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The traffic loading is a typical cyclic loading with variable confining pressure and always lasts long, and is believed to have a significant effect on the subgrade soil, especially for the subgrade filled with soft clay. However, the mechanics have yet to be fully understood. Given that the duration of traffic loading lasts long enough, the partially drained conditions should be considered for the soft clay under the long-term cyclic loading, rather than the undrained conditions adopted commonly by most previous researches. In this study, 28 cyclic tests were conducted on the remolded saturated soft clay, utilizing both constant confining pressure and variable confining pressure under partially drained and undrained conditions. The effect of cyclic confining pressure and different drainage conditions is analyzed in relation to the evolution of pore pressure and deformation behaviors. Incorporating both the cyclic confining pressure and cyclic stress ratio, a concise pre-diction model of permanent strain is proposed and validated by the experimental results. [ABSTRACT FROM AUTHOR]

The cyclic loading of foundation structures in sand leads to an accumulation of plastic deformations in the structures. For shallow foundations of high and slender structures such as wind energy converters (WECs), an accumulation of the plastic rotations is expected under cyclic eccentric loading that is imposed by wind loads, which could be crucial for the proof of serviceability. A practical approach to predict the behavior of shallow foundations under high-cycle eccentric loading is under research. In this paper, a numerical approach, the cyclic strain accumulation method (CSAM), which has been validated for cyclically loaded monopiles, is adopted for shallow foundations under eccentric cyclic loading. Modifications to the CSAM are described, which are necessary to apply it to shallow foundations. The results that are gained with the modified method are compared with a medium-scale model test, in which the deformations of a footing with a diameter of 2.0 m under eccentric one-way cyclic loading were investigated. It can be concluded that the CSAM can make realistic predictions and shows satisfying agreement with the measured cyclic behavior. Although more experiments are needed to finally validate the method, the CSAM could be a promising numerical approach to account for the cyclic behavior of shallow foundations under eccentric cyclic loading in sand. [ABSTRACT FROM AUTHOR]

We report room‐temperature bulk plasticity mediated by dislocations in single‐crystal cubic potassium tantalate oxide (KTaO3), contrasting the conventional knowledge that single‐crystal KTaO3 is susceptible to brittle fracture. A mechanics‐based combinatorial experimental approach using cyclic Brinell indentation, scratching, and uniaxial bulk compression consistently demonstrates room‐temperature dislocation plasticity in KTaO3 from the mesoscale to the macroscale. This approach also delivers tunable dislocation densities and plastic zone size. Scanning transmission electron microscopy analysis underpins the activated slip system to be <110> {11¯$\bar{1}$0}. Given the growing significance of KTaO3 as an emerging electronic oxide and the increasing interest in dislocations for tuning the physical properties of oxides, our findings are expected to trigger synergistic research interest in KTaO3 with tunable dislocation densities. [ABSTRACT FROM AUTHOR]

We report room‐temperature bulk plasticity mediated by dislocations in single‐crystal cubic potassium tantalate oxide (KTaO3), contrasting the conventional knowledge that single‐crystal KTaO3 is susceptible to brittle fracture. A mechanics‐based combinatorial experimental approach using cyclic Brinell indentation, scratching, and uniaxial bulk compression consistently demonstrates room‐temperature dislocation plasticity in KTaO3 from the mesoscale to the macroscale. This approach also delivers tunable dislocation densities and plastic zone size. Scanning transmission electron microscopy analysis underpins the activated slip system to be <110> {11¯$\bar{1}$0}. Given the growing significance of KTaO3 as an emerging electronic oxide and the increasing interest in dislocations for tuning the physical properties of oxides, our findings are expected to trigger synergistic research interest in KTaO3 with tunable dislocation densities. [ABSTRACT FROM AUTHOR]

This paper introduces a comprehensive computational framework, comprising a finite deformation crystal inelasticity constitutive model and phase field model, for modeling crack growth in superelastic nitinol polycrystalline microstructures. The crystal inelasticity model represents crystal stretching and lattice rotation from elastic mechanisms, as well as local inelastic deformation due to austenite-martensite phase transformation. The phase field formulation decomposes the Helmholtz free energy density into stored elastic energy, phase transformation energy, and crack surface energy components. The elastic energy accounts for tension-compression asymmetry with the formation of the crack through a spectral decomposition. Kinetic Monte Carlo simulations generate equilibrium area fractions of different surface orientations, which serve as weights for the surface energy. An adaptive wavelet-enhanced hierarchical finite element (FE) model is introduced to alleviate high computational overhead in phase field crack simulations. Simulations with the coupled inelasticity phase field model are conducted under various loading conditions including Mode-I tension, a quasi-static Kalthoff experiment, and cyclic loading of polycrystalline microstructures. Crack propagation is effectively predicted by this model, providing valuable insights into the material mechanical behavior with growing cracks. [ABSTRACT FROM AUTHOR]

Since dielectric elastomers (DEs) exhibit obvious nonlinear visco-hyperelasticity, and remarkable temperature dependence, it is difficult to accurately predict the cyclic deformation of DEs at various temperatures. To address this issue, an improved visco-hyperelastic constitutive model is proposed here to reproduce the complex temperature-dependent cyclic deformation of DEs. In the improved model, the Ogden model is chosen to provide the strain energy density representing the hyper-elastic response, a nonlinear viscosity evolution equation is used to depict the strong viscosity of DEs, and specific temperature-dependent parameters are incorporated to describe the cyclic deformation of DEs at various temperatures. Finally, the prediction capability of the proposed visco-hyperelastic model is validated by reproducing the cyclic deformation of VHB 4910 DE observed in experiments at different temperatures. This study provides a theoretical basis for the rational design of DE devices. [ABSTRACT FROM AUTHOR]

