Facet Planes Research Articles

Quantitative Characterization of Microscale Fracture Features in Titanium Alloys

Quantification of the fracture mechanisms is important for design and sustainment of fatigue–critical components and for improved life prediction models. The traditional fractography in a scanning electron microscope (SEM) provides important, but qualitative, information on fracture mechanisms. In this study, the fatigue fracture features at the crack-initiation site in a near-α titanium alloy were characterized quantitatively in an SEM. The crack initiated in a surface-located primary α grain, with the resultant formation of a facet. A serrated feature was observed on the fatigue crack-initiating facet within an α grain for the first time in this study. The spatial orientations of the crack-initiating facet and the fracture lines forming the serration were determined in 3D with the quantitative tilt fractography technique, which consists of analyzing an SEM image pair acquired at different stage tilt angles. The electron backscatter diffraction (EBSD) data were collected nondestructively from the grain associated with faceted crack-initiation, without recourse to cross-sectional polishing. Combining the spatial orientation and the EBSD data established that the facet plane was basal and the lines forming the serrated feature were along 〈a〉 \( \left(\text{i.e.,}\; {\left\langle {2\bar{1}\bar{1}0} \right\rangle } \right) \)-type slip directions. The methodology presented in this study is applicable to quantification of crystallography for other planar and linear features in crystalline materials.

Modeling method on acoustic scattering from penetrable objects using a hybrid Kirchhoff/ray approach

A method is put forward to investigate the acoustic scattering from double-sided water loaded targets which is penetrable even in high frequency. The present approach is an extension of the TriKirch method which was elaborated for non-penetrable targets [J. Acoust. Soc. Am. 140(3), 1878-1886 (2016)] and complex targets are dispersed into many triangular planar facets. Reflection coefficient of plane facet is introduced to calculate the scattering amplitude of each non-rigid triangular facets combined with TirKirch method, and the total scattering amplitude of target is obtained by superposing the amplitude of all facets’ contributions coherently. Double bounce (DB) contributions to the scattering is calculating by ray-tracing method. Computations are made for a double-sided water loaded finite cylindrical shell with perforated ring ribs, and are compared with the experimental results，and both results show good agreement.

Effect of Nickel Contents on the Microstructure and Mechanical Properties for Low-Carbon Bainitic Weld Metals

Multi-pass weld metals were deposited on Q345 base steel using metal powder-flux-cored wire with various Ni contents to investigate the effects of the Ni content on the weld microstructure and property. The types of the microstructures were identified by optical microscope, scanning electron microscope, transmission electron microscope, and micro-hardness tests. As a focusing point, the lath bainite and lath martensite were distinguished by their compositions, morphologies, and hardness. In particular, a number of black plane facets appearing between lath bainite or lath martensite packets were characterized by laser scanning confocal microscope. The results indicated that with the increase in Ni contents in the range of 0, 2, 4, and 6%, the microstructures in the weld-deposited metal were changed from the domination of the granular bainite to the majority of the lath bainite and/or the lath martensite and the micro-hardness of the weld-deposited metal increased. Meanwhile, the average width of columnar grain displays a decreasing trend and prior austenite grain size decreases while increases with higher Ni content above 4%. Yield strength and ultimate tensile strength decrease, while the reduction in fracture area increases with the decreasing Ni mass fraction and the increasing test temperature, respectively. And poor yield strength in Ni6 specimen can be attributed to elements segregation caused by weld defect. Finally, micro-hardness distribution in correspondence with specimens presents as a style of cloud-map.

Structural Morphology and Performance of Plated Structures with Planar Quadrilateral Facets

The aim of this paper is to present some innovative strategies for the design of plated shell structures. Fabrication constraints are carefully considered, as the obtained shapes are covered with planar quadrilateral facets only. Different corrugation strategies are investigated, and our method guarantees extension of the shape generation to complex topologies. Few parameters control the amplitude of corrugations, which also gives us the opportunity to perform a sensitivity analysis on the influence of corrugations on the structural performance of folded-plate structures. The study focuses on the influence of the mechanical attachment between plates on the overall structural performance as well as fabrication rationality.

