Fracture Response Research Articles

An enhanced deep learning approach for vascular wall fracture analysis

This work outlines an efficient deep learning approach for analyzing vascular wall fractures using experimental data with openly accessible source codes (https://doi.org/10.25835/weuhha72) for reproduction. Vascular disease remains the primary cause of death globally to this day. Tissue damage in these vascular disorders is closely tied to how the diseases develop, which requires careful study. Therefore, the scientific community has dedicated significant efforts to capture the properties of vessel wall fractures. The symmetry-constrained compact tension (symconCT) test combined with digital image correlation (DIC) enabled the study of tissue fracture in various aorta specimens under different conditions. Main purpose of the experiments was to investigate the displacement and strain field ahead of the crack tip. These experimental data were to support the development and verification of computational models. The FEM model used the DIC information for the material parameters identification. Traditionally, the analysis of fracture processes in biological tissues involves extensive computational and experimental efforts due to the complex nature of tissue behavior under stress. These high costs have posed significant challenges, demanding efficient solutions to accelerate research progress and reduce embedded costs. Deep learning techniques have shown promise in overcoming these challenges by learning to indicate patterns and relationships between the input and label data. In this study, we integrate deep learning methodologies with the attention residual U-Net architecture to predict fracture responses in porcine aorta specimens, enhanced with a Monte Carlo dropout technique. By training the network on a sufficient amount of data, the model learns to capture the features influencing fracture progression. These parameterized datasets consist of pictures describing the evolution of tissue fracture path along with the DIC measurements. The integration of deep learning should not only enhance the predictive accuracy, but also significantly reduce the computational and experimental burden, thereby enabling a more efficient analysis of fracture response.

Fracture response of thermal-treated granite under mode III loading: Through the edge-notched diametrically compressed disk specimen

The deep rock mass is subject to a high degree of coupling of geothermal and complex loading, and complex mechanical and hydraulic loading induces out-of-plane progression of primary fractures, culminating in the formation of pure mode III fractures. To study the impact of high temperatures on the fracture behavior of pure mode III, the edge-notched diametrically compressed (ENDC) granite discs were heat treated at different temperatures (25, 200, 400, 500, and 600 °C). Subsequently, comparative tests were conducted on both pure mode III and pure mode I fracture, using the digital image correlation (DIC) method and the acoustic emission (AE) technique. The results demonstrate that as the temperature increases, the mass and P-wave velocity decrease. Furthermore, under pure mode III loading, the ENDC sample exhibits higher peak loads and fracture toughness (KIIIc) compared to mode I (KIc), which shows a decrease of 60.72 % in KIIIc and 73.75 % in KIc after thermal treatment at 600 °C compared to the ambient conditions. Simultaneously, the elevated temperature augmentes the cumulative AE counts during loading. The variations in horizontal displacement elevation deviation (HDED) on either side of the deformation concentration zone indicate that the samples are more resistant to crack extension under pure mode III loading. In addition, a positive linear correlation is noted between KIIIc and KIc of ENDC disc samples. The relationship between rebound values and fracture toughness of ENDC discs was discussed, and discovered that the KIIIc and KIc values are quadratic with the rebound values tested by the complete disc. The discussed results may serve as an initial prediction of fracture toughness values.

Fracture behavior of sandstone with partial filling flaw under mixed-mode loading: Three-point bending tests and discrete element method (DEM) numerical approach

The fracture behavior of natural fracture in the geological reservoir subjected to filling property, affects the crack initiation and propagation under stress perturbation. Partial filling flaws were intermediate between open fractures and filled fractures, the fracture response may be worth exploring. In this work, the effect of the filling property of sandstone with partial filling flaws on the fracture behavior was systematically investigated based on three-point bending tests and the numerical approach of discrete element method (DEM). In the laboratory, semi-circular three-point bending tests were carried out with partial filling flaws of various filling strengths. Based on this, numerical simulations were used to further investigate the effect of the filling ratio and the inclination of the partial filling flaw on the mechanical and fracture responses, and the effect of the partial filling flaw under mixed-mode loading on the fracture mechanism was elucidated coupled with acoustic emission (AE) characteristics. The obtained results showed that the increase in filling strength and filling ratio of partial filling flaw led to an increase in peak strength, with a decreasing trend in peak strength with the inclination of partial filling flaw. In terms of crack propagation pattern, the increasing filling strength of the partial filling flaw induced the transformation of the fracture mechanism toward deflection, with a tortuosity path, while the filling ratio and inclination of partial filling flaw led to fracture mechanism change from deflection to penetration and attraction, accompanied with a larger AE event source in filler. Accordingly, the b-value based on the Gutenberg-Richter equation fluctuated between 5 and 4 at low filling ratio and inclination and remained around 5 at high filling ratio and inclination of partial filling flaw. Related results may provide an application prospective for reservoir stimulation using the natural fracture system.

