Matrix Fracture Research Articles

Damage Characterization of GFRP Hollow Ribbed Emergency Pipes Subjected to Low-Velocity Impact by Experimental and Numerical Analysis.

This paper investigates the low-velocity impact response and damage behavior of glass fiber reinforced polymer (GFRP) hollow ribbed emergency pipes of our design under different impact heights. Drop hammer impact tests with impact velocities of 8.41 m/s, 8.97 m/s, and 9.50 m/s were conducted using an impact platform. A progressive damage model for low-velocity impact was developed using Abaqus/Explicit finite element software. The model used the three-dimensional Hashin damage initiation criteria and a damage evolution model based on the equivalent strain method to simulate the initiation and evolution of intralaminar damage in the pipe ring. A cohesive zone model (CZM) based on a bilinear traction-separation law was used to simulate delamination. The results show that the pipe rings experienced fiber or matrix fractures and delamination damage during the impact process. Additionally, the pipe ring specimens underwent bending vibrations under the impact load, leading to fluctuating contact forces at all three impact heights. Analysis of the simulation results reveals that the primary damage modes in the GFRP hollow ribbed emergency pipe are fiber tension damage, matrix tension damage, and fiber compression damage, with delamination occurring mainly in the impact area and the interface area on both sides of the rib.

Hole drilling in basalt-reinforced sustainable composites using abrasive waterjet for construction applications

This study aimed to develop, characterize, and optimize abrasive waterjet (AWJ) machining of sustainable basalt fiber-reinforced polymer composites for construction and industrial applications. Dynamic mechanical analysis, thermogravimetric analysis, and X-ray diffraction revealed enhanced thermal stability, increased decomposition temperatures, and improved crystallinity, correlating with improved tensile strength of developed composites. To address drilling-induced damage that can compromise long-term quality and applicability, AWJ drilling parameters were optimized to minimize damage while enhancing material removal rates. A novel quantification method for entry total surface damage (ETD) was implemented to assess machining defects. Results showed that standoff distance significantly influences ETD and exit delamination, while higher water pressure reduces entry damage. Abrasive flow rate primarily affected the material removal rate. FE-SEM analysis revealed microstructural changes in drilled surfaces, including damage zones and matrix fractures specific to AWJ processing. Multi-objective optimization using Genetic Algorithm is performed to enable flexible parameter selection and informed decision making, balancing machining efficiency and minimal damage.

Comparative Analysis and Application of Mass and Heat Transfer Simulation in Fractured Reservoirs Based on Two Fracture Models

The projection-based embedded discrete fracture model (pEDFM) and its counterpart, the embedded discrete fracture model (EDFM), have become standard tools for the depiction of the fractures in reservoir simulations. Despite their widespread use, there are still some unclear areas in modeling the complex processes of mass and heat transfer within fractured reservoirs, particularly in both single-phase and multiphase flow scenarios. Our research introduces a numerical methodology for simulating the mass and heat transfer in fractured reservoirs which is developed by extending the framework of the pEDFM and EDFM. To gauge the effectiveness of these models, we devised two cases which were designed to evaluate the adaptability of the pEDFM and EDFM in scenarios involving an ultra-low permeability fracture or a high permeability fracture under single-phase and multiphase conditions. By using local grid refinement (LGR) as a reference, the results of the pEDFM were in reasonably good agreement with the LGR in terms of pressure, temperature, and saturation distributions. This comparison suggests that the pEDFM has a significant advantage in depicting the mass and heat transfer at the matrix–fracture interface compared to the EDFM. Furthermore, a comprehensive analysis of the flow trajectories in both the pEDFM and EDFM provided a reasonable explanation for their differences. Furthermore, the numerical applications involving the heat extraction of Enhanced Geothermal Systems (EGSs) and the water flooding in fractured reservoirs illustrate the adaptability of the pEDFM in the numerical simulation for complex geological conditions. The insights and conclusions obtained in this paper can enhance our understanding of the distinctions between the pEDFM and EDFM, aiding in the selection of the most suitable method for characterizing the fractures in numerical simulations.

