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A combination of characterization techniques has been used to provide new understanding of the complex crystallization behavior of as-sprayed amorphous Yb2Si2O7-based air-plasma-sprayed environmental barrier coatings (EBCs). During crystallization heat-treatment, initially a mixture of metastable α-Yb2Si2O7 and X1-Yb2SiO5 phases form, along with stable β-Yb2Si2O7 and X2-Yb2SiO5 phases. Eventually the metastable phases transform to the stable β-Yb2Si2O7 (major) and X2-Yb2SiO5 (minor) phases. The significant volume expansion associated with these transformations partially contributes towards the anomalous expansion measured in these EBCs after crystallization, but it does not account for all the measured expansion. In this context, in similar EBCs, it is also observed that the porosity increases upon crystallization heat-treatment, primarily in the form of thin, interconnected pores, which also contributes to the measured anomalous expansion. Based on this understanding, guidelines are provided for ‘near-net-shape’ crystallization of phase-pure, dense β-Yb2Si2O7 EBCs that are free of vertical cracks.

Volume fracturing in horizontal wells represents a principal technology in the effective economic development of unconventional shale oil and gas reservoirs. However, the number of intervals that were effectively fractured by this technology only account for 20%–50% of the total designed sections. Fracture development characteristics and the factors controlling artificial fracture growth in organic-rich shale require detailed evaluation; this cannot be accomplished using microseismic monitoring technology or well-log interpretation. In this paper, formation processes of micro- and nano-scale fractures in the organic-rich shales of the Lucaogou Formation, Jimusaer Sag, Junggar Basin, northwestern China, were presented. The study focused on the application of in situ, nano-scale CT imaging technology, in combination with rock mechanics analysis. Results allowed the visualization of fracture growth in the shale reservoirs, and revealed the influence of organic matter, mineral composition, and pore structure on the formation and distribution of artificial fractures. A three-dimensional dynamic growth model of micro- and nano-scale fractures in organic-rich shale was established. Data revealed that the Lucaogou Formation shale contained dolomite and illite intragranular pores, with a low abundance of organic pores; pore size ranged between 200 nm and 2 μm. Micro- and nano-size fractures were observed. The development of artificial fractures was positively correlated with the loading stress. The initiation stress of new generated fractures was 475 mN, which could break up dolomite, albite, K-feldspar, and the original pore system as well. The original pore system was generally conducive to fracture extension and expansion. As loading stress increased from 50 mN to 515 mN, the sample extension increased from 2 μm to 14 μm, and artificial fracture width increased from 0.3 μm to 10 μm. The total porosity increased from 5.45% to 8.35%, and volume growth rate reached 53.2%. These findings provide valuable insights into the study of fracture growth in organic-rich shales, and have implications for the design of hydro-fracturing in organic-rich shales.

In situ studies using X-ray tomography have gained immense popularity in the recent past owing to their non-destructive nature and ability to capture the microstructure of a wide range of materials in 3D. In this work, we have conducted in situ micropillar compression and studied damage evolution in Al/SiC nanolaminates using a laboratory-based nanoscale X-ray microscope. Nanoscale defects present in the microstructure were characterized in 3D. The effect of these nanopores on damage initiation was quantified and is discussed. Additionally, the effect of Ga+ ion milling on micropillar fabrication was characterized by performing a comparative experiment on pillars fabricated using Ga+ and Ne+ ion source based focused ion beams.

Most technologically-relevant materials exhibit a microstructural heterogeneity over multiple length scales, and it is this heterogeneity that ultimately determines their performance. For example, the efficiency of polycrystalline silicon (poly-Si) photovoltaic cells is critically dependent on the nature of the grain boundaries and foreign metal impurities in the bulk. Here, we probe the characteristics and distributions of these defects in three dimensions by using a novel, integrated, and non-destructive imaging platform. In particular, recent advances in laboratory-based diffraction contrast tomography (LabDCT) enable us to measure grain centroid, volume, orientation, and shape. From this crystallographic information, we extract the five-parameter grain boundary distributions in poly-Si. By using a combination of LabDCT, attenuation-based tomography, and electron microscopy, we determine that the location of the impurity particles is non-random in the bulk and strongly dependent on grain boundary character. The correlative analysis not only demonstrates the degree of interaction between foreign metal impurities and structural defects in poly-Si, but also highlights the viability of burgeoning tomographic methods such as LabDCT. It is anticipated that our integrated approach can be extended to other complex microstructures with minimal sample-specific tuning.