Fracture Density Prediction of Basement Metamorphic Rocks Using Gene Expression Programming

Many methods have been developed to detect and predict the fracture properties of fractured rocks. The standard data sources for fracture evaluations are image logs and core samples. However, many wells do not have these data, especially for old wells. Furthermore, operating both methods can be costly, and, sometimes, the data gathered are of bad quality. Therefore, previous research attempted to evaluate fractures indirectly using the widely available conventional well-logs. Sedimentary rocks are widespread and have been studied in the literature. However, fractured reservoirs, like igneous and metamorphic rock bodies, may also be vital since they provide fluid migration pathways and can store some hydrocarbons. Hence, two fractured metamorphic rock bodies are studied in this study to evaluate any difference in fracture responses on well-log properties. Also, a quick and reliable prediction method is studied to predict fracture density (FD) in the case of the unavailability of image logs and core samples. Gene expression programming (GEP) was chosen for this study to predict FD, and ten conventional well-log data were used as input variables. The model produced by GEP was good, with R2 values at least above 0.84 for all studied wells, and the model was then applied to wells without image logs. Both selected metamorphic rocks showed similar results in which the significant parameters to predict FD were the spectral gamma ray, resistivity, and porosity logs. This study also proposed a validation method to ensure that the FD value predictions were consistent using discriminant function analysis. In conclusion, the GEP method is reliable and could be used for FD predictions for basement metamorphic rocks.

Three-Dimensional Heterogeneity of the Pore and Fracture Development and Acoustic Emission Response Characteristics of Coal Rocks in the Yunnan Laochang Block

Studying the heterogeneity of coal reservoirs is significant to coal bed methane (CBM) exploitation. To investigate the development of the pore–fracture and acoustic emission response characteristics of the coal rock in the Yunnan Laochang block, four cores were extracted from the same coal rock in different directions. Through a comprehensive analysis using CT scanning and three-axis compression tests combined with synchronous acoustic emission experiments, a three-dimensional visualization of the pore–fracture structure and an analysis of the acoustic emission process during the elastic phase were conducted. Additionally, the impact of the heterogeneous development of pore–fractures on the acoustic emission characteristics was discussed. The results show that: there is strong heterogeneity in pore and fracture development within the coal rock, with the most significant development occurring along the direction of vertical stratification; the acoustic emission process in the elastic phase can be divided into three stages: strong–weak–strong; the development of pores and fractures affects the acoustic emission characteristics, with both counts and signal strength increasing as the percentage of voids rises; and the inferred in situ stress aligns with strike-slip faulting stress using acoustic emission. These results can provide a reference for the actual project.

A continuum damage model for Mg/Al composite sheets rolling: Theoretical development and application

Edge cracks, which are typical formability defects, severely limit the widespread application of Mg/Al composite sheets. Accurate prediction of damage is crucial for understanding the underlying mechanisms behind crack formation. In this study, a continuum damage model that incorporates the stress-state function and effective equivalent plastic strain into the standard Lemaitre model is proposed. This enhanced model effectively addresses the issues of damage-evolution linearization and tension–compression asymmetry in the standard Lemaitre model. Thus, it can be successfully applied to predict the fracture response of ductile composite materials under pressure-forming conditions. Considering AZ31B Mg alloy and 5052 Al alloy as experimental materials, physical experiments and numerical validation are performed under a 50% reduction and 350 °C. The findings show that the proposed model effectively captures crack initiation and propagation during the rolling process, with errors of only 23.1% and 19.9% for average crack quantity and length, respectively. Results of numerical analysis reveals that the high-stress triaxiality at the edge of the sheet contributes significantly to crack formation. Additionally, the strain along the normal direction in the Al alloy significantly affects crack propagation and the formation of serrated cracks on the side of Mg alloy. This study provides important theoretical foundations for the development of Mg-based composite sheets.

