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Understanding the cracking behaviour of biological composite materials is of practical importance. This paper presents the first study to track the interplay between crack initiation, microfracture and plastic deformation in three dimensions (3D) as a function of tubule and collagen fibril arrangement in elephant dentin using in situ X-ray nano-computed tomography (nano-CT). A nano-indenter with a conical tip has been used to incrementally indent three test-pieces oriented at 0°, 45° and 70° to the long axis of the tubules (i.e. radial to the tusk). For the 0° sample two significant cracks formed, one of which linked up with microcracks in the axial-radial plane of the tusk originating from the tubules and the other one occurred as a consequence of shear deformation at the tubules. The 70° test-piece was able to bear the greatest loads despite many small cracks forming around the indenter. These were diverted by the microstructure and did not propagate significantly. The 45° test-piece showed intermediate behaviour. In all cases strains obtained by digital volume correlation were well in excess of the yield strain (0.9%), indeed some plastic deformation could even be seen through bending of the tubules. The hoop strains around the conical indenter were anisotropic with the smallest strains correlating with the primary collagen orientation (axial to the tusk) and the largest strains aligned with the hoop direction of the tusk. This paper presents the first comprehensive study of the anisotropic nature of microfracture, crack propagation and deformation in elephant dentin using time-lapse X-ray nano-computed tomography. To unravel the interplay of collagen fibrils and local deformation, digital volume correlation (DVC) has been applied to map the local strain field while the crack initiation and propagation is tracked in real time. Our results highlight the intrinsic and extrinsic shielding mechanisms and correlate the crack growth behavior in nature to the service requirement of dentin to resist catastrophic fracture. This is of wide interest not just in terms of understanding dentin fracture but also can extend beyond dentin to other anisotropic structural composite biomaterials such as bone, antler and chitin. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Arthropod cuticle has extraordinary properties. It is very stiff and tough whilst being lightweight, yet it is made of rather ordinary constituents. This desirable combination of properties results from a hierarchical structure, but we currently have a poor understanding of how this impedes damage propagation. Here we use non-destructive, time-lapse in situ tensile testing within an X-ray nanotomography (nCT) system to visualise crack progression through dry beetle elytron (wing case) cuticle in 3D. We find that its hierarchical pseudo-orthogonal laminated microstructure exploits many extrinsic toughening mechanisms, including crack deflection, fibre and laminate pull-out and crack bridging. We highlight lessons to be learned in the design of engineering structures from the toughening methods employed. Statement of Significance We present the first comprehensive study of the damage and toughening mechanisms within arthropod cuticle in a 3D time-lapse manner, using X-ray nanotomography during crack growth. This technique allows lamina to be isolated despite being convex, which limits 2D analysis of microstructure. We report toughening mechanisms previously unobserved in unmineralised cuticle such as crack deflection, fibre and laminate pull-out and crack bridging; and provide insights into the effects of hierarchical microstructure on crack propagation. Ultimately the benefits of the hierarchical microstructure found here can not only be used to improve biomimetic design, but also helps us to understand the remarkable success of arthropods on Earth. [ABSTRACT FROM AUTHOR]

[Display omitted] • Propagation of short fatigue cracks tracked through fine, medium and coarse microstructured cast Al-Si alloy. • Microstructurally Short cracks grow transgranularly close to low index crystallographic planes in some grains. • Secondary fatigue cracks nucleated from coarse unmodified hard particles. • Short crack growth rate fluctuates significantly due to local microstructure. • Cast Al-Si alloys with finer microstructures show greater crack propagation resistance. The role of microstructure on the short fatigue crack behaviour of cast Al-Si alloy under high cycle loading conditions is investigated by tracking the progress of cracks through fine, medium and coarse microstructured samples. Generally, in the early stage of crack growth, short cracks mainly grow transgranularly, with cracks growth close to low index crystallographic planes (mainly {1 0 0}) in some grains and frequently inhibited at grain boundaries. In the late stage, the crack growth mode gradually shifts from crystallographic stage-I to non-crystallographic stage-II. The short cracks grow faster and fluctuate significantly according to local microstructure. Our results show that finer microstructures offer greater crack nucleation and propagation resistance. [ABSTRACT FROM AUTHOR]

