started by assessing crack inter- action mechanisms that were hypothesised to be both stagnating and accelerating crack growth, depending on specific length scales and crack formations. This was performed by integrating available experimental data to calibrate a phase field model that could predict the extension of cracks for different crack separations and layouts. The modelling results clearly characterised the length scales needed to encourage crack shielding, and which crack formations would see a stress intensification and consequently crack coalescence. These results informed the decision to revisit the experimental setup to optimise which experiments were performed. Using this newly developed methodology, the salt deposi- tion method was amended with the aim of isolating the deposition sites to minimise crack interaction mechanisms. The hypothesis was that significantly longer cracks would be ob- ii served if this could be achieved. This was performed for both the C-ring (at 550°C), and corrosion-fatigue (at 700°C) tests. In the case of CMSX-4, the results were striking, with the C-ring seeing cracks as much as ten times the size of those previously seen. CMSX-10 however, did not show a significant difference, as such, a microstructural characterisation analysis was conducted, whereby the γ/γ′ structure for the two alloys was replicated from microscopy data and further phase field models were run. The results showed that a more regular structure was more resistant to crack propagation owing to the misalignment of γ′ , which caused stress relaxation in the γ channel and at the interface. Finally, this thesis shows how the model, once calibrated for one material and species, can be used to approximate the response expected for another single-crystal nickel alloy or a change in the embrittling species, while accounting for a degree of uncertainty. This is not to say that modelling can or should replace experiments but rather to highlight that preliminary modelling results can be used to build a test matrix that can reduce the number of experiments that are run. It should be noted that this thesis does not focus on the chemical/corrosive aspects in much detail, but rather investigates the importance of stress. This thesis summarises the importance of integrating modelling, microscopy, and experiments to set and answer hypotheses more efficiently.
Open Access
Analytical fatigue life formulation for notches informed by crystal plasticity
(Elsevier, 2022-06-17) Ashraf, Farhan; Cini, Andrea; Castelluccio, Gustavo M.
Damage from small manufacturing defects often go unnoticed until fatigue cracks have grown beyond repairability. These cracks initiate at defects with dimensions on par with the microstructure length scale (e.g., 5–200 µm deep), which affects fatigue variability and renders most engineering prognosis methods inapplicable. This work develops a novel microstructure-sensitive formulation that reduces computational efforts by decoupling geometric and microstructural contributions to fatigue cracking. Crystal plasticity finite element models with and without geometry induced strain gradients were considered to assess the role of defects independently from the microstructure. The analysis results in a fatigue life analytical formulation whose parameters depend on the microstructure and defect morphology.
Open Access
Assessment of fatigue crack initiation after overloads with substructure-sensitive crystal plasticity
(Elsevier, 2025-09) Dindarlou, Shahram; Castelluccio, Gustavo M.
Microstructure-sensitive fatigue initiation prognosis approaches typically assume uniform periodic loading and often overlook in-service overloads, which increase uncertainty and reduce life prediction accuracy. Similarly, certification efforts rarely evaluate experimentally the impact of different overloads due to the prohibitive costs. Therefore, predictive models that estimate overload effects on fatigue initiation damage without extensive experimental data are valuable to improve prognosis approaches. However, the literature lacks microstructure-sensitive approaches capable of assessing overload effects with models that simultaneously predict monotonic and cyclic responses without recalibration. This work presents a novel strategy to predict the effects of overloads on early cyclic damage by evaluating the refinement dislocation structures. A substructure-based crystal plasticity approach relies on independent parameterizations from monotonic and cyclic loading to predict overload responses, without requiring additional experiments. The model agreement with macroscale experiments was further validated by comparing dominant mesoscale structures after overloads in single- and poly-crystals for metals and alloys. The analysis also identified overload-resistant crystal orientations and demonstrated that overloads increase the likelihood of initiating fatigue cracks in low apparent Schmid factor grains under low-amplitude fatigue. We conclude by discussing the value of material-invariant mesoscale parameters to rank overloads effect for materials and loading conditions for which no experiments are available.