Enhancing mechanical properties and crack resistance of high-strength SHCC/ECC for durable transportation through ethylene-vinyl acetate polymer modification

Strain-hardening cementitious composites (SHCC) possess excellent ductility and toughness, making them suitable for reinforcement and repair projects of transit infrastructures, such as tunnel linings, bridges, and highways. Especially, polyethylene (PE) fiber is admixed to SHCC for fabricating high-strength PE-SHCC. However, the hydrophobic nature of PE fibers results in relatively weak interfacial frictional bond strength with cementitious matrix, ultimately leading to larger crack widths and wider gaps. This poses durability and safety concerns for the practical applications of PE-SHCC in transit infrastructure. In this study, ethylene-vinyl acetate (EVA) dispersible polymer is selected to address this problem. The effect of admixing EVA on mechanical and direct tensile properties of PE-SHCC is investigated. The compressive strength, first crack strength and matrix fracture toughness of PE-SHCC tended to decrease after EVA modification, however, the tensile strength and tensile strain increased significantly with doping. After that, the single fiber pullout test combined with flaw size/distribution analysis is performed to explore the improvement mechanism of PE-SHCC after EVA modification. It was found that the addition of EVA could significantly improve the interfacial transition zone (ITZ), increase the interfacial friction between PE fibers and matrix, and optimise the defect distribution within the matrix. The recommended dosage of EVA is 3–6 % comprehensive consideration of the tensile strength, strain energy, crack width, and mechanical strengths of the EVA-modified PE-SHCC. The enhancement of mechanical strengths and crack resistance in PE-SHCC contributes to the development of transit infrastructure towards greater reliability, durability, and resilience.

Influence of Temperature and Bedding Planes on the Mode I Fracture Toughness and Fracture Energy of Oil Shale Under Real-Time High-Temperature Conditions

The anisotropic fracture characteristics of oil shale are crucial in determining reservoir modification parameters and pyrolysis efficiency during in situ oil shale pyrolysis. Therefore, understanding the mechanisms through which temperature and bedding planes influence the fracture behavior of oil shale is vital for advancing the industrialization of in situ pyrolysis technology. In this study, scanning electron microscopy (SEM), CT scanning, and a real-time high-temperature rock fracture toughness testing system were utilized to investigate the spatiotemporal evolution of pores and fractures in oil shale across a temperature range of 20–600 °C, as well as the corresponding evolution of fracture behavior. The results revealed the following: (1) At ambient temperature, oil shale primarily contains inorganic pores and fractures, with sizes ranging from 50 to 140 nm. In the low-temperature range (20–200 °C), heating primarily causes the inward closure of inorganic pores and the expansion of inorganic fractures along bedding planes. In the medium-temperature range (200–400 °C), organic pores and fractures begin to form at around 300 °C, and after 400 °C, the number of organic fractures increases significantly, predominantly along bedding planes. In the high-temperature range (400–600 °C), the number, size, and connectivity of matrix pores and fractures increase markedly with rising temperature, and clay minerals exhibit adhesion, forming vesicle-like structures. (2) At room temperature, fracture toughness is highest in the Arrester direction (KIC-Arr), followed by the Divider direction (KIC-Div), and lowest in the Short-Transverse direction (KIC-Shor). As the temperature increases from 20 °C to 600 °C, both KIC-Arr and KIC-Div initially decrease before increasing, reaching their minimum values at 400 °C and 500 °C, respectively, while KIC-Shor decreases continuously as the temperature increases. (3) The energy required for prefabricated cracks to propagate to failure in all three directions reaches a minimum at 100 °C. Beyond 100 °C, the absorbed energy for crack propagation along the Divider and Short-Transverse directions continues to increase, whereas for cracks propagating in the Arrester direction, the absorbed energy exhibits a ‘W-shaped’ pattern, with troughs at 100 °C and 400 °C. These findings provide essential data for reservoir modification during in situ oil shale pyrolysis.

