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In this study, the Liu–Murakami (LM) creep damage-coupled model was considered to evaluate the creep properties of martensitic stainless steel. The degree of creep damage was examined at two temperatures (565 ℃ and 593 ℃) to assess mechanically and thermally activated processes. A series of high applied stresses (applied stress/ultimate strength > 0.5) was considered for accelerated creep loadings. A full set of creep constants was determined by combining the Norton and LM models. Constitutive equations were used to quantitatively estimate experimental creep curves. The variation in creep constants was discussed based on stress sensitivity, such as stress triaxiality and applied stress, depending on the power of stress. The creep strain–time curves were successfully estimated. The comparison between the experimental and analytical results was in good agreement in the tertiary regime. In addition, the compensation of the two applied temperatures provides a supplementary explanation of the relationship between the ultimate strength and rupture time in terms of temperature sensitivity. The analytical results show that different applied stresses and temperatures could be compensated to characterize the creep behavior of the material. Thus, the creep strain–time and creep strain rate–certain rupture time curves were finally achieved. The analytical process in this study provides a laboratory-scale assessment of creep properties using the accelerated creep test and LM model.

Here, we report a facile method to synthesize a series of macrocycles with different conformations. The planar macrocycle dimer (1), twisted macrocycle trimer (2) and "figure-eight" tetramer (3) are clearly elucidated by X-ray single-crystal analysis, in which the electron-rich phenanthrene units offer the possibility of supramolecular assembly. As expected, in the solid state, 1 and 3 assemble into a columnar stack and an interlocking dimer, respectively, via π-π interactions between the phenanthrene units. Compared to the rigid conformation of dimer 1, the structure of tetramer 3 is more flexible due to its enlarged ring size. 3 can deform from a figure-eight into a boat-shaped geometry to host a planar electron-deficient guest using its electron-rich phenanthrene units. When assembled with spherical electron-deficient C60 , interestingly, 3 further undergoes a conformational transformation from a figure-eight to a belt shape in order to host C60 . These supramolecular assembly behaviors of 3 demonstrate that it is an adaptable macrocyclic host for both planar molecules and fullerenes.

A new Mn(II) coordination polymer with the formula {[Mn2(bma)2(2,2′-bpy)(H2O)]}n (1) (H2bma = 2-benzylmalonicacid, 2,2′-bpy = 2,2′-bispyridine), was hydrothermally synthesized and then characterized by single-crystal X-ray diffraction. Complex 1 possesses infinite one dimensional ladder structure based on linear tetranuclear Mn(II) clusters. TGA experiment shows that complex 1 can maintain its framework integrity before 225 °C. In addition, the magnetic data indicate the existence of dominant antiferromagnetic behavior within the tetranuclear cluster.

The radial conjugated π-system of cycloparaphenylenes (CPPs) makes them intriguing fluorophores and unique supramolecular hosts. However, the bright photoluminescence (PL) of CPPs was limited to the blue light and the supramolecular assembly behavior of large CPPs was rarely investigated. Here we present the synthesis of tetra-benzothiadiazole-based [12]cycloparaphenylene (TB[12]CPP), which exhibits a lime to orange PL with an excellent quantum yield up to 82 % in solution. The PL quantum yield of TB[12]CPP can be further improved to 98 % in polymer matrix. Benefiting from its enlarged size, TB[12]CPP can accommodate a fullerene derivative or concave-convex complexes of fullerene and buckybowl through the combined π-π and C-H⋅⋅⋅π interactions. The latter demonstrates the first case of a ternary supramolecule of CPPs.

Generally, the conjugated homo-macrocycles (CHMs) are synthesized by covalently linking the repeating subunits. However, large subunits are often difficult to conjugate together due to severe stereo-hindrance. Meanwhile, large polyaromatic blocks can not only incorporate its appealing electronic and optical properties into CHMs but also distort the CHMs from planar to three-dimensional (3D) molecular structure. Here we synthesized the 3D CHM composed of large polyaromatic units by post-π-extension. Specifically, cyclo-m-phenylenes, as the cyclic precursor, were π-extended by C-C coupling and then subjected to dehydrocyclization, affording cyclo-1,3-dibenzo[e,1]pyrenylenes (CMDP). The structures of CMDPs were unambiguously characterized by single crystal X-ray diffraction, showing a congested and strained 3D conformation, which was also confirmed by theoretical calculations. Compared with the monomer, CMDPs showed redshifted absorption and emission, as well as a tenfold enhancement in photoluminescence quantum yield, which could be attributed to their 3D conformation.

Void growth, as a critical stage in ductile fracture, could play some important role in the ductility of high entropy alloys (HEAs). Under a high-strain-rate tension (strain rate: 0.1~0.4/ns), our atomistic simulations reveal a severely suppressed growth of void (initial diameter: 4.0~9.1 nm) in HEAs at a low temperature, compared with that in Ni metal or Ni-based binary alloys. The emission of unclosed glide loops is found critical to void growth. Void growth is suppressed, once dislocation emission is suppressed due to the solute drag effect. Regarding the alloying elements, we find the void suppression relevance as Fe>Co and Cr>Fe>Mn.

The PbTiO3 nanorods were synthesized by a hydrothermal method using 4.4 mol/L ammonia solution as the pH-adjusting agent. The influence of Pb/Ti molar ratio in the Pb–Ti precursors, precursor concentration, reaction temperature, and time on formation of PbTiO3 nanorods was investigated. The dendritic PbTiO3 nanorods were obtained by controlling the process parameters. The preparation of dendritic PbTiO3 nanorods mainly involved two steps: in the first step of formation of PbTiO3 nanorods, the classical nucleation and growth dominates the nanorod growth, and in the second step of formation of dendritic PbTiO3 nanorods, the oriented attachment dominates the dendritic grain growth. The PbTiO3 nanorods grew along the [001] c-axis, and the oriented attachment was along the [001] c-axis to form the dendritic PbTiO3 nanorods.