A physically‐based constitutive modeling framework is proposed for the cyclic deformation and softening of Ni‐based superalloys. The constitutive model accounts for underlying mechanisms of grain size strengthening, dislocation strengthening, solid solution strengthening, and precipitate strengthening, commonly observed in these alloys. A constitutive model is proposed for the shearing of precipitates on their interaction with glide dislocations during cyclic deformation. This is the primary contributor to the experimentally observed cyclic softening behavior in Ni‐based superalloys. Model predictions of the cyclic stress–strain response and the cyclic softening (quantified in terms of the peak stress) are compared with the experimental counterparts for a range of strain amplitudes under fully‐reversed cyclic loading of Inconel 718 (IN 718). Further, model predictions of precipitate size are also compared with the experimentally measured transmission electron micrographs of precipitate sizes at the end of deformation. Concurrence in the cyclic stress–strain response, peak stress, and precipitate size provides validation for our constitutive modeling framework. Highlight: Development of a physically‐based constitutive modeling framework for cyclic deformation.Microstructure‐based strengthening mechanisms are considered in the model.Model incorporated the physical mechanisms of cyclic softening due to precipitate shearing. [ABSTRACT FROM AUTHOR]

The aggregation and evolution of dislocations form different configurations, which are the preferred locations for fatigue crack initiation. To analyze the spatial distribution of the same dislocation configuration and the resulting configuration morphologies on different observation planes, several typical hysteresis loops and dislocation configurations in fatigued face-centered cubic single crystals with various orientations were compared. The crystal orientations of these specimens were determined by the electron back-scattering diffraction technique in a Cambridge S360 Scanning Electron Microscope. It is well known that dislocation ladder and wall structures, as well as patch and vein structures, are distributed on their respective observation planes, (1 2 ¯ 1) and (111) . These correspond to the point defect direction and line defect direction of dislocations, respectively. Therefore, the wall structures on the (1 2 ¯ 1) and (111) planes consist of point defects and line defects, which can be defined as point walls and line walls, respectively. Furthermore, the walls on the (1 2 ¯ 1) plane consist of Persistent Slip Band ladders connected with each other, corresponding to the formation of deformation bands. The evolution of dislocation patterns follows a process from patch to ladder and from vein to wall. The formation of labyrinths and dislocation cells originates from the activation of different secondary slip systems. In one word, it can help us better understand the physical nature of metal fatigue and failure by studying the distribution and evolution of different configurations. [ABSTRACT FROM AUTHOR]

Deformation-induced phase transformation significantly enhances the fatigue properties of gradient nanostructured (GNS) austenitic stainless steels, making it essential to understand their cyclic deformation and fatigue behavior when this transformation is suppressed. Here, the steady-state austenitic stainless steel, Fe–25Cr–20Ni, was used to fabricate GNS specimen by surface mechanical rolling treatment. Fully reversed strain-controlled tension-compression fatigue experiment and uniaxial tension experiment were conducted on GNS and coarse-grained specimens at room temperature. Mechanical experimental results show that the GNS layer with a thickness of 1.4 mm increases the yield strength and tensile strength by 96.5% and 19.5%, respectively, and the hardness of the outermost layer is increased by 2.75 times compared to the CG specimen. The fatigue results show that the GNS specimen exhibits a ' hardening-softening ' feature and mean stress relaxation behavior, and the pseudo fatigue limit of GNS specimen increases by 58.3% compared to CG specimen. The enhanced fatigue strength in the low cycle fatigue regime results from the thicker GNS layer, while the poor fatigue ductility of the surface nanograins contributes to the deterioration of fatigue life. In the high cycle fatigue (HCF) regime, GNS specimens achieves the synergy of fatigue ductility and fatigue strength due to synergistic strengthening of multiple factors. Fractography show that the strain amplitude of 0.45% is a kink point at which cracks initiate from the surface and core. The GNS layer not only inhibits surface crack initiation in HCF regime, and alters the fatigue crack initiation location to delay crack propagation.

This paper describes an application of a machine learning approach for parameter optimization. The method is demonstrated for the elasto-viscoplastic model with both isotropic and kinematic hardening. It is shown that the proposed method based on long short-term memory networks allowed a reasonable agreement of stress–strain curves to be obtained for cyclic deformation in a low-cycle fatigue regime. The main advantage of the proposed approach over traditional optimization schemes lies in the possibility of obtaining parameters for a new material without the necessity of conducting any further optimizations. As the power and robustness of the developed method was demonstrated for very challenging problems (cyclic deformation, crystal plasticity, self-consistent model and isotropic and kinematic hardening), it is directly applicable to other experiments and models. [ABSTRACT FROM AUTHOR]

In this section of Resonance, we invite readers to pose questions likely to be raised in a classroom situation. We may suggest strategies for dealing with them, or invite responses, or both. "Classroom" is equally a forum for raising broader issues and sharing personal experiences and viewpoints on matters related to teaching and learning science. G Gamow's alpha-decay theory (1928) is somewhat ad hoc for the reason that an alpha-particle inside a radioactive nucleus is supposed to move back and forth, through the dense mass of nucleons (retaining its identity), a number of times before it comes out. This short paper attempts to address this shortcoming via nuclear disintegration. [ABSTRACT FROM AUTHOR]