Time-lapse X-ray computed tomography is used to image the evolution of calcite precipitation during flow through microporous quartz over the course of 400 h. The growth rate decreases by more than seven times, which is linked to the clogging of flow paths that restricts flow to some regions of the column. Fewer precipitates are observed as a function of column depth, which is found to be related to a differential nucleation density along the sample. A higher nucleation density closer to the inlet implies more crystal volume increase per unit of time without affecting the rate if normalized to the surface area of crystals. Our overall growth rates measured in porous media are orders of magnitude slower than growth rates derived from traditional precipitation experiments on free surfaces. Based on our time-lapse results we hypothesize a scenario where the evolving distribution of precipitates within a pore structure during precipitation progressively modifies the local transport through the pores. Within less permeable regions the saturation index may be lower than along the main flow paths. Therefore, the reactive crystal surfaces within those regions grow at a slower rate than that expected from the bulk fluid composition. Since the amount of reactive surface area within these less permeable regions increases over time, the overall growth rate decreases without a necessary significant change of the bulk fluid composition along more permeable flow paths. In conclusion, the overall growth rates in an evolving porous media expected from bulk fluid compositions alone can be overestimated due to the development of stagnant sub-regions where the reactive surface area is bath by a solution with lower saturation index. In this context we highlight the value of time-lapse 3D studies for understanding the dynamics of mineral precipitation in porous media. [ABSTRACT FROM AUTHOR]

Abstract: A method of ring artefact suppression in X-ray computerised tomography (CT) reconstructions is proposed. The method is based on the assumption that a sinogram is a smooth function along the horizontal spatial coordinate. Methods based on the theory of ill-posed problems are applied to find a regularised solution. An analytical formula for the solution is proposed allowing fast ring artefact suppression. Its performance is demonstrated for parallel beam synchrotron X-ray tomography. [ABSTRACT FROM AUTHOR]

Almost every area of science has been revolutionized by our ability to collect two-dimensional images of increasingly fine detail, ranging from radio signals of far-off solar systems, to high-resolution electron microscopy images. With the advent of digital image capture, tomography – the art of reconstructing a sliceable virtual three-dimensional copy of the object from two-dimensional images – is becoming increasingly popular across a range of imaging modalities and length scales. One area attracting a lot of attention is the area of submicron X-ray tomography, popularly dubbed X-ray nanotomography. [Copyright &y& Elsevier]

The particulate properties of α-lactose monohydrate (αLMH), an excipient and carrier for pharmaceuticals, is important for the design, formulation and performance of a wide range of drug products. Here an integrated multi-scale workflow provides a detailed molecular and inter-molecular (synthonic) analysis of its crystal morphology, surface chemistry and surface energy. Predicted morphologies are validated in 3D through X-ray diffraction (XCT) contrast tomography. Interestingly, from aqueous solution the fastest growth is found to lie along the b-axis, i.e. the longest unit cell dimension of the αLMH crystal structure reflecting the greater opportunities for solvation on the prism compared to the capping faces leading to the former's slower relative growth rates. The tomahawk morphology reflects the presence of β-lactose which asymmetrically binds to the capping surfaces creating a polar morphology. The crystal lattice energy is dominated by van der Waals interactions (between lactose molecules) with electrostatic interactions contributing the remainder. Predicted total surface energies are in good agreement with those measured at high surface coverage by inverse gas chromatography, albeit their dispersive contributions are found to be higher than those measured. The calculated surface energies of crystal habit surfaces are not found to be significantly different between different crystal surfaces, consistent with αLMH's known homogeneous binding to drug molecules when formulated. Surface energies for different morphologies reveals that crystals with the elongated crystal morphologies have lower surface energies compared to those with a triangular or tomahawk morphologies, correlating well with literature data that the surface energies of the lactose carriers are inversely proportional to their aerosol dispersion performance. A predictive workflow for inhalation drug formulation highlighting the 4-stage pathway from the molecular state through solid-state and surface properties to the blended powder. [Display omitted] • Lattice energy dominated by van der Waals interactions with electrostatic interactions contributing about 13%. • Predicted 3D crystal morphology agrees with aqueous solution grown data as measured using X-ray Computed Tomography. • Polar "tomahawk" morphology reflects differential adsorption of β-lactose molecules between {010} and {0-10} surfaces. • Predicted surface energies agree with IGC data albeit with higher predicted dispersive energies compared to measurements. • Low variation between face-specific surface energies consistent with observed homogenous binding of crystals when blended. [ABSTRACT FROM AUTHOR]