Concurrent experimental testing and computational micromechanical modeling of a UD NCF GFRP composite ply

The current research work presents a detailed and thoroughly validated computational micromechanical modeling methodology to study the damage initiation and propagation in a uni-directional (UD) glass fiber-reinforced non-crimp fabric (NCF) composite ply. Under the applied transverse tension and compression loads, the effect of various microscale material and geometrical parameters on the ply level stress–strain behavior is studied. To this end, along with the distinctly modeled individual microscale constituents of the UD NCF composite ply (axial fibers, backing fibers, and matrix), the generated RVE (Representative Volume Element) model consists of manufacturing-induced defects and variabilities such as voids as well as the backing fiber’s out-of-plane waviness. The fiber/matrix interface failure behavior in the generated RVE model is simulated using cohesive zone formulations that follow bi-linear traction-separation law. Whereas the hydrostatic pressure-dependent non-linear stress–strain response followed by the fracture of the epoxy matrix is captured using the linear Drucker-Prager plasticity model coupled with the stress triaxiality-based failure criterion. The backing fibers stress–strain and failure behavior is modeled using the linear elastic and isotropic material model in conjunction with the maximum stress criterion.The proposed numerical methodology is thoroughly validated both qualitatively and quantitatively by conducting detailed experiments on a neat epoxy as well as at the composite laminate level. Upon comparing the experimental and computational results, the observed knee or slope change in the bi-linear stress–strain response of the UD NCF composite ply under transverse tension is attributed to the loss of the load-carrying ability of the axial fiber bundle due to fiber/matrix interface debonding followed by the ply splitting. Under the application of transverse compression load, the composite ply failure behavior is governed by the formation of a dominant matrix plastic shear band in the axial fiber bundles, which is in turn triggered by the fiber/matrix interface failure. Under the applied loads in the matrix-dominated direction, the presented research work provides a detailed insight into the microscale damage initiation and propagation in a UD NCF composite ply and its consequent influence on the macroscale stress–strain response.

Damage behavior and toughening mechanism of SiCf/SiC-Ti3SiC2 composites: A combination of digital image correlation and acoustic emission

Matrix modification is an effective method to improve the mechanical properties of ceramic matrix composites, while the elucidation of corresponding damage mechanism is essential for the design and engineering application of composites. In this work, Ti3SiC2 particles were introduced into SiC matrix to fabricate Ti3SiC2 modified SiCf/SiC (SiCf/SiC-Ti3SiC2) composites by a hybrid technique of slurry suspension impregnation combined with polymer infiltration and pyrolysis. Compared with SiCf/SiC composites, the flexural strength and modulus of SiCf/SiC-Ti3SiC2 composites were increased by 17.8 % and 61.0 %, respectively. The three-point flexural damage behavior and failure mechanism of composites were systematically investigated and compared by the combination of digital image correlation and acoustic emission techniques. Based on the collaborative analysis of in-situ damage process, matrix micro-zone toughness and fracture morphology, the modification effect and toughening mechanism of Ti3SiC2 were revealed. The improved mechanical properties of SiCf/SiC-Ti3SiC2 composite could be ascribed to the more sufficient matrix cracking before composite failure and the increased matrix fracture energy by microcrack deflection. After matrix modification, the failure mechanism was dominated by the gradual propagation and growth of microcracks until the critical crack size, instead of the fast and unstable propagation of main crack.

Fracture Criteria for Matrix and Fibers in Unidirectional Polymeric Composites at Static Loadings

When analyzing the strength of structures made of layered fibrous polymer composite materials; the criteria for failure of a monolayer – a unidirectional reinforced composite – are used. A criterion of strength according to the conditions of matrix fracture is formulated, corresponding to conical limiting surfaces and the lowest destructive loads. The criterion of strength according to the condition of fiber failure, which does not allow the paradox of increasing strength in the region of transition from fiber destruction to matrix failure, is given. Experimental verification of the criteria for volumetric, planar, and one-dimensional loads is carried out. Their better correspondence to empirical data is shown and their advantages in comparison with known criteria are marked. A small number of easily detectable parameters of these criteria contribute to their reliability and stability in strength calculations of composite structural elements.