The traffic loading is a typical cyclic loading with variable confining pressure and always lasts long, and is believed to have a significant effect on the subgrade soil, especially for the subgrade filled with soft clay. However, the mechanics have yet to be fully understood. Given that the duration of traffic loading lasts long enough, the partially drained conditions should be considered for the soft clay under the long-term cyclic loading, rather than the undrained conditions adopted commonly by most previous researches. In this study, 28 cyclic tests were conducted on the remolded saturated soft clay, utilizing both constant confining pressure and variable confining pressure under partially drained and undrained conditions. The effect of cyclic confining pressure and different drainage conditions is analyzed in relation to the evolution of pore pressure and deformation behaviors. Incorporating both the cyclic confining pressure and cyclic stress ratio, a concise pre-diction model of permanent strain is proposed and validated by the experimental results.

The dependence of low cycle fatigue (LCF) behavior and microstructure evolution of Fe–22Mn-0.6C twinning-induced plasticity (TWIP) steel on the alloying element Al has been investigated under fully reversed total strain amplitude control with a nominal strain rate of 0.006 s−1 and strain amplitudes ranging from 0.002 to 0.010 at room temperature. The results indicate a strong dependence of LCF response and evolved microstructure on the addition of Al, owing to its effect on the stacking fault energy (SFE). At all strain amplitudes, the 3Al steel with a higher SFE exhibits a visibly lower cyclic hardening and a higher cyclic softening, resulting in a lower cyclic yield strength than the 0Al steel. As compared with the 0Al steel, the relatively higher SFE of the 3Al steel causes higher accumulated plastic strain, decreased slip planarity and weaker reversibility of dislocations, thereby decreasing the fatigue life. The optical microstructure is featured by increase in slip band density with increasing strain amplitude for both steels. However, the slip band density of the 3Al steel is higher than that of the 0Al steel. Moreover, cyclic loading promotes the formation of dislocation cells, rough labyrinths as well as planar dislocation arrays. Deformation twins are observed only in the 0Al steel with a visible lower critical twinning stress due to its low SFE as compared to the 3Al steel.

The influence of the roughness of a steel surface on the slipping friction coefficient and wear of a sealing gasket in a flanged joint is studied. The dependence of the frictional coefficient on the surface roughness Ra of the steel part and the applied force is established. The critical tangential stress for the flange–gasket assembly is determined: at the critical stress, the surface layer of the sealing gasket fails, and sealing of the joint is lost. [ABSTRACT FROM AUTHOR]

In this study, the microstructural evolution of a Ti-15Mo medical alloy was investigated, when the in situ cyclic tensile strain had 2% amplitude and the tension–compression cyclic deformation had 1%, 2%, and 3% amplitude. The Vickers hardness and wear resistance of the alloy were also optimized due to the grain-refining effect after cyclic deformation and annealing. The twinning-induced plasticity (TWIP) was considered the main deformation mechanism of the Ti-15Mo alloy during the tensile–compressive cycle deformation with suitable strain amplitude. The {332}<113> twins and boundaries were the main contributors to the grain refinement. The optimal microstructure, hardness, and wear resistance were obtained in the alloy deformed by tension–compression cyclic strain with a 3% strain amplitude. The wear resistance of the annealed alloy in Hank's solution was excellent in contrast to the original Ti-15Mo alloy due to its reasonable microstructure and hardness. It is clear that abundant twins were formed and retained in the coarse grains of the original alloy after cyclic deformation and annealing, which provided the expected refined grains and performance. [ABSTRACT FROM AUTHOR]

The aggregation and evolution of dislocations form different configurations, which are the preferred locations for fatigue crack initiation. To analyze the spatial distribution of the same dislocation configuration and the resulting configuration morphologies on different observation planes, several typical hysteresis loops and dislocation configurations in fatigued face-centered cubic single crystals with various orientations were compared. The crystal orientations of these specimens were determined by the electron back-scattering diffraction technique in a Cambridge S360 Scanning Electron Microscope. It is well known that dislocation ladder and wall structures, as well as patch and vein structures, are distributed on their respective observation planes, (12¯1) and (111). These correspond to the point defect direction and line defect direction of dislocations, respectively. Therefore, the wall structures on the (12¯1) and (111) planes consist of point defects and line defects, which can be defined as point walls and line walls, respectively. Furthermore, the walls on the (12¯1) plane consist of Persistent Slip Band ladders connected with each other, corresponding to the formation of deformation bands. The evolution of dislocation patterns follows a process from patch to ladder and from vein to wall. The formation of labyrinths and dislocation cells originates from the activation of different secondary slip systems. In one word, it can help us better understand the physical nature of metal fatigue and failure by studying the distribution and evolution of different configurations.

Two single crystals with compositions Fe-Ni-Co-Al-Ta and Fe-Ni-Co-Al-Ta-B were selected and fabricated by Bridgman method. Subsequently, ingots were homogenized, oriented and subjected to a two-step heat treatment process in order to obtain fine and coherent γ' precipitates. Subsequently, superelastic cycling experiments were performed at 77 K. The next step included detailed microstructural characterization using transmission electron microscopy and high-energy synchrotron X-ray diffraction measurements together with Rietveld refinement. The results show that the number of fully reversible superelastic strains is very sensitive to the size of γ' precipitates. The smaller (3 nm) γ' precipitates ensured more superelastic response compared to material with larger γ' particles size (5 nm), in which the material did not receive its original shape after 10 cycles even after being heated.