In digital rock physics, the intrinsic permeability of a porous rock sample can be evaluated from its micro-computed tomography ($$\upmu$$-CT) image through lattice Boltzmann method (LBM) simulation. The LBM permeability evaluation has been increasingly adopted by the oil and gas industries, especially when the access to core samples is limited. In order to accurately evaluate the permeability of porous media, this digital approach requires high-quality $$\upmu$$-CT images with sufficient resolution and size. In practice, however, the LBM simulation is often performed using images of reduced resolution, due to limitations in computing power and simulation time. As a result, the permeability results obtained are often compromised with significant errors, known as the resolution effect. In this study, the resolution effect is quantitatively investigated to identify the primary causes of error, based on which an error correction model for the LBM permeability evaluation is proposed. The model uses such geometric attributes as connected porosity, specific surface area and diffusion tortuosity to quantify the resolution effect and achieve error correction. Demonstrated on various types of porous media including sandstone, carbonate rock, sand pack, synthesis silica, etc., the proposed error correction model can effectively correct the errors in LBM permeability evaluation due to the resolution effect. Our error correction model makes image resolution reduction more meaningful and creditable for LBM permeability evaluation of porous media, thereby supporting its adoption in practical applications.

BaTi5O11 nanocrystals were synthesized by a hydrothermal method. The influence of Ba/Ti molar ratio in the Ba–Ti precursors on the morphology and dielectric properties of BaTi5O11 nanocrystals was investigated. In the precursors, the Ba2+ ion concentration was decreased from 0.02 to 0.01 mol/L, and the Ti4+ ion concentration was increased from 0.08 to 0.09 mol/L. The rice-like BaTi5O11 nanocrystals were synthesized at Ba/Ti molar ratios of 20:80 and 18:82, while the flower-like BaTi5O11 nanocrystals were formed at Ba/Ti molar ratios of 15:85, 12:88 and 10:90. The pure BaTi5O11 phase was synthesized at Ba/Ti molar ratio of 18:82 in the precursor, and the material had the permittivity of 38.9 at 8 GHz, which was close to that of the bulk BaTi5O11 ceramics.

Water splitting is thermodynamically uphill reaction, hence it cannot occur easily, and also highly complicated and challenging reaction in chemistry. In electrocatalytic water splitting, the combination of oxygen and hydrogen evolution reactions produces highly clean and sustainable hydrogen energy and which attracts research communities. Also, fabrication of highly active and low cost materials for water splitting is a major challenge. Therefore, in the present study, γ-Fe2O3 nanowires were fabricated from highly available and cost-effective iron plate without any chemical modifications/doping onto the surface of the working electrode with high current density. The fabricated nanowires achieved the current density of 10 mA/cm2 at 1.88 V vs. RHE with the scan rate of 50 mV/sec. Stability measurements of the fabricated Fe2O3 nanowires were monitored up to 3275 sec with the current density of 9.6 mA/cm2 at a constant potential of 1.7 V vs. RHE and scan rate of 50 mV/sec.

In order to improve the wear resistance of 27SiMn steel substrate, Fe-based alloy coatings were prepared by laser cladding technology in the present study. In comparison to the conventional gravity powder feeding (GF) process, high-speed powder feeding (HF) process was used to prepare Fe-based alloy coating on 27SiMn steel substrate. The effect of diversified energy composition of powder materials on the microstructure and properties of coatings were systematically studied. X-ray diffractometer (XRD), optical microscope (OM) and scanning electron microscope (SEM) were used to analyze the phase structure and microstructure of Fe-based alloy coatings, and the hardness and tribological properties were measured by the microhardness tester and ball on disc wear tester, respectively. The results show that the microstructure of conventional gravity feeding (GF) coatings was composed of coarse columnar crystals. In comparison, owing to the diversification of energy composition, the microstructure of the high-speed powder feeding (HF) coatings consists of uniform and small grains. The total energy of the HF process was 75.5% of that of the GF process, proving that high-efficiency cladding can be achieved at lower laser energy. The refinement of the microstructure is beneficial to improve the hardness and wear resistance of the coating, and the hardness of the HF coating increased by 9.4% and the wear loss decreased to 80.5%, compared with the GF coating. The wear surface of the HF coating suffered less damage, and the wear mechanism was slightly adhesive wear. In contrast, wear was more serious in the GF coating, and the wear mechanism was transformed into severe adhesive wear.

PbZr0.52Ti0.48O3 nanocrystals were synthesized by a hydrothermal method. The effect of NaOH concentration, reaction temperature and time on nucleation and growth of PbZr0.52Ti0.48O3 nanocrystals was investigated. As the 0.05 mol/L PbZr0.52Ti0.48O3 precursors were heated at 200 °C for 21 h with NaOH concentration of 0.5 mol/L, the tetragonal PbZr0.52Ti0.48O3 nanocrystals were formed, and the grain size was more than 20 nm. With increasing the NaOH concentration from 0.5 to 1.5 mol/L, the grain size of PbZr0.52Ti0.48O3 nanocrystals decreased. When the precursors were heated at different temperatures (140 °C to 200 °C) for 21 h with 1.0 mol/L NaOH, single-phase PbZr0.52Ti0.48O3 nanocrystals were obtained at 160 °C to 200 °C. With increasing the reaction temperature from 160 °C to 200 °C, the grains size of PbZr0.52Ti0.48O3 nanocrystals increased from 5 nm to 9 nm. When the precursors were heated at 160 °C in different reaction times from 6 h to 21 h, the evolution from amorphous to crystalline PbZr0.52Ti0.48O3 nanocrystals in correlation with the reaction time was observed. Single crystalline PbZr0.52Ti0.48O3 nanocrystals with narrow size distribution (from 5 nm to 9 nm) were synthesized by controlling the NaOH concentration, reaction temperature and time. The obtained results can find potential application in preparing PbZr0.52Ti0.48O3 thin films on flexible substrates.

