Three-dimensional X-ray Microscopy Research Articles

Effects of Cu content and heat treatment process on microstructures and mechanical properties of Al−Si−Mg−Mn−xCu cast aluminum alloys

The effects of Cu content and heat treatment process on the microstructures and mechanical properties of a series of Al−Si−Mg−Mn−xCu cast aluminum alloys prepared by the vacuum die casting process were investigated by three-dimensional X-ray microscopy, optical microscopy, scanning electron microscopy, transmission electron microscopy and microhardness testing. It was found that the number density and size of gas porosities increase with increasing Cu content. However, the Cu addition will promote the formation of Cu-containing primary phases (Q-Al5Cu2Mg8Si6 and θ-Al2Cu) during the solidification, which will improve the properties of the alloys. Five different primary phases were observed, namely eutectic Si, α-Al(Fe, Mn)Si, β-Mg2Si, Q-Al5Cu2Mg8Si6, and θ-Al2Cu phases. With increasing the Cu content, the θ phase area fraction increases significantly, while the α-Al(Fe, Mn)Si phase area fraction decreases initially, followed by a slight increase, with the Q phase area fraction displaying the opposite trend relative to α-Al(Fe, Mn)Si phase. These primary phases present different evolution rules during heat treatment process. During subsequent aging, the synergic effect of precipitating Q' and θ' phases can significantly increase the alloy hardening response.

Interactions between Catalyst Layer Degradation and Liquid Water Distribution in Polymer Electrolyte Fuel Cells

Managing liquid water distribution in PEFCs is critical to desirable high power density operation and cell durability [1–3]. Degradation modes such as carbon corrosion in the cathode catalyst layer (CCL) are believed to depend on local humidification [2,4], while the distribution of liquid water may also be influenced by performance drop associated with such degradation [3]. Although some studies have shown the influence of carbon corrosion on liquid water distribution [2,3], the possible reverse effect of liquid water distribution on the CCL degradation requires further investigation.The objective of the present work is to establish a deeper understanding of the cause-and-effect interactions between CCL degradation and liquid water distribution. This is achieved experimentally by carrying out voltage-cycling accelerated stress tests (ASTs) on fuel cells which differ only in the constituent gas diffusion layers (GDLs); namely, SGL 22 BB and a proprietary Avcarb. Three-dimensional X-ray microscopy is used to observe both degradation effects and liquid water distribution at different stages of the ASTs. A relatively rapid operando two-dimensional visualization technique [5] was also used to investigate the differences in liquid water distribution between the two GDLs. The fuel cells imaged are analyzed and exhibit different liquid water distributions, whereby the Avcarb exhibits a higher liquid water condensation close to the CCL, compared to the SGL. Supported by model results, this difference in liquid water distribution is shown to be attributable to the different transport properties of the GDLs. The degradation results, such as the CCL thickness (Fig. 1) show that the Avcarb cell experiences a faster CCL degradation than the SGL cell. Furthermore, the Avcarb liquid water distribution is seen to change with increasing AST cycles in a manner indicating higher vapour phase removal. These results provide insights for GDL design consideration, showing that GDL transport properties may influence liquid water distribution at the electrode with important implications for CCL durability. Acknowledgement Funding for this research was provided by the Natural Sciences and Engineering Research Council of Canada,Ballard Power Systems, Canada Foundation for Innovation, British Columbia Knowledge Development Fund,and Canada Research Chairs.