Candida albicans is an opportunistic yeast and the primary etiological factor in oral candidiasis and denture stomatitis. The pathogenesis of C. albicans could be triggered by several variables, including environmental, nutritional, and biomaterial surface cues. Specifically, biomaterial interactions are driven by different surface properties, including wettability, stiffness, and roughness. Dental biomaterials experience repetitive (cyclic) stresses from chewing and biomechanical movements. Pathogenic biofilms are formed over these biomaterial surfaces under cyclic strain. This study investigated the effect of the cyclic strain (deformation) of biomaterial surfaces on the virulence of Candida albicans. Candida biofilms were grown over Poly (methyl methacrylate) (PMMA) surfaces subjected to static (no strain) and cyclic strain with different levels ( ε ˜ x =0.1 and 0.2%). To evaluate the biomaterial-biofilm interactions, the biofilm characteristics, yeast-to-hyphae transition, and the expression of virulent genes were measured. Results showed the biofilm biomass and metabolic activity to be significantly higher when Candida adhered to surfaces subjected to cyclic strain compared to static surfaces. Examination of the yeast-to-hyphae transition showed pseudo-hyphae cells (pathogenic) in cyclically strained biomaterial surfaces, whereas static surfaces showed spherical yeast cells (commensal). RNA sequencing was used to determine and compare the transcriptome profiles of cyclically strained and static surfaces. Genes and transcription factors associated with cell adhesion (CSH1, PGA10, and RBT5), biofilm formation (EFG1), and secretion of extracellular matrix (ECM) (CRH1, ADH5, GCA1, and GCA2) were significantly upregulated in the cyclically strained biomaterial surfaces compared to static ones. Genes and transcription factors associated with virulence (UME6 and HGC1) and the secretion of extracellular enzymes (LIP, PLB , and SAP families) were also significantly upregulated in the cyclically strained biomaterial surfaces compared to static. For the first time, this study reveals a biomaterial surface factor triggering the pathogenesis of Candida albicans , which is essential for understanding, controlling, and preventing oral infections. Fungal infections produced by Candida albicans are a significant contributor to various health conditions. Candida becomes pathogenic when certain environmental conditions change, including temperature, pH, nutrients, and CO 2 levels. In addition, surface properties, including wettability, stiffness, and roughness, drive the interactions between Candida and biomaterials. Clinically, Candida adheres to biomaterials that are under repetitive deformation due to body movements. In this work, we revealed that when Candida adhered to biomaterial surfaces subjected to repetitive deformation, the microorganism becomes pathogenic by increasing the formation of biofilms and the expression of virulent factors related to hyphae formation and secretion of enzymes. Findings from this work could aid the development of new strategies for treating fungal infections in medical devices or implanted biomaterials. [Display omitted] [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) techniques, such as wire arc additive manufacturing (WAAM), offer unique advantages in producing large, complex structures with reduced lead time and material waste. However, their application in fatigue-critical applications requires a thorough understanding of the material properties and behavior. Due to the layered nature of the manufacturing process, WAAM structures have different microstructures and mechanical properties compared to their substrate counterparts. This study investigated the mechanical behavior and fatigue performance of Ti-6Al-4V fabricated using WAAM compared to the substrate material. Tensile and low-cycle fatigue (LCF) tests were conducted on both materials, and the microstructure was analyzed using optical microscopy and scanning electron microscopy (SEM). The results showed that the WAAM material has a coarser and more heterogeneous grain structure, an increased amount of defects, and lower ultimate tensile strength and smaller elongation at fracture. Furthermore, strain-controlled LCF tests revealed a lower fatigue strength of the WAAM material compared to the substrate, with crack initiation occurring at pores in the specimen rather than microstructural features. Experimental data were used to fit the Ramberg–Osgood model for cyclic deformation behavior and the Manson–Coffin–Basquin model for strain-life curves. The fitted models were subsequently used to compare the two material conditions with other AM processes. In general, the quasi-static properties of WAAM material were found to be lower than those of powder-based processes like selective laser melting or electron beam melting due to smaller cooling rates within the WAAM process. Finally, two simplified estimation models for the strain-life relationship were compared to the experimentally fitted Manson–Coffin–Basquin parameters. The results showed that the simple "universal material law" is applicable and can be used for a quick and simple estimation of the material behavior in cyclic loading conditions. Overall, this study highlights the importance of understanding the mechanical behavior and fatigue performance of WAAM structures compared to their substrate counterparts, as well as the need for further research to improve the understanding of the effects of WAAM process parameters on the mechanical properties and fatigue performance of the fabricated structures. [ABSTRACT FROM AUTHOR]

Temperature and frequency are significant extrinsic factors that influence the cyclic deformation behaviour of face-centred cubic crystal (fcc) single crystals. For Cu single crystals, an increase in temperature causes the disappearance of the plateau region in the cyclic stress–strain (CSS) curves and a significant decrease in the saturation resolved shear stress at low strain amplitudes. This is attributed to the enlargement of the space between Persistent Slip Band (PSB) ladders, resulting in a lower volume fraction of the rungs in PSBs, leading to a lower saturation shear stress. Conversely, an increase in frequency does not affect the appearance of the plateau behaviour in CSS curves, but it slightly increases the corresponding plateau stress. This is because a higher frequency increases the probability of interaction between edge dislocations, leading to an increase in the local flow stress in the rungs, ultimately resulting in an increment of the saturation stress. [ABSTRACT FROM AUTHOR]