Pb(Zr0.52Ti0.48)O3 nanocrystals were synthesized by a hydrothermal method. The poly(vinyl pyrrolidone) (PVP) was used as the surfactant to control growth of the Pb(Zr0.52Ti0.48)O3 nanocrystals. The effect of PVP concentration, reaction temperature and time on morphologies and crystallinity of Pb(Zr0.52Ti0.48)O3 nanocrystals were investigated. The tetragonal PbZr0.52Ti0.48O3 grains were obtained, as they were prepared at 200 °C for 4 h with PVP concentration from 0.1 to 10.0 g/L. With increasing the PVP concentration from 0.1 to 10.0 g/L, the size of PbZr0.52Ti0.48O3 grains decreased. When the PbZr0.52Ti0.48O3 grains were prepared at 200 °C for 12 h with PVP concentration of 6.0 g/L, the PbZr0.52Ti0.48O3 nanocrystals with average diameter of 30 nm were formed.

Geological carbon storage in deep aquifers involves displacement of resident brine by supercritical CO2 (scCO2), which is an unstable drainage process caused by the invasion of less viscous scCO2. The unstable drainage is greatly complicated by aquifer heterogeneity and anisotropy and regarded as one of the key factors accounting for the uncertainty in storage capacity estimates. The impacts of pore-scale characteristics on the unstable drainage remain poorly understood. In this study, scCO2 drainage experiments were conducted at 40 °C and 9 MPa using a homogeneous elliptical micromodel with low or high anisotropy, a homogeneous/isotropic hexagonal micromodel, and a heterogeneous sandstone-analog micromodel. Each initially water-saturated micromodel was invaded by scCO2 at different rates with l o g C a (the capillary number) ranging from −7.6 to −4.4, and scCO2/water images were obtained. The measured CO2 saturations in these centimeter-scale micromodels vary considerably from 0.08 to 0.93 depending on the pore-scale characteristics and capillary number. It was also observed that scCO2 drainage follows the classic flow-regime transition from capillary fingering through crossover to viscous fingering for either of the low-anisotropy elliptical and heterogeneous micromodels, but with disparate crossover zones. The crossover zones of scCO2 saturation were then unified with the minimum scCO2 saturation occurring at l o g C a * = - 4.0 using the complete capillary number ( C a * ) that considers pore characteristics. For the hexagonal and the high-anisotropy elliptical micromodels, a monotonic increase in scCO2 saturation with increasing C a * (without crossover) was observed. It appears that the complete capillary number is more appropriate than the classic capillary number when characterizing flow regimes and CO2 saturation in different pore networks.

In a first effort, the dislocation structure and related mass transfer in a macroporous FCC metal is studied via atomistic simulation. The interaction between the void and its periodic image has been intense ever since the onset of dislocation emission. The accumulated mass transfer is due to the emission of multiple shear loops, which shapes the morphology of the macroporous metal. The removal of mass from the intervoid ligament triggers its breakdown, connecting the voids. The strengthening of intervoid interaction is shown by running multiple cases with atom count ranging from 7.1 million to 95.4 million. The critical stress for dislocation emission versus the size of void is in a good agreement to the Lubarda model adjusted by the Gibson-Ashby scaling law. Nevertheless, the critical stress of void with a short intervoid ligament distance (ILD) demonstrates a surprisingly insensitivity of strain rate compared with the void that can be deemed standalone.

Understanding and characterization of immiscible-fluid displacement mechanisms in pore structures are required for enhanced hydrocarbon resource recovery in unconventional tight reservoirs. The displacement process of immiscible fluids in a porous structure on the pore scale has been widely simulated and characterized via lattice Boltzmann (LB) methods. However, owing to the heterogeneity and tortuosity of rock pore structures, it is difficult to numerically represent the real irregular geometry and accurately describe the varied immiscible interfaces in experiments using LB simulation. A low mesh resolution is usually applied, which causes simulation inaccuracy compared to realistic displacement behaviors. In this study, we introduce a multicomponent LB model with high-resolution meshes to investigate immiscible oil-water displacement in heterogeneous pore structures. The pore-scale LB model is established using information extracted from a realistic reservoir rock. A parallel computing algorithm is integrated into the model to accelerate the LB simulation. To verify the LB simulation, an oil-water displacement experiment is conducted using a transparent pore model replicated using three-dimensional printing (3DP) technology and information on the real porous rock. Owing to the sensitivity of the interfacial condition at the inlet, the inlet buffer was designed to relieve injecting perturbations in experiments, and an artificial velocity profile was applied in the simulation to approximate this relieved interface. Comparison of the LB simulation and experiment data indicates that the suggested parallel multicomponent LB method can simulate the oil-water displacement process in heterogeneous pore structures well. This study provides a method for characterizing the immiscible fluid displacement mechanism in a porous structure and forecasting the preferential flow path in a heterogeneous structure with a certain water wettability.

Mass transfer during the formation and emission of a dislocation loop without non-conservative motions can be very tricky. We combine the molecular statics, nonsingular dislocation theory, finite element (FE) method and molecular dynamics (MD) approach to offer new insights. It is proved both theoretically and numerically that the formation and the dynamic emission of a full shear loop can grow a nanovoid. For the first time, a novel approach is proposed to create a shear loop via a hemispherical surface cut by the atomistic simulation. Such a formation process can produce a similar shear loop to that via a flat surface cut, and yet lead to void growth. We incorporate the non-singular dislocation theory into a FE model to calculate the potential energy regarding different surface cuts. Among possible cuts to create a shear loop, the potential energy would favour the one that grows a void under triaxial tension. We show that the arbitrariness regarding the surface cut of dislocation segments should also be recognized during the dynamic emission process. Under triaxial tension, we confirm the mass transfer during the cross-slipping of V-shape shear loops prior to the completion of prismatic loops. By comparison, the uniaxial tension case shows that a V-shape shear loop is not necessarily the precursor of a prismatic loop. Hence, its mass transfer mechanism should be treated differently.