3D printed different polymer fuel grains for hybrid rocket engine

The advent of various additive manufacturing technologies, such as 3D printing, has changed the structural design and preparation process of rocket fuels. In order to investigate the combustion properties of various common polymer materials that can be additively manufactured by fused deposition, the combustion tests of hybrid rocket fuels prepared by 3D printing were carried out. These materials include polylactic acid (PLA), wood-like polylactic acid (Wood), acrylonitrile-butadiene-styrene (ABS), acrylonitrile-styrene-acrylate (ASA), copolymers of nylon 6 and nylon 6,6 (CoPA), polycarbonate-polybutylene terephthalate (PC-PBT), flame retardant polycarbonate (PC-FR) and polyethylene terephthalateco-1,4-cylclohexylenedimethylene terephthalate (PETG). Thermogravimetric-differential scanning calorimetry (TG-DSC) analysis was carried out on these materials, the printing effect of the fuel grains was observed by three-dimensional X-ray microscopy (μCT) and the combustion performance of these fuels in gaseous oxygen flow (GOX) was recorded by high-speed photography at a constant pressure of 1 MPa. The results show that ASA and ABS exhibit good printing results. The regression rates of PC-PBT, PETG, ABS, ASA, CoPA and PLA are 0.792 mm/s, 0.592 mm/s, 0.536 mm/s and 0.477 mm/s, 0.368 mm/s, 0.339 mm/s (AtGOX=220kg/(m2·s)), respectively.

A Drive Towards Elemental Simplicity in Cathode Design by Controlling Grain Growth Behavior

Sodium-ion battery technologies are emerging as an alternative to lithium-ion batteries by utilizing the earth abundant, widely distributed, and low-cost sodium resources. Among different types of sodium ion cathodes, transition metal based layered oxide cathodes have a superior edge due to their comparatively higher energy density, lower cost, environment friendly raw materials, and similar synthesis chemistry as the already commercialized lithium-ion battery cathode materials. They also enable the incorporation of iron, an abundant, low-cost, and environmentally benign element, replacing the toxic and expensive cobalt.In such layered oxide-based cathodes, transition metals exhibit heterogenous elemental and oxidation state distribution at different depths of the particles (e.g., from the surface to bulk) which can influence the stability, mechanical integrity, and electrochemical performance of these particles to a significant extent. The inherent local structural and electronic state heterogeneity developed in these materials during synthesis can modulate the charge distribution heterogeneity and consequent phase transitions during cycling, ultimately controlling the battery performance.In this work, a sodium transition metal layered oxide cathode is synthesized using a co-precipitation method followed by high temperature calcination under different calcination durations. Calcining the material at different conditions lead to the formation of particles with different morphologies and grain growth behavior. Using electron microscopy and Xray diffraction techniques, the grain growth behavior at different stages of calcination is studied. This will guide the design of particles with better morphologies and grain orientation which demonstrate improved electrochemical performance. Transition metal distribution and oxidation state change at different depths of the particles are probed using synchrotron based Xray absorption spectroscopy and three-dimensional Transmission Xray microscopy. The particles are probed at the surface, subsurface and deep into the bulk, which show heterogeneity in the distribution of transition metal oxidation state and provide insight into the phase transitions during calcination. This study can pave the way for better understanding of phase evolution during synthesis and improved design of cathode particle morphology and composition by identifying and eliminating the detrimental phases occurring during different stages of calcination.

Study on the impermeability and microstructure of cement mortar blended with silicon carbide nanowhiskers

Silicon carbide (SiC) nanowhiskers have many application prospects owing to their excellent mechanical properties, thermal conductivity, and good chemical stability. Herein, we examined the effect of enhancing the mechanical properties and impermeability of cement mortar (CM) by improving the microstructural compactness and reducing the porosity after mixing CM using SiC nanowhiskers. Macroscopic and microscopic tests and analyses of CM blended with different amounts of SiC nanowhiskers were performed using an electro-hydraulic flexural and compressive testing machine, cement mortar penetration tester, field-emission scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, and three-dimensional X-ray microscopy. Results demonstrated that the incorporation of SiC nanowhiskers can lead to the following: (1) enhance the mechanical properties of CM, especially in the early stage; (2) fulfill the role of crystal nucleation and promote the hydration reaction; (3) fill the pores, play the role of micro-aggregate filling, improve the compactness, and reduce the porosity and relative permeability coefficient; and (4) play a bridging role and connect internal structures. Our results provide a valuable reference for developing nanowhisker-blended CM.

