Anisotropic Orientation Research Articles

Real-time super-resolution mapping of locally anisotropic grain orientations for ultrasonic non-destructive evaluation of crystalline material

Estimating the spatially varying microstructures of heterogeneous and locally anisotropic media non-destructively is necessary for the accurate detection of flaws and reliable monitoring of manufacturing processes. Conventional algorithms used for solving this inverse problem come with significant computational cost, particularly in the case of high-dimensional, nonlinear tomographic problems, and are thus not suitable for near-real-time applications. In this paper, for the first time, we propose a framework which uses deep neural networks (DNNs) with full aperture, pitch-catch and pulse-echo transducer configurations, to reconstruct material maps of crystallographic orientation. We also present the first application of generative adversarial networks (GANs) to achieve super-resolution of ultrasonic tomographic images, providing a factor-four increase in image resolution and up to a 50% increase in structural similarity. The importance of including appropriate prior knowledge in the GAN training data set to increase inversion accuracy is demonstrated: known information about the material’s structure should be represented in the training data. We show that after a computationally expensive training process, the DNNs and GANs can be used in less than 1 second (0.9 s on a standard desktop computer) to provide a high-resolution map of the material’s grain orientations, addressing the challenge of significant computational cost faced by conventional tomography algorithms.

Can we predict the microstructure of a non-woven flax/PLA composite through assessment of anisotropy in tensile properties?

Flax/Poly-(lactide) non-woven composites are an alternative to conventional glass/poly-(propylene), offering a potentially lower environmental impact solution for the automotive industry. To understand this complex material, its detailed architecture and void distribution are examined through 3D microtomography. Anisotropy in fibre orientation is also observed, further verified through off-axis tensile tests. Then micro-mechanics and laminate theory are used, taking into account fibre orientation distribution, to predict mechanical properties and compare with experimental measurements. Even though some deviation is observed at off-axis angles greater than 45°, we report that off-axis tensile tests (property) can be used to predict fibre orientation (structure) in industrial production facilities as a simple means of quality control and tailored design of new non-woven preforms.

Azimuthal anisotropy from eikonal tomography: example from ambient-noise measurements in the AlpArray network

SUMMARY Ambient-noise records from the AlpArray network are used to measure Rayleigh wave phase velocities between more than 150 000 station pairs. From these, azimuthally anisotropic phase-velocity maps are obtained by applying the eikonal tomography method. Several synthetic tests are shown to study the bias in the Ψ2 anisotropy. There are two main groups of bias, the first one caused by interference between refracted/reflected waves and the appearance of secondary wave fronts that affect the phase traveltime measurements. This bias can be reduced if the amplitude field can be estimated correctly. Another source of error is related to the incomplete reconstruction of the traveltime field that is only sparsely sampled due to the receiver locations. Both types of bias scale with the magnitude of the velocity heterogeneities. Most affected by the spurious Ψ2 anisotropy are areas inside and at the border of low-velocity zones. In the isotropic velocity distribution, most of the bias cancels out if the azimuthal coverage is good. Despite the lack of resolution in many parts of the surveyed area, we identify a number of anisotropic structures that are robust: in the central Alps, we find a layered anisotropic structure, arc-parallel at mid-crustal depths and arc-perpendicular in the lower crust. In contrast, in the eastern Alps, the pattern is more consistently E–W oriented which we relate to the eastward extrusion. The northern Alpine forleand exhibits a preferential anisotropic orientation that is similar to SKS observations in the lowermost crust and uppermost mantle.

Controllable magnetic anisotropy and spin orientation of a prototypical easy-plane antiferromagnet on a ferromagnetic support

The control of the spin orientation in antiferromagnets is of key importance in modern spintronics. Here, the authors demonstrate controllable antiferromagnetic spin switching in a synthetically fabricated epitaxial ferromagnet/antiferromagnet bilayer. Thanks to the precise nanoengineering of ferromagnet anisotropy and interface exchange coupling, two orthogonal spin states in the antiferromagnet can be either thermally stabilized in a field-free manner or written by a small external magnetic field.

