Institute Of Mechanics,Chinese Academy of Sciences
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On faults induced stress shielding to account for the formation of deep-buried reservoirs
No full textIt is commonly accepted that the formation of oil and gas reservoirs in deep-buried strata is almost impossible due to the huge compaction of in-situ crustal stresses. Nevertheless, recent hydrocarbon explorations in the Tarim Basin have discovered reservoirs at depths exceeding 8 km. The reservoirs exhibit a strong correlation to the strata's faults and large fractures, yet the precise underlying mechanical mechanism remains obscure. To illuminate how the faults may facilitate the existence of such deep-buried reservoirs, we consider three ideal scenarios involving unconventional hole-crack interactions under remote biaxial compression. Our focus is on the stress concentration of the hole, influenced by the long main cracks. Closed-form compressive stress solutions are obtained based on our simple theoretical models, showing that long cracks significantly reduce the stress concentration of nearby holes. We quantify the reducing effect of the cracks' angle, surface friction, and pressure on the maximum shear and von Mises stresses around a hole, combining with finite element analysis results. The stress shielding effect is qualitatively consistent with the available experimental observations that the deep-buried caves are often located near the faults and large fractures in carbonate strata. Our results will be beneficial for future exploration of superdeep petroleum reservoirs
Probing the combustion characteristics of micron-sized aluminum particles enhanced with graphene fluoride
No full textGraphene fluoride (GF) with its two-dimensional structure and high fluorine content on the surface can be used to enhance the combustion characteristics of micron-sized Aluminum (mu Al) particles. However, the enhancing mechanisms of GF in Al combustion remain not fully understood. In this work, the effects of GF on combustion temperature, flame emission spectrum, ignition delay time, and condensed combustion products (CCPs) size of mu Al were studied using laser ignition and optical diagnostic experiments. The combustion characteristics of GFor polytetrafluoroethylene (PTFE)-modified mu Al composite particles were compared to elucidate the ignition and combustion mechanism of different fluorides. The results show that the thermal decomposition behavior and the energy distribution among excited Al atoms differ significantly between GF and PTFE. Compared with PTFE, GF and its decomposition products have stronger excitation ability for high energy Al atoms, which is conducive to increasing the combustion temperature of particle flame. In addition, the ignition delay time and CCPs size of Al/ GF are approximately 49 similar to 66 % and 10 % less than those of Al/PTFE, respectively. These results provide a fundamental understanding and data support for the application of functionalized graphene in metal fuels and solid propellants
A new sharing function for the common-weights WENO reconstruction of the Euler equations
No full textRecently, one kind of common-weights weighted essentially non-oscillatory (Co-WENO) scheme was proposed to solve the Euler equations of the compressible flows. Different from the usual component-wise weighting methods, common-weights means that, on a global stencil, one set of weights is commonly shared by all components. Hence, the Co-WENO scheme can keep the same contribution on each component numerical flux and is more efficient than the component-wise weighting methods. This paper develops the Co-WENO reconstruction of the primitive variables applied in the Riemann solvers of Euler equations. Amore robust sharing function (used to calculate the common weights) is proposed by taking into account the characteristic of the compressible wave (the effect of Mach number). Numerical results show that the Co-WENO scheme based on the new sharing function has good robustness and low numerical dissipation
Strengthening effect of nanoprecipitates on twinned copper: a discrete dislocation dynamics simulation study