• Graphite-based composites are fabricated infiltrating SiC and Si 3 N 4 inclusions into the graphite porosity. • The thermal conductivity of graphite increases 30 and 56 % infiltrating 12 vol.% of SiC and 19 vol.% of Si 3 N 4 , respectively. • The model predictions suggesting good heat transfer between the graphite matrix and the SiC and Si 3 N 4 particles. High thermal conductivity, wear resistant graphite is desirable for a range of applications, for example as an electrode to minimize energy consumption in aluminium smelting. This paper demonstrates that by infiltrating the porosity by reactive infiltration with SiC at levels ranging from 4 to 12 vol.% or Si 3 N 4 ranging from 7 to 19 vol.% the thermal conductivity can be raised progressively from ∼41 W/m K to ∼53 and 64 W/m K respectively. A simple analytical model predicts thermal conductivity rises with increasing reinforcement fraction only 7–9 % higher than that observed. This suggests that heat transfer between the graphite and the reinforcing particles is good making these materials good options where improved thermal conductivity and wear resistance over graphite is required. [ABSTRACT FROM AUTHOR]

SiC fibers are widely used in composites exposed to high temperature oxidizing environments. The present study compares the oxidation behavior of SiC fibers and the associated changes in tensile strength upon their exposure to dry air and steam for up to 50 hours at temperatures from 950°C to 1350°C. In both cases, the scale thickness and oxide microstructure were analyzed by scanning electron microscopy. When the SiC fibers were oxidized in air, a crack-free amorphous oxide layer formed at temperatures up to 1200°C, whereas a cracked, crystallized oxide layer was found at 1350°C. By contrast under steam environment, a crystalline oxide forms at 950°C for oxidation times longer than 30 h. In both environments, the fiber strength decreased with increasing exposure time and temperature, the degradation being faster after oxidation in steam compared to dry air. This appears to relate to residual stress in the oxide scale and a reduction in the cross section of the load-bearing unoxidized SiC. An increase in defect size may also contribute to the loss of strength. The oxide scale follows parabolic growth kinetics in both dry air and in steam from 950°C to 1350°C, except at 1350°C for over 30 hours. The oxidation rate in steam is faster than that in dry air, with activation energies of 79.8±1.4 kJ/mol in steam and 153.6±3.4 kJ/mol in dry air, respectively. This work is relevant to the application of SiC fibers and SiC fiber reinforced composites in air and steam environments at high temperature. [ABSTRACT FROM AUTHOR]

The progressive infiltration of a free-standing air plasma spray (APS) thermal barrier coating (TBC) by calcium-magnesium-alumino-silicate (CMAS) at 1250°C is followed non-destructively by time-lapse X-ray micro-computed tomography (µ-CT). The top ∼50 µm of the TBC expands rapidly (within the first 20 min) by as much as 70% due to the physical ingress of the CMAS along the splat boundaries and becomes exfoliated. The ingress and resulting exfoliation are shown to be driven by capillary forces with the exfoliated depth dependent on the CMAS loading. The remainder of the TBC swells at a slower rate (ultimately by 15%) but remains intact. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Effects of cross-flow velocity, filtration pressure, and solid concentration on filter cake properties are studied by using a new filtration setup that allows performing filtration tests under a wide range of operating conditions. The main feature of this setup is that pressure and cross-flow velocity are decoupled, so it was possible to independently investigate the effect of these variables on filter cake properties. Filtration tests have demonstrated that particle invasion into filter media pores occurs initially, leading to the formation of an external filter cake. The increased cross-flow velocity creates an erosive shear stress at the surface of the external cake, which limits cake growth, indirectly maintaining a high filtrate flow rate. This high filtrate rate imparts a considerable drag force onto suspended particles, driving a high count into the porous substrate where these particles could deposit. Increasing pressure amplifies this internal particle deposition, particularly where there is no or limited external filter cake to limit filtrate drag and screen particles at the cake surface. The effect of cross-flow velocity on pore blocking and filter cake structure is observed and demonstrated by CT scanning and scanning electronic microscopy. • Initial filtration relies on standard blocking when particles are smaller than substrate pores. • Pressure and solid concentration affect steady state in cross-flow filtration. • Shear stress inhibits cake filtration. • Drag force linearly affects particle deposition and invasion in cross-flow filtration. [ABSTRACT FROM AUTHOR]