3D printing is a process of hierarchically fabricating three-dimensional microstructures by successively adding materials in a bottom-up manner. The technology has been rapidly advancing, especially in the manufacturing of high-strength, lightweight industrial composite materials. Thus far, many studies have focused on the spontaneous alignment of short reinforcing fibers that are subject to adjustment during the 3D-printing process, along with an inevitable void formation arising due to an intrinsic nature of the additive process. However, systematic examination of the 3D-printed anisotropic microstructures, related with a markedly high degree of fiber alignment and formation of voids in the matrix, has not been sufficiently conducted to analyze its effect on the anisotropic mechanical behaviors of fiber-reinforced composites. Here, we sought to examine in detail the internal morphology of fibers and voids in 3D-printed composites by 3D X-ray microscopy to explore their anisotropic architecture. The position, length, and alignment of fibers and voids were identified, visualized, and quantitatively characterized with a help of computational tomography (CT). Furthermore, the anisotropy approximation of the 3D-printed composites, precisely predicted through CT-assisted simulation, was derived based on the quantitative data obtained from the 3D reconstruction image. These measurements were effective in exploring the process-induced alignment nature of fibers and voids in the local region layers on the microscopic scale, and the corresponding microstructure resulted in a change in the elastic modulus of the composites with the printing direction. The comparative results showed that the experimental results were well supported by the simulation-based estimations, but did not exactly match the rule-of-mixture of the composites in terms of interfacial nature due to the distinctive microstructure with the fiber-to-matrix interface as well as the filament-to-filament interface.

The characteristics of fracture propagation in heterogeneous tight sandstones are critical to volumetric fracturing, which is the key to unlocking unconventional resources in tight sandstones. Quantification of the influence of pre-existing pore systems and particle arrangements on the propagation of fractures is challenging due to inadequate imaging of the internal void systems in tight sandstones from three-dimensional (3D) aspect. In this study, the 3D geometry of tight sandstones from the Chang 7 member in the Ordos Basin is continuously imaged under different loading stresses, and the voxel resolution of the X-ray computed tomography is 2.5 μm. The data set captured in this process shows the changes in the samples at the microstructural level as they approach fracturing. The data are stored as a time series of 3D images. The results demonstrate that: (i) fractures propagate progressively and gradually link with pre-existing pores, resulting in macroscopic fractures with a maximum width of 250 μm, while newly generated fractures could break up particles and may not follow the line of pre-existing fractures; and (ii) three stages were identified in the failure process of tight sandstones, with new fractures running at an angle of about 30° to the general direction of the stress of compression. The total volumes of both the sample and pore-fractures, and the damage index, which were extracted from the 3D images, all increased when approaching fracturing. The final volume of pore-fracture systems could be 11 times that of the initial pore volume. All of these observations provide valuable insights and design guidelines for hydraulic fracturing in unconventional tight sandstones, and a quantified model of the dynamics and the morphology of fracture propagation with increasing stress approaching failure, which may shed light on dynamic critical transitions in the Earth's crust.

article i nfo Bisphosphonates are widely used to treat osteoporosis, but have been associated with atypical femoral fractures (AFFs) in the long term, which raises a critical health problem for the aging population. Several clinical studies havesuggested that theoccurrence of AFFs may berelated tothe bisphosphonate-induced changes of bone turn- over, but large discrepancies in the results of these studies indicate that the salient mechanisms responsible for any loss in fracture resistance are still unclear. Here the role of bisphosphonates is examined in terms of the po- tential deterioration in fracture resistance resulting from both intrinsic (plasticity) and extrinsic (shielding) toughening mechanisms, which operate over a wide range of length-scales. Specifically, we compare the me- chanical properties of two groups of humeri from healthy beagles, one control group comprising eight females (oral doses of saline vehicle, 1 mL/kg/day, 3 years) and one treated group comprising nine females (oral doses of alendronate used to treat osteoporosis, 0.2 mg/kg/day, 3 years). Our data demonstrate treatment-specifi cr e- organization of bone tissue identified at multiple length-scales mainly through advanced synchrotron x-ray ex- periments. We confirm that bisphosphonate treatments can increase non-enzymatic collagen cross-linking at molecular scales, which critically restricts plasticity associated with fibrillar sliding, and hence intrinsic toughen- ing, at nanoscales. We also observe changes in the intracortical architecture of treated bone at microscales, with partial fillingof the Haversiancanalsandreductionof osteon number.We hypothesize thatthereducedplasticity associated with BP treatmentsmay induce an increaseinmicrocrack accumulation and growth undercyclic daily loadings, and potentially increase the susceptibility of cortical bone to atypical (fatigue-like) fractures.