Integration of Geological Model and Numerical Simulation Technique to Characterize the Remaining Oil of Fractured Biogenic Limestone Reservoirs

AbstractFine geological modeling leads to accurate reservoirs numerical simulations. Fractured biogenic limestone has abundant storage spaces and flow paths to accumulate oil and gas. The complexity and diversity of fractured biogenic limestone also lead to challenges in accurately characterizing its pore volume and remaining oil. This investigation aimed to enhance the understanding of fractured biotite reservoir properties via geological modeling. Numerical simulations were used to characterize the remaining oil during the late stage of field development. Considering the differences in porosity and permeability between fractures and matrix, a facies-controlled stochastic modeling technique was used to establish a dual-porosity and dual-permeability (DPDP) model for numerical simulation. Core information, logging data, and multiple seismic attributes were combined to guide low-level sequence fault interpretation for tectonic refinement. Based on classified seismic inversion, sedimentary phases were reconstructed. A discrete fracture network (DFN) model was obtained based on fracture occurrences and density models. The optimized discrete adjoint (ODA) algorithm was utilized to calibrate model parameters. The findings revealed that dense tectonic fractures develop in thick biogenic limestone areas. Combined with advanced reservoir simulation technology, these findings suggest that areas of thicker biogenic limestone were consistent with areas of higher fracture matrix conductivity multipliers. The remaining oil distribution patterns were investigated, and to deploy new wells was guided. Therefore, it is essential to better understand the tectonic characteristics of fractured biogenic limestone reservoirs and their remaining oil distribution patterns by integrating multiple sources of information and mastering advanced reservoir simulation technology for oilfield development.

Experimental and Numerical Investigations of Tensile Properties of SiC Particle‐Reinforced Composites

In this study, experiments and finite element modeling (FEM) are performed to study the tensile mechanical properties of SiC particle‐reinforced 6061 Al‐matrix composites (SiCp/6061Al) at various volume fractions (VFs) of SiCp. The Young's modulus, yield strength, and tensile strength of SiCp/6061Al display an overall upward trend with the increment of the VF of SiCp. The fracture analysis results demonstrate that the fracture of SiCp/6061Al is a hybrid of matrix fracture, reinforcement fracture, and interface debonding. An algorithm is developed to construct the mesostructure of particle‐reinforced composites, based on the random sequential absorption algorithm. The VFs of the particles of the representative volume element (RVE) model constructed using the novel algorithm are as high as 42%. The tensile mechanical properties of SiCp/6061Al are predicted by replacing the irregular particle reinforcements in SiCp/6061Al with spherical particles in the RVE model. Comparisons reveal that the stress–strain curves obtained via experiment and FEM are highly consistent in the elastic‐plastic stage, which verifies the effectiveness and rationality of the novel algorithm.

Laboratory and numerical investigations on land-sourced solute transport in coastal fractured aquifers

Land-based pollutants threaten coastal aquifers, highlighting the need to protect groundwater and nearshore marine ecosystems. While aquifer heterogeneity has been recognized as a significant factor affecting solute behavior, the impact of fractures on land-sourced solute transport in coastal aquifers remains unclear. This study attempted to address this issue through laboratory experiments and discrete fracture matrix (DFM) models. The impact of horizontal fractures on the temporal and spatial characteristics of solute transport, spreading, and discharge under seawater intrusion was analyzed based on variations in fracture position and length. The results show that fractures/low-velocity zones (LVZ) can accelerate/delay solutes, dividing them into different transport modes and enhancing/prolonging their spreading/discharge duration. Changes in fracture position and length also affect its transport acceleration and path deviation abilities, which ultimately determine when solute discharge occurs. The mixing zone and unsaturated zone, in addition to the LVZ, hinder solute transport, reducing the rate and delaying the end of solute discharge. Meanwhile, fractures facilitate solute transport into the saltwater wedge, expanding the solute discharge zone. However, if solutes are initially within the LVZ, their entry into the fracture rely on their distance from the fracture's near-land edge and the size of the fracture's convergence zone.