A picosecond laser for incremental annular trench cutting is combined with digital image correlation (DIC) to extend the incremental ring-core method to the profiling of residual stress in thick (>100 μm) coatings. In this case the local residual stress in a TBC is depth profiled after exposure to 1150 °C for 190 h. The topcoat was found to be in compression with an average compressive stress of −94 ± 8 MPa which is representative of the stresses that would be generated elastically on cooling from a stress-free temperature of ~970 °C. The stress profile measurements have been validated by high-energy synchrotron X-ray diffraction measurements. Unlabelled Image [ABSTRACT FROM AUTHOR]

The degradation of an Electron Beam-Physical Vapour Deposition Thermal Barrier Coating caused by thermal cycling at 1150 °C has been followed in 3D non-destructively by time-lapse X-ray micro-computed tomography (μ-CT). Quantitative analysis of X-ray μ-CT virtual cross-sections on small samples is validated by destructive cross-sectional scanning electron microscopy (SEM) micrographs of larger ones. The evolution of thermally-grown oxide (TGO) is quantified. The TGO/bond coat interface roughness is measured in 3D. No significant rumpling is observed. Undulations are found locally at the interface of the as-deposited sample. Such undulations can increase in amplitude during cycling providing locations for interfacial cracks to initiate. [ABSTRACT FROM AUTHOR]

Objectives To quantify the extent of crack-tip plasticity, crack opening displacement (COD) and crack bridging for crack growth perpendicular (HAH) and parallel (RAR) to the tubules in elephant dentin under both hydrated and dry conditions to better understand their influence on intrinsic and extrinsic toughening during crack growth. Methods Compact tension test-pieces were prepared from a tusk of African elephant ivory. Crack-tip strain mapping and COD measurements by digital image correlation (DIC) technique were made under incremental loading and unloading of cracks for hydrated and dry dentin of different orientations. Results For the RAR test-piece the plastic zones were significantly larger in the hydrated condition compared to when dry. By contrast, the plastic strains in the HAH test-piece were negligible in both wet and dry conditions. In the RAR condition the crack front was broken up into overlapping longitudinal ‘fingers’ with crack bridging regions in between, the ligaments extending 400 μm behind the crack front in the dry case. This could only be seen in 3D by X-ray CT. Extrinsic shielding reduces the crack-tip stresses by 52% and 40% for hydrated and dry RAR test-pieces respectively. No significant bridging was found in the HAH case. Significance For crack growth parallel to the tubules, collagen plasticity determines the intrinsic toughening, whereas microcracking from the tubules governs extrinsic shielding via ligament bridging, which is maintained further behind the crack in the hydrated case. For cracks grown perpendicular to the tubules, neither toughening mechanisms are significant. [ABSTRACT FROM AUTHOR]

Compressive failure in a notched cross-ply IM7/8552 carbon fiber reinforced polymer (CFRP) laminate is studied experimentally by time-lapse in-situ synchrotron radiation computed tomography (CT). The focus is on tracking and quantifying the fiber damage evolution in the 0° plies under compression for the first time via a specimen design that exhibits quasi-stable damage accumulation. A novel segmentation algorithm has been developed and applied to extract morphological features of interest including the kink band width, inclination angle, and the extent of propagation from the notch. In the four innermost 0 ∘ plies, shear-driven fiber fracture initiates from the notch tip and propagates as a single fracture plane inclined about 45° to the compression axis. This shear-driven fiber fracture transitions to a kink band at a distance of about 300 μ m from the notch, which propagates at a shallower angle. During the later stages of the test, the kink bands propagate in the reverse direction to areas that previously initiated by shear-driven fiber fracture, which may explain why post-mortem observations seldom reveal the fiber shear fracture mechanism. The fiber damage initiation and evolution appears distinctly different from the classical parallel plane kink bands formed by plastic microbuckling under uniaxial compression in that the dominant mechanism appears to be shear-driven fiber fracture. [Display omitted] [ABSTRACT FROM AUTHOR]