Spin pumping contribution to the magnetization damping in Tm3Fe5O12/W bilayers

In this work, thulium iron garnet (Tm3Fe5O12 – TmIG (20 nm)/Tungsten(W)(t) bilayers, sputtered on top of gadolinium gallium garnet (111) substrate, were used to investigate spin pumping (SP) line broadening mechanism in Ferromagnetic Resonance (FMR). The TmIG, films prior and after tungsten cap layer deposition, were investigated employing FMR and X-ray diffraction techniques. The TmIG films showed (111) orientation and perpendicular magnetic anisotropy (PMA). Due to the interface TmIG/W, when the TmIG magnetization is in resonance a spin current is pumped out the TmIG into the W layer, increasing the damping of the magnetization. Measuring the out-of-plane angular dependence of the FMR resonance field and linewidth, we were able to obtain solely the SP contribution to the line broadening, filtering Gilbert, mosaicity, and two magnon scattering mechanisms.

Highly Nonlinear Solitary Waves to Estimate Orientation and Degree of Anisotropy in Rocks

This paper delves into the use of highly nonlinear solitary waves for the nondestructive identification and characterization of anisotropy in rocks. The nondestructive testing approach proposed expands upon a technique developed recently by some of the authors for the nondestructive characterization of engineering materials and structures. The technique uses the characteristics of solitary waves propagating in a periodic array of spherical particles in contact with the rock to be characterized. The features of the waves that bounce off the chain rock interface are used to infer some properties of the geomaterial under consideration. Numerical models and experimental validation were conducted to explore the feasibility of the method and to standardize the methodology for future widespread applications.

Surface-Orientation Elimination of Vapor-Deposited PbI2 Flakes for Efficient Perovskite Synthesis on Curved Solar Cells.

Vapor deposition of perovskite solar cells (PSCs) has attracted considerable interest for its dry processing characteristics. However, a two-step sequential vapor deposition method suffers from ineffective conversion of PbI2 to perovskite with reasons still unclear. In this report, we carefully investigated the crystallization orientation of PbI2 films deposited by physical vapor deposition via synchrotron grazing-incidence wide-angle X-ray scattering (GIWAXS) and observed an asymmetric scattering pattern with respect to the qz-axis. The observed oriented morphology and texture hinder the diffusion of MAI molecules in the PbI2 films synthesized by vapor deposition, resulting in over 15% PbI2 remaining at the buried interface after reaction with MAI vapor. As a result, the MAPbI3 synthesized in this way was also highly oriented, especially in the surface layers. Surface fumigation (SF) step was introduced to decrease the orientational anisotropy of PbI2, which successfully breaks the diffusion barriers of MAI molecules by forming a complex layer on the PbI2 surface with polar solvent vapors, like dimethyl sulfoxide or 1,3-dimethyl-2-imidazolidinone. We infer that the SF treatment changes the vapor-solid reaction mechanism from reaction-crystallization to dissolution-recrystallization, which largely promotes the conversion of PbI2 to perovskite. Defects were reduced in perovskite synthesized in this way, and a p-i-n device with 19.56% efficiency was fabricated, which is among the highest efficiencies reported for sequential-vapor-deposited PSCs. Notably, this method enables the fabrication of conformal perovskite layers on uneven substrates. An exemplary PSC showing efficiency of 8.93% was fabricated on a precurved substrate. We believe that the method is applicable to the fabrication of tandem or curved PSCs that are compatible with wearable or building/autocar-integrated photovoltaics in the future.

Porttipahta end moraine in Finnish Lapland is constrained to Early Weichselian (MIS 5d, Herning stadial)

