Stress Grain Research Articles

3D in situ observations of stress redistribution in Ti-6Al-4V within rogue grain neighborhoods during monotonic and cyclic loading

Grain-scale stress redistribution events are characterized within the Ti-6Al-4V (Ti64) hexagonal close-packed α phase using far-field high-energy X-ray diffraction microscopy. Specimens were deformed in monotonic uniaxial tension and under cyclic tensile loading with approximately 7000 grains probed in each specimen. Analyses focused on the evolution of the resolved shear stresses applied to the basal 〈a〉, prismatic 〈a〉, and pyramidal 〈c+a〉 slip systems, as well as normal stresses applied to basal planes, within individual grains. Slip system softening is observed in the basal 〈a〉 and prismatic 〈a〉 slip systems across the ensemble, while hardening is observed for the pyramidal 〈c+a〉 slip systems during both monotonic and cyclic loading. In addition, discrete stress redistribution events in which increases of normal stresses in grains not favorably oriented for slip that may lead to crack initiation are analyzed. It is observed that these increases in normal stresses are correlated to crystallographic slip in multiple neighboring grains favorably oriented for slip.

Revealing the anisotropic response of grain structures in additive manufactured Al-Mn-Sc alloys: Modeling based on experiments

The anisotropy of yield strength of additive manufactured (AM) Al-Mn-Sc alloy is attributed to the diverse distribution characteristics of grain size, aspect ratio and orientation. This work focus on controlling the yield strength and anisotropy of AM aluminum through microstructure design. In this work, microstructures information of laser powder-bed fusion (LPBF) processed Al-Mn-Sc alloys were obtained by electron back scatter diffraction (EBSD) analysis. The impact of grain size, aspect ratio and orientation on strength and anisotropy are quantitatively researched through modeling. Base on quantitative effect of orientation on strength and anisotropy, all microstructure partition schemes are calculated by MATLAB. Microstructure partition schemes of alloy with low anisotropy and high yield strength were predicted and simulation was enforced to certify the credibility of predication. Local stress in grain and orientation variation during deforming were obtained by simulation. It is concluded that the impact of orientation is more obvious than grain size and aspect ratio. Compared with strength and anisotropy obtained by simulation, the prediction of calculation shows fine precision. The impact of microstructures on mechanical properties and the reliability of modeling were verified.

Genome-Wide Identification and Expression Analysis of Sucrose Transporter Gene Family in Wheat Lines under Heat Stress

Sucrose transporters (SUTs) play vital roles in phloem sucrose unloading and transportation in wheat grains. However, the genomic information regarding the SUT gene family and their expression patterns in response to heat stress in grains of male-sterile wheat (Triticum aestivum L.) lines has not been systematically studied. In this study, a thorough examination of the wheat SUT gene family was conducted, focusing on their expression patterns in male-sterile lines under heat stress conditions in grain tissues. A total of 19 SUT genes were identified, with phylogenetic analysis indicating their classification into five distinct groups. Polyploidization was identified as a substantial factor in the expansion of SUT genes, with segmental duplication being the predominant mechanism driving the evolutionary expansion of the SUT gene family in wheat. Transcriptome data indicate that the expression levels of TaSUT1 and TaSUT2 were higher than other SUT genes in grains of male-sterile lines. The TaSUT1 expression showed a gradual decreasing trend, while TaSUT2 showed a reverse trend with the process of grain filling. After heat stress, the TaSUT1 expression in grains of male-sterile lines was first significantly increased and then significantly decreased with the filling stage extension, aligning with the observed trend of sucrose levels, indicating that heat stress may decrease the grain weight by reducing sucrose unloading and transportation process in grains. These results provide a systematic analysis of the SUT gene family and lay a theoretical foundation for us to study the grain filling of male-sterile lines in response to abiotic stress.