In order to reveal the dislocation evolution law of body-centered cubic axle steel EA4T during cyclic deformation and provide an experimental basis for the subsequent construction of cyclic constitutive models based on microscopic physical mechanisms, macroscopic deformation experiments were first conducted on axle steel EA4T, including monotonic tensile experiments under different deformation amounts, symmetric strain cycling experiments under a different number of cycles, and ratcheting deformation experiments under a different number of cycles. Then, systematic observations of different samples at different deformation stages were conducted using a Transmission Electron Microscope (TEM) to investigate the dislocation configuration and evolution during strain cycling and ratcheting deformation. The observed results show that the dislocation evolution law of axle steel EA4T during the uniaxial tensile experiment, symmetrical strain cycling, and ratcheting deformation is basically the same, and the dislocation density increases with the increase in plastic deformation and number of cycles. The dislocation configuration gradually develops from low-density dislocation configurations such as dislocation lines and dislocation pileups to high-density dislocation configurations such as severe dislocation tangles and dislocation walls. The microscopic mechanism of the uniaxial ratcheting evolution of axle steel EA4T can be qualitatively explained by the dislocation configuration and evolution. [ABSTRACT FROM AUTHOR]

Two single crystals with compositions Fe-Ni-Co-Al-Ta and Fe-Ni-Co-Al-Ta-B were selected and fabricated by Bridgman method. Subsequently, ingots were homogenized, oriented and subjected to a two-step heat treatment process in order to obtain fine and coherent γ' precipitates. Subsequently, superelastic cycling experiments were performed at 77 K. The next step included detailed microstructural characterization using transmission electron microscopy and high-energy synchrotron X-ray diffraction measurements together with Rietveld refinement. The results show that the number of fully reversible superelastic strains is very sensitive to the size of γ' precipitates. The smaller (3 nm) γ' precipitates ensured more superelastic response compared to material with larger γ' particles size (5 nm), in which the material did not receive its original shape after 10 cycles even after being heated. [ABSTRACT FROM AUTHOR]

In offshore technology, especially in offshore wind energy converters, permanent deformations of the structures must be limited. For that purpose, the accumulation of permanent deformation due to cyclic loading must be predicted as accurately as possible. To account for this accumulation in non‐cohesive soils, different approaches such as semi‐empirical methods, p‐y curve methods and numerical methods are available. Among the numerical approaches, the Stiffness Degradation Method (SDM) has the advantage of practical feasibility. However, it is only compatible with a relatively simple constitutive law and does not consider the influence of un‐ and reloading stress paths in the soil. With the basic concept of SDM, a new method termed Cyclic Strain Accumulation Method (CSAM) is proposed. In CSAM, the weaknesses of SDM, especially its incompatibility with advanced constitutive laws, are overcome, while retaining the practical feasibility as the main advantage of SDM. Through numerical calculations of a monopile, it is found that the CSAM is able to reproduce SDM results if the same material law is applied. The results of SDM and CSAM for the case of a vertical loaded strip footing have been presented. The comparison shows that the CSAM results are more realistic than the SDM results. Besides, CSAM is computationally more efficient and open for further optimisation. The effects of sophisticated material law and the consideration of un‐ and reloading are investigated. Results show that CSAM is a promising new approach to account for the deformation of foundations under cyclic loading in non‐cohesive soils. [ABSTRACT FROM AUTHOR]

The macroscopic response of short fiber reinforced composites (SFRCs) is dependent on an extensive range of microstructural parameters. Thus, micromechanical modeling of these materials is challenging and in some cases, computationally expensive. This is particularly important when path‐dependent plastic behavior is needed to be predicted. A solution to this challenge is to enhance micromechanical solutions with machine learning techniques such as artificial neural networks. In this work, a recurrent deep neural network model is trained to predict the path‐dependent elasto‐plastic stress response of SFRCs, given the microstructural parameters and the strain path. Micromechanical mean‐field simulations are conducted to create a database for training the validating the model. The model gives very accurate predictions in a computationally efficient manner when compared with independent micromechanical simulations. [ABSTRACT FROM AUTHOR]

In this work, derivation of the main thermodynamic relationships is realized together with the applied calculation of some parameters, providing the systematized description of non-linear thermo-mechanical deformation at dynamic mechanical analysis (DMA). Obtained equations and values agree well with experiments on different ribbon metallic glasses. We generalize the main initial conditions (i.e., experimental and numerical parameters) by that the proposed model can be used for the investigation of DMA in different materials. The further opportunities of the found approach are also discussed in frames of phase transitions in metallic glass. [ABSTRACT FROM AUTHOR]

• LCF of fine-, coarse-, and irregular-grained GH4742 at 650 °C is investigated. • Fine-grained material shows a transition strain dividing LCF into two regimes. • A new LCF model incorporating transition strain improves prediction accuracy. The effect of grain size and shape on low cycle fatigue of a nickel-based superalloy at elevated temperature was investigated. Fatigue testing was performed using GH4742 specimens having fine, coarse, and irregular grains. The fine-grained material exhibits a transition strain separating the fatigue life diagram into two regimes with distinct slopes while the other two do not. A piecewise log-linear model was proposed to incorporate the transition strain, yielding more accurate predictions. Crack initiation modes and cyclic deformations at half-life were investigated to explain the observed difference and fatigue behavior characteristics of the three grain types. [ABSTRACT FROM AUTHOR]