Litho- and chronostratigraphy of the Early Weichselian time period, or Marine Isotope Stages (MIS) 5e-5a, is insufficiently established in Northern Fennoscandia and still more ambiguous is the regional-scale distribution of the corresponding end moraines. We applied Light Detection And Ranging Digital Elevation Models (LiDAR DEMs), electromagnetic (EM) sedimentary anisotropy (orientation) and ground penetrating radar (GPR) to reveal till-covered landforms diagnostic to the Early Weichselian phase(s) in Finnish Lapland. Morphometric and geophysical data revealed that sands and gravels of the Porttipahta end moraine were deposited from the north-northwest and are overlain by one diamicton (till) unit deposited from the southwest and most likely being correlative to the Late Weichselian (MIS 2). Sub-till OSL-ages yielded 91 ± 19, 96 ± 14, 100 ± 16 and 120 ± 26 ka, thus correlative with the MIS 5c interstadial (Brørup). The Porttipahta end moraine deposited during the deglaciation of the Early Weichselian 5d stadial (Herning).The NW-SE oriented till-covered eskers and rock drumlins in the area suggest Late Saalian (MIS 6) phase. Southwest of the Porttipahta area the end moraine complex is deformed by earthquake(s) attributable to glacial isostatic adjustment (GIA) probably during the MIS 5d phase. The morphological appearance is similar to Veiki moraine in Norrbotten, Sweden, and high-resolution LiDAR DEMs emphasize that both landforms exhibit a minute erosion by the later stadials. It remains unresolved, if the Porttipahta end moraine represents the maximum extent of the MIS 5d or if it represents a recessional stage.

Molecular orientation anisotropy and hole transport properties of diluted semiconducting films of poly(p-phenylenevinylene) derivative

The electrical and optical properties of certain semiconducting polymers are improved in blend films with inert host materials. The improvements have been attributed to the dilution effect of electron traps and interchain species in semiconductor materials. In this paper, we report on anisotropy in the blend films of poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and its strong dependence on an inert host material, such as polystyrene (PS) or polyvinylcarbazole (PVK). We found that the orientation of the MEH-PPV backbone in the blend film changed from horizontal to random on dilution with PS. Moreover, the in-plane hole conductivity was enhanced in the MEH-PPV:PVK blend film, although the out-of-plane conductivity reduced owing to excessive dilution. Mott–Schottky analysis of the capacitance–voltage characteristics revealed opposite trends for dilution with PS and PVK; i.e., PS increased the accumulated charge density in the bulk of the blend film, whereas PVK reduced it. These results demonstrate that isotropy was induced in the PS blend films, whereas anisotropy was induced in the PVK blend films. Anisotropy is an important factor for understanding the hole transport characteristics in the diluted films. • Anisotropy of hole transport property was found in the diluted polymer films. • Anisotropy in the diluted films strongly depends on the inert host material. • Anisotropy is an important factor for understanding the hole transport properties.

Electrically tunable polarization independent liquid crystal lenses based on orthogonally anisotropic orientations on adjacent micro-domains.

Polarization dependency is an intrinsic property of liquid crystals (LC) devices but major problem is optical efficiency. We demonstrated a polarization independent liquid crystal phase modulation based on the orthogonal nematic LC (OLC) mode wherein the optics axes of nematic liquid crystal molecules are set orthogonally to adjacent sub-domains for the first time. Such an OLC mode includes sub-domain with anisotropic orientations but collectively presents a capability of a polarizer-free optical phase modulation. An OLC mode cell provides a tunable optical phase of ∼3.35π radians for unpolarized light and different linearly polarized light. Among the polarizer-free LC mode, the proposed OLC mode is single-layered with large tunable optical phase. We also demonstrated a polarizer-free LC micro-lens. We expect this novel LC mode provide alternatives technology roadmap for upcoming optical applications, such as electrically tunable ophthalmic lenses and optical systems for augmented reality.

Splitting of the Magnetic Loss Peak of Composites under External Magnetic Field

Composite materials filled with ferromagnetic inclusions are useful in the development of various microwave devices. The performance of such devices is determined both by material properties (such as the saturation magnetization and the permeability) and by the demagnetization effects. The paper is devoted to the study of the demagnetization effect on the permeability measurements of composites under external magnetic bias. The microwave permeability of composites filled with flake sendust (Fe-Si-Al alloy) particles is measured as a function of frequency and the external magnetic field. The measurements are carried out by the Nicolson–Ross–Weir technique in a 7/3 coaxial line in the frequency range of 0.1 to 20 GHz by a vector network analyzer. It is found that the magnetic loss peak is split under external fields of more than 1.5 kOe. The main aim of this paper is to study the causes of this splitting and to interpret the observed magnetic loss peaks. To study this effect, the samples of various thicknesses and the samples with isotropic and anisotropic orientations of particles are measured. The particles in the anisotropic samples are oriented by a strong uniform magnetic field. At a small fraction of inclusions, the permanent magnetic field is demagnetized on the individual particles rather than the whole sample. The splitting of the magnetic loss peak of the isotropic sample is caused by different orientations of particles in the sample. At a high fraction of inclusions, the permanent magnetic field is demagnetized on the whole sample and the magnetic loss peak of the isotropic sample is not split. The saturation magnetization of the material is found by measurements under the external magnetic field of the anisotropic sample.