No full textIntroducing twin boundaries (TBs) and nanoprecipitates has emerged as a highly effective approach for enhancing the mechanical properties of metallic materials. In this paper, the dislocation-precipitate and dislocation-TB interaction models were incorporated into the three-dimensional discrete dislocation dynamics (DDD) framework. The effect of nanoprecipitates on the mechanical properties of single crystal and twinned copper under various loading direction angles was investigated. For single crystal copper containing precipitates, the synergistic strengthening effects of forest dislocations and precipitates were explored by theoretical models. For twinned copper, the TB strengthening effect is derived from DDD simulation results and theoretical models. Analyses revealed that when the loading direction angle is 0 degrees and 90 degrees, the introduction of precipitates has almost no impact on the TB strengthening effect. When the loading direction angle is 90 degrees, the trans-twin dislocations spanning across two lamellae were identified, and the nanoprecipitates hindered the slip of the trans-twin dislocations. When the loading direction angle is 75 degrees, the nanoprecipitates suppressed the strength softening caused by twinning deformation. Furthermore, the accumulation of twinning dislocations on TBs, facilitated by nanoprecipitates, increased the difficulty for dislocations to interact with TB. This study shows the potential of employing DDD for investigating plasticity mechanisms in materials with diverse microstructures, paving the way for future designs of metallic materials through DDD simulations
Nanoindentation behavior of the laser-repaired CoCrFeNiV high-entropy alloy
No full textHigh-entropy alloys (HEAs) are solid-solution alloys composed of multiple elements, exhibiting excellent mechanical properties. The unique plastic deformation mechanism induced by their specific solid solution structures has attracted considerable attention but remains incompletely understood, particularly at the micro-scale. In this study, the surface morphology, chemical composition, and microstructures of CoCrFeNiV HEA before and after laser remelting repair were investigated. Nanoindentation testing was employed to characterize the surface hardness and creep behavior of the repaired surface. The distribution of surface hardness before and after laser remelting, as well as the indentation creep behavior under different loads, were studied. The mechanism of indentation creep on the repaired surface was discussed and analyzed. The effect of microstructures of HEAs, including precipitated phases and sub-grain boundaries, on dislocation-dominated micro-scale plastic deformation was elucidated by the transmission electron microscope (TEM). This study contributes to an in-depth understanding of the creep behavior and micro-scale deformation mechanisms in HEAs
Influence of atomic coordination on the activity of lattice oxygen and catalytic oxidation of toluene over regular Cu2O crystalline
No full textVOCs oxidation over transition metal catalyst is commonly understood via the Mars-van Krevelen mechanism involving the crucial role of lattice oxygen (OL) activity, however, how it is influenced by atomic coordination is still unclear. Herein, we use model catalysts of Cu2O-cub, Cu2O-oct and Cu2O-dod with crystal planes of (100), (111) and (110), respectively, to investigate the OL activity and catalytic oxidation of toluene. The activity of Cu2O-oct is found to be the highest, followed by Cu2O-cub and Cu2O-dod. Experiments results combined with density functional theory show that, although low di-coordinated O atoms leads to the lowest surface oxygen vacancy formation energy (2.47 eV) and the highest surface OL activity of Cu2O-cub, it cannot determine the activity. The lowest bulk oxygen vacancy formation energy (3.16 eV) in Cu2O-oct terminated with tricoordinated O atoms and open surface can accelerate the migration and replenishment of OL, thereby promoting the catalytic activity
Deciphering the α relaxation and the anelastic-to-plastic transition in the deep glassy state
No full textIn contrast to their conventional crystalline counterparts, amorphous solids exhibit diverse dynamic relaxation mechanisms under external stimuli. The challenge to understanding their behavior lies in unifying microscopic dynamics, relaxation, and macroscopic deformation. This study establishes a potential link by quantifying the characteristic time of the anelastic-to-plastic transition through dynamic mechanical relaxation and stress relaxation tests across a wide temperature range in both the supercooled liquid and the glassy state. It is found that the stress relaxation time in the glassy solids follows an Arrhenius relationship, aligning with the main alpha relaxation time, and unveils a finding: alpha relaxation continues to govern deformation even below the glass transition, challenging previous assumptions of the role of secondary beta relaxation. A hierarchically constrained atomic dynamics model rationalizes the temperature dependence of alpha relaxation and the transition from beta to alpha relaxation, also providing evidence that the stretched exponent in the Kohlrausch-Williams-Watts equation can serve as an order parameter. This work highlights the role of alpha relaxation in the glassy state and contributes to elucidating the potential correlation between relaxation and deformation in amorphous materials
