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The range of sensor technologies for structural health monitoring (SHM) systems is expanding as the need for ongoing structural monitoring increases. In such a case, damage to the monitored structure elements is detected using an integrated network of sensors operating in real-time or periodically in frequent time stamps. This paper briefly introduces a new type of sensor, called a Customized Crack Propagation Sensor (CCPS), which is an alternative for crack gauges, but with enhanced functional features and customizability. Due to those characteristics, it is necessary to develop a family of computer-aided supporting models for rapid prototyping and analysis of the new designs of sensors of various shapes and configurations, which this paper presents by use of simulation tools. For a prototyping of the sensor lay out, an algorithm is elaborated, based on an application created in LabVIEW 2022 software, which generates two spreadsheets formatted by the requirements of Autodesk Inventor 2014 and COMSOL Multiphysics 5.6 software, based on data entered by the user. As a result, a tailored-in-shape CCPS layout is prepared. A parametric model of the sensor is prepared in Autodesk Inventor software, which automatically changes its geometric dimensions after changing data in an MS Excel spreadsheet. Then, the generated layout is analyzed to obtain electromechanical characteristics for defined CCPS geometry and materials used in the COMSOL Multiphysics software. Another application is devoted to purely mechanical analysis. The graphical user interface (GUI) add-on based on the Abaqus 2018 software engine is prepared for advanced mechanical analysis simulations of sensor materials in selected loading scenarios. The GUI is used for entering material libraries and the selection of loading conditions and a type of specimen, while the results of the numerical analysis are delivered through Abaqus. The main advantage of the developed GUI is the capacity for personnel inexperienced in using the Abaqus environment to perform analysis. Some results of simulation tests carried out in both COMSOL Multiphysics as well as Abaqus software are delivered in this paper, using a predefined parametric sensor model. For example, using a rigid epoxy resin for an insulating layer shows a negligible difference in the level of strain compared to the structure during a simulated tensile test, specifically in the tested layer thickness range of up to 0.3 mm. However, during bending tests, an approx. 17% change in principal strain level can be observed through the top to bottom edge of the epoxy resin layer. The adopted methodology for carrying out simulation studies assumes the parallel use of a set of various computer-aided tools. This approach allows for taking advantage of individual software environments, which allows for expanding the scope of analyses and using the developed models and applications in further research activities. [ABSTRACT FROM AUTHOR]

In hydraulic fracturing tests, the initial crack length and the compressibility of the injection system have a significant effect on the initiation and propagation of the fracture. Numerical or theoretical models that ignore the compressibility of the injection system are unable to accurately predict fracture behavior. In this paper, a 2D analytical/numerical model based on linear elastic fracture mechanics is presented for the initiation and propagation of hydraulic fracturing from two transversely symmetrical cracks in a borehole wall. It is assumed that the fracture is driven by compressible inviscid fluid in a permeable medium. To solve the problem, the governing equations are made dimensionless and the problem is solved in the compressibility–toughness-dominated propagation regime. According to the results, the initial crack length and the compressibility of the injection system have a significant effect on fracture initiation behavior. When the initial flaw length is small or compressibility effects are important, the initiation of the fracture is accompanied by instability and the occurrence of a sudden decrease in borehole pressure and a sudden increase in crack length. If the initial crack length is large or the compressibility effects are negligible, the crack propagation is stable. The leak-off coefficient has no effect on the pressure level required for crack propagation, but with an increase in leak-off, more time is required to reach the conditions for crack propagation. The results obtained in this paper provide good insights into the design of hydraulic fracturing processes. [ABSTRACT FROM AUTHOR]

Fatigue damage on the surface of brake discs can seriously affect the train braking safety. In this paper, the effect of various braking conditions on the crack propagation of train brake discs is investigated based on the co-simulation of Abaqus and Franc3D. The relationship of the braking mode, initial speed, braking time and braking force to the stress intensity factor, crack propagation rate, and propagation life is discussed. The findings show that the initial speed is the major factor influencing disc crack propagation during emergency and service braking, while the braking force and time are more important during ramp braking. Besides, the temperature increasing rate and temperature field distribution are significant factors influencing crack propagation. Thus, reasonable design of braking condition parameters can help slow down the crack propagation of brake discs and ensure the safety of braking. [ABSTRACT FROM AUTHOR]