Preterm birth alters the development of cortical microstructure and morphology at term-equivalent age

IntroductionThe dynamic nature and complexity of the cellular events that take place during the last trimester of pregnancy make the developing cortex particularly vulnerable to perturbations. Abrupt interruption to normal gestation can lead to significant deviations to many of these processes, resulting in atypical trajectory of cortical maturation in preterm birth survivors. MethodsWe sought to first map typical cortical micro- and macrostructure development using invivo MRI in a large sample of healthy term-born infants scanned after birth (n = 259). Then we offer a comprehensive characterization of the cortical consequences of preterm birth in 76 preterm infants scanned at term-equivalent age (37–44 weeks postmenstrual age). We describe the group-average atypicality, the heterogeneity across individual preterm infants, and relate individual deviations from normative development to age at birth and neurodevelopment at 18 months. ResultsIn the term-born neonatal brain, we observed heterogeneous and regionally specific associations between age at scan and measures of cortical morphology and microstructure, including rapid surface expansion, greater cortical thickness, lower cortical anisotropy and higher neurite orientation dispersion. By term-equivalent age, preterm infants had on average increased cortical tissue water content and reduced neurite density index in the posterior parts of the cortex, and greater cortical thickness anteriorly compared to term-born infants. While individual preterm infants were more likely to show extreme deviations (over 3.1 standard deviations) from normative cortical maturation compared to term-born infants, these extreme deviations were highly variable and showed very little spatial overlap between individuals. Measures of regional cortical development were associated with age at birth, but not with neurodevelopment at 18 months. ConclusionWe showed that preterm birth alters cortical micro- and macrostructural maturation near the time of full-term birth. Deviations from normative development were highly variable between individual preterm infants.

Multiscale investigation of microstructure optimization in the arc additive manufacturing and arc welding by self-induced ultrasound

In the arc welding and arc additive manufacturing processes, utilizing self-induced ultrasound has attracted widespread attention for obtaining intensive arc plasma and optimizing metallurgical characteristics of molten pool, featuring with increased penetration, suppressed dendrites and refined grains in the deposited layer and weld joint of metal. However, the ultrasound emitting mechanism remains unclear and process optimization remains limited by incomplete understanding of ultrasound in the arc plasma and molten pool. In our work, Multiscale experiments and modeling (MHD and MHD waves modeling at meso scale, coupled phase-field and fluid flow modeling and fluid-structure modeling at micro scale) are proposed to reveal the physical essence of ultrasound generation, ultrasound induced streaming, suppressed dendrites growth and dendrites fragmentations.It demonstrates the effectiveness and efficiency of utilizing self-induced ultrasound in controlling microstructures of 316 stainless steel with a maximum of 24% decrease in grain size and transition from anisotropy orientation to isotropy orientation, and concrete directions of process optimization arc identified for facilitating the successful industrial use. We expect introducing self-induced ultrasound energy could be a more efficient and cost effective technology for controlling of microstructure in the arc metal processing related fields.

Processing and mechanical characterization of short carbon fiber-reinforced epoxy composites for material extrusion additive manufacturing

Fiber-reinforced polymer composites have been extensively utilized in recent years as feedstock materials for material extrusion additive manufacturing (AM) processes to improve strength, stiffness, and functionality of printed parts over unfilled printed polymers. However, the widespread adoption of AM of fiber-reinforced polymer composites requires a deeper understanding of the process-structure-property relationships in printed components, and such relationships are not well understood yet. Fiber length is critically important to the mechanical performance of short fiber composites, but very few studies to-date have focused on how the fiber length distribution (FLD) evolves during processing of composite feedstocks and how this evolution affects printing behavior and mechanical properties in 3D-printed composites. In this work, FLD is measured for carbon fiber reinforced epoxy composites over a wide range of ink compositions and shear mixing times, and the distributions are fit with a Weibull-type distribution function. The effects of FLD on the tradeoff between ink processability, ink rheology, printing behavior and mechanical properties are investigated. Furthermore, the effects of printing parameters (nozzle size and print speed) on mechanical anisotropy and fiber orientation distribution (FOD) in printed composites are explored. Mechanical properties of printed composites are characterized via 3 pt-flexural testing, and microstructure is investigated using optical and scanning electron microscopy (SEM), and x-ray computed tomography. Finally, the fitted Weibull parameters are fed into a composite model that incorporates FLD and FOD, and model predictions are found to be in excellent agreement with experimental observations.