Preparation of ultra-thin sandwich Cu-Cu/CNTs-Cu composite foil with high tensile strength by electrodeposition

In this experiment, CNTs were co-deposited with Cu2+ in the acid electrolyte by acidizing sulfuric and nitric acid and protonating cationic surfactant poly diallyldimethylammonium chloride (PDDA). Subsequently, Cu-Cu/CNTs-Cu composite copper foil (1) with a sandwich thickness of 8 μm was prepared by combining additives of 3-mercapto-1-propanesulfonate (MPS) and Cl−. The results show that the resistivity of the composite foil is 1.89 × 10−8 Ω·m, which increased only 2%. The tensile strength σ is 582 MPa, the elongation ε is 3.27%, and the elastic modulus and hardness of the nano-indentation test are 97.5 GPa and 2.38 GPa respectively. These are due to the uniform distribution of CNTs as enhanced phases in the crystal, and importantly, nano twins appear in size smaller than 10 nm, thereby constructing a micro-nano organizational structure and greatly improving the mechanical properties of the composite foil. In addition, the main peak of XRD is shifted from (1 1 1) to (2 2 0) crystal plane, which shows reduced stress in grains, effectively inhibits the phenomenon of self-annealing, and ensures long-term stability of copper foil microstructure.

Microstructural characteristics governing the lattice rotation in Al-Mg alloy using in-situ EBSD

The lattice rotation behavior of Al-4%Mg alloy subjected to tensile deformation is studied through in-situ electron backscatter diffraction (EBSD). The emphasis is laid on the effect of the orientation of neighbors, second phase particles, and the local deformation state on the lattice rotation characteristics. The results obtained show that the lattice rotation response of grains with similar initial orientation is largely different characterized by differences in the magnitude of rotation, rotation rate, rotation path, and activation of slip systems. The rotation path of grains towards reaching the stable end orientations is found to be governed by the microstructural relationships such as the misorientation and fraction of grain boundary segment shared with the immediate neighbors. Also, the local reorientations associated with the second phase particles, slip plane kinking, and triple junctions due to disruption of the slip activity and deformation heterogeneity of the neighbors significantly affect the average rotation of the grains and the rate of rotation. The rotation path of such local lattice rotations in grains is not strictly bound by the microstructural relationship with the neighbors. Further, when the shape change of grains introduced by local deformation mechanisms is significant, lattice rotations accompanying slip deviate from the rotation tendency based on the microstructural relationship with the neighbors. The observed dependence of lattice rotation of grains with simple slip activity on the misorientation and fraction of grain boundary segment shared with the immediate neighbors is also validated through full-field crystal plasticity simulation using DAMASK software. Simulation results also reveal the state of stress in grains that favor the initiation of local deformation mechanisms and the associated lattice reorientations observed experimentally. Altogether, this study renders gainful insights on the dependence of the lattice rotation of polycrystalline Al-4%Mg alloy on the microstructural characteristics which are of significant considerations to the development of constitutive description of crystal plasticity models in improving the accuracy of predicting the bulk engineering properties and texture development.

MODELING THE INFLUENCE OF METAL PHASE IN DIAMOND GRAINS ON SELF-SHARPENING OF GRINDING WHEELS ON CERAMIC BONDS

The article presents the results of theoretical studies using finite element modeling, which made it possible to determine the rational characteristics of diamond wheels based on ceramic and polymer bonds. The effect of the parameters of the diamond-bearing layer on the change in its stress-strain state in the process of microcutting of hard alloys and superhard materials has been studied. It is established that the determining factor in the occurrence of critical stresses during grinding is the temperature in the cutting area, the increase of which in the presence of metal phase inclusions in diamond grains with high values of thermal expansion coefficient can lead to destructive stresses in grains and, consequently, their premature destruction. It is advisable to use diamond grains with a minimum content of metal phase and the use in the manufacture of synthetic diamonds solvent metals with a low value of this coefficient, which will significantly increase the use of potentially high resource diamond grains.