The impact of age and sex on the inflammatory response during bone fracture healing.

Inflammation is thought to be dysregulated with age leading to impaired bone fracture healing. However, broad analyses of inflammatory processes during homeostatic bone aging and during repair are lacking. Here, we assessed changes in inflammatory cell and cytokine profiles in circulation and in bone tissue to identify age- and sex-dependent differences during homeostasis and repair. During homeostatic aging, male mice demonstrated accumulation of CD4+ helper T cells and CD8+ cytotoxic T cells within bone while both pro-inflammatory "M1" and anti-inflammatory "M2" macrophage numbers decreased. Female mice saw no age-associated changes in immune-cell population in homeostatic bone. Concentrations of IL-1β, IL-9, IFNγ, and CCL3/MIP-1α increased with age in both male and female mice, whereas concentrations of IL-2, TNFα, TNFR1, IL-4, and IL-10 increased only in female mice - thus we termed these "age-accumulated" cytokines. There were no notable changes in immune cell populations nor cytokines within circulation during aging. Sex-dependent analysis demonstrated slight changes in immune cell and cytokine levels within bone and circulation, which were lost upon fracture injury. Fracture in young male mice caused a sharp decrease in number of M1 macrophages; however, this was not seen in aged male mice nor in female mice of any age. Injury itself induced a decrease in the number of CD8+ T cells within the local tissue of aged male and of female mice but not of young mice. Cytokine analysis of fractured mice revealed that age-accumulated cytokines quickly dissipated after fracture injury, and did not re-accumulate in newly regenerated tissue. Conversely, CXCL1/KC-GRO, CXCL2/MIP-2, IL-6, and CCL2/MCP-1 acted as "fracture response" cytokines: increasing sharply after fracture, eventually returning to baseline. Collectively, we classify measured cytokines into three groups: (1) age-accumulated cytokines, (2) female-specific age-accumulated cytokines, and (3) fracture response cytokines. These inflammatory molecules represent potential points of intervention to improve fracture healing outcome.

Three-dimensional peridynamic modeling of deformations and fractures in steel beam-column welded connections

The integrity of steel structures depends primarily on the strength of beam-column connections. The paper presents a new and novel three-dimensional (3D) peridynamic model to study the fracture behavior of steel beam-column welded connections. The mesh-free nature of the peridynamic method enables simulating the excessive deformation and fractures in steel elements. The 3D peridynamic model is validated by comparing its fracture and deformation results with experimental data from several beam-column welded connections. According to the proposed model, there are two conditions for the failure of steel beam-column welded connections as follows: 1) crack propagation in the steel elements (beam or column) or bonds’ breakage in the welding zone (welding defects); 2) sudden drop of the load value in the load–displacement curve. The study emphasizes its originality by presenting an efficient tool for researchers and engineers to examine fracture responses in steel beam-column welded connections under various conditions. The inclusion of different steel section profiles adds versatility to the study. The paper also explores the performance of new steel beam-column welded connection cases. Moreover, the paper examines the effects of welding defects in the fracture mechanism of steel beam-column welded connections. This study demonstrates that welding defects can determine the failure source and mechanism. Moreover, the load capacity of steel beam-column welded connections decreases due to the welding defects. This finding underscores the importance of welding quality in maintaining the structural integrity of these connections.