In this research, we proposed a highly sensitive hydrogen sensor based on a new suspended structure of cross-stacked multiwall carbon nanotube (MWCNT) sheet. MWCNT sheet is a kind of CNT film which has a super-high CNT alignment and can be easily prepared by drawing from the spinnable CNT array in large scales. By stacking the sheets onto an electrode with a 1 × 1 cm hole in mutually perpendicular directions, sensors with suspended cross-stacked structure were realized. Afterwards, a two-side Pd functionalization was introduced. The effects of suspended structure, cross-stacked structure and two-side Pd functionalization were investigated respectively. It was observed that the sample with 2 + 1 layers of cross-stacked MWCNT sheet and two-side 3 nm Pd deposition showed the best gas sensing performance with a relative resistance change of 35.30% at 4% H2. This result indicates that the proposed sensor is one of the best among all reported MWCNT based hydrogen sensors. The method demonstrated in this research gives a potential solution for the mass production of CNT-based sensors with high sensitivity and reliability.

Quintulene, a non-graphitic cycloarene with fivefold symmetry, has remained synthetically elusive due to its high molecular strain originating from its curved structure. Here we report the construction of extended quintulene, which was unambiguously characterized by mass and NMR spectroscopy. The extended quintulene represents a naturally curved nanocarbon based on its conical molecular geometry. It undergoes dimerization in solution via π−π stacking to form a metastable, but isolable bilayer complex. Thermodynamic and kinetic characterization reveals the dimerization process as entropy-driven and following second-order kinetics with a high activation energy. These findings provide a deeper understanding of the assembly of conical nanocarbons. Comparison of optical properties of monomer and dimer points toward a H-type interlayer coupling in the dimer., Quintulene, a quintuple non-graphitic cycloarene, is challenging to synthesize. Here, the authors synthesize and characterize the cone-shaped extended quintulene and its bilayer dimer, and disclose its dimerization as an entropy-driven, second-order reaction with a substantial activation energy.

Understanding and characterizing the transport of shale gas (methane) through the nanopores of kerogens are critical for the accurate prediction of shale gas recovery. However, the key factors that regulate shale gas transport through highly roughened nanopores of shale kerogens are not fully understood. In this work, methane transport in organic nanopores with a high relative roughness is characterized using equilibrium and non-equilibrium molecular dynamics methods. According to our results, the CH4 mass flux has a linear relationship with the pressure gradient, consistent with previous studies, while the calculated slip lengths and gas fluxes varied with different roughness geometries in the order of sigmoidal ≥ triangular > rectangular. Surface slip flow can be a major contributor to the overall gas flux, but surprisingly, the relative contribution of surface slip flow is independent of the pressure gradient. In contrast, the contributions of both slip flow and the average gas fluxes vary strongly with pore diameters. Typical contributions of the adsorbed layer to the overall gas flux are in the range 20–40% but vary from as high as 74% in a 4-nm pore to as low as 6% in a 16-nm pore. Compared to smooth nanopores, we find that, in nanopores with realistically high degrees of relative roughness, methane confinement in cavities decouples slip flow from the flow in the pore interior, significantly reducing the overall flux.

In nature, rock discontinuities, e.g., cracks, voids and joints, are usually three-dimensional, which to a large extent control the volumetric fracturing behaviors of rock masses. Understanding their growth behaviors and effects on rock volumetric fracturing properties is crucial for the stability assessment of rock engineering. In this study, three-dimensional printing (3DP) method was adopted to fabricate resin-based artificial rocks containing single flaw and double pre-existing penny-shaped 3D internal flaws. Static uniaxial compression tests were, subsequently, conducted on these samples to investigate the influence of flaw number, flaw angle (α) and ligament angle (β) on the volumetric fracturing behaviors of the 3DP artificial rocks. The results indicate that flaw geometry has remarkable influence on the mechanical and fracture behaviors of the flawed samples. The single flawed sample with α equal to 60° has the lowest compressive strength (σc) and axial strain at the peak stress (ea). σc and ea of the double flawed sample generally increase when β changes from 45° to 105°. When the flaw number increases from one to two, the initiation stress of the first wing crack, σc and ea decrease. With the aid of high-speed cameras, we studied 3D crack growth inside the transparent 3DP resin samples in real-time for the first time. Wing and anti-wing cracks wrapped around the flaw edge could only propagate for approximately 1–1.5 times the length of the initial flaw. Wing cracks generated at the inner tips of the flaws cannot coalesce, except for the sample with β of 105°. The maximum crack propagation velocity in single flawed specimens is higher than that in double flawed samples. The continuous propagation of the secondary cracks developed after the peak stress lead to the burst-like failure of the flawed samples. This study could enhance our understanding of volumetric fracturing behaviors of rocks.