Extreme Strain Fluctuations in Polycrystalline Materials

The stochastic structure of polycrystalline materials causes a high inhomogeneity of the kinematic and force fields in grains of materials and large fluctuations of these fields. The inhomogeneity and fluctuations are insignificant in some cases, but they become crucial in the study of various critical phenomena whose occurrence strongly depends on the type of material microstructure. Fluctuations mainly arise due to the elastic interaction of grains, which has a long-range effect. Therefore, it is necessary to account for the interaction of a large number of grains, which is difficult to do using conventional methods (direct computer modeling and others). In the present paper, inhomogeneous mesostrain fluctuations in grains of polycrystalline materials were estimated using a field-theoretical approach to a boundary-value problem of microheterogeneous material deformation. Particular attention is paid to the calculation of extreme fluctuations that are important for some critical phenomena, such as, e.g., crack initiation under gigacycle fatigue when the macrostress amplitude and the mean stresses in grains are much lower than the quantities included in any macroscopic damage or fatigue criteria. Phe maximum mesostrains in grains can exceed several times the macrostrains. Extreme fluctuations in a grain are generated in grain clusters of specific configuration. Phe applied approach makes it possible to predict patterns of such clusters. Extreme fluctuations in the bulk grains of a polycrystalline body are much higher than in the surface grains, due to which the behavior of the material surface layers and bulk volumes is different. Quantitative data are given for the case of uniaxial tension of polycrystalline zinc.

Accumulation and metabolism of di(n-butyl) phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) in mature wheat tissues and their effects on detoxification and the antioxidant system in grain

Di(2-ethylhexyl) phthalate (DEHP) and di(n-butyl) phthalate (DBP) are the major phthalic acid esters to be used during the plastic manufacturing process; they have emerged as pollutants that result in serious environmental problems. However, their impacts on wheat at the reproductive stage remain unclear. Here, we examined the distribution of DEHP and DBP and their respective metabolites mono(2-ethylhexyl) phthalate (MEHP) and mono-n-butyl phthalate (MBP) in mature wheat, along with the mechanism of detoxification and oxidative burst in wheat grains under DBP and DEHP stress conditions in a pot experiment. High-performance liquid chromatography showed that the contents of DBP and DEHP, as well as their metabolites, i.e., MBP and MEHP, presented the highest values in the grain, followed by the stem, leaf, and root. Entry of DBP and DEHP into the grain from the soil induced the production of reactive oxygen species, accompanied by the upregulated expression and activity of the antioxidant enzymes (e.g., cytochrome P4503A4 and peroxidase). The metacaspase type I gene was also upregulated in response to DBP and DEHP stress in grains, which is indicative of programmed cell death to maintain normal physiological activities and to resist cell damage. DBP and DEHP stress-damaged cells in the grains underwent programmed cell death by upregulating the expression levels of the metacaspase type I gene. These results provide a new perspective for improving wheat tolerance to DBP and DEHP through the use of genetic engineering strategies.

Influence of the creep ageing process on the fatigue properties of components from V95pchT2 (analog 7175T76) and V95ochT2 (analog 7475) aluminium alloys

Influence of conditions of technological process of forming thick panels of a given geometry on fatigue limit of flat specimens from the V95ochT2 and V95pchT2 (analogues 7475 and 7175T76) alloys (Al-Mg-Cu-Zn) has been analysed. The process has been simulated experimentally on flat samples for temperatures 20, 165 and 420°C. The process includes: non-elastic strain in the range 10-5 - 10-2 s-1 up to 2% of total strain, followed by heat treatment according to T2 mode (quenching and aging). Fatigue life tests were carried out both on solid samples and on samples with a hole. It has been shown that resistance to fatigue of the observed alloys after forming at the annealing temperature (420°C) is comparable to the basic material resistance to fatigue. Meso-structure analysis showed absence of stress in grains. It is established that, on average, the shape of the grains is the same for a series of samples for different temperatures and loading rates. The results of testing samples with a hole showed that fatigue limit slightly decreases in samples which were previously deformed at (420°C), with respect to the durability of samples from the material in basic state. With an increase in rate of pre-strain, the relative number of cycles before destruction occurs increased.