Mechanical, Thermal Properties and Void Characteristics of Bamboo Fiber-Reinforced Epoxy Resin Composites Prepared by Vacuum-Assisted Resin Transfer Molding Process

ABSTRACT This study aimed to examine the effect of epoxy resin (EP) systems on the impregnation of bamboo fibers (BFs) by EP and the properties of BF/EP composites prepared by vacuum-assisted resin transfer molding (VARTM) process. BF preforms obtained by solution suspension method were used as reinforcement, and epoxy/anhydride system (EP-1), epoxy/amine system (EP-2) and two-component epoxy system (EP-3) were employed as matrix; on this basis, BF/EP-1, BF/EP-2 and BF/EP-3 composites were prepared by VARTM. The physical, mechanical and thermal properties and void characteristics of BF/EP composites were characterized. The results showed that EP-1 with a viscosity of 265 mPa·s at 23°C and an operating time of room temperature without curing was beneficial for the EP-1 to impregnate BFs adequately and uniformly. The incorporation of BFs into EP-1 significantly improved the flexural, shear and impact properties, thermal properties and interface properties of EP-1. Moreover, the properties of BF/EP-1 composites were better than those of BF/EP-2 and BF/EP-3 composites. Three-dimensional X-ray microscopy scans revealed that the volume and distribution of voids in the BF/EP composites differed significantly depending on the EP systems, and the percentage of void volume in the BF/EP-1 composites was only 0.14% in 3D reconstruction models.

Comparative Analysis of Robotics-Assisted and Manual Insertions of Cochlear Implant Electrode Arrays.

Robotics-assisted cochlear implant (CI) insertions will result in reduced intracochlear trauma when compared with manual, across multiple users. Whether intracochlear trauma and translocations are two factors that may contribute to significant variability in CI outcomes remains to be seen. To address this issue, we have developed a robotics-assisted insertion system designed to aid the surgeon in inserting electrode arrays with consistent speeds and reduced variability. This study evaluated the effect of robotics-assisted insertions on the intracochlear trauma as compared with manual insertions in cadaveric cochleae in a simulated operative environment. Twelve neurotologists performed bilateral electrode insertions into cochleae of full cadaveric heads using both the robotics-assisted system and manual hand insertion. Lateral wall electrodes from three different manufacturers (n = 24) were used and randomized between surgeons. Insertion angle of the electrode and trauma scoring were evaluated using high-resolution three-dimensional x-ray microscopy and compared between robotics-assisted and manual insertions. Three-dimensional x-ray microscopy provided excellent resolution to characterize the in situ trauma and insertion angle. Robotics-assisted insertions significantly decreased insertional intracochlear trauma as measured by reduced trauma scores compared with manual insertions (average: 1.3 versus 2.2, device versus manual, respectively; p < 0.05). There was no significant difference between insertion angles observed for manual and robotics-assisted techniques (311 ± 131° versus 307 ± 96°, device versus manual, respectively). Robotics-assisted insertion systems enable standardized electrode insertions across individual surgeons and experience levels. Clinical trials are necessary to investigate whether insertion techniques that reduce insertional variability and the likelihood of intracochlear trauma also improve CI auditory outcomes.

A high-resolution study of PM2.5 accumulation inside leaves in leaf stomata compared with non-stomatal areas using three-dimensional X-ray microscopy

Plant leaves retain atmospheric particulate matter (PM) on their surfaces, helping PM removal and risk reduction of respiratory tract infection. Several processes (deposition, resuspension, rainfall removal) can influence the PM accumulation on leaves and different leaf microstructures (e.g., trichomes, epicuticular waxes) can also be involved in retaining PM. However, the accumulation and distribution of PM on leaves, particularly at the stomata, are unclear, and the lack of characterization methods limits our understanding of this process. Thus, in this study, we aimed to explore the pathway through which PM2.5 (aerodynamic diameter ≤ 2.5 μm) enters plant leaves, and the penetration depth of PM2.5 along the entry route. Here, an indoor experiment using diamond powder as a tracer to simulate PM2.5 deposition on leaves was carried out. Then, the treated and non-treated leaves were scanned by using three-dimensional (3D) X-ray microscopy. Next, the grayscale value of the scanned images was used to compare PM2.5 accumulation in stomatal and non-stomatal areas of the treated and non-treated leaves, respectively. Finally, a total PM2.5 volume from the abaxial epidermis was calculated. The results showed that, first, a large amount of PM2.5 accumulates within leaf stomata, whereas PM2.5 does not accumulate at non-stomatal areas. Then, the penetration depth of PM2.5 in stomata of most tree species was 5–14 μm from the abaxial epidermis. For the first time, 3D X-ray microscope scanning was used to confirm that a pathway by which PM2.5 enters the leaves is through the stomata, which is fundamental for further research on how PM2.5 translocates and interacts with tissues and cells in leaves.