Open Access
Comparison of the low and high/very high cycle fatigue behaviors in Ni microbeams under bending
(Springer, 2021-02-16) Barrios, Alejandro; Kakandar, Ebiakpo; Castelluccio, Gustavo M.; Pierron, Olivier N.
The present work demonstrates a micromechanical technique to investigate the low cycle fatigue (LCF) behavior of Ni microbeams under fully reversed bending loadings. The technique extends the range of measured fatigue lives from the previously reported technique for high and very high cycle fatigue (HCF/VHCF) characterization in the same microbeams. The results highlight significant differences in the slope of stress and strain-life behavior and crack propagation rates that differ from an average of 10–12 m/cycle in HCF/VHCF to an average of 10–8 m/cycle in LCF. These results, in addition to postmortem fractography work, suggest that the mechanisms follow the conventional mechanisms of crack tip stress intensification in the LCF regime. This is in stark contrast to the void-controlled mechanisms that were previously identified in the HCF/VHCF regime. These results demonstrate that the transition in governing mechanisms from void-controlled to conventional mechanisms is highly influenced by the size effects present in the microbeams.
Open Access
A computational and experimental comparison on the nucleation of fatigue cracks in statistical volume elements
(Elsevier, 2020-04-05) Kakandar, Ebiakpo; Barrios, Alejandro; Michler, Johann; Maeder, Xavier; Pierron, Olivier N.; Castelluccio, Gustavo M.
The failure of micron-scale metallic components presents significant variability as a result of their size being comparable to microstructural length scales. Indeed, these components do not represent the bulk of the material but correspond to statistical volume elements (SVEs). This work investigates the role of SVEs on fatigue crack nucleation with a novel comparison between microbeam experiments and microstructure-sensitive simulations. We recreate multiple microstructural computational realizations to estimate fatigue crack nucleation lives and orientations by means of physics-based crystal plasticity models. We demonstrate a unique approach to validate microstructure sensitive models and quantify the fatigue crack stochasticity associated with small volumes.
Open Access
Computational and experimental study of crack initiation in statistical volume elements
(EDP Sciences, 2019-12-02) Kakandar, Ebiakpo; Castelluccio, Gustavo M.; Barrios, Alejandro; Pierron, Olivier; Maeder, Xavier
Fatigue crack formation and early growth is significantly influenced by microstructural attributes such as grain size and morphology. Although the crystallographic orientation is a primary indicator for fatigue cracking, the neighbourhood conformed by the first and second neighbour grains strongly affect the fatigue cracking driving force. Hence, two identical grains may result in different fatigue responses due to their interactions with their microstructural ensemble, which determines the fatigue variability. Naturally, macroscopic samples with millions of grains and thousands of competing microstructural neighbourhoods can effectively resemble a representative volume element in which fatigue failure may seem deterministic. However, when considering systems in which fatigue failure is controlled by hundreds or less of grains, fatigue failure is stochastic in nature and the samples are not a representative but a statistical volume. This work studies fatigue crack nucleation in micron-scale Ni beams that contain a few hundred grains. This work presents 3D crystal plasticity finite element models to compute stochastic distribution of fatigue indicator parameters that serve as proxies for crack nucleation in statistical volume elements. The integration of experiments with models provides a method to understand the irreversible deformation at the grain level that leads to fatigue cracking. Our results explain the role of grain morphology of crack nucleation distribution
Open Access
Crack tip microplasticity mediated by microstructure gradients
(Wiley, 2021-06-14) Castelluccio, Gustavo M.; Lim, Hojun; Emery, John M.; Battaile, Corbett C.
Traditional fracture theories infer damage at cracks (local field) by surveying loading conditions away from cracks (far field). This approach has been successful in predicting ductile fracture, but it normally assumes isotropic and homogeneous materials. However, myriads of manufacturing procedures induce heterogeneous microstructural gradients that can affect the accuracy of traditional fracture models. This work presents a microstructure-sensitive finite element approach to explore the shielding effects of grain size and crystallographic orientation gradients on crack tip microplasticity and blunting. A dislocation density-based crystal plasticity model conveys texture evolution, grain size effects, and directional hardening by computing the constraint from dislocation structures. The results demonstrate that the microstructure can act as a buffer between the local and far fields that affects the crack tip microplasticity variability. For nominal opening loading, grain size and texture affect the local ductility and induce a non-negligible multiaxial plastic deformation. Furthermore, driving forces based on measuring displacements away from the crack tip are less affected by the microstructure, which suggests that traditional experimental methods smear out important crack tip variability.