Dissolution trapping is one of the most important mechanisms for geological carbon storage (GCS). Recent laboratory and field experiments have shown non-equilibrium dissolution of supercritical CO2 (scCO2) and coupled scCO2 dissolution and water flow, i.e., scCO2 dissolution at local pores/pore throats creating new water-flow paths, which in turn enhance dissolution by increased advection and interfacial area. However, the impacts of pore-scale characteristics on these coupled processes have not been investigated. In this study, imbibition and dissolution experiments were conducted under 40 °C and 9 MPa using a homogeneous/isotropic hexagonal micromodel, two homogeneous elliptical micromodels with low or high anisotropy, and a heterogeneous sandstone-analog micromodel. The four micromodels, initially saturated with deionized (DI)-water, were drained by injecting scCO2 to establish a stable scCO2 saturation. DI water was then injected at different rates with logCa (the capillary number) ranging from −6.56 to −4.34. Results show that bypass of scCO2 by displacing water is the dominant mechanism contributing to the residual CO2 trapping, triggered by heterogeneity in pore characteristics or pore-scale scCO2-water distribution. Bypass can be enhanced by pore heterogeneity or reduced by increasing transverse permeability, resulting in relatively low (

This study evaluated the low-cycle fatigue (LCF) life of type 316 austenitic stainless steel to determine the effect of multiple high-density pulsed electric currents (HDPECs). Fatigue properties were analyzed with the fatigue crack growth (FCG) and LCF tests by considering different conditions of multiple HDPECs and its application. The HDPEC densities of 100, 150 and 200 A/mm2 with application numbers from 1 to 17 times were used. The LCF results were assessed by using fatigue models, and the effectiveness of the application methods was examined. Under the HDPEC density of 200 A/mm2, increasing the number of HDPECs during the period of crack propagation is the best way for delaying FCG. Multiple applications of HDPEC caused a decrease in the length and an increase in the depth of striations in the specimen’s fatigue fracture surface, and the degree of ductility was increased thereby leading to the delay in FCG. The proposed conditions pave the way toward improving the LCF life of the material.

Early experiments showed that short helical dislocations can be generated near an inhomogeneity in crystal materials under hydrostatic loading. For the first time, atomistic simulations also reveal that a nano-inhomogeneity can not only induce rows of prismatic loops but also helical dislocations under hydrostatic loading. Two new mechanisms of helical dislocation formation are discovered via molecular dynamics (MD) simulations. Both concern the pinch-off process between dislocation segments. The first mechanism is the pinch-off failure of an unclosed prismatic loop. The second mechanism is the early pinch-off between two nested, cross-slipped shear loops before evolving into prismatic ones. The configuration of the two closing-in dislocation segments is crucial. Two screw segments with opposite line directions will feel a strong attractive force, while other configurations may not. Thus, the pinch-off process is either promoted or hindered. The reduction of screw components can be viewed as a need to lower the interaction energy between dislocation loops. The stress required to sustain the formation of dislocation helix is found much lower than that needed to trigger dislocation emission. In addition to the formation mechanism, the ongoing material transport is studied and its distribution is revealed concerning the helical turns. To our best knowledge, the formation of helical dislocations near a nano-inhomogeneity in an initially dislocation-free matrix has never been studied via atomistic simulations.

Coal as the fundamental element in underground coal mining is well-known as a heterogeneous geomaterial, and the knowledge of its deformation processes and failure mechanisms is important for the prediction and prevention of dynamic disasters and the design of stable underground structures . In this paper, after analysing the pre-peak strain hardening, the post-peak strain softening , and the associated dilation behaviours of heterogeneous coal under loading, a plastic strain-based damage model that consists of the heterogeneity function, the damage stress-strain function, the cohesion function and the dilation angle function, was developed. In this model, the heterogeneity was characterised by considering the micro-unit strength as referring to the Weibull function. The damage stress-strain function was defined by the Weibull function and the plastic strain based on the continuous damage mechanics theory. The cohesion and the dilation angle were expressed by a modified damage function while the friction angle is constant, which were simultaneously implemented in a geotechnical simulator together with the heterogeneity function and the Mohr-Coulomb yield criterion with an embedded tension cut-off. The numerical results are consistent with the experimental and theoretical results. It can be concluded that a large variety of stress-strain relation curves, characterised by the pre-peak elastic and strain-hardening and the post-peak strain-softening, as well as their dilation behaviour, can be accurately reproduced by a group of fitted parameters.

Accurate knowledge of spontaneous imbibition in irregular channels is fundamentally important for a better understanding of the transport in a porous media. During the spontaneous imbibition, the wetting fluid is driven by the capillary pressure and retarded by the viscous drag, both of which are highly influenced by the channel geometry. As a result, accurate simulation of the process in complex geometries becomes important. In this study, an improved fluid-solid interaction force in the two-phase pseudopotential lattice Boltzmann method is proposed for the accuracy and stability in simulating the spontaneous imbibition behavior. After validation the simulated results against the theoretical results in a 2D straight channel, the method is employed to simulate the spontaneous imbibition in irregular channel models, which include a sine-shape channel, a wedge-shape channel and bifurcated channels. The results quantitatively revealed the influence of tortuosity, channel shape on the imbibition behavior and the competing interfaces advancing behavior in bifurcated channels.

Quantitative visualization and characterization of stress-field evolution during fracture rapid growth is critical for understanding the mechanisms that govern the deformation and failure of solids in various engineering applications. However, the direct capture and accurate characterization of a rapidly-changing stress field during crack propagation remains a challenge. We report an experimental method to quantitatively visualize and characterize rapid evolution of the stress-field during crack propagation in a transparent disc model containing a penetrating fusiform crack. Three-dimensional (3D) printing technology and a stress-sensitive photopolymer resin were adopted to produce the disc model and to alleviate the residual processing stress that usually blurs the dynamic stress field due to overlap. A photoelastic testing system that synchronized a high-speed digital camera and a pulsed laser with a nanosecond full width at half maximum (FWHM) was used to capture the rapid evolution of the stress field in the vicinity of crack tips. The results show that the proposed method is suitable to directly visualize and quantitatively characterize the stress-field evolution during crack rapid propagation. It is proved that the crack propagation velocity is strongly governed by the stress field around the crack tips.

The single-crystalline BaTi5O11 nanocrystals were synthesized by a hydrothermal method. The Barium acetate (Ba(CH3COO)2) and tetrabutyl titanate (Ti(C4H9O)4) were used as the starting materials, and the NaOH was used as a pH-adjusting agent. In the aqueous precursor, the NaOH concentration was 2.0 mol/L, and the concentrations of Ba2+ and Ti4+ ions were 0.01 and 0.09 mol/L, respectively. As the precursor was heated at 280 °C for 20 h by the hydrothermal method, the white precipitate was formed. The white precipitate was confirmed to be the elongated BaTi5O11 nanocrystals. The single-phase BaTi5O11 nanocrystals were successfully synthesized.