• Cyclic response depends on the strain amplitude. • Progressive phase transformation occurs during cyclic loading. • Grain boundaries and triple junctions are preferred sites for transformation. Stress-induced FCC-BCC phase transformation plays a crucial role in the mechanical behaviors of high-entropy alloys (HEAs). While there has been extensive research on this transformation during monotonic deformation, studies on fatigue behavior are extremely limited. Here, we use molecular dynamics simulations to investigate phase transformation and dislocation evolution in HEAs under strain-controlled symmetric tension–compression cycles. Our results show that cyclic deformation behavior is sensitive to strain amplitude, revealing three distinct cyclic responses. Notably, a progressive FCC-BCC phase transformation process occurs at a high strain amplitude of 4.8%. Grain boundaries and their triple junctions are identified as preferred sites for phase transformation under cyclic loading conditions. These findings provide valuable atomic-scale insights for understanding fatigue deformation in HEAs with transformation-induced plasticity. [ABSTRACT FROM AUTHOR]

Tensile properties and low cycle fatigue behavior of 316LN austenitic stainless steel were investigated after varied thermal aging durations at 773 K up to 30000 h. After thermal aging for 30000 h, the material exhibits remarkable degradations in both the yield stress and ultimate tensile strength at room temperature and 623 K, and there is a significant decrease in cyclic hardening level at 623 K. These facts indicate that the long-term thermal aging treatment induces softening of this material, which results in the decrease of plastic strain energy density under low cycle fatigue test and the prolongation of fatigue life. From the observation of microstructures, it is found that in the aged material, there existed differences in dislocation structure, the increase of grain size, the transformation of second phase distribution, and the decrease of grain boundaries, which are the significant reasons for the decreasing of cyclic hardening. By introducing the evolution of grain size and thermal aging effect, a modified visco-plasticity constitutive model based on the Ohno-Wang Ⅱ kinematic hardening rule is proposed and successfully used to predict the cyclic behavior of virgin and thermal aged material at both room and elevated temperatures. • Tensile and cyclic deformation behaviors of thermal aged 316LN are analyzed at room and 623K. • Increasing of grain size, transformation of second phase and degradation of twin boundary are observed in the aged material. • A modified constitutive model with the evolution of grain size is proposed to account for the thermal aging effect. • The cyclic hardening and softening behavior of virgin and aged material is described well with the proposed model. [ABSTRACT FROM AUTHOR]

The present work deals with revealing the fatigue and dwell-fatigue behavior and correlated damage mechanisms of Fe–Mn–Al–C lightweight steel. Surprisingly, alteration in loading mode from monotonic to cyclic induces reversible dislocation movement and facilitates the occurrence of dynamic strain aging. Additionally, applying dwell time by an acceleration of strain aging intensified stress asymmetry during dwell fatigue. The occurrence of strain aging has a bilateral effect on the crack initiation and growth. On one hand, strain aging stimulates twin formation and retards fatigue crack initiation, however, on the other hand, reduces hardening capacity, restricts the plastic deformation and facilitates crack propagation.

In order to reveal the dislocation evolution law of body-centered cubic axle steel EA4T during cyclic deformation and provide an experimental basis for the subsequent construction of cyclic constitutive models based on microscopic physical mechanisms, macroscopic deformation experiments were first conducted on axle steel EA4T, including monotonic tensile experiments under different deformation amounts, symmetric strain cycling experiments under a different number of cycles, and ratcheting deformation experiments under a different number of cycles. Then, systematic observations of different samples at different deformation stages were conducted using a Transmission Electron Microscope (TEM) to investigate the dislocation configuration and evolution during strain cycling and ratcheting deformation. The observed results show that the dislocation evolution law of axle steel EA4T during the uniaxial tensile experiment, symmetrical strain cycling, and ratcheting deformation is basically the same, and the dislocation density increases with the increase in plastic deformation and number of cycles. The dislocation configuration gradually develops from low-density dislocation configurations such as dislocation lines and dislocation pileups to high-density dislocation configurations such as severe dislocation tangles and dislocation walls. The microscopic mechanism of the uniaxial ratcheting evolution of axle steel EA4T can be qualitatively explained by the dislocation configuration and evolution.

Turbine blades are subjected to cyclic deformation and intensive hyper-gravity force during high-speed rotation. Therefore, understanding the dynamic mechanical behavior is important to improve the performance of the blade. In this work, [001](010), [110](−110), and [11−2](111) pre-existing crack models of nickel single crystals under increasing cyclic tensile deformations were studied by using molecular dynamics simulations. In addition, a novel hyper-gravity loading method is proposed to simulate the rotation of the blade. Four hyper-gravity intensities, i.e., 1 × 1012 g, 3 × 1012 g, 6 × 1012 g, and 8 × 1012 g, and different temperatures were applied during the cyclic deformation. The fatigue life decreased rapidly with the elevated hyper-gravity strength, although the plastic mechanism is consistent with the zero-gravity condition. The stress intensity factor for the first dislocation nucleation indicates that the critical stress strongly depends on the temperatures and hyper-gravity intensities. Moreover, the crack length in relation to hyper-gravity intensity is discussed and shows anisotropy along the direction of hyper-gravity. A temperature-induced brittle-to-ductile transition is observed in the [001](010) crack model. The present work enhances our understanding of the fatigue mechanism under hyper-gravity conditions from an atomistic viewpoint. [ABSTRACT FROM AUTHOR]