Dynamic fracture response of adhesive joints subjected to mode-I impact wedge loading

ABSTRACT This paper aims to examine the behavior of cracked adhesive joints experimentally and numerically when they are subjected to quasi-static and dynamic loads using the tensile and falling-wedge impact tests, respectively. Double cantilever beam (DCB) specimens were manufactured and tested under impact loading with varying impact energies to analyze the adhesive joint mode-I dynamic fracture response. To determine quasi-static and dynamic mode-I fracture energies, the compliance-based beam method (CBBM) was utilized accounting for the axial force exerted by the wedge. It was found that by changing the loading condition from quasi-static to impact, the maximum force and fracture energy of adhesively bonded joints were considerably increased by 275% and 452%, respectively. However, within the impact test conditions, increases of 10% and 22% were obtained in maximum force and fracture energy when the impact energy was tripled. The adhesive joints tested under static loading experienced a mixed interfacial/cohesive failure pattern, whereas by shifting the loading condition to impact, the failure pattern turned fully cohesive. The quasi-static and dynamic fracture responses of adhesive joints were modeled using the cohesive zone model employing a triangular traction-separation law. The numerical and experimental results exhibited reasonable correlation.

Parametric optimization of constitutive and failure model to numerically simulate the dynamic fracture response of AA7475-T7351 under extreme thermomechanical loading

The ability to regulate a material’s fracture toughness is critical for achieving ductile fracture arrest design for the transportation and defiance industry. The present study utilized the data of split Hopkinson tensile bar experiments and uniaxial quasi-static tensile experiments to evaluate the parameters of Johnson-Cook constitutive and failure models for AA7475-T7351. Estimated constitutive and fracture parameters are further optimized using programming and numerical simulation for better predictability. The dynamic three-point bend experiments were performed to assess the fracture toughness of AA7475-T7351 using a modified Hopkinson pressure bar under different temperatures and strain rates. The findings indicate that the fracture behaviour is affected by material orientations, loading rates and temperatures. The 3D-digital image correlation (DIC) technique was used to get the full field displacement data of the three-point bend (TPB) and tensile specimens. The experimental findings of the TPB specimen from DIC post-processing were further compared with the numerical outcome in terms of load point displacement (LPD), crack mouth opening displacement (CMOD) and crack mouth opening displacement contour. A comprehensive error analysis is used to correlate the experimental and numerical results. The numerical and experimental findings are reasonably in agreement with one another. The determined constants for the JC Constitutive and Failure models are applicable for strain rate approximately 5000 s−1 and temperatures ranging from −200 to 250 °C.

Discrete Lattice Element Model for Fracture Propagation with Improved Elastic Response

This research presents a novel approach to modeling fracture propagation using a discrete lattice element model with embedded strong discontinuities. The focus is on enhancing the linear elastic response within the model followed by propagation of fractures until total failure. To achieve this, a generalized beam lattice element with an embedded strong discontinuity based on the kinematics of a rigid-body spring model is formulated. The linear elastic regime is refined by correcting the stress tensor at nodes within the domain based on the internal forces present in lattice elements, which is achieved by introducing fictitious forces into the standard internal force vectors to predict the right elastic response of the model related to Poisson’s effect. Upon initiation of the first fractures, the procedure for the computation of the fictitious stress tensor is terminated, and the embedded strong discontinuities are activated in the lattice elements for obtaining an objective fracture and failure response. This transition ensures a shift from the elastic phase to the fracture propagation phase, enhancing the predictive capabilities in capturing the full fracture processes.