The Facet Orientation of the Subaxial Cervical Spine and the Implications for Cervical Movements and Clinical Conditions.

Computed tomography study. To obtain detailed information on the facet orientation in the subaxial cervical spine and explore the correlation to the cervical movements and relevant clinical conditions. Although facet orientation was well studied in the lumbar spine, the literatures on the cervical facet orientation were limited and the descriptions were nonspecific. The computed tomography scans of 100 individuals were reconstructed. For each level from C2/C3 to C6/C7, the horizontal plane, the mid-sagittal plane, the coronal plane, and the two facet planes were established. The normal vectors of the five planes were used for the calculation of the facet orientation and the facet tropism. The angle of the facet plane with respect to the horizontal plane at the C6/7 level was the largest (left side: 64.34° ± 6.60°, right side: 63.37° ± 6.81°, P >0.05). The angle of the facet plane with respect to the coronal plane decreased from C2/C3 level to C6/C7 level. Regarding the angle of the facet plane with respect to the sagittal plane, for the paired facet joints, three types were found: posteromedially oriented, posterolaterally oriented, and ipsilaterally oriented. All (100%) of the facet joints at the C2/C3 level and 65% at the C3/C4 level were posteromedially oriented. In the lower levels of the cervical spine, the posteromedially oriented facet joints were less common. The facet tropism was common phenomenon in the subaxial cervical spine. This study provided detailed information on the facet orientation in the subaxial cervical spine. The cervical facet orientation correlated well with the spinal movements and related clinical conditions. 3.

Investigation of fatigue crack initiation facets in Ti-6Al-4V using focused ion beam milling and electron backscatter diffraction.

In the very high cycle fatigue regime, internal crack initiation can occur in Ti-6Al-4V because of the formation of facets, which are α grains that have fractured in a transcrystalline and planar manner. Because this crack initiation phase occupies most of the fatigue life, it is essential to understand which mechanisms lead to facet formation. Fatigue tests have been performed on drawn and heat-treated Ti-6Al-4V wires, and the facets at internal crack initiation sites have been analysed in detail in terms of their appearance, their spatial orientation and their crystallographic orientation. The facets were not smooth, but showed surface markings at the nanoscale. In nearly all cases, these markings followed a linear pattern. One anomalous facet, in a sample with the largest grain size, contained a fan-shaped pattern. The facets were at relatively steep angles, mostly between 50° and 70°. Cross-sections of the fracture surfaces have been made by focused ion beam milling and were used to measure the crystallographic orientation of facets by electron backscatter diffraction. Most facet planes coincided with a prismatic lattice plane, and the linear markings were parallel to the prismatic slip direction, which is a strong indication that prismatic slip and slip band formation led to crack initiation. However, the anomalous facet had a near-basal orientation, which points to a possible cleavage mechanism. The cross-sections also exposed secondary cracks, which had formed on prismatic lattice planes, and in some cases early stage facet formation and short crack growth phenomena. The latter observations show that facets can extend through more than one grain, and that there is crack coalescence between facets. The fact that drawn wires have a specific crystallographic texture has led to a different facet formation behaviour compared to what has been suggested in the literature.

Deep-ultraviolet polychromatic emission from three-dimensionally structured AlGaN quantum wells

Three-dimensional (3D) AlGaN/AlN quantum wells (QWs) were fabricated on trench-patterned AlN templates using a regrowth technique based on metalorganic vapor phase epitaxy. The 3D structures are composed of planar (0001) facets, facets, and misoriented (0001) planes with bunched steps. Cathodoluminescence spectroscopy revealed double-peaked deep-ultraviolet (DUV) emissions: the shorter-wavelength emission was attributed to the (0001) facets, whereas the longer-wavelength emission arose from bunched step structures located around the bottom corner of the AlN trench, a region in which the AlGaN QWs possessed a relatively high Ga concentration and a thick well width compared with planar (0001) QWs.