Duplex stainless steels (DSS) have become more attractive than single-phase austenitic and ferrite grades in industrial application due to their high strength and corrosion resistance in chloride-containing media. Due to low ductility region under hot working conditions these materials require special attention during processing. As heat treatments influence low cycle fatigue characterisation. The characteristics and properties of the industrially employed duplex grades has been discussed, moreover the presence and precipitation of sigma phases has been highlighted through ageing treatments. Based on up to date achieved outcomes, it appears that a quite homogeneous and good mechanical properties can be obtained by controlled composition and heat treatments.and it also enhances the wear properties. The most commonly formed and observed pernicious phase in DSS is sigma phase particles precipitation in a short period of time over a wide range of temperature. Hence an attempt has been made in our investigation to evaluate the low cycle fatigue changes when they are subjected to temperature 1100°C for a shorter duration for about 60 minutes. The low-cycle fatigue behaviour of a DSS was comparatively studied in standard heat-treated and aged at 800°C for 4 h. [ABSTRACT FROM AUTHOR]

A microstructure-based multistage fatigue (MSF) model was employed to study the process–structure–property relations for cyclic damage and fatigue life of NiTi alloy fabricated via an additive manufacturing (AM) technique. Various defect characteristics (i.e., level of porosity, pore size, and their spacing) and microstructural features (i.e., grain size, mean grain orientation, and misorientation angles), dictated by the manufacturing and post-manufacturing heat treatment processes, were used to predict the fatigue life of AM and wrought NiTi specimens. The specimens fabricated via AM underwent two different heat treatment conditions (i.e., aging followed by air cooling and annealing followed by water quenching). Using the process-dependent parameters, the MSF model could capture the differences in fatigue behavior of each condition. The predicted lower and upper bounds of fatigue life based on the range observed for microstructural features and defect characteristics were able to account for the scatter observed in experimental fatigue data. [ABSTRACT FROM AUTHOR]

• The effects of rafting extent, type and orientation on the monotonic and cyclic deformation behaviours are investigated. • The deformed γ'/γ microstructure and dislocation configurations under different rafting states are characterized. • A microstructural state-based constitutive model to account for the role of rafting extent and type is proposed. • The rafting morphology-related Bauschinger effect during cyclic deformation is well captured by a micromechanics-based back stress model. Monotonic tensile and cyclic deformation behaviours are investigated under different microstructural rafting states of a SC Ni-based superalloy, with emphasis on the influences of the rafting extent, type and loading orientation. The deformed microstructures and the dislocation configurations are characterized to give a micro-based understanding on the varying of deformation behaviours due to rafting. It is found that the decreases in the initial yield point and cyclic stress amplitude are only related to the rafting extent. Nevertheless, the rafting type (namely, the plate-like and needle-like morphology) has an undeniable contribution to the shape of hysteresis loops, where the plate-like rafting morphology results in more significant Bauschinger effect than needle-like rafting morphology. The variation of monotonic and cyclic deformation induced by rafting shares affinity with the alteration of internal stress and the movement of dislocations. Afterwards, a microstructure-sensitive constitutive model with two-phase flow rules has been developed. The effect of rafting on the monotonic and cyclic stress-strain responses is captured by introduce a series of microscopic mechanisms and a micromechanics-based back stress model that considers the morphology and size of the γ'/γ two-phase structures. The developed model is used to simulate the macroscopic stress-strain responses of the SC Ni-based superalloy under different rafting states. Model predictions are in good agreement with tests, capturing the reduction of cyclic stress amplitudes and the change in hysteresis loops. Finally, the impacts of the two-phase flow rules and the micromechanics-based back stress on the simulation capability have been discussed. [ABSTRACT FROM AUTHOR]

The present investigation highlights a comparison of strain-controlled low cycle fatigue (LCF) behaviour between the additively manufactured (AM) and wrought (WR) Inconel625 alloys at the total strain amplitude levels of ±0.4, ±0.5, ±0.6 and ±0.8 % at 650 °C. The cyclic life has been found to be lower in the AM alloy as compared to the WR alloy. The evolution of precipitates such NbC and γ″ are found in both type of alloys after LCF tests. However, the AM alloy has shown a significant presence of (Cr,Mo) 23 C 6 along the grain boundaries, which acts as a potential source of generation of the intergranular cracks during cyclic deformation. Although, a relatively fine grain structure and enhanced number density of high-angle boundaries have been identified in the LCF-tested samples of AM alloy through EBSD analyses, the formation of intergranular cracks in the AM alloy has resulted in the reduction of cyclic life of the AM alloy. [ABSTRACT FROM AUTHOR]

The computer-aided development of the leveling technology for high-strength steel flat sheet products is the primary goal of the research. The roll leveler setups are evaluated from the final product point of view with an acceptable flatness level and stress state at the same time. First, a reliable hardening model is developed based on experimental and numerical investigation. The combined isotropic-kinematic model is selected to capture material behavior under cyclic loading conditions. The inverse analysis approach is used for the high-quality model parameters identification stage. Then the roll leveling process for a wide range of machine setups is simulated using a finite element model. Examples of results in the form of final flatness and stress distributions are presented within the work. As an outcome, a set of process parameters is identified that provides a good quality product for both investigated criteria. [ABSTRACT FROM AUTHOR]