Spiral bevel gears (SBGs) are often used because of their strong carrying capacity and lower vibration. However, this heightened load capacity can sometimes result in the development of tooth surface cracks. This study aims to simulate the three-dimensional propagation of cracks in SBGs under various assembly conditions and explore how the presence of cracks affects mesh characteristics. This paper investigates crack propagation in SBGs by applying principles of fracture mechanics. Employing a combination of finite element software ABAQUS and fracture mechanics software FRANC3D, the study conducts a three-dimensional analysis of crack propagation in SBGs. The study analyzes the impact of crack propagation on the lifespan and mesh characteristics of SBGs, including crack propagation morphology, transmission error, time-varying meshing stiffness (TVMS), gear life, and tooth surface force, under various assembly errors. [ABSTRACT FROM AUTHOR]

The diffusion process and effect of grouting in rock fractures are affected by the grouting parameters, fracture parameters, and external environment. On the basis of theoretical research, a numerical simulation method of rough fracture grout propagation refinement based on Bingham–Papanastasiou rheological model is established in this paper. The propagation test of fracture grouting is designed, and the correctness of the numerical simulation method is verified by comparison between the model test and numerical simulation under standard working condition. Based on the standard working condition, the influences of grout water–cement ratio, grouting pressure, water-rich environment and filling rate on grout propagation are investigated, and the temporal and spatial distribution characteristics of velocity field and pressure field during grout propagation are analyzed. A simplified model of fissure-filling grouting infiltration is used to determine the geometric equivalence of the fissure-filling rate, and an empirical constant term fitting method for the Forchheimer infiltration equation of a Bingham flow-type grout is proposed. Highlights: On the basis of theoretical analysis and model tests, this paper fills the gap in numerical simulation research on grout diffusion to some extent. This study establishes a refined numerical simulation method of rough fracture grout diffusion based on the Bingham–Papanastasiou rheological model. This study explores the effects of the water-cement ratio, the grouting pressure, water-rich environments and the filling rate on grout diffusion. This paper proposes a fitting method for the empirical constant terms in the Forchheimer seepage equation for Bingham grouts. The research helps to quantify the influences of multiple factors on grouting reinforcement and summarize the grout diffusion effect law. [ABSTRACT FROM AUTHOR]

The development of bedding planes was a prominent feature of shale, and the stress interference between hydraulic fractures and bedding planes played a key role in forming fracture networks. Elucidation of the mechanism of the mutual interference between hydraulic fractures and bedding planes could help improve the fracturing technology of the shale fracture network. To simultaneously reflect the roles of both hydraulic fractures and bedding planes in the model, a series of large-size three-dimensional numerical models were established in this study using the ABAQUS finite element software. The cross-cohesive unit and the pipe flow unit were employed to simulate the cross-extension of the fracture with the bedding plane and the injection of fracturing fluid into the wellbore, respectively. Moreover, the correctness of the numerical models was verified by the analytical solution of the PKN simplified fracture model. The cohesive zone model (CZM) considered the softening effect and plastic zone at the top of cracks in quasibrittle rocks (e.g. shale), obtaining a more accurate crack geometry and in-seam pressure than linear elastic fracture mechanics. The cross-cohesive unit realized different traversal morphologies of the cracks when they interacted with the bedding plane. This paper analyzed the distribution of induced stresses generated by hydraulic fractures and bedding fractures. The induced stresses generated by hydraulic fractures were concentrated at the base of hydraulic fractures, and the stress shadows at the fracture tip made it easier for hydraulic cracks to cross bedding planes; the distribution plane of induced stresses generated by bedding fractures was parallel to bedding planes, and this induced stress was an essential factor influencing the traversal morphology of fractures. The results showed that the properties of the bedding plane significantly affected hydraulic fracture propagation in the height direction and the morphology of the fracture network. On the one hand, diverting the bedding plane limited the vertical propagation of hydraulic fractures. On the other hand, the induced stresses generated by the opened bedding plane hindered the opening of subsequent bedding planes. Highlights: A series of three-dimensional numerical models with multiple clusters and bedding planes considering the dynamic flow distribution and perforation friction were established. Considering the development of shale bedding, this paper focused on the influence of three bedding structural parameters, namely, bedding strength, bedding spacing and bedding density, on fracture propagation patterns. Both the interference mechanism between hydraulic fractures and bedding planes and between bedding planes themselves was revealed. [ABSTRACT FROM AUTHOR]

