Mechanical surface modification such as shot peening offer powerful enhancement of fatigue properties of metals and other materials. Cavitation usually causes surface damage in hydraulic machineries. ...However, careful selection of process parameters allowed developing an approach known as “cavitation peening.” Its advantage is surface roughness increase is lower than in conventional shot peening as there are no solid collisions involved. As cavitation is a hydrodynamic phenomenon, an understanding of both fluid dynamics and materials science is required. Cavitation peening is distinguished from “water jet peening,” in which water column impulse is used. Another flavor is “Submerged laser peening” that involves the use of a pulsed laser and can be considered a type of cavitation peening where cavitating bubbles are generated due to laser ablation. Ultrasound vibration, a popular method for generating cavitation for cleaning, has also been adapted for cavitation peening. The present comparative review presents key insights and achievements and addresses future directions that are required for advancing cavitation peening technology by considering the mechanisms of cavitation peening based on the reported data for water jet, pulsed laser, and ultrasonic cavitation peening. The data and methods are critically considered and summarized in comparison with shot peening. Strategic view of future challenges is presented.
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•Fatigue resistance enhancement using water jet, pulsed laser and ultrasonic cavitation peening was quantified•Cavitation peening using jet, pulsed laser & ultrasonic enhanced fatigue properties•Cavitation peening clearly distinguished from water jet peening•Cavitation peening benefits shown to exceed those by shot peening•Dislocation density induced by cavitation peening was lower than by shot peening•Importance of vortex cavitation is shown for experimental and numerical future work
Rechargeable lithium ion batteries have ruled the consumer electronics market for the past 20 years and have great significance in the growing number of electric vehicles and stationary energy ...storage applications. However, in addition to concerns about electrochemical performance, the limited availability of lithium is gradually becoming an important issue for further continued use and development of lithium ion batteries. Therefore, a significant shift in attention has been taking place towards new types of rechargeable batteries such as sodium-based systems that have low cost. Another important aspect of sodium battery is its potential compatibility with the all-solid-state design where solid electrolyte is used to replace liquid one, leading to simple battery design, long life span, and excellent safety. The key to the success of all-solid-state battery design is the challenge of finding solid electrolytes possessing acceptable high ionic conductivities at room temperature. Herein, we report a novel sodium superionic conductor with NASICON structure, Na3.1Zr1.95Mg0.05Si2PO12 that shows high room-temperature ionic conductivity of 3.5 × 10(-3) S cm(-1). We also report successful fabrication of a room-temperature solid-state Na-S cell using this conductor.
The introduction of an overload or underload within a constant amplitude loading fatigue test leads to a retardation or acceleration of the Fatigue Crack Growth Rate (FCGR). The understanding of the ...causes of these effects is essential in the context of variable amplitude fatigue loading, since in principle any loading history can be represented as a sequence of overloads and underloads. In the case of overload, along with some other minor causes, the residual stress changes at the crack tip and crack closure behind the tip can be thought of as the main factors that affect the fatigue crack growth rate. Whilst this has been recognised and accepted for many decades, controversy persists regarding the relative significance and presence of these two effects, and consensus is yet to emerge. The effect of crack closure, when the baseline loading ratio is high enough, can be inhibited so that the main cause of retardation becomes doubtless the residual stress present ahead the crack tip.
In the present paper we report our attempt to deconvolve the contributions of crack closure and residual stress on crack retardation following an overload. To accomplish this task we analyse the results of fatigue tests run at two baseline load ratios, namely R=0.1 and R=0.7. At the load ratio of R=0.7 the crack closure effect is not operative, as confirmed by Digital Image Correlation analysis of the crack flanks close to the tip, and post mortem fractographic analysis of crack surfaces. Therefore, for R=0.7 the compressive residual stress region created by the overload ahead of the crack tip is the sole mechanism causing crack retardation. Therefore, for R=0.7 the focus must be placed entirely on the strain field around the crack tip. To this end, line profiles along the crack bisector of elastic strain in the crack opening direction were collected at several stages of crack propagation past the overload using in situ Synchrotron X-ray Powder Diffraction (SXRPD) technique.