In order to analyze the suppression effects and mechanisms of ABC powder on ethylene gas (C2H4)/polyethylene (PE) hybrid explosion, to explore the suppression characteristics of gas-solid two-phase explosion, the 20-L apparatus are used for the test of the explosion overpressure. The results show that when the volume fraction of C2H4 is 3%, the concentration of ABC powder required to completely inhibit the explosion of 300 g/m3 PE dust increases from 200 g/m3 to 1200 g/m3. When increasing the volume fraction of ethylene to 5% and 7%, the explosion overpressure reduction in the mixture is 40.68% and 28.59%. The results of thermal analysis show that the addition of ABC powder improves the thermal stability of PE particle. Through the physical effects of heat absorption, oxygen insulation, and thermal transmission weakened and the chemical effect of eliminating explosive radicals, ABC powder reduces the rate of explosive chain reaction and heat release rate, thus producing an effective inhibition effect. But C2H4 will induce the explosion process of the mixture from two-phase combustion to homogeneous combustion to promote the explosion, and its effect is opposite to that of ABC powder pyrolysis in the system, which makes the explosion of mixed system more difficult to be suppressed.

The interior deformation or rupture of materials is usually derived from measuring the surface deformation of specimens. In this study, a set of uniaxial compression tests combined with in situ X-ray computed tomography (CT) was performed on siltstone specimens with a pre- existing three-dimensional (3D) surface flaw with various inclination angles (α = 30◦, 45◦, 60◦). The ratio of flaw depth to specimen thickness was 0.26. Based on the CT images of the specimens under different loads, the digital volumetric speckle photography procedure was applied to quantifying the 3D interior deformation of the specimens, and 3D displacement and major principal strain e1 distribution in different sections were determined. The characteristics of internal strain before specimen fracturing indicated strain localization, which could describe the propagation mechanism of the single 3D surface flaw.

The accurate knowledge and characterization of the full-field stress distributions and evolution in assembled lining structures underlie the design, construction, and maintenance of tunnel linings. However, it is challenging for traditional field monitoring and laboratory experiments to identify directly and quantify accurately such distributions and evolution. Numerical simulations, as alternative solutions, are limited, as their results are significantly dependent on the accuracy of mechanical parameters, constitutive laws, failure criteria, mesh optimization, and boundary conditions, which are difficult to determine experimentally. In this study, a plane-stress-model-based photoelastic testing method was developed for the direct observation and quantification of the full-field stress distribution and evolution in an assembled lining structure based on additive manufacturing or three-dimensional printing technology and phase shifting methods. Three-dimensional printing techniques and stress- sensitive photopolymers were employed to fabricate transparent assembled models based on the information of real lining structures. The model split-merge technique, phase-shifting method, and unwrapping algorithm were combined to determine the full-field distribution of the principal stress difference and shear stress within the assembled segments. The proposed method was verified based on a comparison of the calculated and measured fringe orders at different loading stages. The experimental results indicated that the largest stress concentration was around the joint that connected the adjacent Segment L1 and basic Segment B1, which formed the potential critical failure zone of the assembled structure. An approximate X-shaped shear band was also identified. Comparisons of the results verified that the boundary and contact conditions, which are difficult to simulate, can lead to significantly different simulation results with respect to the distribution and evolution of the principal stress difference and shear stress. This study shows that the proposed method can effectively and quantitatively characterize the full-field stress distributions and evolution within complex assembled lining structures.

In this study, we investigated the relationship between intermetallic compounds (IMCs) and electromigration (EM)-based metallic micro-/nanowire growth and concluded that IMC has a negative effect on the wire growth. One of the key features of the sample structure in EM-based wire growth is passivation, which mechanically suppresses the deformation of the metallic interconnect due to the accumulation of atoms diffused by EM. Thicker passivation allows for higher pressure generation for wire growth; thus, the wire can be extruded by the higher pressure. However, as the compressive residual stress of passivation (which causes delamination) increases with the thickness of passivation deposited by sputtering, it is implied that excessively thick passivation causes delamination, which in turn relieves the pressure essential for wire growth, by releasing the interconnect constraints. In EM-based wire growth, generally a sample structure consisting of thin-film multilayers was used, and it often resulted in the delamination due to interlayer separation between the metallic interconnect and the topmost passivation. Mitigation of delamination enables the stable EM-based growth of a wire. To prevent delamination, Ti was introduced between the metallic interconnect and passivation. The relation of IMC formation behavior to the wire growth was investigated. It was experimentally shown that IMC contributed to the prevention of delamination but inhibited the wire growth. Therefore, sandwiching the metallic interconnect with materials that do not form IMC is advantageous for EM-based wire growth.

Cold spray (CS) has significant technical advantages in additive manufacturing of aluminum matrix composites. In this study, Al with different content of Al2O3 composite deposits was successfully produced by CS. The effect of Al2O3 content and heat treatment temperature on the microstructure and mechanical properties of the deposits was comprehensively studied. The results show that as the content of Al2O3 increases, the hardness, Ultimate Tensile Strength (UTS), and elongation of the deposits gradually improve in the as-sprayed state. Due to the significant hammering effect of Al2O3 particles on Al particles, there is a local metallurgical bond between adjacent Al particles in Al-50 and Al-75 deposits, and dimples appear in the fracture morphology of the deposit. With the increase of the heat treatment temperature, the diffusion of atoms at the particle-particle interface transforms the bonding between Al particles from mechanical interlocking to metallurgical bonding, so that the deposit exhibits improved ductility. However, heat treatment also eliminates the residual compressive stress and introduces grain growth through recovery and recrystallization processes, resulting in the decrease of hardness and UTS of the deposits.