Open Access
Designing nickel coatings for water erosion performance: optimisation of grain size and thickness
(Elsevier, 2025-06-15) Gaddavalasa, Nithin Chandra; Lodh, Arijit; Cini, Andrea; Saaran, Vinodhen; Mehmanparast, Ali; Starr, Andrew; Castelluccio, Gustavo M.
Metallic coatings are gaining interest as an alternative to classical polymeric layers for erosion damage prevention due to their extended durability and sustainability. However, their implementation requires a thorough understanding of protective potential and reliability. This study explores the use of brush-plated nickel coatings on carbon-fibre reinforced composites to enhance their performance against water erosion. A combination of experimental analysis and computational modeling explores the effect of different coating thickness and properties to withstand water droplet erosion damage. Findings reveal a minimum critical coating thickness around 40 μ m can significantly improve the erosion resistance.
Open Access
Effect of NaCl and SO2 on the stress corrosion cracking of CMSX-4 at 550°C
(Taylor and Francis, 2023-05-01) Duarte Martinez, Fabian; Syed, Adnan; Dawson, Karl; Tatlock, G. J.; Morar, N. I.; Kothari, M.; Tang, C.; Leggett, J.; Mason-Flucke, J. C.; Gibson, G.; Nicholls, John R.; Gray, Simon; Castelluccio, Gustavo M.
In the pursuit of more efficient gas turbine engines, components are required to operate for longer times at elevated temperatures. This increased time in service, together with a complex loading regime, can expose the material to environmental attack. This work has demonstrated that the interaction of stress, NaCl and a sulphur-containing environment is critical to cause crack initiation in the early stages of the exposure and accelerated corrosion rates in CMSX-4 at 550°C. The effect of having small concentrations of moisture in the gaseous environment or as water crystallisation in the salt is still to be investigated. A working hypothesis is that the interaction of alkali chlorides with a sulphur-containing atmosphere is the trigger to a self-sustaining cycle where metal chloride formation, vaporisation and oxidation lead to high amounts of hydrogen injection in a rapid manner and, therefore, hydrogen embrittlement.
Open Access
Estimation of thermal barrier coating fracture toughness using integrated computational materials engineering
(Elsevier, 2023-05-15) Geng, Xibo; Wellman, Richard; Arrom, Luis Isern; Chalk, Christine; Castelluccio, Gustavo M.
The fracture toughness of thermal barrier coatings (TBC) is a critical mechanical property that governs damage resistance. Catastrophic delamination of TBC under erosion conditions occurs in TBC with low toughness. Prior research has explored indirect and complex experiments to measure TBC toughness, but the miniaturized nature of the multi-layered coating makes it difficult to quantify its intrinsic toughness. This paper integrates computational modeling and experimental approaches to estimate the TBC toughness and the substrate delamination strength. The results show that a typical newly fabricated yttrium stabilized zirconia coating under service conditions has a toughness estimated in the range of 0.1–0.5 MPa m1/2 and a toughness of thermally grown oxide layer in between 1.5 and 1.7 MPa m1/2. The analysis also determined that a thermally grown oxide with a fracture toughness above 2.0 MPa m1/2 would not delaminate under the service conditions. Overall, the approach demonstrates the value of integrated computational material approaches, which can save time and enhance predictive power.
Open Access
Fabrication and mechanical testing of mesoscale specimens
(Springer, 2023-05-08) Lodh, Arijit; Keller, Clement; Castelluccio, Gustavo M.