Critical bed shear stress and threshold of motion of maerl biogenic gravel

A determination of the critical bed shear stress of maerl is a prerequisite for quantifying its mobility, rate of erosion and deposition in conservation management. The critical bed shear stress for incipient motion has been determined for the first time for samples from biogenic free-living maerl beds in three contrasting environments (open marine, intertidal and beach) in Galway Bay, west of Ireland. The bed shear stress was determined using two methods, Law of the Wall and Turbulent Kinetic Energy, in a rotating annular flume and in a linear flume. The velocity profile of flowing water above a bed of natural maerl grains was measured in four runs of progressively increasing flow velocity until the flow exceeded the critical shear stress of grains on the bed. The critical Shields parameter and the mobility number are estimated and compared with the equivalent curves for natural quartz sand. The critical Shields parameters for the maerl particles from all three environments fall below the Shields curve. Along with a previously reported correlation between maerl grain shape and settling velocity, these results suggest that the highly irregular shapes also allow maerl grains to be mobilised more easily than quartz grains with the same sieve diameter. The intertidal beds with the roughest particles exhibit the greatest critical shear stress because the particle thalli interlock and resist entrainment. In samples with a high percentage of maerl and low percentage of siliciclastic sand, the lower density, lower settling velocity and lower critical bed shear stress of maerl results in its preferential transport over the siliciclastic sediment. At velocities ∼10 cm s−1 higher than the threshold velocity of grain motion, rarely-documented subaqueous maerl dunes formed in the annular flume.

Assessment of the AquaCrop Model for simulating Canola under different irrigation managements in a semiarid area

Field experiments were conducted in 2005-2006 and 2007-2008 and the data were used tocalibrate and validate yield and biomass of AquaCrop Model for canola (Brassica napus l.). Themodel was calibrated with the first year and then was validated with the second year data. Fivewater stress treatments at different growth stages were performed including fully irrigatedduring whole growing period (I1), water stress at vegetative stage in spring (I2), water stress atflowering stage (I3), water stress in grain filling stage (I4) and severe water stress conditionsduring whole growing period with supplemental irrigation in planting and germination stage(I5). AquaCrop model coefficients were calibrated for I1 in 2005-2006 and the calibratedparameters were used for other treatments in both year. In this simulation model was assessedbased on measured values of the water content in root zone, evapotranspiration, canopy coverand final yield and dry matter that the latter are the important trait for the farmers The accuracyof the model in calibration was tested using RMSE, NRMSE and d, which were 0.92 t ha-1,12.37% and 0.98 for yield and 0.92 t ha-1, 12.37% and 0.98 for biomass, respectively. TheRMSE, NRMSE and d values in 2007-2008 (validation year) were obtained as 0.26 t ha-1,10.01% and 0.92 for yield and 0.84 t ha-1, 14.93% and 0.92 for biomass, respectively. The resultof calibration and validation for volumetric water content was acceptable. AquaCrop modelestimated the evapotranspiration acceptable in the first year, while the accuracy of model topredict this parameter decreased for validation. Therefore, the model was calibrated effectivelyfor yield and biomass; however, the results were less satisfactory when it came to the simulationof the severe stress (I5).

A Crystal-Plasticity-Based Damage Model Incorporating Material Length-Scale

A crystal-plasticity-based damage model that incorporates material length-scale through use of the slip-plane lattice incompatibility is developed with attention to the physical basis for the evolution of damage in a “bulk” shear deformation and without resort to ad hoc measures of shear deformation. To incorporate the physics of the shear damage process recently found by Kweon et al. (2010, “Experimental Characterization of Damage Processes in Aluminum AA2024-O,” ASME J. Eng. Mater. Technol., 132(3), p. 031008), the development of tensile hydrostatic stress in grains due to grain-to-grain interaction, two existing theories, crystal plasticity, and the void growth equation by Cocks and Ashby (1982, “On Creep Fracture by Void Growth,” Prog. Mater. Sci., 27(3–4), pp. 189–244) is combined to make the model in this study. The effect of the void volume increase onto the constitutive behavior is incorporated by adding the deformation gradient due to the void volume growth into a multiplicatively decomposed kinematics map. Simulations with the proposed model reveal the physics of shear and reproduce the accelerated damage in the shear deformation in lab experiments and industrial processes: the gradient of hydrostatic stress along with the development of macroscopic normal stress (hydrostatic stress) components amplifies the development of the local hydrostatic stress in grains under tensile hydrostatic stress.