The Bi4Ti3O12 nanocrystals were synthesized by a hydrothermal method, and NaOH was used as a pH-adjusting agent. The effect of reaction temperature on formation and morphologies of Bi4Ti3O12 nanocrystals was investigated. The single-phase Bi4Ti3O12 nanocrystals were prepared at 140–220 °C. As the Bi4Ti3O12 nanocrystals were synthesized at 140 °C, it consisted of the fine grains with 10–30 nm grain size. With increasing the reaction temperature, the flake-like Bi4Ti3O12 grains were formed and grew up. At high reaction temperatures (200–220 °C), they mainly consisted of the flake-like grains.

The understanding and prediction of preferential fluid flow in porous media have attracted considerable attention in various engineering fields because of the implications of such flows in leading to a non-equilibrium fluid flow in the subsurface. In this study, a novel algorithm is proposed to predict preferential flow paths based on the topologically equivalent network of a porous structure and the flow resistance of flow paths. The equivalent flow network was constructed using Poiseuille’s law and the maximal inscribed sphere algorithm. The flow resistance of each path was then determined based on Darcy’s law. It was determined that fluid tends to follow paths with lower flow resistance. A computer program was developed and applied to an actual porous structure. To validate the algorithm and program, we tested and recorded two-dimensional (2D) water flow using an ablated Perspex sheet featuring the same porous structure investigated using the analytical calculations. The results show that the measured preferential flow paths are consistent with the predictions.

The combination of three-dimensional (3D) printing techniques and photoelastic testing is a promising way to quantitatively determine the continuous whole-field stress distributions in solids that are characterized by complex structures. However, photoelastic testing produces wrapped isoclinic and isochromatic phase maps, and unwrapping these maps has always been a significant challenge. To realize the visualization and transparentization of the stress fields in complex structures, we report a new approach to quantify the continuous evolution of the whole-field stress in photosensitive material that is applicable to the fabrication of complex structures using 3D printing technology. The stress fringe orders are determined by analyzing a series of continuous frames extracted from a video recording of the fringe changes over the entire loading process. The integer portion of the fringe orders at a specific point on the model can be determined by counting the valleys of the light intensity change curve over the whole loading process, and the fractional portion can be calculated based on the cosine function between the light intensity and retardation. This method allows the fringe orders to be determined from the video itself, which significantly improves characterization accuracy and simplifies the experimental operation over the entire processes. To validate the proposed method, we compare the results of the theoretical calculations to those of experiments based on the diametric compression of a circular disc prepared by a 3D printer with photosensitive resin. The results indicate that the method can accurately determine the stress fringe order, except for points where the deformation is too large to differentiate the fringes pertaining to photoplasticity.

Soil–rock mixture (SRM) is a unique type of geomaterial characterized by a heterogeneous composition and a complicated structure. It is intractable for the continuum-based soil and rock mechanics theories to accurately characterize and predict the SRM’s mechanical properties. This study reports a novel numerical method incorporating microfocus computed tomography and PFC3D codes to probe the deformation and failure processes of SRM. The three-dimensional (3D) PFC models that represent the SRM’s complex structures were built. By simulating the entire failure process in PFC3D, the SRM’s strength, elastic modulus and crack growth were obtained. The influence of rock ratios on the SRM’s strength, deformation and failure processes, as well as its internal mesoscale mechanism, were analyzed. By comparing simulation results with experimental data, it was verified that the 3D PFC models were in good agreement with SRM’s real structure and the SRM’s compression process, deformation and failure patterns; its intrinsic mesomechanism can be effectively analyzed based on such 3D PFC models.

One of the challenges limiting the application of laser cladded Fe-based coatings is the coarse columnar grains formed during the process. In order to improve the microstructure homogeneity of laser cladded coatings, Fe-based alloy (Fe78.5Cr15.6Ni4.0Si0.7) composite coatings with different La2O3 additions were prepared on the surface of 45-steel substrate by laser cladding. The effect of La2O3 content on the microstructure and properties composite coatings were systematically studied. X-ray diffractometer (XRD) and scanning electron microscope (SEM) were used to analyze the phase structure and microstructural evolution of Fe-based alloy composite coatings, and the hardness and tribological properties were measured by the microhardness tester and ball on disc wear tester, respectively. The results show that the addition of La2O3 plays the role of grain refinement, and certain amount of addition can completely eliminate the coarse columnar grains. Due to the fine-grain strengthening and dispersion strengthening of La2O3, the hardness and wear resistance of Fe-based alloy composite coatings have been improved. Especially, when the content of La2O3 is 1 wt%, the hardness increases to 3.1 times and the wear loss decreases to 27.7%, compared with the substrate material. The wear surface of composite coating with 1 wt% La2O3 suffered minor damage, and the wear mechanism is slightly abrasive wear. In contrast, higher amount of 2 wt% La2O3 addition has less effective grain refining where some columnar grains appear on the interface, and the hardness and wear resistance of composite coatings decrease as well. Meanwhile, the wear mechanism is transformed into a mixed mode of abrasive wear and adhesive wear.

Quantitative visualization of the full-field stress and strain in porous structures is of significance to reveal the mechanism of the damage and failure of engineering materials. To quantitatively characterize the full-field stresses and strains, optical measurement methods, such as photoelasticity for determining the stress fields, moire and digital image correlation (DIC) methods for measuring the strain fields, have been developed in previous works. However, it is challenging to combine these methods to measure stress and strain fields simultaneously because the speckles and gratings for strain measurement will disturb the interference fringes in the photoelasticity. In this study, a method incorporating photoelasticity and DIC techniques was developed to determine the stress and strain fields simultaneously in different porous structures which were fabricated by three-dimensional (3D) printed technique. The tested models were printed with a highly transparent, colourless material and the speckles on the front surface of the tested models were printed with a translucent, magenta material. Under compressive loads, the stress fields in these models were obtained based on the photoelastic patterns and the strain fields were determined by DIC method. The results indicate the proposed method can simultaneously determine the full-field stresses and strains and the comparison of the distribution of the principal stress and strain difference and the distribution of the shear stress and strain verified its good accuracy. In addition, the stress and strain distribution in different pore structures were compared and found that the optimal design of the pore distribution can greatly change the concentration of the stress and strain fields.