The mechanical response of metallic materials results from a complex hierarchy of deformation mechanisms across length scales. The need to understand these mechanisms independently has driven the miniaturization of testing samples, including small scale samples and single crystal micropillars. However, difficulties in machining and testing small samples have hampered the evaluation of the mechanical response of mesoscale samples with dimensions between tens to hundreds of microns. This paper innovates with a simple approach for the manufacturing and test of dog-bone specimens with a minimum gauge width up to 50 μm. The results demonstrate a pronounced sample size effects on the mechanical response for the dimensions analysed and highlights the need to advance the characterization of mesoscale samples. We also demonstrated the capability of testing the tensile response of single crystals from engineering alloys.
Open Access
History and temperature dependent cyclic crystal plasticity model with material-invariant parameters
(Elsevier, 2022-12-06) Ashraf, Farhan; Castelluccio, Gustavo M.
Cyclic deformation of metallic materials depends on the interaction of multiple mechanisms across different length scales. Solid solution atoms, vacancies, grain boundaries, and forest dislocations interfere with dislocation glide and increase the macroscopic strength. In single phase metallic materials under cyclic loading, the localization of dislocation densities in sessile substructures explains a significant fraction of the strain hardening. Upon cycling, these dislocation structures evolve across stable configurations, which depend on the strain accumulation. This work advances substructure-sensitive crystal plasticity models capable of quantifying the cyclic hardening history at various temperatures for single phase FCC materials. The framework predicts the cyclic evolution of dislocation substructure based on the activation of cross slip activation for Al, Cu, and Ni single- and poly-crystals up to 0.5 homologous temperature. The increase in cross slip with temperature and deformation induces a transformation in dislocation structures, which predicts secondary hardening without any additional provision. Moreover, the approach relies on material-invariant mesoscale parameters that are specific to dislocation substructures rather than a material system. Hence, we demonstrate that crystal plasticity predictive power can be augmented by parameterizing the model with single crystal experimental data from multiple materials with common substructures. As a result, the crystal plasticity model shares parameter information across materials without the need for additional single crystal experimental data for calibration.
Open Access
Interaction of stress corrosion cracks in single crystals Ni-Base superalloys
(Elsevier, 2024-02-02) Elsherkisi, Mustafa; Martinez, Fabian Duarte; Mason-Flucke, Julian; Gray, Simon; Castelluccio, Gustavo M.
Stress corrosion cracking (SCC) can be detrimental to nickel-based superalloy components exposed to harsh environments in aero-gas turbines. During flight, engines consume contaminants deposited on the surface of a blade, often leading to degradation. Cracking can initiate within minutes and rapidly propagate, depending on the temperature, contaminants, and applied stress. This study investigated the interaction between cracks in single-crystal turbine blades at intermediate temperatures by integrating experimental and computational methods. We performed C-Ring tests to quantify the time required for cracking, along with microscopic characterisation of the damage. In parallel, we developed a finite-element simulation for C-Ring tests using a phase field model calibrated to match the location of the cracks. The results demonstrated that the crack's characteristic spacing and length determine the likelihood of shielding or coalescing mechanisms.
Open Access
Investigation into the effects of salt chemistry and SO2 on the crack initiation of CMSX-4 in static loading conditions
(Springer, 2020-08-29) Martinez, Fabian Duarte; Morar, Nicolau I.; Kothari, Maadhav; Gibson, G.; Leggett, J.; Mason-Flucke, J. C.; Nicholls, John R.; Castelluccio, Gustavo M.; Gray, Simon
Although evidence exists of the potential impact of stress, co-incident with corrosive environments at high temperature, for single crystal turbine blades, the mechanism responsible is not fully understood. This work explores the effect of CaSO4, Na2SO4 and sea salt on the scale formation and crack initiation of CMSX-4 at 550°C in 50 ppm of SO2 and synthetic air under a static stress of 800 MPa. The cross-sectional analysis showed that the CaSO4 and the Na2SO4 salted specimens did not undergo a significant degree of corrosion degradation and no cracks were detected after 400 hours of exposure. However, sea salt caused significant degradation to the scale and cracks were detected by X-ray CT scanning after 400 hours of exposure. The findings from this study suggests that the sulfation of chlorine containing species in sea salt led to the formation, vaporisation and re-oxidation of metal chlorides and this mechanism was found to play a key role in the formation of a non-protective scale. An active oxidation mechanism has been proposed to interpret the results. In conclusion, it is hypothesized that due to the synergistic effect of stress and the formation of a non-protective scale, fast diffusion paths for sulfur, oxygen and chlorine ingress were formed. Further work is currently being undertaken to understand the effect of these species on the local embrittlement of CMSX-4 that ultimately led to the initiation of cracks in the specimen.