Phase transition and electrical properties of Ni1−x Zn x Mn2O4 (0 ≤ x ≤ 1.0) NTC ceramics

The Ni1−x Zn x Mn2O4 (0 ≤ x ≤ 1.0) negative temperature coefficient (NTC) ceramics were prepared by the traditional solid state reaction method. X-ray diffraction results show that the as-sintered ceramics transformed to tetragonal spinel (x = 1) gradually from cubic spinel (x = 0). Scanning electron microscope images show that the shape of grains changed with increasing Zn ions content, because of the stress in grains induced by phase transition. The resistivity decreased slightly with increasing Zn ions content for x ≤ 0.25, but increased remarkably for higher Zn ions content. The values of ρ 25, B 25/50 and activation energy for Ni1−x Zn x Mn2O4 (0 ≤ x ≤ 0.8) NTC thermistors were in the range of 3,511–136,780 Ω cm, 3,913–4,491 K and 0.3271–0.3691 eV, respectively. The values of relative resistance drift △R/R 0 (0 ≤ x ≤ 0.8) were 0.25), were attributed to the increase of grain boundaries resistance.

Arrangement of Internal Stresses in Grains with Simple or Complex Bends in Deformed Austenitic Steel

Arrangement of internal stresses in deformed austenitic steel is studied. The internal stresses are determined using parameters of bending extinction contours observing on electron microscope images of steel.

Microplasticity in Polycrystals: A Thermomechanical Experimental Perspective

In this paper, thermomechanical couplings at the grain scale in metallic polycrystals are studied during the deformation process through an original experimental setup and improved calibration tools and full-field treatments. In order to perform intragranular thermomechanical analysis in a metallic polycrystal at the grain scale, a crystallography-based technique for the projection of the temperature and displacement fields on a polynomial basis is proposed. It enables intragranular coupled analysis of strain and temperature full-field data. Macroscopic, mesoscopic and granular analysis are then conducted and it is shown that the determination of a macroscopic yield stress as well as a critical resolved shear stress in grains is possible. Early local microplastic activity is therefore thermomechanically confirmed.

Study of Mechanical Behaviour of Polycrystalline Materials at the Mesoscale Using High Energy X-Ray Diffraction

Owing to its selectivity, diffraction is a powerful tool for analysing the mechanical behaviour of polycrystalline materials at the mesoscale, i.e. phase and grain scale. In situ synchrotron diffraction (transmission mode) during tensile tests and modified self-consistent elastoplastic model were used to study elastic and plastic phenomena occurring in polycrystalline specimens during deformation. The evolution of stress for grains which belong to different phases of duplex stainless steel and pearlitic steel was analyzed.

Orientation-dependent evolution of the dislocation density in grain populations with different crystallographic orientations relative to the tensile axis in a polycrystalline aggregate of stainless steel

Line profile analysis was carried out on neutron diffraction patterns collected by the energy-dispersive method for an in situ tensile-deformed AISI-316 stainless steel specimen. The experiments were carried out at the VULCAN engineering beam line of the spallation neutron source of the Oak Ridge National Laboratory. Both the dislocation densities and the local stresses in grains oriented with different hkl crystal directions along the tensile axis were determined. The work-hardening equation of Taylor was tested for the hkl-dependent phenomenological constant α. The grain-orientation-dependent α values were directly related to the heterogeneity of dislocation distribution in correlation with previous transmission electron microscopy data.