By performing comparison between the two loading conditions (R=0.7 and R=0.1), information was extracted regarding the role of residual stress alone, and then, by subtracting this effect for the R=0.1 sample, for crack closure alone. To enable this analysis, we propose a introducing the concept of equivalent effective stress intensity factor range, ∆Keq,eff proposed by Walker. Afterwards, the SIF range reduction ratio, β, which represents the “knock down” factor with respect to the steady state growth was assessed. It is in terms of these newly introduced parameters that the magnitude and extent of the overload-induced crack growth rate retardation can be plotted, fitted and decomposed into closure and residual stress effects, respectively. It is concluded that although the residual stress effect is present at all values of the load ratio R, its effect is relatively short-lived, whilst the closure effect that is dominant at low values of R causes longer range retardation.
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•Observation of crack opening reveals that high load ratio (R=0.7) inhibits crack closure during fatigue crack propagation.•The effect of residual stress-strain field generated during overload vanishes when the crack tip advances past the overload plastic zone.•When operative, crack closure mechanism has a longer lasting retardation effect on the crack growth rate than residual stress.
•Simulation-based multi-scale statistical analysis of stress and strain reveals the prevailing statistical distributions.•The fundamental origins of local strain and stress statistics are ...identified.•The statistical method is seen to give guidance for rational design for structural integrity.
Multiscale stresses and strains in polycrystalline metals are always inhomogeneous. In this study, a rate-independent crystal plasticity formulation was implemented for a cubic representative volume element (RVE) of an fcc polycrystal generated by 3D Delaunay tessellation. Multiple realizations were generated with crystallographic orientation permutations and different grain morphologies in order to investigate the statistical distribution of stress, elastic lattice strain and total strain at the macro-, meso- and micro-scale. Macroscopically, at 1.55% total strain (elasto-plastic deformation), the overall stress statistics among different RVEs were observed to follow a normal distribution, whose profile shape is affected by the parameters that describes the lognormal grain size distribution. On the mesoscale, the orientation-specific elastic strains were accurately reproduced via the use of diffraction post-processing and validated by neutron diffraction data for a polycrystalline alloy. Microscopically, the local elastic strains (and hence stresses) universally follow a normal distribution, while plastic strains follow a lognormal probability distribution. Reliable knowledge of the statistical distributions of stresses and strains give new guidance for the determination of the minimum RVE size. The above finding reveals the nature of stress and strain inhomogeneity at multiple scales and emphasizes the fact that the dispersion of local stress and strain is much larger than that of the macroscopic average. The statistical analysis of stress and strain distribution at multiple scales provide further rich insights into the connection between microstructure and mechanical properties under monotonic and cyclic loading.
Post weld heat treatment (PWHT) process has an important role on fabrication of advanced ultra-supercritical power plant turbines. This process relieves the residual stresses formed as a result of ...welding by converting elastic strains into creep strains. In order to analyse the residual stress relief mechanism during the PWHT process, a novel simulation approach based on experimental data was developed for the analysis of residual stress states from complex manufacturing processes which are welding and heat treatment. This model uses permanent plastic strains (eigenstrains) formed as a result of welding process to set the initial mechanical state of the sample. The distribution of eigenstrains in the whole body was determined using displacement data obtained from contour measurements. The use of eigenstrains to set the initial residual stress state of the creep model reduced the number of uncertainties. This allowed the use of the principles of artificial intelligence for the development of a new fuzzy finite element model (fFEM) that determines the eigenstrain-creep model parameters through an evolution process. Subsequent to the determination of the model parameters, conditions of the PWHT process are investigated to analyse residual stress relaxation in Inconel Alloy 740H weldments.
We present a combined experimental and numerical study that provides the understanding of deformation mechanisms and stresses in Mg AZ31B alloy across scales, from macro-scale (Type I) to micro- ...(inter-granular, Type II) and nano-scale (intra-granular, Type III). The combination of in situ synchrotron X-ray diffraction (XRD), in situ electron backscattered diffraction (EBSD) and crystal plasticity finite element (CPFE) modeling of crystal slip and twinning/detwinning was employed. The crystal rotation observed directly in the XRD and EBSD experiments revealed the onset and completion of the twinning/detwinning processes during in situ cyclic compression-tension loading. It also allowed reliable calibration of the key model parameters, in particular critical resolved shear stress (CRSS) of detwinning. The validation of the model was performed at distinct different scales corresponding to all stress types. Direct comparison with the data from the loading device provided the confirmation of the model validity in terms of correct description of the macroscopic stress-strain response (Type I stresses). The calibration led to the CRSS detwinning value of 23 MPa, and twinning of 46.5 MPa. At the inter-granular micro-scale (Type II stresses), the model satisfactorily predicted the transition between different plastic deformation modes (slip, twinning and detwinning), as confirmed by the comparison with peak intensities in XRD experiments. For the intra-granular (nano-scale) Type III stresses, it was concluded that the model was also valid at the level of statistical description (rather than local behavior). Namely, it has not been possible to predict correctly the real morphology of the twins observed in EBSD experiments.