Machine Learning Provides Fracture Analysis, Mapping for CCUS

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 214996, “Machine-Learning Application for CCUS Carbon Storage: Fracture Analysis and Mapping in the Illinois Basin,” by Guoxiang Liu, SPE, US Department of Energy, and Abhash Kumar and William Harbert, SPE, Contractors, et al. The paper has not been peer reviewed. _ The monitoring of storage reservoirs to ensure safe, long-term storage of CO2 and to derisk operations and storage management is undergoing dynamic shifts, expanding opportunities for implementing innovative techniques and applications, especially for commercial-scale deployment. In the complete paper, a method with multitiered analysis has been developed to leverage advanced machine-learning (ML) techniques to process passive seismic monitoring data acquired during an injection period along with pumping/injection pressure and rate in the Illinois Basin for potential fracture and fault analysis. Introduction This study is part of the Science-Informed ML for Accelerating Real-Time Decisions in Subsurface Applications (SMART) Initiative funded by the US Department of Energy Carbon Storage Program. The outcomes of the SMART Initiative are science-informed, ML-based tools that can be applied at carbon storage sites throughout the nation and the world to achieve the following objectives: - Improve the ability to consolidate technical knowledge, site-specific characterization information, and real-time data in a digestible way - Enable the optimization of carbon-storage reservoirs by creating a capability for real-time forecasting of the behavior of such reservoirs - Improve the ability to understand and communicate subsurface behavior during carbon-storage operations to nonexperts Methodology In the authors’ study, a multitiered, data-driven approach was created by integrating all available measurement data to visualize fracture networks. The data sets included measurements from drilling, log and core testing, injection and downhole pressure measurements, and five vertical-pressure-monitoring gauges, providing a wealth of detail on the fracture networks. A fracture network encompasses natural fractures, induced or hydraulic fractures, and the dynamic response of such fractures, culminating in a comprehensive understanding of this system. Because of the wide range of resolutions and scales of the data sets, the fracture network was mapped into 19 distinct time windows over a 3-year injection period by analyzing pumping data, which included CO2 injection and bottomhole pressure. Passive seismic data (microseismic) were compartmentalized into these time windows, similar to the industry practice of compartmentalizing microseismic data into separate stages for high-pressure fluid- injection activities (i.e., induced fracturing). In each of these time windows, the b-value of the associated microseismic population was estimated. Furthermore, event-occurrence time and distance from the treatment well were used to identify the distinct triggering front of microseismicity likely associated with pre-existing fractures and faults within the reservoir. Seismogenic b-value and diffusivity analyses were applied to identify triggered fronts for further clustering and fracture-plane and 3D fracture-distribution analysis. The potential of several unsupervised ML algorithms was leveraged to identify the spatial clusters of microseismic events within each triggering front of individual time windows by following the work flow described in Fig. 1 of the complete paper. Furthermore, these ML techniques were implemented to determine the best-fitting surface for each spatial cluster of microseismicity to infer the directional and spatial distributions of fractures.

Effect of accelerated carbonation of fully recycled aggregates on fracture behaviour of concrete

Accelerated carbonation of recycled aggregates (RAs) enables fast carbon sequestration while improving engineering properties of prepared concrete. This paper presents a systematic experimental study on the fracture behaviour of concrete with carbonated recycled coarse and fine aggregates (RCA and RFA), in terms of fracture parameters and fracture process zone (FPZ). The relevant influencing mechanism was investigated by relating the macroscopic fracture responses to microstructural features. Results indicate that carbonated RFA mainly enhanced the initial fracture toughness of concrete, while carbonated RCA primarily increased its unstable fracture toughness. The enhancement of fracture energy was closely associated with carbonated RCA and RFA. The utilization of RFA resulted in the looseness and higher porosity of mortar matrix, which reduced the crack initiation resistance of concrete, mainly affecting its initial cracking stage. The incorporation of RCA reduced crack bifurcation and deflection of concrete, leading to a smaller width of FPZ, which made the initial descending segment of the tension softening curve (TSC) steeper and its tail segment shorter. The carbonation treatment of RAs improved the densification of the adhered old mortar and reduced the porosity of prepared concrete, rising the cracking resistance and inducing a wider FPZ. As a result, the initial descending segment of TSC became flatter and its tail segment tended to be longer.

The effect of abrading treatment method on the bonding surface characteristics and fracture behavior of glass fiber-epoxy composite adhesive joints

The effect of the mechanical abrading method on the bonding surface characteristics and fracture response of glass fiber-reinforced polymer (GFRP) composite adhesively bonded joints was investigated. Double cantilever beam specimens were manufactured by bonding GFRP substrates with an epoxy adhesive to evaluate the mode-I adhesive joint fracture response. The bonding surfaces were treated with degreasing and abrading methods utilizing sandpapers with various grit sizes ranging from P60 to P800. The results showed that the sandpaper grit size can considerably change the bonding surface properties comprising the surface energy, roughness, morphology, and water drop contact angle and consequently, it can affect the joint fracture behavior. Reducing the sandpaper grit size continuously increased the surface roughness but there were optimum values for the surface energy and water drop contact angle. The fracture resistance of adhesive joints followed the trend of bonding surface energy as the higher the bonding surface energy, the higher the joint fracture resistance. The fracture energy and load-bearing capacity of adhesive joints were improved by 62 and 34%, respectively, when the joint bonding surfaces were abraded with P240. However, further reducing the sandpaper grit size to P60 caused a decrease in the fracture energy and load-bearing capacity of adhesive joints by 18 and 44%, respectively, compared to the joint with degreased and non-abraded bonding surfaces. Moreover, the abrading method considerably changed the microscopic and macroscopic failure modes of adhesive joints.