Effect of the heating rate on the thermal explosion behavior and oxidation resistance of 3D-structure porous NiAl intermetallic

Porous NiAl intermetallic compounds demonstrate great potential in various applications by their high porosity and excellent oxidation resistance. However, to obtain a controllable NiAl intermetallic structure by tuning different process parameters remains unclear. In this work, porous NiAl intermetallic compounds were fabricated by economic and energy-saving thermal explosion (TE) reaction. The relationship between microstructure and process parameters was revealed using three-dimensional X-ray microscopy (3D-XRM) with high resolution and non-destructive characteristics. The geometrical features and quantitative statistics of the porous NiAl obtained at different heating rates (2, 10, 20 °C min−1) were compared. The result of the closed porosity calculation showed that a lower heating rate (2 °C min−1) promoted the Kirkendall reaction between Ni and Al, resulting in a high closed porosity (5.25%). However, at a higher heating rate (20 °C min−1), a homogeneous NiAl phase was observed using the threshold segmentation method, indicating uniform and complete TE reaction can be achieved at a high heating rate. The result of the 3D fluid simulation showed that the sample heated at 10 °C min−1 had the highest permeability (2434.6 md). In this study, we systematically investigated the relationship between the heating rates and properties of the porous NiAl intermetallic, including the phase composition, porosity, exothermic mechanism, oxidation resistance, and compression resistance. Our work provides constructive directions for designing and tailoring the performance of porous NiAl intermetallic compounds.

Mechanism of void healing in cold rolled aeroengine M50 bearing steel under electroshocking treatment: A combined experimental and simulation study

M50 bearing steel, as the important material used in aeroengine bearing, exhibits low cold working capacity with high susceptibility to produce voids. This would lead to the deterioration of mechanical property, which critically limits the industrial application of cold ring rolling (CRR) in M50 bearing rings. In this work, the mechanism of void healing in cold rolled aeroengine M50 bearing steel subjected to electroshocking treatment (EST) was investigated by combining experimental and simulation studies. The experimental results obtained using the three-dimensional X-ray microscopy (3D-XRM) technique show that the porosity of the CRR samples decreases from 0.26% to 0.09% after EST. The healing effect of larger voids is not obvious, while small voids are likely to be healed under EST. The simulation results indicate that due to the inhomogeneous distribution of the physical field, the local thermal compressive stress of as high as 2565.9 MPa is generated around the ellipsoidal void and thus drives void healing process. The healing process of ellipsoidal voids under EST can be divided into elastic and plastic deformation stages considering von Mises yield criterion. In the initial stage, only a small elastic deformation of 53.53 nm occurs in the minor axis direction of the void. In the plastic deformation stage, the material flows along the normal direction of the void with a reduction in the aspect ratio, thereby compressing the void surfaces and promoting their healing. Additionally, the degree of void healing depends on the shape characteristics (curvature and aspect ratio) of the void rather than the current direction. This research elucidates a new elastoplastic mechanism of void healing under EST, which also provides a promising prospect for the application of CRR in M50 bearing steel. • In situ characterization of voids before and after EST was realized using 3D-XRM. • A new elastoplastic mechanism of void healing under EST was elucidated. • The driving force of void healing was revealed by analysing the physical field distribution. • The ellipsoidal void is healed with the reduction in the aspect ratio. • The degree of void healing depends on the shape of the void rather than the current direction.