Wastewater Disposal Has Not Significantly Altered the Regional Stress State in Southern Kansas

Abstract Wastewater disposal is primarily responsible for the increased seismicity rate since ∼2013 in southern Kansas. Previous work that used shear-wave splitting (SWS) in southern Kansas interpreted an ∼90° temporal rotation in the fast polarization direction and attributed it to increased pore pressures resulting from fluid injection. However, this interpreted rotation coincided with a change in the stations used to make the SWS measurements. We investigate the temporal variability of fast azimuths in southern Kansas by making SWS measurements on earthquake families with similar source–receiver paths recorded on a stable local seismic network. We select high-quality SWS measurements by investigating the stability of results across 65 different frequency bands between 0.5 and 15 Hz. We find that the fast polarization direction in southern Kansas is relatively constant with an average east-northeast (∼N79°E) orientation between 2014 and 2017. Our fast polarization measurements are primarily a reflection of the maximum principal horizontal stress direction (SHmax). We observe a slight spatial change in SHmax to the northeast (∼N55°E) near the Nemaha ridge in Oklahoma. However, we do not observe any significant temporal rotation of SHmax or variation in delay time (i.e., crack density) in southern Kansas, contrary to the earlier study. The previously interpreted ∼90° rotation may either be a reflection of a very local stress change or a misinterpretation of SWS results potentially due to the use of inconsistent source–receiver paths. Our SWS measurements cover the period of peak wastewater disposal and seismicity rates and suggest an absence of significant temporal rotations in the local anisotropy and stress orientations associated with wastewater disposal.

Design of Novel POB/h-BN Co-Filled PTFE Composites with Enhanced Thermal–Mechanical Properties

Polytetrafluoroethylene (PTFE) is provided with excellent self-lubricating properties and corrosion resistance. However, the lower thermal resistance greatly limits its high-temperature applications. In the present work, two types of fillers with rigid organic polymers and submicron-sized inorganic hexagonal boron nitride (h-BN) were added to the PTFE matrix. The microstructure and thermal–mechanical properties of PTFE-based composites with different filler types or ratios were comparatively investigated. The results suggested that the polyphenyl ester (POB)/h-BN co-filled PTFE composites exhibited excellent thermal–mechanical properties compared with the polyimide (PI)/h-BN/PTFE materials at high temperature. The optimal ratios of POB and h-BN were 25 wt.% and 5 wt.%, respectively. The Vicat softening temperature of 25 wt.% POB/5 wt.% PI/PTFE composite increased by 41.3% compared to that of pure PTFE, which was due to the cross-linked reticulation structure with regularly distributed pores and higher crystallization degree. The storage modulus increased from 51.99 MPa to 685.76 MPa at 260 °C and reached 187.82 MPa at 320 °C. The uniform distribution of anisotropic orientation of the h-BN flakes showed an obvious pinning effect, and further improved the thermal–mechanical stability of POB/h-BN/PTFE composites.

Update 3.0 to “PuMA: The Porous Microstructure Analysis software”, (PII:S2352711018300281)

A major update of the Porous Microstructure Analysis (PuMA) software is presented. PuMA is a framework for computing effective material properties and response based on material microstructures. Version 3.0 of the software extends the PuMA capabilities to include computation of anisotropic conductivity, elasticity, permeability, per-voxel material or fiber orientation estimation, as well as expanded computational material generation capabilities. Version 3.0 also introduces pumapy, a Python version of the PuMA software.

Exploring Nanoscale Lubrication Mechanisms of Multilayer MoS2 During Sliding: The Effect of Humidity.