Теоретико-полевой подход к описанию деформирования многокомпонентных поликристаллических материалов

Most of inorganic structural materials (metallic alloys, ceramics, minerals etc.) are polycrystalline aggregates, consisted of macroscopically large quantity of single-crystal grains (crystallites). The mechanical behavior of the specimen of polycrystalline material is governed by the physical and mechanical processes in the grains and interaction of the grains. Thus the deformation of polycrystalline material is a cooperative phenomenon typical for condensed matter physics and mechanics of heterogeneous materials. The passing of these processes depends on many parameters, including stress states of individual grains and its evolution during macrodeformation. In this paper we note a mathematical analogy between the equations of the mechanics of heterogeneous polycrystalline materials and the equations of quantum theory of particles scattering. This analogy allows to apply the methods of quantum field theory to solution of the equations of solid mechanics for heterogeneous media. We consider the application of Corringa-Kohn-Rostoker method, used in quantum theory for calculating wave function of electrons in metallic alloys, to elasticity of polycrystals. This approach allows, for instance, to calculate probability distribution density function for stresses in grains under arbitrary macrodeformation of polycrystal. Application of the method to classical problem of homogenization gives new formulae for the effective moduli of disordered polycrystalline medium.

Effect of Salicylic Acid Pretreatment on Yield, Its Components and Remobilization of Stored Material of Wheat under Drought Stress

Due to higher needs of food in growing populations leads to accelerate the efforts of food production now days. Yield which is obtained from cereal farm is not at the amount of what we expected from their genetic potential. So it is possible to use different agro-techniques to increase total yield and help the crops to reach their genetic potential. In order to investigate the effect of salicylic acid on total yield and yield component of wheat under stress condition an experiment was conducted base on split factorial design with three replications. Treatments were drought stress at three levels (control, drought stress in mid florescence and drought stress in grain filling stage). Second treatment was application of salicylic acid as a priming agent, foliar application at beginning of tillering and foliar application of salicylic acid at beginning of flowering, and the third treatment was different dosage of salicylic acid (0, 0.7, 1.2 and 2.7 mmol). Results of experiment showed that drought stress significantly decreased grain yield, efficiency of material distribution while the highest grain yield was obtained at non-stressed condition with application of 0.7 mmol Salicylic acid. The highest redistribution of stored material, redistribution efficiency and partitioning was at time of salicylic application in vegetative stage, whereas the highest proportion of the metabolism in the grain yield observed in control condition (without stress). Grain yield exhibited high and positive correlation with number of spikes in m2, number of grain in spike, biological yield and harvest index.

Spatial variations in surface sediment structure in riffle–pool sequences: a preliminary test of the Differential Sediment Entrainment Hypothesis (DSEH)

ABSTRACTRiffle–pool sequences are maintained through the preferential entrainment of sediment grains from pools rather than riffles. This preferential entrainment has been attributed to a reversal in the magnitude of velocity and shear stress under high flows; however the Differential Sediment Entrainment Hypothesis (DSEH) postulates that differential entrainment can instead result from spatial sedimentological contrasts. Here we use a novel suite of in situ grain‐scale field measurements from a riffle–pool sequence to parameterize a physically‐based model of grain entrainment. Field measurements include pivoting angles, lift forces and high resolution digital elevation models (DEMs) acquired using terrestrial laser scanning, from which particle exposure, protrusion and surface roughness were derived. The entrainment model results show that grains in pools have a lower critical entrainment shear stress than grains in either pool exits or riffles. This is because pool grains have looser packing, hence greater exposure and lower pivoting angles. Conversely, riffle and pool exit grains have denser packing, lower exposure and higher pivoting angles. A cohesive matrix further stabilizes pool exit grains. The resulting predictions of critical entrainment shear stress for grains in different subunits are compared with spatial patterns of bed shear stress derived from a two‐dimensional computational fluid dynamics (CFD) model of the reach. The CFD model predicts that, under bankfull conditions, pools experience lower shear stresses than riffles and pool exits. However, the difference in sediment entrainment shear stress is sufficiently large that sediment in pools is still more likely to be entrained than sediment in pool exits or riffles, resulting in differential entrainment under bankfull flows. Significantly, this differential entrainment does not require a reversal in flow velocities or shear stress, suggesting that sedimentological contrasts alone may be sufficient for the maintenance of riffle–pool sequences. This finding has implications for the prediction of sediment transport and the morphological evolution of gravel‐bed rivers. Copyright © 2012 John Wiley & Sons, Ltd.