Achieving High Current Density of Perovskite Solar Cells by Modulating the Dominated Facets of Room-Temperature DC Magnetron Sputtered TiO2 Electron Extraction Layer.

The short circuit current density of perovskite solar cell (PSC) was boosted by modulating the dominated plane facets of TiO2 electron transport layer (ETL). Under optimized condition, TiO2 with dominant {001} facets showed (i) low incident light loss, (ii) highly smooth surface and excellent wettability for precursor solution, (iii) efficient electron extraction, and (iv) high conductivity in perovskite photovoltaic application. A current density of 24.19 mA cm-2 was achieved as a value near the maximum limit. The power conversion efficiency was improved to 17.25%, which was the record value of PSCs with DC magnetron sputtered carrier transport layer. What is more, the room-temperature process had a great significance for the cost reduction and flexible application of PSCs.

Universal Approach for Predicting Crystallography of Heterogeneous Epitaxial Nanocrystals with Multiple Orientation Relationships.

Heteroepitaxial nanocrystals are one of the most fundamentally and technologically important classes of materials systems. The correlation between form, dictated by crystallographic features such as growth habit and direction, and function, in terms of the ultimate physio-chemical properties is well established, thus placing an onus on precise synthesis control of nanocrystal morphology. Yet, nanocrystal heteroepitaxy can be a frustrating, time-consuming iterative process, particularly during the initial stages of development. What is desired is a powerful predictive tool that is able to successfully predict not only the interface or habit plane, but also rationalize the occurrence of epitaxial growth complexities such as multiple orientation relationships (MORs) and high-index faceting planes for a diverse range of materials. Here we provide such a powerful approach that is based on an invariant deformation element (IDE) model, and fundamentally founded on the crystallography of diffusional phase transformations. We demonstrate its impact by detailed computations supported by transmission electron microscopy evidence, for an archetypical complex metal oxide nanocrystal system (that has up to five MORs for three differing growth orientations). The method is then applied to successfully explain growth for different materials ranging from metals to metal carbides to transition metal oxides, even in thin film form. Thus, this relatively simple yet powerful predictive guide significantly reduces the systemic inefficiencies of guesswork and blind growth. Ultimately it can be easily integrated with machine learning techniques toward reliable and efficient advanced nanomaterials fabrication.

Linear buckling of quadrangular and kagome gridshells: A comparative assessment

The design of gridshells is subject to strong mechanical and fabrication constraints, which remain largely unexplored for non-regular patterns. The aim of this article is to compare the structural performance of two kind of gridshells. The first one is the kagome gridshell and it is derived from a non-regular pattern constituted of triangles and hexagons. The second one results from a regular pattern of quadrangles unbraced by diagonal elements. A method is proposed to cover kagome gridshells with planar facets, which reduces considerably the cost of fabrication of the cladding.The sensitivity of kagome gridshells to geometrical imperfections is discussed. The linearised buckling load of kagome gridshells is then compared to the one of quadrilateral gridshells. The most relevant design variables are considered in the parametric study. Two building typologies are studied for symmetrical and non-symmetrical load cases: dome and barrel vault. It reveals that the kagome gridshell outperforms quadrilateral gridshell for a very similar construction cost.

Synthesis of silver nanoparticles by endosymbiont Pseudomonas fluorescens CA 417 and their bactericidal activity.