The low-porosity, ultra-low-permeability tight sandstone oil and gas reservoirs are characterized by extensive reserves and widespread distribution, thus holding significant promise for exploration and development. In the Bohai Bay Basin, the Bozhong 25–1 (BZ25-1) oilfield presents a geological characteristic where sand–mud interbeds vertically develop within the third member of the Shahejie Formation (Es3). However, the previously employed hydraulic fracturing conditions, characterized by 'low injection rates and high fluid viscosity', encountered difficulties in achieving effective cross-layer propagation of hydraulic fractures, consequently yielding suboptimal outcomes in terms of fracturing modifications. At present, the integrated offshore hydraulic fracturing vessels have gradually entered the development of offshore oil fields, which has improved the pumping capacity of offshore fracturing and can significantly improve the fracturing effectiveness. Therefore, this paper has established multiple sets of three-dimensional fluid–solid coupled finite element models, verifies the reliability through physical simulation experiments, and analyzes the rules of fracture cross-layer propagation from both geological and engineering perspectives. The results indicate that: (1) Increasing the injection rate can directly improve the vertical propagation capability of hydraulic fractures while also affect the length of the fractures. (2) The increase of viscosity will make it easier for hydraulic fractures to pass through the barriers. Once a specific viscosity threshold is exceeded, as the viscosity continues to increase, there is no longer a significant change in the injection volume of fracturing fluid required for fracture propagate through interlayers and the change in fracture geometry becomes less pronounced. (3) Variations in the minimum horizontal principal stress differential between layers notably impact the cross-layer propagation capability, leading fractures to preferentially propagate within layers characterized by lower stress. (4) The increase of reservoir thickness results in an expanded fracture area within the target reservoir, subsequently influencing the effect of fracture propagation across layers. The conclusions drawn from this study can provide theoretical guidance for the extensive hydraulic fracturing development of the Es3 in BZ25-1 region. Highlights: With the improvement of fracturing conditions in offshore oil fields by offshore hydraulic fracturing vessels, this paper investigates the vertical propagation of hydraulic fractures in the sand–mud interbedded reservoirs of the third member of Shahejie Formation in BZ25-1 offshore oilfield. A multiple interbedded physical simulation rock sample is prepared and subjected to hydraulic fracturing experiment through the triaxial large-scale physical simulation experimental system, thereby validating the numerical methods. The seepage–stress–damage coupled mathematical model is employed to establish multiple three-dimensional fluid–solid coupling finite element models representative of sand–mud interbedded formations. By varying the interlayer thickness and the altering geological conditions or engineering factors, this paper analyzes the propagation patterns of hydraulic fractures within interbedded rock formations. [ABSTRACT FROM AUTHOR]

The microstructural changes and crack propagation in the carburized layer of SUS304 stainless steel due to repeated vacuum carburizing quenching as a heat treatment basket were investigated in this paper. As a result, beneath a graphite scale formed on the outermost surface, it was revealed that there were three types of carburized layers with different morphologies: M7C3 layer, M7C3/M23C6 mixed layer, and M23C6 layer (M = Cr, Mn, Fe). In addition, the surface was found to be uneven due to the occurrence of metal dusting. Besides, repeated heating and quenching caused the formation of voids in carbides and matrix in the carburized layer, and micro cracks appeared in the surrounding areas. Under the loading stress during vacuum carburizing quenching, these voids, micro cracks, and the uneven surface are considered to be the initial points for cracking. [ABSTRACT FROM AUTHOR]

In the process of deep mining, the dynamic disasters of coal and rock occur frequently under the action of high stress and high seepage pressure, the essence of which is energy-driven coal rock failure. In order to explore the energy evolution law and damage mechanism of sandstone with intermittent cracks under the coupling effect of stress and seepage, in this paper, by comparing the differences in mechanical characteristics between fractured rock and intact rock, the energy evolution characteristics, crack propagation, and micro-damage mechanism of fractured rock under different confining pressures and seepage pressures are analyzed. The research shows that: (1) The local stress drop phenomenon occurs in the fractured rock during the loading process, and the stress–strain shape is 'bimodal'. At the same time, there is stress concentration at both ends of the fracture. (2) The energy conversion of the fractured rock changes in stages during loading. As confining pressure rises, the energy storage limit and the maximum dissipation energy go up. The increase in seepage pressure reduces the energy storage limit, while the dissipation energy shows an upward trend. The energy consumption ratio curve shows 'concave' evolution during the loading process. (3) Based on the dissipation energy and residual stress, the damage state of the specimen is analyzed, and the proposed damage variable can reasonably explain the whole process of the damage evolution of intermittent fractured rock under stress and seepage. (4) The increase in confining pressure increases the friction between the particles inside the sample and promotes the transformation of the sample from tensile failure to shear failure. The seepage pressure reduces the friction between the particles in the sample through the air wedge effect to deepen the damage degree, thus promoting the tensile failure of the sample. [ABSTRACT FROM AUTHOR]