The aim of this study was to identify cyclic deformation behavior of a high‐pressure die‐cast Silafont®‐36 automotive cast aluminum alloy consisting of heterogeneous composite‐like microstructures of nearly circular eutectic silicon particles embedded in Al matrix, with particular attention to fatigue life prediction. The alloy exhibited superior fatigue resistance at higher strain amplitudes, where cyclic hardening occurred. The fatigue life of the alloy could be well predicted via a strain‐energy density based accumulative damage model using a new method proposed to calculate the intrinsic fatigue toughness. The predicted fatigue life was in good agreement with the experimental life, and also lay in‐between the results obtained via other methods. Fatigue crack initiation was observed to occur from the sample surface or near‐surface defects and crack propagation was characterized by fatigue striations along with tear ridges in the primary Al‐grains. [ABSTRACT FROM AUTHOR]

Fatigue failure usually occurs on the subsurface in rolling bearings due to multiaxial and non-proportional fatigue loadings between rolling elements. One of the main stress components is the alternating shear stress. This paper focuses on the micromechanism of plastic accumulation and damage initiation in bearing steels under cyclic shear deformation. The distribution of subsurface shear stress in bearings was firstly investigated by finite element simulation. An atomic model containing bcc-Fe and cementite phases was built by molecular dynamics (MD). Shear stress–strain characteristics were discussed to explore the mechanical properties of the atomic model. Ten alternating shear cycles were designed to explore the mechanism of cyclic plastic accumulation and damage initiation. Shear stress responses and evolutions of dislocaitons, defect meshes and high-strain atoms were discussed. The results show that cyclic softening occurs when the model is in the plastic stage. Severe cyclic shear deformation can accelerate plastic accumulation and result in an earlier shear slip of the cementite phase than that under monotonic shear deformation, which might be the initiation of microscopic damage in bearing steels. [ABSTRACT FROM AUTHOR]

A two-step low-cycle fatigue test on a pure-aluminium single crystal with a single-slip orientation was performed in the full pull–push mode under constant plastic shear-strain amplitude. In the first-step test, a plastic-shear-strain amplitude of 5 × 10-3 within the plateau region of the cyclic stress–strain curve was employed at 77 K. In the second-step test, similar plastic-shear-strain amplitude was employed at room temperature. In the first-step test, the shear-stress amplitude showed initial hardening to saturation. However, in the second-step test, it gradually decreased with an increase in the cumulative plastic-shear strain. After the first-step test, the matrix-vein structure and persistent slip bands (ladder structure) were well developed. The ladder structure transformed into the cell structure in the initial stage of the second-step test, the area fraction of the cell structure gradually increased with an increase in the cumulative plastic shear-strain, and the specimen was entirely covered with the well-developed cell structure at the end of the second-step test. [ABSTRACT FROM AUTHOR]

A bio‐ceramic coating was prepared on the surface of ZK60 magnesium alloys by micro‐arc oxidation (MAO) method. The substrate (BM) and coated (MAO) specimens were pre‐corroded in a simulated body fluid (SBF) for 12 h. Strain‐controlled and stress‐controlled loading modes were used to conduct fatigue tests for the specimens with non‐corroded and pre‐corroded, and the cyclic deformation behavior of different specimens was studied. The fatigue life of pre‐corroded MAO specimen is higher than that of pre‐corroded BM specimen. The mechanism of cyclic deformation under different loading conditions is related to twinning and slip. For the same specimens, the higher the absolute value of ratcheting strain, the lower the fatigue life. A modified total strain energy model is proposed, and the precision of life prediction is higher than that of traditional fatigue model. Highlights: A bio‐ceramic MAO coating was prepared on the surface of ZK60 magnesium alloys.Fatigue tests were carried out by strain‐controlled and stress‐controlled loading.Ratcheting behavior of non‐corroded and pre‐corroded specimens was studied.A modified total strain energy model was used to predict the fatigue life. [ABSTRACT FROM AUTHOR]

Whether in turbine components or exhaust gas heat exchangers, vacuum-brazed nickel-based joints are subjected to varying cyclical loads during their applications, often in corrosive environments. The microstructure of the brazed seam, which is determined by the alloy composition and the brazing process parameters, is essential for the service life. In this experimental study a modified BNi-5a foil was produced and used to braze cylindrical AISI 304L butt joints with two different holding times. Using energy dispersive spectroscopy analyses, a direct correlation of the element distribution at the brazing seam with the holding time was detected as a result of diffusion processes. Individual phases were identified, and it could be shown that the longer holding time led to a reduction of borides and silicides as well as to a more even microhardness curve through the seam. The effect of the microstructure on the corrosion fatigue properties was evaluated using multiple amplitude tests by a stepwise increase of the maximum stress amplitude in synthetic exhaust gas condensate. Thereby, improved corrosion fatigue and cyclic deformation behaviors were achieved for the more homogeneous microstructure. Afterwards, topography analyses of the fracture surfaces and cross-sectional fracture investigations enabled an understanding of microstructure-dependent damage mechanisms including fatigue crack initiation and propagation.

The limited understanding of additive manufacturing process-structure–property inter-relationships raises some concerns regarding the structural reliability, which limits the adoption of this emerging technology. In this study, laser beam-powder bed fusion is leveraged to fabricate an austenitic stainless steel with a microstructure containing minimal known crack initiation features. Ex-situ microstructural observations of the crack initiation features and mechanisms are carried out for interrupted fatigue tests via electron backscatter diffraction mapping of the micro-cracks. Results show that the additive manufactured stainless steel alloy has improved fatigue resistance compared to its wrought counterpart as a result of the unique microstructural features.