The present study emphasizes on biogenic synthesis of silver nanoparticles and their bactericidal activity against human and phytopathogens. Nanoparticle synthesis was performed using endosymbiont Pseudomonas fluorescens CA 417 inhabiting Coffea arabica L. Synthesized nanoparticles were characterized using hyphenated spectroscopic techniques such as UV-vis spectroscopy which revealed maximum absorption 425nm. Fourier transform infrared spectroscopy (FTIR) analysis revealed the possible functional groups mediating and stabilizing silver nanoparticles with predominant peaks occurring at 3346 corresponding to hydroxyl group, 1635 corresponding carbonyl group and 680 to aromatic group. X-ray diffraction (XRD) analysis revealed the Bragg's diffraction pattern with distinct peaks at 38° 44°, 64° and 78° revealing the face-centered cubic (fcc) metallic crystal corresponding to the (111), (200), (220) and (311) facets of the crystal planes at 2θ angle. The energy dispersive X-ray spectroscopy (EDS) analysis revealed presence of high intense absorption peak at 3keV is a typical characteristic of nano-crystalline silver which confirmed the presence of elemental silver. TEM analysis revealed the size of the nanoparticles to be in the range 5-50nm with polydisperse nature of synthesized nanoparticles bearing myriad shapes. The particle size determined by Dynamic light scattering (DLS) method revealed average size to be 20.66nm. The synthesized silver nanoparticles exhibited significant antibacterial activity against panel of test pathogens. The results showed Klebsiella pneumoniae (MTCC 7407) and Xanthomonas campestris to be more sensitive among the test human pathogen and phyto-pathogen respectively. The study also reports synergistic effect of silver nanoparticles in combination with kanamycin which displayed increased fold activity up to 58.3% against Klebsiella pneumoniae (MTCC 7407). The results of the present investigation are promising enough and attribute towards growing scientific knowledge on development of new antimicrobial agents to combat drug resistant microorganisms. The study provides insight on emerging role of endophytes towards reduction of metal salts to synthesize nanoparticles.

In situ assessment of the roughness of a uniformly eroded cylindrical magnetron target

We present an experimental approach for the in situ characterization of the surface roughness of an eroded magnetron target based on the reflectance pattern of a laser beam. The surface of the eroded region was modeled as a random arrangement of tilted plane facets with large surface extensions as compared to the wavelength of the laser. A simple algorithm was used to reconstruct surface profiles form the reflected intensity values from the eroded surface. The surface profiles of Al, Cu and Ti targets were reconstructed under high vacuum conditions without disturbing the processing parameters of the magnetron sputtering plant. From these generated profiles, the roughness parameters, root mean square roughness, correlation length, skewness and kurtosis of different target materials were calculated by this in situ technique. The results measured with this in situ technique are in good agreement with comparable measurements using a mechanical profilometer outside the sputtering system. However, some deviation was observed for surfaces with higher roughness and mean tilt angles. This method can be used for in situ monitoring of sputter targets to extract the surface features which may correlate with thin film properties and may precede dangerous events like target melting or other catastrophic failures.

(Invited) Strain Engineered Crack-Free GaN on Si for Integrated Vertical High Power GaN Devices with Si CMOS

We demonstrated beyond 10 µm thick crack-free GaN growth on Si substrate using selective area growth technique. Systematic characterization by scanning electron and optical microscopy on the grown samples revealed that cracks nucleate and propagate on {1-1 00} planes in <1-2 10> directions. By developing {1 -101} facet planes in selective area growth, thermal mismatch strain relief at facet surfaces eliminate cracking and enable growth over 10 µm thick crack-free GaN on Si. These grown structures exhibited high crystalline quality throughout the thickness of the structure as validated by selective area diffraction in high resolution transmission electron microscopy, with a dislocation density of 2-3 x 108 cm-2 at the GaN surface. On the same Si substrate, we were able to fabricate enhancement mode CMOS devices. The overall progress reported here paves the way for monolithically integrated GaN technologies for RF and high power applications on Si CMOS devices.