Micro-CT imaging and finite element models reveal how sintering temperature affects the microstructure and strength of bioactive glass-derived scaffolds

This study focuses on the finite element simulation and micromechanical characterization of bioactive glass-ceramic scaffolds using Computed micro Tomography (μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu$$\\end{document}CT) imaging. The main purpose of this work is to quantify the effect of sintering temperature on the morphometry and mechanical performance of the scaffolds. In particular, the scaffolds were produced using a novel bioactive glass material (47.5B) through foam replication, applying six different sintering temperatures. Through μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu$$\\end{document}CT imaging, detailed three-dimensional images of the scaffold’s internal structure are obtained, enabling the extraction of important geometric features and how these features change with sintering temperature. A finite element model is then developed based on the μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu$$\\end{document}CT images to simulate the fracture process under uniaxial compression loading. The model incorporates scaffold heterogeneity and material properties—also depending on sintering temperature—to capture the mechanical response, including crack initiation, propagation, and failure. Scaffolds sintered at temperatures equal to or higher than 700 ∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{\\circ }$$\\end{document}C exhibit two-scale porosity, with micro and macro pores. Finite element analyses revealed that the dual porosity significantly affects fracture mechanisms, as micro-pores attract cracks and weaken strength. Interestingly, scaffolds sintered at high temperatures, the overall strength of which is higher due to greater intrinsic strength, showed lower normalized strength compared to low-temperature scaffolds. By using a combined strategy of finite element simulation and μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu$$\\end{document}CT-based characterization, bioactive glass-ceramic scaffolds can be optimized for bone tissue engineering applications by learning more about their micromechanical characteristics and fracture response.

Water Effects on Elastic S-Wave Propagation and Attenuation Across Single Clay-Rich Rock Fractures: Insights from Ultrasonic Measurements

Though previous studies have shown that the presence of water strongly influences wave responses of rock fractures, water effects on wave behaviours across clay-rich rock fractures have been ambiguous until now. In the present study, we conducted considerable ultrasonic measurements on single rock fractures filled with kaolinite-dominant gouges at varying water saturation degrees to investigate the water effects on elastic S-wave propagation and attenuation across clay-rich rock fractures. The experimental results reveal that the S-wave velocity across single clay-rich rock fractures slightly increases and decreases with the progressively increasing water saturation degree. An increase in water saturation leads to a concave trend of the spectral amplitudes, while it moderately affects the central frequency of transmitted S-waves. In addition, the seismic quality factor across single clay-rich rock fractures follows an exponential growth trend with the water saturation, suggesting the exponentially negative relation between S-wave attenuation and the water saturation. We attribute the water saturation-dependent S-wave attributes across single clay-rich rock fractures to the combined effects of the local flow and the degradation of grain contacts. Compared to P-wave, S-wave exhibits less sensitivity to varying water saturation of clay-rich rock fracture. Upon increasing water saturation, S-waves display similar velocity and central frequency trends with P-waves. The tendencies of spectral amplitude and seismic quality factor for S-waves are approximately opposite to those for P-waves as the water saturation degree increases. We interpret these discrepancies by the fact that S-wave attributes across single water-saturated clay-rich rock fractures mainly depend on the properties of the skeletal frame, while the characteristics of the particles, pore fluid, and skeleton frame dominate P-wave behaviours. The outcomes of the current work facilitate our understanding of the fluid effects on the interaction of waves with clay-rich rock discontinuities.