Moisture in coal seams changes gas adsorption capacity, induces coal deformation, and affects coal porosity. However, fewer studies have investigated the dynamic process of moisture loss. In this study, a fully coupled multi-physical model for coal deformation, gas flow and moisture loss was implemented. It validated the coal-gas-moisture interactions of the decay of gas adsorption capacity and the coal shrinkage. Subsequently, the proposed model was applied to a simulation of coal seam gas recovery from wet reservoir and solved using the finite method in COMSOL Multiphysics 3.5. Analyses of the component factors and the sensitive parameters of moisture loss on coal porosity and permeability were comprehensively studied at last. The results reveal that moisture loss enhances coal porosity and permeability. The decay of gas adsorption capacity decreases coal permeability while the coal shrinkage promotes it. The decrease of the adsorption decay coefficient and the increase of the initial density of saturated water vapor and water evaporation constant can enhance the permeability of wet coal seams. Keywords: Coal seam gas, Porosity and permeability, Coal-gas-moisture interaction, Moisture loss, Numerical simulation

From a microscopic point of view, nano-scale pores are dominant in shale matrix, which provide transport space for natural gas. Accordingly, a pore-scale modeling, which can accurately capture the complex pore morphology and its effects on gas flow behavior, is crucial for understanding the gas transport mechanisms in shale matrix. In this study, the focused ion beam-scanning electron microscope (FIB-SEM) technique was employed to observe and characterize the morphology of the nanopores in shale. Based on the morphology characterizations, three representative porous models (i.e. intergranular pore model, micro-crack model and “honeycomb” pore model) were proposed and generated by numerical methods. The high-Knudsen gas flows in these generated structures were simulated by the lattice Boltzmann method (LBM). A comparison of the simulation results among these three porous models suggests that the nano-scale pore morphology plays an important role in the gas transport properties. Moreover, the high-Knudsen effect leads to a larger apparent permeability for each nano-scale porous model. Our work indicates the importance of the nano-scale pore morphology and the high-Knudsen effect on gas transport properties of shale matrix.

The distinct spalling performances of reactive powder concrete (RPC) specimens with various silica fume (SF) contents exposed to high temperatures were observed via high-resolution photography. The RPC microstructures and pore structures after high-temperature exposure were characterized using scanning electron microscopy and mercury intrusion porosimetry. The results provide experimental evidence of the high-temperature spalling mechanism of RPC. Increasing the SF content in RPC increases its compressive strength and compactness, offering greater mitigation of devastating spalling behaviour, but also producing more pulverized spalling remnants. This is attributed to the post-heating cracked microstructure and refined pores, which promote localized rather than entirely explosive spalling.

We investigate the effect of pulsed electric current on fatigue-crack growth and the fatigue properties of aluminum alloy (A6061-T6) at current densities of 0–150 A/mm2. The fatigue life of most of the treated specimens increases substantially when compared with that of untreated specimens. SEM imaging of the treated specimens shows local melting on the fracture surfaces. To clarify the effect of local melting on fatigue-crack propagation, we examine crack propagation utilizing the plastic replication method. We find that the delay of crack propagation is attributable to the crack-shielding effect arising from current-induced local melting.

TiBw/TC4 composite was brazed to Ti60 alloy successfully using TiZrNiCu amorphous filler alloy, and the interfacial microstructures and mechanical properties were characterized by SEM, EDX, XRD and universal tensile testing machine. The typical interfacial microstructure was TiBw/TC4 composite/β-Ti + TiB whiskers/(Ti, Zr)2(Ni, Cu) intermetallic layer/β-Ti/Ti60 alloy when being brazed at 940 °C for 10 min. The interfacial microstructure evolution was influenced strongly by the diffusion and reaction between molten fillers and the substrates. Increasing brazing temperature decreased the thickness of brittle (Ti, Zr)2(Ni, Cu) intermetallic layer, which disappeared finally when the brazing temperature exceeded 1020 °C. Fracture analyses indicated that cracks were initialized in the brittle intermetallic layer when (Ti, Zr)2(Ni, Cu) phase existed in the brazing seam. The maximum average shear strength of joints reached 368.6 MPa when brazing was conducted at 1020 °C. Further increasing brazing temperature to 1060 °C, the shear strength was decreased due to the formation of coarse lamellar (α+β)-Ti structure.

Characterization of the three-dimensional stress field of concrete materials is crucial to understanding their mechanical properties and failure mechanisms, but their hidden and complex meso-scale structure makes physically extracting and visualizing this information intractable. This paper therefore presents a new approach that uses 3D printed models based on X-ray microfocus computed tomography (CT) imaging of a concrete sample to replicate its complex aggregate structure in a transparent matrix. The associated three-dimensional stress field is visually characterized at mesoscale through uniaxial compression tests and photoelastic techniques that incorporate a three-dimensional frozen-stress test to analyse the effects of randomly distributed aggregates. These results are used to validate the accuracy of simulated data created using the finite element method, which allows a comparison to be made between two-dimensional and three-dimensional heterogeneous aggregated models. The study indicates that meso-heterogeneity has more influence on the stress state of localized areas than the entire field. Compared to 2D structures, 3D structures possess a lower stress concentration due to the lateral inertial confinement effect. The difference in stress field between the two structure types is therefore attributable to a combination of structural heterogeneity and lateral inertial confinement.