Microstructure, Quality, and Release Performance Characterization of Long-Acting Polymer Implant Formulations with X-Ray Microscopy and Quantitative AI Analytics.

Long-acting implants are typically formulated using carrier(s) with specific physical and chemical properties, along with the active pharmaceutical ingredient (API), to achieve the desired daily exposure for the target duration of action. In characterizing such formulations, real-time in-vitro and in-vivo experiments that are typically used to characterize implants are lengthy, costly, and labor intensive as these implants are designed to be long acting. A novel characterization technique, combining high resolution three-dimensional X-Ray microscopy imaging, image-based quantification, and transport simulation, has been employed to provide a mechanistic understanding of formulation and process impact on the microstructures and performance of a polymer-based implant. Artificial intelligence-based image segmentation and image data analytics were used to convert morphological features visualized at high resolution into numerical microstructure models. These digital models were then used to calculate key physical parameters governing drug transport in a polymer matrix, including API uniformity, API domain size, and permeability. This powerful new tool has the potential to advance the mechanistic understanding of the interplay between drug-microstructure and performance and accelerate the therapeutic development long-acting implants.

Open Localization in 3D Package with TSV Daisy Chain Using Magnetic Field Imaging and High-Resolution Three-Dimensional X-ray Microscopy

With the development of 3D integrated packaging technology, failure analysis is facing more and more challenges. Defect localization in a 3D package is a key step of failure analysis. The complex structure and materials of 3D package devices demand non-destructive defect localization technology for full packages. Magnetic field imaging and three-dimensional X-ray technology are not affected by package material or form. They are effective methods to realize defect localization on 3D packages. In this paper, magnetic field imaging and high-resolution three-dimensional X-ray microscopy were used to localize the open defect in a 3D package with a TSV daisy chain. A two-probe RF method in magnetic field imaging was performed to resolve isolation of the defect difficulties resulting from many different branches of TSV daisy chains. Additionally, a linear decay method was used to target sub-micron resolution at a long working distance. Multiple partition scans from a high-resolution 3D X-ray microscopy with a two-stage magnification structure were used to achieve sub-micron resolution. The open location identified by magnetic field imaging was consistent with that identified by a three-dimensional X-ray microscope. The opening was located on the top metal in the proximity of the fifth via. Physical failure analysis revealed the presence of a crack in the top metal at the opening location.

Airborne Submicron Particle Accumulates at Leaf Stomata Rather than Non-Stomatal Areas: A Contrast Experimental Study by Using Three-Dimensional X-Ray Microscopy

Airborne Submicron Particle Accumulates at Leaf Stomata Rather than Non-Stomatal Areas: A Contrast Experimental Study by Using Three-Dimensional X-Ray Microscopy

Testing the X-ray computed microtomography on microfossil identification: An example from Sergipe-Alagoas Basin, Brazil

Micropaleontology is crucial branch of Earth Sciences, with a pivotal role in the success of the oil and gas industry over the decades. This sector of paleontology is based on the taxonomical description of microfossils, which encompass fossils with size variation from 0.001 mm to 1 m. Normally these microorganisms have a high rate on preservation, thus they are widely accepted as reliable evidence to infer about paleodepositional settings and paleoclimate change. Furthermore, microfossils are critical to understanding the evolution through time, being many of them recognized as index fossil and providing useful biozones to correlation. Since 1950, microfossils have been taxonomically described mainly by stereomicroscopes. However, as the technology progress, traditional ways to study these organisms are challenged and improved by nondestructive three-dimensional imaging techniques, as X-ray tomographic microscopy (SRXTM), three-dimensional X-ray microscopy (3D-XRM), the X-ray computed microtomography (microCT) and X-ray computed nanotomography (nanoCT). Recently, one of the most compelling research areas in micropaleontology is the desire to automatize and enhance the details of systematic classification. Thereby, an increasing number of researches have applied the high-resolution X-ray analysis aiming to improve the morphological, taxonomic and taphonomic examination. Most of them have detailed the enhancement provided by the technique when compared with the standard microscopes, and raised questions about the traditional characters used on the microfossil systematic taxonomy. Nevertheless, even with the surpassing detail on microfossil characterization, the application of microCT has been hampered by the costs and sometimes by the needs of specific computer skill. Thus, this research has evaluated the use of microCT as the technique to classify a random bulk of microfossil (comprising foraminifers, ostracods, radiolarians, gastropods and echinoderms) with no further software treatment. No standard microscope analysis was performed. Despite chemical composition of microfossils, most of the specimens morphology, especially internal structures, have been easily acquired and analyzed. 96% of the microfossils of the dataset were identified at least on genus level. Irrespective of the deepness of detail, when considering the overall taxonomic identification, the microCT seems to be effective as the standard microscope. Nonetheless, when problematic specimens are evaluated, the microCT seems to be a more reliable and practical tool than other methods as Scanning Electron Microscopy. Thus, the technique can be used solo or as a complementary method to the stereomicroscope. Additionally, the high-resolution has the potential to lead to the expected automatized micropaleontology, since they can provide numerous images in several planes. This may create a strong database necessary to machine learning and computer identification.