Temperature effect on the low cycle fatigue behavior of a directionally solidified nickel-base superalloy

The effect of temperature on low cycle fatigue behavior of a directionally solidified nickel-base superalloy has been investigated from 550 to 850°C. The fatigue life reached maximum at about 700°C. The fracture modes can be divided into three types: crystallographic plane facets fracture (shear fracture) at low temperature region (<600°C), mixed fracture mode at middle temperature region (600–700°C) and non-crystallographic fracture (I type fracture) at higher temperature region (>700°C). The dominant reason of the fracture mode transition with temperature is the deformation of the γ′ precipitated phase at different temperatures. The precipitated phase is sheared by dislocations which are restricted to the primary {111} slip planes at 600°C. As the temperature increases, the deformation of γ′ precipitated phase becomes anomaly and some secondary precipitates can be observed in the matrix.

Atomic Structure of Self-Assembled Monolayer of Thiolates on a Tetragonal Au92 Nanocrystal.

Unveiling the ligand binding mode on the crystalline surfaces is important for deciphering the long-standing structural enigma in self-assembled monolayers (SAMs). Here, the binding and patterning structures of thiolates (SR) on the Au(100) crystalline facet are revealed on the basis of the atomic structure of a highly regular, single crystalline Au92(SR)44 nanocrystal. The six exposed facets of this tetragonal nanocrystal give rise to six pieces of "nanoSAMs". We found that thiolates bind to the planar (100) facets of the nanocrystal via a simple bridge-like mode and are assembled into an overlayer with c(2 × 2) symmetry. The Au-S binding mode and translational symmetry in the kernel and on the surface of the Au92 nanocrystal can be generalized infinitely to construct the bulk two-dimensional SAMs and various tetragonal nanocrystals.

FACETS : A CLOUDCOMPARE PLUGIN TO EXTRACT GEOLOGICAL PLANES FROM UNSTRUCTURED 3D POINT CLOUDS

Geological planar facets (stratification, fault, joint…) are key features to unravel the tectonic history of rock outcrop or appreciate the stability of a hazardous rock cliff. Measuring their spatial attitude (dip and strike) is generally performed by hand with a compass/clinometer, which is time consuming, requires some degree of censoring (i.e. refusing to measure some features judged unimportant at the time), is not always possible for fractures higher up on the outcrop and is somewhat hazardous. 3D virtual geological outcrop hold the potential to alleviate these issues. Efficiently segmenting massive 3D point clouds into individual planar facets, inside a convenient software environment was lacking. FACETS is a dedicated plugin within CloudCompare v2.6.2 (&amp;lt;a href="http://cloudcompare.org/"target="_blank"&amp;gt;http://cloudcompare.org/&amp;lt;/a&amp;gt; ) implemented to perform planar facet extraction, calculate their dip and dip direction (i.e. azimuth of steepest decent) and report the extracted data in interactive stereograms. Two algorithms perform the segmentation: Kd-Tree and Fast Marching. Both divide the point cloud into sub-cells, then compute elementary planar objects and aggregate them progressively according to a planeity threshold into polygons. The boundaries of the polygons are adjusted around segmented points with a tension parameter, and the facet polygons can be exported as 3D polygon shapefiles towards third party GIS software or simply as ASCII comma separated files. One of the great features of FACETS is the capability to explore planar objects but also 3D points with normals with the stereogram tool. Poles can be readily displayed, queried and manually segmented interactively. The plugin blends seamlessly into CloudCompare to leverage all its other 3D point cloud manipulation features. A demonstration of the tool is presented to illustrate these different features. While designed for geological applications, FACETS could be more widely applied to any planar objects.