Ru and Pd are fission products released through SiC layer in TRISO fuel at high temperature. This study investigates the corrosion behaviour of Ru-Pd on SiC layers of tri-structural isotropic (TRISO) particles. Specifically, it explores the effects of Pd (strongly reactive FP) on Ru (weakly reactive FP)-induced corrosion. In Pd-Ru/SiC systems, a Ru-Pd-Si liquid phase forms at high temperatures even with minimal Pd, accelerating corrosion along SiC grain boundaries. Comparing Pd's role in Ru/SiC and Ag/SiC systems underscores the importance of liquid phases in FP migration. A novel approach is proposed for predicting the corrosion effects of multiple FPs on SiC through enthalpic interaction analysis. [Display omitted] • Ru-SiC corrosion below 1500°C remains solid, with slow and uniform reaction. • High Pd content (>1 %) causes Pd-SiC corrosion only, preventing Ru-SiC corrosion. • Low Pd content (<1 %) induces Ru-Pd-Si liquid migration through SiC grain boundaries. • Liquid phase and reactive FPs are crucial factors for FP fast migration in SiC. • A novel way for predicting corrosion effect of multiple FPs on SiC is proposed. [ABSTRACT FROM AUTHOR]

Ceramic composites that are both tough and strong are needed for extreme environments, ranging from aerospace and nuclear, to medical applications. Bioinspired ceramic composites tackle this challenge by mimicking tough natural structures. Nacre-like aluminas (NLAs) are ceramics processed using advanced colloidal techniques to obtain a microstructure resembling the brick-and-mortar structure of nacre. NLAs can achieve flexural strengths up to 600 MPa and fracture toughnesses ranging from 5 MPa.m1/2 up to 16 MPa.m1/2 after crack propagation. These high values mainly rely on deflection mechanisms; these can operate at temperatures up to 1200°C and under impact testing. The fracture properties have been found to be highly dependent on the mortar composition and processing technique used. However, we still don't know how far we can extend the structural properties of NLAs by changing their mortar strength and brick morphology. In this study, we combine mode I wedge splitting testing and in situ synchrotron X-ray microtomography of mixed-mode SENB fracture testing along with a kinked crack analytical formulation to study the microstructure-properties relationship in NLAs having two mortar compositions/morphologies. We compare the toughness values obtained in mode I and II with deflection models and study the effect of mode-mixity on the NLA toughness. Our findings show the grain morphology strongly influences the fracture behaviour, with the longer grain material showing longer stable crack deflection which could be further optimised going forwards. By contrast the mortar properties which provide deflection and local toughening mechanisms may be nearing their optimal strength. [Display omitted] [ABSTRACT FROM AUTHOR]

The present study investigates the microstructure evolution and subsequent mechanical properties of SiC fiber /BN/SiBCN matrix composites after high temperature exposure. These composites display a tough failure response under three-point bending retaining 80 % of the as-processed strength, even after elevated temperature exposure up to 1350 °C for 10 h. This is due to crack deflection accompanied by extensive fiber pull-out. In addition, both thermodynamic modelling and phase analysis by XRD show higher matrix degradation in vacuum than in N 2 atmosphere due to the lower N 2 partial pressure. After thermally exposure at 1500°C, carbothermal reaction in the matrix leads to the formation of a porous composite, and the composites retains a tough failure response. Meanwhile, SiBCN matrix degradation and SiC fiber strength degradation occurs, which results in a significant decrement in composite strength. Modest increases in the fiber/matrix interfacial shear strength occur upon exposure at temperatures up to 1350°C, and then significantly reduce upon exposure to 1500 °C in N 2. [ABSTRACT FROM AUTHOR]