Industrial-scale sustainable rare earth mining enabled by electrokinetics
No full textOwing to their irreplaceable role in several essential technologies, rare earth elements (REEs) are critical raw materials for the global economy. However, the supply of REEs raises serious sustainability concerns due to the large environmental footprint of conventional mining processes. We previously proposed an electrokinetic mining (EKM) technique that could enable green and selective extraction of REEs from ores. Here we further develop this technique to industrial scale by addressing challenges related to electrode reliability and flow leakage and evaluate its mining efficiency, environmental footprint and economic performance. Moreover, a voltage gradient barrier strategy based on electroosmosis is developed to facilitate electrokinetic REEs mining. As a result, we successfully achieved a high REE recovery efficiency of 95% on a 5,000-ton REEs ore. A rigorous environmental risk assessment revealed a 95% reduction of ammonia emissions, indicating a notably reduced environmental footprint. A comparative technoeconomic analysis between the conventional and the EKM techniques demonstrates the economic viability of the EKM technique. This work validates a new sustainable path for REEs mining, paving the way to a greener resources supply
Assessment of the Reynolds-stress model-based hybrid RANS/LES method for junction flow around a fully appended underwater vehicle
No full textThe hybrid Reynolds-averaged Navier-Stokes (RANS)/large eddy simulation (LES) method has gained prominence in simulating underwater vehicle flows, but its performance heavily depends on the RANS model used. In this paper, we evaluate a Reynolds-stress model (RSM)-based improved delayed detached eddy simulation (IDDES) for a fully appended underwater vehicle, compared with the shear-stress transport (SST) model-based IDDES and wall-resolved LES (WRLES). We focused on the sail-hull junction flow, particularly the horseshoe vortex and corner separation. WRLES reproduced the unsteady oscillations of the horseshoe vortex, revealing a "transporting -> merging -> diffusing" evolution process. RSM-IDDES accurately predicted the Reynolds stress anisotropy, resulting in a time-averaged primary vortex (PV) position closer to WRLES than SST-IDDES. The predicted PV position affects the trailing-edge corner separation of the sail through a vorticity suppression effect on the corner vortex strength. Consequently, RSM-IDDES effectively reproduced corner flows similar to WRLES and experimental results, highlighting its advantage in junction flow simulations. A comparison with SST-IDDES demonstrates the sensitivity of IDDES to RANS models, particularly in vortex distribution and Reynolds stress anisotropy, which are crucial for simulations of complex flows around underwater vehicles.</p
Enhancing fatigue performance of laser powder bed fused metals through controlling contour parameters and structures
No full textSide surface quality is a critical concern in the fatigue performance of laser powder bed fused (PBF-LB) components. Increasing contour passes with customized parameters along sample edge can tune side surface/subsurface quality and thereby enhance fatigue resistance. This study critically evaluates the surface and subsurface characteristics resulting from varying contour parameters and their impact on the fatigue performance of PBF-LB 304L steel through multiple detailed characterizations. The fatigue damage mechanisms for varying contour parameters are investigated through fatigue fractography, temperature field analysis, and microstructural evolution. Results indicate that optimal contour parameters differed from infill parameters due to the energy absorption from powder fusion and solidification remelting. The contour defects, including spherical vapor cavities and irregular lack-of-fusion (LoF) defects resulting from inappropriate parameters, significantly degrade fatigue lifetime due to their high-stress concentration factors. Appropriate contour parameters (approximately 300 J/ mm3 in energy density) can minimize defect content while simultaneously enhancing microstructural heterogeneity in the contour region. The identified physical mechanisms of defect formation and fatigue damage will assist in designing and optimizing contour process for enhancing fatigue performance