FACETS : A CLOUDCOMPARE PLUGIN TO EXTRACT GEOLOGICAL PLANES FROM UNSTRUCTURED 3D POINT CLOUDS

Abstract. Geological planar facets (stratification, fault, joint…) are key features to unravel the tectonic history of rock outcrop or appreciate the stability of a hazardous rock cliff. Measuring their spatial attitude (dip and strike) is generally performed by hand with a compass/clinometer, which is time consuming, requires some degree of censoring (i.e. refusing to measure some features judged unimportant at the time), is not always possible for fractures higher up on the outcrop and is somewhat hazardous. 3D virtual geological outcrop hold the potential to alleviate these issues. Efficiently segmenting massive 3D point clouds into individual planar facets, inside a convenient software environment was lacking. FACETS is a dedicated plugin within CloudCompare v2.6.2 (http://cloudcompare.org/ ) implemented to perform planar facet extraction, calculate their dip and dip direction (i.e. azimuth of steepest decent) and report the extracted data in interactive stereograms. Two algorithms perform the segmentation: Kd-Tree and Fast Marching. Both divide the point cloud into sub-cells, then compute elementary planar objects and aggregate them progressively according to a planeity threshold into polygons. The boundaries of the polygons are adjusted around segmented points with a tension parameter, and the facet polygons can be exported as 3D polygon shapefiles towards third party GIS software or simply as ASCII comma separated files. One of the great features of FACETS is the capability to explore planar objects but also 3D points with normals with the stereogram tool. Poles can be readily displayed, queried and manually segmented interactively. The plugin blends seamlessly into CloudCompare to leverage all its other 3D point cloud manipulation features. A demonstration of the tool is presented to illustrate these different features. While designed for geological applications, FACETS could be more widely applied to any planar objects.

Surface structure of the Ag-In-(rare earth) complex intermetallics

We present a study of the surface structure of the Ag-In-RE (RE: rare-earth elements Gd, Tb, and Yb) complex intermetallics using scanning tunneling microscopy and low-energy electron diffraction. The surface of the Ag-In-Yb approximant prepared by sputter-annealing methods under ultrahigh-vacuum conditions produces a flat (100) surface with no facets. However, the Ag-In-Gd and Ag-In-Tb 1/1 approximants, which have a surface miscut of about ${12}^{\ensuremath{\circ}}$ relative to the (100) plane, develop surface facets along various crystallographic directions. The structure of each facet can be explained as a truncation of the rhombic triacontahedral clusters, i.e., the main building blocks of these systems. Despite their differences in atomic structure, symmetry, and density, the facets show common features. The facet planes are In rich. The analysis of the nearest-neighbor atom distances suggests that In atoms form bonds with the RE atoms, which we suggest is a key factor that stabilizes even low-density facet planes.

Acoustic beamfolding: New potentials enabled by interfacing reconfigurable origami and acoustic structures

Acoustic transducer arrays yield large spatial and spectral change in energy transmission through strategic positioning of planar array elements. Yet, unless array elements are actively tuned through phase delay controls, the array performance characteristics remain fixed and suitable for limited purposes. Origami, the art of paper folding, is a means to introduce enormous topological change through simple, kinematic translation and rotation of connected, planar facets, which is one reason for its growing attention as a fluent vehicle to remarkably adapt system properties for multifunctional purposes. In this research, we integrate acoustic transducer array development and origami design principles to establish a new framework for adaptive acoustic energy shaping effected by simple geometric and kinematic folding relations. From a flat-folded strip to an unfolded plane, our theoretical and experimental results show that this transducer design concept leads to powerful means to tune the significance of radiated acoustic energy across orders of magnitude and to easily tailor the acoustic power transmission to the far field.

A numerical approach to the yield strength of shell structures

This work investigates the formulation of lower and upper bound finite elements for the yield design (or limit analysis) of shell structures. The shell geometry is first discretized into triangular planar facets so that previously developed lower bound equilibrium and upper bound kinematic plate finite elements can be coupled to membrane elements. The other main novelty of this paper relies on the formulation of generalized strength criteria for shells in membrane-bending interaction via an implicit upscaling procedure. This formulation provides a natural strategy for constructing lower and upper bound approximations of the exact shell strength criterion and are particularly well suited for a numerical implementation using second-order cone programming tools. By combining these approximate strength criteria to the previously mentioned finite elements, rigorous lower and upper bound ultimate load estimates for shell structures can be computed very efficiently. Different numerical examples illustrate the accuracy as well as the generality and versatility of the proposed approach.