Despite its importance when considering jet engine environments, the behavior of ceramic matrix composites following high temperature exposure in steam has received much less attention than in air. The present study investigates the oxidation behavior and the corresponding mechanical properties of a SiC/BN/SiBCN composite after exposure to steam at 950°C, 1050°C, 1200°C and 1350°C for 30 h. The SiBCN matrix shows crack-filling behavior, whereby microcracks are filled with oxide hindering internal oxidation of the composite. The oxide layers formed on both the SiC fiber and the SiBCN matrix exhibit a double layer structure, with the outer layer being more porous. With increasing temperature, the BN interphase is consumed and replaced by borosilicate glass that bonds the fiber and matrix. This alters the debonding location from the fiber/BN interface to the BN/SiBCN matrix interface. Three-point bending test shows the composite retains good flexural strength and a tough failure response even after exposure to steam at 1350°C. Single fibre push-out test shows a slight increase in interfacial shear strength with increasing thermal exposure. • SiC/BN/SiBCN composites show crack-filling behavior and strength-retain property. • The oxide layer on both SiC fiber and SiBCN matrix shows a double layer structure. • Internal oxidation occurs preferentially at the fibre/BN interface. • Gradient BN interphase microstructure leads to gradient internal BN oxidation. [ABSTRACT FROM AUTHOR]

The effects of CO 2 exposure on sodium sulfate-activated blast furnace slag cement paste have been characterised by X-ray (attenuation) computed tomography revealing changes in micron-scale pore structure, and X-ray diffraction computed tomography (XRD-CT) elucidating changes in the spatial distribution of crystalline and semi-crystalline phases. Accelerated carbonation reduced ettringite volumes and induced formation of hydrotalcite, demonstrating the critical role of Mg-Al-SO 4 -layered double hydroxide phases in the CO 2 uptake of these cements. These changes yield a refinement of small pores and increase the overall porosity, reaching values comparable to those of blended Portland cements. Formation factor values were determined considering the pore solution electrical resistivity, calculated from thermodynamic modelling, and the porosity. A correlation between simulated tortuosity and porosity is proposed to estimate the diffusion tortuosity and formation factor of sodium sulfate-activated slag pastes. This approach represents a significant step forward for assessing carbonation resistance and CO 2 uptake capacity of cementitious pastes. [ABSTRACT FROM AUTHOR]

Fish-scale-like melt pool structures and internal defects are characteristic features in additively manufactured (AM) metals. These play a critical role in the damage and fracture processes under different service loading conditions. However, the relationship between these damage features and loading conditions, as well as the spatial interactions between melt pool structures and internal defects remains poorly understood. Using in situ time-lapse synchrotron X-ray tomography and diffraction, we identify the initiation and growth events of life-limiting damage under tensile, low cycle fatigue (LCF), and high cycle fatigue (HCF) loading. A novel transition from meso-structure insensitive, defect-dominated short fatigue crack propagation to a meso-structure sensitive mechanism occurs as the plastic zone expands ahead of a growing crack from HCF to LCF to tensile loading. Under tension and LCF, the damage accumulation gradually increases and micro-voids nucleate at the melt pool boundaries (MPBs) after which the crack path follows the MPBs. In contrast, under HCF, surface defects initiate fatigue cracking and the MPBs have a very limited effect on the crack propagation path. Finally, a physics-informed machine learning method is introduced to develop a novel methodology for predicting fatigue life by including three-dimensional features of defects in AM parts. [Display omitted] [ABSTRACT FROM AUTHOR]

The toughness of SiC fiber reinforced ceramic matrix composites (CMCs) can be significantly improved by the adoption of a pyrolytic carbon (PyC) interphase but this cannot be exposed to oxidizing environments at high temperatures. Here we considered a BN interphase as an alternative and investigated the flexural properties of SiC f /BN/SiBCN CMCs before and after high temperature exposure (1050 °C, 1200 °C and 1350 °C) in air. The flexural and interfacial shear strengths were determined by three-point bending and single fiber push-out tests, respectively. The flexural strength of the composites decreased from 325 ± 23 MPa to 165 ± 15 MPa, while the interfacial shear strength increased from 32 ± 9 MPa to 88 ± 18 MPa after oxidation at 1350 °C for 30 h. Digital image correlation (DIC) was used to visualize crack initiation and growth during the bending tests. This revealed that cracks formed on the tensile side of the specimens before being deflected and eventually passed through the fiber tow. The oxidation of the SiC f /BN/SiBCN composite at high-temperature resulted in the formation of borosilicate glass along the interphase area, and a porous structure was observed after oxidation at high temperatures due to its evaporation. The interfacial shear strength between the fiber and matrix increased after oxidation at high temperatures, which resulted in brittle failure of the composite. [ABSTRACT FROM AUTHOR]