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•Crystal plasticity finite element model experimentally validated at all scales: macro(Type I)/micro(Type II)/nano(Type III).•Calibrated Model parameters: CRSS for twinning of 46.5 MPa, for detwinning of 23 MPa.•Macro-scale: model prediction matches macroscopic stress-strain response.•Micro-scale: prediction of slip/(de)twinning, peak intensities from in situ XRD tests, intra-granular stress statistics
The ability to predict the sizes of secondary and tertiary γ' precipitate is of particular importance for the development and use of polycrystalline nickel-based superalloys in demanding ...applications, since the size of the precipitate exerts a strong effect on the mechanical properties. Many studies have been devoted to the development and application of sophisticated numerical models that incorporate the influence of chemical composition, concentration gradients, and interfacial properties on precipitate size and morphology. In the present study, we choose a different approach, concentrating on identifying a correlation between the mean secondary and tertiary γ' size and the cooling rate from solution treatment temperature. The data are collected using the precipitate size distribution analysis from high-resolution scanning electron microscopy. This correlation is expressed in the form of a power law, established using experimental measurement data and rationalized using a re-derivation of McLean's theory for precipitate growth, based on well-established thermodynamic principles. Specifically, McLean's model is recast to consider the effect of cooling rate. The derived model captures the correlation correctly despite its simplicity, and is able to predict the mean secondary and tertiary γ' precipitate size in a nickel superalloy, without complex modeling.
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•The main source of welding residual stress is identified by investigating the distribution of permanent plastic strains (eigenstrains) in Inconel Alloy 740H specimens.•A new inverse ...eigenstrain model that combines data from well-designed experiments with finite element simulations is developed to determine boundaries of eigenstrain fields.•The proposed computational method calculates displacements and residual stresses using eigenstrain fields and provides a high quality of match with experimental results.•The experimentally validated model allows reliable prediction of residual stresses in the whole body.
The main source of welding residual stress is identified by investigating the distribution of permanent plastic strains in as-welded and post-weld heat treated specimens of Inconel 740H. For this purpose, inverse eigenstrain problem is solved using experimental displacement data obtained by high precision coordinate measuring machine measurements from the surface of transversal wire-cut of electric discharge machining. A new multi-component iterative inverse eigenstrain model is developed and, in total, three different inverse eigenstrain models are analysed to get a high-quality fit with experimental data and have a reasonable prediction of residual stresses in the whole body of nonuniform bead-on-plate specimen design. In order to determine the boundaries of permanent plastic strains, which are the main source of welding residual stress, eigenstrain distribution size is analysed in terms of mean squared error using three models. The distribution size that provides the best match between the calculated displacements and the measured deplanation on the surface of cut is determined. The multi-component iterative eigenstrain reconstruction model validated itself by providing a good agreement with experimentally determined displacement and residual stress profiles, and this model is used to predict residual stress distribution in the whole body.
Abstract
Cracking from a fine equiaxed zone (FQZ), often just tens of microns across, plagues the welding of 7000 series aluminum alloys. Using a multiscale correlative methodology, from the ...millimeter scale to the nanoscale, we shed light on the strengthening mechanisms and the resulting intergranular failure at the FQZ. We show that intergranular AlCuMg phases give rise to cracking by micro-void nucleation and subsequent link-up due to the plastic incompatibility between the hard phases and soft (low precipitate density) grain interiors in the FQZ. To mitigate this, we propose a hybrid welding strategy exploiting laser beam oscillation and a pulsed magnetic field. This achieves a wavy and interrupted FQZ along with a higher precipitate density, thereby considerably increasing tensile strength over conventionally hybrid welded butt joints, and even friction stir welds.
In the present study we elucidate the nature of local strain statistics evolution during tensile deformation in polycrystalline materials. A rate-independent formulation was implemented within a ...crystal plasticity framework by the means of representative volume element (RVE) analysis. Local elastic strain, as well as stress, were found to obey a normal distribution, whereas the statistics of local plastic strain conforms to a lognormal distribution. In line with experimental observations, the plastic strain becomes progressively localised and the local regions of large strains make significant contribution to the overall average strain increase. The results reveal the nature of strain inhomogeneity at the microscale and emphasize the fact that in metallic materials the elastic strain accumulation represents an additive process, whereas plastic deformation is a multiplicative process.
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