Dynamic Progressive Failure Analysis of 3D Five-directional Braided Composites under Transverse Compression Based on Macro-scale Heterogeneous Model

At present, there are few systematic researches on macro-scale heterogeneous modeling and numerical simulation of dynamic mechanical properties of 3-D braided composites. In this paper, the parametric virtual simulation model of 3D five-directional braided composites is realized in the way of “point-line-solid” based on the integrated design idea of process-structure-performance. And the impact compression numerical simulation of the material is carried out by using multi-scale analysis method. The effects of strain rate and braiding angle on transverse impact compression properties and fracture characteristics of composites is studies and verified by comparing the test results with the numerical simulation results systematically. The dynamic failure mechanism of the matrix and fiber bundles during the impact compression process is revealed. The results show that the macro-scale heterogeneous simulation model of 3D five-directional braided composites established is effective, and the numerical simulation results agree well with the test results. The matrix fracture and shear failure of fiber bundles are presented simultaneously under transverse impact compression. The failure of fiber bundles and matrix mainly concentrates on two main fracture shear planes. And the included angle between the fracture shear planes and the vertical direction is consistent with the corresponding internal braiding angle of specimens.

The cruciality of particle size and shape on fracture mechanism of aluminum matrix composites

Metal matrix composites are generally believed to achieve better performance with spherical reinforcements than irregular ones. In this work, through experiments and computational simulations, we have demonstrated that spherical reinforcements do not necessarily enhance the tensile ductility of composites. There exists a critical size for spherical particles. Using an Al2O3-Al2024 composite as an example, we found that when the size of spherical Al2O3 particles is less than 3 µm, they are not fractured during deformation, resulting in enhanced ductility. We elucidated the competitive mechanism between particle and matrix fracture under various reinforcement sizes and volume fractions, and constructed a deformation map that can be utilized to determine fracture mechanisms. This work clarifies the micro-mechanical mechanisms of reinforcements on material fracture behavior, providing guidance for the design and fabrication of strong and ductile metal matrix composites.

An overview of tensile and shear failure mechanisms of silicon carbide-based ceramic matrix composites

The successful applications of silicon carbide-ceramic matrix composites (SiC-CMCs) in aeronautical and aerospace industries require deeper understanding of their mechanical behaviors and failure mechanisms. The overview on tension and shear is then presented from meso-mechanics perspective, including matrix cracking, interface de-bonding and sliding, matrix crack propagation as well as fiber bridging. The results reveal that the matrix cracking stress is proportional to the interface sliding stress and the matrix fracture energy. The ratio of tensile to shear stress of the matrix cracking remains constant both in tension and in shear. In addition, the deflection of matrix cracks in the interface depends on the elastic modulus matching parameter, the angle between matrix cracks and interface, as well as the residual thermal stress. The matrix cracks propagate in a random or periodic pattern, which are proportional to the sliding length at the matrix cracking stress. The fiber bridging mechanism, related to the Weibull distribution of the fiber strength, determines the tensile and shear behaviors after the saturation of matrix cracks.

Effects of Externally Applied Stress on Multiphase Flow Characteristics in Naturally Fractured Tight Reservoirs