Trans-layer and inter-layer fracture behavior of extrusion-based 3D printed concrete under three-point bending

This paper presents a systematic study on the effect of layer-by-layer printing process on the fracture behavior of hardened extrusion-based 3D printed concrete (3DPC). Based on three-point bending tests on center-notched beams, the fracture response of printed specimens with two fracture patterns including crack propagation across layers (trans-layer fracture) and crack propagation along layers (inter-layer fracture) was compared with that of cast specimens. The fracture mechanism of 3DPC was explored using the fracture parameters and fracture process zone (FPZ) characteristics. Experimental phenomena can be explained by the additional interlaminar cracking in FPZ of concrete introduced by the layer-by-layer stacking process. It could produce a toughening effect if cracks propagate through layers, as it is beneficial to reduce stress concentration and improve deformability. In the printing process design of 3DPC, such feature can be rationally utilized to transform the process-induced weak interfaces from inherent defects to toughening means.

Thermal stimulation mechanical response and shear dilatation predictive model improvement of granite fractures in an enhanced geothermal system

The exploitation of shear dilatation behavior exhibited by natural rock fractures can serve as an effective strategy for stimulating reservoirs in the enhanced geothermal systems (EGS). However, few studies have considered the shear dilatation characteristics of rock fractures treated by real-time high temperature. Firstly, the self-developed Mechanical(M)-Thermal(T) coupling shear test cell and the MTS816.01 rock shear test system were used to carry out the direct shear tests of granite fractures. The M-T coupling effect on granite's physical properties such as cohesion, the mechanical properties such as shear strength, and strain energy characteristics such as dissipated strain energies were analyzed. On these Base, the shear dilatation mechanism of granite fractures treated by real-time high temperature is further revealed. Subsequently, based on the dynamic changes in the area degradation degree of granite fractures, the shear dilatation model of rock fractures treated by real-time high temperature were improved and verified. The results reveal that the M-T coupling effect can considerably impair the shear dilatation behavior of granite fractures. The temperature undermines the shear dilatation behavior of granite fractures by negatively affecting their physical and mechanical properties, while the normal stress deteriorates their shear dilatation behavior by constraining the normal displacement of the rock fractures. The modified shear dilatation model of rock fractures exhibits high accuracy and can accurately represent the shear dilatation behavior of rock fractures under M-T coupling effects. The novel insights provided in this paper contribute to a more comprehensive understanding of the wellbore stability and permeability improvement mechanism of EGS.

Mixed-Mode Fracture behaviour of Si-C-N coatings

Micro-electro-mechanical systems (MEMS) technology has made it possible for the semiconductor industry to construct systems and devices on silicon substrates. Nanocomposite Si-C-N coatings must have reliable characteristics for MEMS as well as in the form of protective coatings for heavy-duty industries like aerospace, automobiles, reactors, etc. Vickers indentation was used to study the fracture response of Si-C-N coatings that were deposited on silicon substrates. Images of the fractured regions which consisted of different types of cracks were analyzed and used for qualitative fracture analysis. The Drucker-Prager (DP) model and subsurface layer distributions were used to evaluate the fractured zones. Microscopic evaluation and supporting image analysis were used to study the growth nature of the coatings.

Study of the Dynamic Failure Characteristics of Anisotropic Shales Under Impact Brazilian Splitting

The mechanical behaviors of shales with transversely isotropic characteristics under dynamic loading have great significance for structural instability in geotechnical engineering. To understand the effect of transverse isotropy on the deformability and tensile strength of shales subjected to dynamic loading, a group of impact Brazilian tests were carried out on shale specimens via a split Hopkinson pressure bar (SHPB) testing system. High-speed digital image correlation technology was applied to monitor the fracture process. The experimental results demonstrate that the failure strength has considerable anisotropy as the bedding angle of the embedded layers changes. Moreover, the tensile strength of shales with vertical bedding is usually higher than that of shales with parallel bedding. The observed failure mode is mainly the interaction between tensile and/or shear fractures, and with increasing loading rate, layer-activated fractures tend to occur. Furthermore, five typical failure patterns of transversely isotropic shales characterized by different mechanisms under dynamic Brazilian testing were found. The shales were sensitive to the strain rate when the deformation and fracture response under dynamic loading were assessed. In addition, the modified Nova‒Zaninetti criterion that considers the strain rate effect was proposed according to the Brazilian splitting data and dynamic coordinate system. The established criterion not only properly represents the law of dynamic strength but also provides a new understanding of the effect of strain rate on strength. It has proven to be effective for predicting the dynamic strength characteristics of shales.