The processing of ceramic scaffolds using the ice-templating, or freeze casting, technique provides a relatively simple means to mimic the hierarchical design of natural materials such as nacre. In the present study, we investigated the architecture of silicon carbide (SiC) scaffolds produced by this technique over a range of cooling rates and suspension characteristics to demonstrate its versatility and effectiveness for fabricating unidirectional porous bodies with controlled lamella thickness, porosity fraction and morphology. An array of microstructures was generated specifically to examine the role of the suspension solid load and cooling rate on the pore morphology and final ceramic fraction. With respect to the morphology of the pores, a transition from lamellar to dendritic structure was found to be triggered by an increase in cooling rate or in suspension concentration. Similarly, the freezing condition and suspension characteristics were seen to influence the transition between particle rejection and entrapment by the ice. Based on this study, the specific processing parameters that result in distinct scaffold morphologies, namely lamellar, dendritic or isotropic morphology (the latter corresponding to particle entrapment), are identified and presented in the form of a “morphology map” to establish the regions of the different architectures of freeze-cast SiC scaffolds.

Synchrotron micro tomography was used to identify the failure process and damage mechanisms during in - situ compressive loading on confined silica sand. In these tomography experiments, sand grains were confined inside a polycarbonate tube. These confined sand grains were loaded under strain control using a custom built X-ray imaging compatible load frame. The behavior of sand under increasing strain was observed in - situ with 23.8 keV X-rays and spatial resolution 1.45 μm/pixel. A software procedure was developed for processing the reconstructed data and for visualizing and understanding crack propagation in the sand grains. Deformation modes were observed macroscopically across many grains and microscopically within the grains. On the scale of a few sand grains, observations showed deformation effects such as preferred orientation of grains along which stresses were transferred. On a microscopic scale, micro-cracking within individual grains was followed by fragmentation of individual sand grains. Over a maximum applied strain of 34% on the column, the observed deformations were localized within a near-field comprising the top 60% of the sand volume.

Recent work presented a Monte Carlo algorithm based on Markov Chain operators for generating replicas of textile composite specimens that possess the same statistical characteristics as specimens imaged using high resolution x-ray computed tomography. That work represented the textile reinforcement by one-dimensional tow loci in three-dimensional space, suitable for use in the Binary Model of textile composites. Here analogous algorithms are used to generate solid, three-dimensional (3D) tow representations, to provide geometrical models for more detailed failure analyses. The algorithms for generating 3D models are divided into those that refer to the topology of the textile and those that deal with its geometry. The topological rules carry all the information that distinguishes textiles with different interlacing patterns (weaves, braids, etc.) and provide instructions for resolving interpenetrations or ordering errors among tows. They also simplify writing a single computer program that can accept input data for generic textile cases. The geometrical rules adjust the shape and smoothness of the generated virtual specimens to match data from imaged specimens. The virtual specimen generator is illustrated using data for an angle interlock weave, a common 3D textile architecture.

A Monte Carlo algorithm is defined for generating replicas of textile composite specimens that possess the same statistical characteristics as specimens imaged using high resolution computed tomography. The textile reinforcement is represented by one-dimensional tow loci in three-dimensional space, which are easily incorporated into the Binary Model of textile composites. A tow locus is expressed as the sum of non-stochastic, periodic variations in the coordinates of the tow centroid and stochastic, non-periodic deviations. The non-stochastic variations have period commensurate with the dimensions of the unit cell of the textile, while the stochastic deviations, which describe geometrical defects, exhibit correlation lengths that may be incommensurate with the unit cell. The model is calibrated with data deduced in prior work from computed tomography images. The calibration obviates the need for assuming any ideal shape functions for the tow loci, which can take very general form. The approach is therefore valid for a wide range of textile architectures. Once calibrated, a Markov Chain algorithm can generate numerous stochastic replicas of a textile architecture very rapidly. These virtual specimens can be much larger than the real specimens from which the data were originally gathered, a necessary feature when real specimen size is limited by the nature of high resolution computed tomography. The virtual specimen generator is illustrated using data for an angle interlock weave.

A new method was developed using AFM images of a fiber surface to regenerate the surface roughness in 3D geometry, such as the cylindrical shape of a “model” fiber. The Langevin equation was used to derive the fluctuations of a carbon fiber surface image. The equation contains two quantities, D (1) ( h ) and D (2) ( h ) which in physics represent drift and diffusion coefficients. Knowing this coefficient and adding a proper noise function, a similar surface of larger dimension with the same statistical properties of the initial data was created. The generated surface was mapped into cylindrical coordinates, then a mesh generated. The resulting reconstructed surface, input over the geometry of a cylindrical shape, can be implemented for finite element analysis of a single fiber surrounded by matrix and generalized to a many fiber model.