Open Access
Investigation into the environmental assisted crack initiation mechanism of CMSX-4 in simulated aero engine environments at 450 - 550°C.
(Cranfield University, 2023-03) Duarte Martinez, Fabian; Nicholls, J. R.; Gray, Simon; Castelluccio, Gustavo M.
The aviation industry has continued to increase the efficiency of gas turbine engines, which are now designed to operate on a wide variety of flight routes. In general, the efficiency drive has led to components spending longer times at temperatures, where accelerated corrosion can occur. This has led to a complex degradation mechanism being identified in the lower shank region under the platform of single-crystal turbine blades. This research aims to understand the mechanism of crack initiation due to the synergistic effect of stress and high temperature corrosion environments on CMSX-4 in the lower operating temperature range, 450°C - 550°C, of an aero gas turbine blade. The first part of the investigation consisted in comparing the effect of different salt deposits in a 50 ppm SO₂ - air environment at 550°C. A 50 ppm SO₂ – air concentration was considered because the air going through the lower shank is fed directly from the compressor, and not from the combustor (which is the main source of sulphur). Characterisation of the resulting scales were carried out using scanning electron microscopy, energy dispersive spectroscopy and X- ray diffraction. Results from thermodynamic modelling are also presented. The first part of the investigation showed that CMSX-4 sample under an applied stress and no applied salt did not experience accelerated corrosion attack or crack formation when exposed to 50 ppm SO₂ - air in a 400-hour period. The same observation was made for a CMSX-4 sample under an applied stress and salted with CaSO₄. Sea salt caused accelerated corrosion attack with cracks up to 1.3 mm through the substrate formed after 400 hours of exposure. Further tests using NaCl salt in 50 ppm SO₂ – air showed that cracks can initiate after just 10 minutes of exposure at 550°C. Crack growth rates are significantly reduced after two hours of exposure within a 50-hour salt cycle. Cracks with NaCl in 50 ppm SO₂ – air have also been observed at temperatures as low as 450°C. When NaCl salt was applied to CMSX-4 and exposed to air only for 50 hours, the corrosion attack was reduced considerably, and the initiation of cracks is either suppressed or significantly delayed beyond a 50-hour period. Although this PhD has only focused on a 50-hour period, longer exposure times should be carried out to determine if air exposures delay crack initiation time, or if crack initiation is completely supressed. This thesis has therefore shown that the interaction of stress, NaCl and a sulphur- containing environment are critical to cause early crack initiation in single crystal nickel-based superalloys in the temperature range 450 - 550°C. The effect of having small concentrations of moisture in the gaseous environment or as inclusions retained in the salt are still to be investigated. A working hypothesis is that that the interaction of alkali chlorides with a sulphur-containing atmosphere is the trigger to a self-sustaining cycle where metal chloride formation, vaporisation and oxidation leads to high amounts of H₂ formed at the scale/alloy interface. Potentially, the H₂ formed at the alloy/scale interface may dissociate into atomic hydrogen, and lead to hydrogen embrittlement. For further verification of this hypothesis, a set of tests have been suggested.
Open Access
Machine learning applied to identify corrosive environmental conditions
(Frontiers, 2022-04-04) Lee, HsinYen; Gray, Simon; Zhao, Yifan; Castelluccio, Gustavo M.