Solid lubricants have received substantial attention due to their excellent frictional properties. Among others, molybdenum disulfide (MoS2) is one of the most studied lubricants. Humidity results in a deterioration of the frictional properties of MoS2. The actual mechanism at the nanoscale is still under debate, although there are indications that chemical reactions are not likely to occur in defect-free structures. In this study, we performed nonequilibrium molecular dynamics simulations to study the frictional properties of multilayer MoS2 during sliding in the presence of water. Moreover, we also investigated the effect of sliding speed and normal load. We confirmed earlier results that a thin layer of water organizes as a solidified, ice-like network of hydrogen bonds as a result of being confined in a two-dimensional fashion between MoS2. Moreover, we found that there exists an energy-driven, rotational dependence of the water network atop/beneath MoS2. This orientational anisotropy is directly related to the dissipative character of MoS2 during sliding. Finally, three distinct frictional regimes were identified, two for a thin layer of water and one for bulk water. In the case of a thin layer and low coverage, water represents a solid-like contaminant, causing high energy dissipation. For a thin layer and high coverage, water starts to act as a solid-like lubricant, reducing dissipation during sliding. Finally, a regime where water acts as a liquid lubricant, characterized by a clear velocity dependence was found.

Effect of grain size or anisotropy on the correlation between uniaxial compressive strength and Schmidt hammer test for building stones

To provide guidance for using Schmidt hammer rebound number (N-type hammer: RN) to predict uniaxial compressive strength (UCS) of heterogeneous building stones, this paper using sandstone (with fine or coarse grain size) and gneiss (with 0°, 45°, 90° inclined anisotropy) respectively explored the effect of grain size or anisotropy on the correlations of UCS-RN. Based on the regression analysis, no significant formula of UCS-RN can be developed for samples with vertical anisotropy. The results show that coarse grain size or 45° inclined anisotropy results in increasing discreteness of UCS and RN data. Then, grain size variation or multidirectional anisotropy deteriorates the statistical performance of equations between UCS and RN. Finally, the accuracy of estimated UCS through RN declines significantly due to the varying grain size or anisotropy orientation. Using the empirical equations ignoring grain size or anisotropy can yield unacceptable error for calculating UCS through RN. The present finding, thus, implies that the Schmidt hammer test should be performed on building stones with single grain size magnitude or unidirectional anisotropy. Also, the Schmidt hammer test parallel to the anisotropy should be used with much care for predicting UCS as no significant correlation.

Crustal and Mantle Deformation Inherited From Obduction of the Semail Ophiolite (Oman) and Continental Collision (Zagros)

AbstractA common deviation from typical subduction models occurs when thrust sheets of oceanic crust and upper‐mantle rocks are emplaced over more buoyant continental lithosphere. The archetypal example of ophiolite obduction is the Semail ophiolite in the United Arab Emirates (UAE)‐Oman orogenic belt, formed and obducted onto the Arabian continental margin during the Late Cretaceous. The Strait of Hormuz syntaxis, the northern extent of the UAE‐Oman mountains, marks the transition from ocean‐continent convergence in the Gulf of Oman to continental collision along the Zagros Mountains. Based on new seismic data from a focused recording network, we infer continental crustal and mantle deformation in the northeastern corner of the Arabian plate (including the southern Zagros and the UAE‐Oman mountains), using observations from anisotropic tomography and shear‐wave splitting (SWS) measurements. We recover a change of ∼90° (from approximately WNW to nearly NS) in the axis of fast‐anisotropic orientations in the crust from the Zagros to the UAE‐Oman mountain belt, consistent with the dominant strike of the orogenic belts. We also find evidence in our SWS parameters for localized fossil deformation in the lithospheric mantle underlying the UAE‐Oman mountain range, possibly related to stress‐induced tectonism triggered by north‐east oriented underthrusting of the proto‐Arabian continental margin beneath the overriding Semail ophiolite. Shear‐wave‐splitting anisotropy orientations along two transects across the northern Musandam peninsula, averaging 15° anticlockwise from the north, provide the first geophysical verification of previous geological evidence that suggests a NE polarity of the Late Cretaceous Oman subduction zone system.