Externally applied stress on the rock matrix plays a crucial role in oil recovery from naturally fractured tight reservoirs, as local variations in pore pressure and in-situ tension are expected. The published literature severely lacks in evaluations of the characteristics of hydrocarbons, displaced by water, in fractured reservoirs under the action of externally applied stress. This study intends to overcome this knowledge gap by resolving complex time- and stress-dependent multiphase flow by employing a coupled Finite Element Method (FEM) and Computational Fluid Dynamics (CFD) solver. Extensive three-dimensional numerical investigations have been carried out to estimate the effects of externally applied stress on the multiphase flow characteristics at the fracture–matrix interface by adding a viscous loss term to the momentum conservation equations. The well-validated numerical predictions show that as the stress loading increases, the porosity and permeability of the rock matrix and capillary pressure at the fracture–matrix interface decrease. Specifically, matrix porosity decreases by 0.13% and permeability reduces by 1.3% as stress increases 1.5-fold. Additionally, stress loading causes a decrease in fracture permeability by up to 29%. The fracture–matrix interface becomes more water-soaked as the stress loading on the rock matrix increases, and thus, the relative permeability curves shift to the right.

High-Order Models for Gas Transport in Multiscale Coal Rock.

The coal reservoirs exhibit great heterogeneity and strong anisotropy in multiscale pore/fracture structures. Developing highly accurate multiscale models for real-time prediction of microgaseous flow in complicated porous media with pronounced contrast in transport coefficients is crucial but not yet available, which is time-consuming, expensive, and even computationally impossible. In this study, a multiscale approximate solution of the gas flow and pressure field is derived in this paper for predicting coalbed methane (CBM) transport in macro-microscopic two-scale porous media of typical coal rocks in Guizhou Province, China, and the detailed finite element algorithm is established. The multiscale approximate solutions are constructed from the first- and second-order auxiliary cell functions and low- or high-order derivatives of the homogenized pressure field, which can accurately approximate the solution of the original problem to a certain extent. The numerical accuracy and validity of the multiscale approximate solutions under various working conditions are analyzed in detail by comparing and verifying the results with the direct numerical simulation results of fine-mesh high-precision finite elements. The results show that the homogenized approximate solution can only roughly capture the characteristics of the macroscopic pressure evolution, the first-order approximate solution can partially reproduce the macro-microscopic pressure oscillation phenomenon, and the second-order approximate solution can accurately predict the pressure profile and its evolution law with time in porous media with macro-micro configuration under various complex conditions. The second- and high-order two-scale approximate solutions constructed in this paper exhibit high numerical accuracy and excellent computational efficiency. We also develop multiscale approximate solutions for predicting microgaseous flow at a low reservoir pressure where the slippage effects are very pronounced. Potential applications of our high-order models to the coal reservoirs with a hierarchical matrix and fractures are discussed. The developed multiscale models exhibit excellent applicability to investigating the crossflow effects and coupling mechanisms between the matrix and cleats or fractures with multiple configurations in the CBM and shale gas reservoirs, which is crucial for the effective implementation of hydraulic fracturing technology. This study provides a fundamental understanding of gas transport in multiscale matrix-fracture networks, which helps to improve the optimization design of hydraulic fracturing in tight reservoirs.

Enhanced LaRC05 failure criteria for investigating low-velocity impact on fiber-reinforced composites: An experimental and computational study

A finite element model was developed using both continuum and discrete damage modeling techniques to provide detailed predictions for ply-by-ply damage progression in composite laminates during low-velocity impact (LVI) events. A new fiber failure model was incorporated into the LaRC05 failure criteria to predict fiber pull-out and fiber crushing during the fiber damage evolution. In addition, the selective range golden section search (SRGSS) algorithm was implemented to efficiently predict fiber breakage, pull-out, splitting, kinking and crushing, and matrix cracking. The delamination was captured by cohesive element layers embedded between every adjacent composite ply. The interactions of intralaminar matrix cracking and delamination were modeled by deploying cohesive elements within each composite ply. The prediction results were validated by 30 J and 75 J drop-weight tests with different-sized impactors, as well as X-Ray CT inspections on 254 mm by 304.8 mm [0/45/90/-45]4s IM7/977–3 laminates. The model predicted the maximum deflection and contact duration with <2 % error, and the peak load, damaged areas, and absorbed energy with <8 % error. The matrix fracture plane and the fiber kink band angle were found with 1° precision 48 % faster via the SRGSS algorithm. The detailed sequences of damage occurrence were predicted by analyzing the energy dissipation histories through various damage modes. Although this modeling methodology was developed for LVI scenarios, it has broad applications for predicting failures in composites.