The reliability of turbine engines depends significantly on the environment experienced during flight. Air humidity, corrosive contaminant substances, and high operating temperatures are among the attributes that affect engine lifespans. The specifics of the environment that affect materials are not always known, and damage is often evaluated by time-consuming manual inspection. This study innovates by demonstrating that machine learning approaches can identify the environmental conditions that degrade jet engine metallic materials. We used the state-of-the-art pre-trained neural network models to assess images of damaged nickel-based superalloy samples to identify the environment temperature, the exposure time, and the deposited amounts of salt contaminants. These parameters are predicted by training the model with a database of approximately 3,600 sample images tested in laboratory conditions. A novel tree classification process results in excellent predictive power for classifying the type of environment experienced by nickel-based superalloys.
Open Access
Mesoscale cyclic crystal plasticity with dislocation substructures
(Elsevier, 2017-06-21) Castelluccio, Gustavo M.; McDowell, David L.
Constitutive formulations have increasingly focused on physically-based approaches that are less phenomenological and incorporate information from multiple scales. Most dislocation-based plasticity approaches reflect many-body dislocation physics without considering the length scales introduced by the self-organization of dislocations into mesoscale structures. These structures promote internal stresses or back stresses that are heterogeneous and long-range in nature and play a critical intermediary role in distinguishing the stress at micro- and nano-scales under cyclic loading. We present a framework that explicitly incorporates length-scales and evolution laws associated with mesoscale dislocation substructures such as cells and persistent slip bands (PSBs) in metallic materials under cyclic loading. A physically-based formulation for the back stress based on the Eshelby inclusion formalism is introduced that explicitly depends on morphology of mesoscale dislocation structures. The approach employs material parameters that can be measured or computed at lower length scales to contrast the response of models and experiments for multiple single crystals orientation and polycrystals for a wide range of strains.
Open Access
Microstructure-sensitive estimation of small fatigue crack growth in bridge steel welds
(Elsevier, 2018-03-15) Yuan, Hao; Zhang, Wei; Castelluccio, Gustavo M.; Kim, Jeongho; Liu, Yongming
A probabilistic finite element model is implemented to estimate microstructurally small fatigue crack growth in bridge steel welds. Simulations are based on a microstructure-sensitive crystal plasticity model to quantify fatigue indicator parameters (FIPs) at the slip system level and a fatigue model that relates FIPs to fatigue lives of individual grains. Microstructures from three weld zones, namely, fusion zone (FZ), heat affected zone (HAZ), and base metal (BM), are constructed based on their microstructural attributes such as grain morphology, size, and orientation. Statistical volume elements (SVEs) are generated and meshed independently for the three welding zones. Each grain within the SVEs is divided into several slip bands parallel to crystallographic planes. During the loading process, cracks nucleate at the slip bands (SBs) with the largest FIP next to the free surface. The crack extension path is assumed to be transgranular along SBs and the number of cycles required to crack the neighbor grain is calculated by the corresponding FIP-based crack growth rate equation. The simulation process is carried out using ABAQUS with a user defined subroutine UMAT for crystal plasticity. After the calibration of the constitutive model and irreversibility parameters, numerical simulations for small crack growth in three zones are presented. The crack length vs. the predicted fatigue resistance shows significant differences in the mean values and variability among the three weld zones.
Open Access
Microstructure-sensitive fatigue modelling of medical-grade fine wire
(Wiley, 2018-06-27) Clark, B. C.; Castelluccio, Gustavo M.; Reiterer, M. W.; McDowell, D. L.; Neu, R. W.
This work presents a modelling methodology to assess the sensitivity to microstructure in high‐cycle fatigue performance of fine wires made from MP35N alloy (35Ni‐35Co‐20Cr‐10Mo in wt%) used as conductors in cardiac leads. The model consists of a microstructure generator that creates a mesh of a statistically representative microstructure, a finite element analysis using a crystal plasticity constitutive model to determine the local response behaviour of the microstructure, and a postprocesser using fatigue indicating parameters to assess the likelihood of fatigue crack initiation. The fatigue crack initiation potency for selected microstructure attributes, boundary and interface conditions, and loading profiles is determined by computing the Fatemi‐Socie fatigue indicating parameter over a physically relevant volume of scale. Case studies are used to investigate (1) the influence of nonmetallic inclusion proximity to the wire surface on fatigue potency and (2) the transition life demarcating lives primarily controlled by fatigue crack initiation versus microcrack fatigue growth.