Tensile Strength and Degradation of GFRP Bars under Combined Effects of Mechanical Load and Alkaline Solution.

Mechanical properties of glass fiber reinforced polymer (GFRP) composites degrade under the combined effects of mechanical load and alkaline solution, affecting the service ability and safety of GFRP reinforced structures. In this study, GFRP bars were loaded with cyclic tension at different stress levels and immersed in alkaline solution for days to investigate the tensile properties and degradation law of GFRP bars. The degradation mechanisms were studied at micro-, meso- and macro-scales with scanning electron microscopy (SEM) and three-dimensional X-ray microscopy, respectively. The results show that tensile strength and degradation rate of GFRP bars are mainly dependent on the different stress levels and alkaline solution. When stress level is higher, the tensile strength degrades more quickly, especially in the early stages of soaking. With the loading and immersion time, the elastic modulus and Poisson’s ratio increase at first and then decrease. The ultimate tensile strain is relatively stable, whereas the ultimate elongation is significantly reduced. A strength-degradation model was proposed and fit well with experimental data, demonstrating that the model can be applied to predict tensile strength degradation under combined effects of the load and alkaline solution.

Failure Analysis of Leakage Current for Multilayer Printed Circuit Board

The leakage current phenomenon of a commercial ten-multilayer printed circuit board (PCB) occurred. Preliminary examination shows that there was a short circuit between the PIN_2 and POUT_4 networks of the PCB measured by a high-resistance meter, after a high-temperature aging treatment. In this case, microstructure and morphology of several layers for PCB sample were observed by optical microscopy, scanning electron microscopy and three-dimensional imaging x-ray microscopy. The chemical composition of the layer was determined by energy-dispersive spectroscopy. After observation and analysis, the results show that the leakage current failure cause of the PCB was that the metal powder impurities were found between the layers of PIN_2 and POUT_4 network, which caused the drop in the electric resistance between the two networks, resulting in the occurrence of the leakage current. The chemical composition of the impurity was only composed of copper.

Characterisation and evolution of the full size range of pores and fractures in rocks under freeze-thaw conditions using nuclear magnetic resonance and three-dimensional X-ray microscopy

Mine slopes in high-altitude and cold regions are susceptible to damage and degradation under long-term freeze-thaw (FT) conditions, which threatens the stability of geotechnical engineering operations. The evolution of pore and fracture structures in rock masses under FT conditions crucially influences the physical and mechanical properties of rocks. However, critical information is often ignored when testing pore structures using conventional methods, owing to the limited applicable size range, which leads to an inaccurate characterisation of the pore structure. Techniques such as nuclear magnetic resonance (NMR) and three-dimensional X-ray microscopy (3D-XRM) provide improved characterisation accuracy of pores smaller than 50 μm (micropores, mesopores, macropores) and the 3D distribution of extra-large pores (>50 μm) and microfractures, respectively. This combined approach allows quantitative characterisation of the full range of fractures in rocks. On this basis, we investigated the evolution of pores and fractures in different types of rocks (granite, limestone, sandstone) under FT conditions. The results show that with increasing FT cycle, the number of mesopores increases in granite, more micropores appear and macropores are generated in limestone, and the number of micropores and mesopores generally increases in sandstone. For extra-large pores and microfractures, fractal dimensions in 2D slices, volumes, specific surface areas and volumetric porosities of pores and fractures exhibit consistent trends. Sandstone parameters are considerably larger than those of limestone and granite in the initial state, and the parameters of limestone and granite are similar. With increasing FT cycle numbers, the parameters of all three rock types increase with sandstone > limestone > granite. The mean equivalent diameters of pores and fractures gradually decrease in granite, increase linearly in limestone and increase slightly in sandstone.