Design-driven approach for engineered geopolymer composite with recorded low fiber content

How to design an engineered cementitious composite (ECC) achieving both economic viability and ultra-sustainability has been the longstanding goal of ECC community. This study presents a design-driven approach to tackle this challenge through yielding a low matrix fracture toughness and a sufficiently strong interfacial bonding between fiber and matrix concurrently. As a result, only 0.2 % fiber content was sufficient for achieving robust strain-hardening in Engineered Geopolymer Composite (EGC), which, to the authors’ knowledge, is the lowest recorded thus far. The tensile strain-to-fiber content ratio reached 25, a remarkable 233 % higher than the existing strain-hardening composites. Besides, the compressive strength was around 40 MPa, marking the highest specific strength among the ECCs with a density below 1450 kg/m3. Leveraging the high porosity of 38 % and the presence of shrinkage micro-cracks in the matrix, a low fracture toughness, combined with a robust friction between fiber and matrix, facilitated the noticeable strain-hardening. The reaction product was identified as a dense alkaline aluminosilicate hydrate (N-A-S-H) gel, benefiting the interfacial bonding and compressive strength. The embodied energy and carbon of the EGC diminished by 27 % and 63 % compared to ordinary concrete, respectively, and the corresponding cost was 79 % lower than the classic M45-ECC, contributing significantly to ultra-sustainability.

Study on ultrasonic elliptical vibration-assisted grinding mechanism and surface quality of C/SiC composite material

2.5D C/SiC composites have excellent mechanical properties and broad application prospects in the aerospace field. This study investigates the ultrasonic elliptical vibration-assisted grinding mechanism of 2.5D C/SiC composites in different structural directions. A surface roughness prediction model considering abrasive grain protrusion height, brittle-plastic transition of materials and the influence of ultrasonic vibration is established. Experimental results show that material removal involves matrix and fiber fracture, fiber pullout and interface debonding. Ultrasonic vibration causes intermittent cutting, producing finer chip particles and numerous cross microgrooves, reducing subsurface damage. The roughness prediction model is in good agreement with the experimental trend. When the grinding speed is increased from 1 m/s to 8.9 m/s, the surface roughness Ra is reduced by 30.1 %. When the feed speed is increased from 50 mm/min to 650 mm/min, the surface roughness Ra is increased by 47.6 %. When the grinding depth is increased from 0.01 mm to 0.04 mm, the surface roughness Ra is increased by 53.2 %. This study provides a reference for efficient and low-damage processing of fiber-reinforced ceramic matrix composites.

Displacement-imbibition coupling mechanisms between matrix and complex fracture during injecting-shut in-production process using pore-scale simulation and NMR experiment

Displacement-imbibition coupling oil production, which involves adjusting the operations of a well group (water injection huff and puff in one well, continuous oil production in another well), is an effective technique for enhancing oil recovery (EOR) for tight oil reservoirs. However, the research on displacement-imbibition coupling mechanisms is still missing, especially the combination of pore-scale numerical simulations and physical experiments. In this paper, a novel self-designed displacement-imbibition online nuclear magnetic resonance (NMR) experiment technique is developed. The effect of changes in fracture morphology on the mechanism of displacement-imbibition (oil saturation field and oil displacement efficiency) has been investigated. Based on the fracture morphology of physical experiments, a pore-scale model is established and solved by the finite element method. The pore-scale oil-water two-phase displacement-imbibition during the injecting-shut in-production process is simulated. The results show that the pressure oscillation makes the counter-current imbibition and co-current imbibition occur simultaneously in the matrix pores, which promotes oil recovery in matrix-fracture systems. The strength of displacement and imbibition effects is affected by the complexity of fractures. When the fracture complexity increases, the imbibition of the dense part of the fracture is stronger, while the displacement effect is weakened.