Compressive fatigue behaviour of ZTAp/40Cr steel matrix composites by three-dimensional structural toughening

Herein, the compressive fatigue behaviour of three-dimensional metal matrix composites/steel (3D-MMCs/steel) is studied. The ZrO2-toughened Al2O3 (ZTA) particle strengthens 40Cr steel composite materials (MMCs) as a reinforcement. The experimental conditions were uniaxial compression fatigue under 500 MPa and 20 Hz. The failure modes of the composites were analysed by three-dimensional x-ray microscopy. The fatigue life of the 3D-MMCs/steel composite is 9.0 × 106 cycles, and for the homogeneous ZTAp/40Cr composite material is 1.03 × 106 cycles. The analysis shows that grids of the matrix area can inhibit the propagation of a crack in the MMC area and can cause it to turn or to disappear. Toughening of the 3D-MMCs/steel composite primarily occurs because the matrix area grids protect the MMC area from tearing.In other words, the presence of the MMC grids causes the toughening of this kind of material.

Effects of interface adhesive and resin cohesive strength on tensile strength of resin sand based on numerical analysis

A plane-strain unit-cell finite element model was proposed to study the effects of resin/sand interface adhesive and resin cohesive strength on the overall tensile strength of resin sand, as well as the fracture modes. The main micro-scale characteristics of the numerical model were extracted from the micrograph of resin sand specimens by three-dimensional X-ray microscopy (3D-XRM). The extended finite element method (XFEM) and cohesive behavior method were employed to explicitly describe the resin fracture and sand/resin interface debonding, separately. The corresponding experimental observation of micro-scale failure behavior based on the scanning electron microscopy (SEM) was presented for a comparison. The numerical results show that the initial failure of the model occurs at the sand/resin interface, followed by consequent resin failure. Dependent on the resin cohesive strength, the location of resin failure varies from the central zones to resin neck arc zones. A typical mixed mode fracture is observed, which is consistent with the corresponding micro-scale experimental observation. When the resin cohesive strength ranges between 8 and 12 MPa, the resin cracks occur at the central zone of resin bridges and propagate perpendicularly to the tensile direction until through cracks happen. At a higher range (between 12 and 16 MPa), interface cracks cross with resin cracks, bonding bridges of resin sand are broken. The interface adhesive strength has a more significant effect on the overall tensile strength of resin sand than the resin cohesive strength. The overall tensile strength of resin sand increases first then keeps stable with the increase of the resin cohesive strength. This work attempts to establish a numerical model which accurately describes the complicated mixed mode fracture of resin sand, which is beneficial to understand deeply the fracture mechanism of resin sand.

Coupled ptychography and tomography algorithm improves reconstruction of experimental data

Three-dimensional (3D) x-ray microscopy by ptychographic tomography requires elaborate numerical reconstructions. We describe a coupled ptychography-tomography reconstruction algorithm and apply it to an experimental ptychographic x-ray computed tomography data set of a catalyst particle. Compared to the traditional sequential algorithm, in which ptychographic projections are reconstructed to serve as input for subsequent tomographic reconstruction, the coupled ptychography-tomography algorithm reconstructs the 3D volume with higher spatial resolution over a larger field of view. Coupling the data from different projections improves the overall reconstruction, and the ptychographic sampling in individual projections can be coarsened beyond the point of overlap between neighboring scan points, still leading to stable reconstructions.