Acid fracturing is an effective method of reservoir stimulation and has been widely used for carbonate reservoir development. However, knowledge on the propagation characteristics of acid-etched fracture is still poor due to the complexities of acidization and stress conditions, as well as the limitations of the fracture network reconstruction method, especially when dealing with large specimens. In this paper, a new method based on image-based 3D object reconstruction is proposed to study the fracture networks of specimens after acid fracturing by cutting rock specimens into thin slices, scanning them, and reconstructing 3D fracture networks. This method is more precise than the method of separating specimens into pieces and scanning, and it has advantages over the method of CT X-ray scanning when dealing with large specimens. Using this approach, the effects of natural fractures, stress conditions, and acid systems on the fracture propagation of specimens after true triaxial acid-fracturing tests were investigated. The fracture initiation and propagation patterns of specimens under different conditions were summarized. The results of the study show that the presence of a natural fracture will induce the propagation of fractures, in addition to demonstrating the positive effect of high horizontal stress difference on fracture initiation and provide an acid system conducive to the formation of a fracture network. [ABSTRACT FROM AUTHOR]

In view of the application status and technical challenges of steel–wood composite joints in architecture, this paper proposes an innovative connection technology to solve issues such as susceptibility to pry-out at beam–column joints and low load-bearing capacity and to provide various reinforcement methods in order to meet the different structural requirements and economic benefits. By designing and manufacturing four groups of beam–column joint specimens with different reinforcement methods, including no reinforcement, structural adhesive and angle steel reinforcement, 4 mm thick steel sleeve reinforcement, and 6 mm thick steel sleeve reinforcement, monotonic loading tests and finite element simulations were carried out, respectively. This research found that unreinforced specimens and structural adhesive angle steel-reinforced joints exhibited obvious mortise and tenon compression deformation and, moreover, tenon pulling phenomena at load values of approximately 2 kN and 2.6 kN, respectively. However, the joint reinforced by a steel sleeve showed a significant improvement in the tenon pulling phenomenon and demonstrated excellent initial stiffness characteristics. The failure mode of the steel sleeve-reinforced joints is primarily characterized by the propagation of cracks at the edges of the steel plate and the tearing of the wood, but the overall structure remains intact. The initial rotational stiffness of the joints reinforced with angle steel and self-tapping screws, the joints reinforced with 4 mm thick steel sleeves, and the joints reinforced with 6 mm thick steel sleeves are 3.96, 6.99, and 13.62 times that of the pure wooden joints, while the ultimate bending moments are 1.97, 7.11, and 7.39 times, respectively. Using finite element software to simulate four groups of joints to observe their stress changes, the areas with high stress in the joints without sleeve reinforcement are mainly located at the upper and lower ends of the tenon, where the compressive stress at the upper edge of the tenon and the tensile stress at the lower flange are both distributed along the grain direction of the beam. The stress on the column sleeve of the joints reinforced with steel sleeves and bolts is relatively low, while the areas with high strain in the beam sleeve are mainly concentrated on the side with the welded stiffeners and its surroundings; the strain around the bolt holes is also quite noticeable. [ABSTRACT FROM AUTHOR]

Thin-layer covers easily crack under traffic load, shortening their service life. Incorporating fiber materials into the mix can enhance crack resistance thanks to their abundance, affordability, and flexibility. However, different types of fibers have different performances in bitumen and mixtures due to different material properties. To explore this problem, basalt fiber, polypropylene fiber, and glass fiber were selected in this paper. The surface characteristics, internal structure, and adsorption capacity of oily substances were observed via scanning electron microscopy and oil absorption rate testing. The effects of fibers on the high-temperature and low-temperature properties of styrene-butadiene-styrene block copolymer-modified bitumen were investigated using the dynamic shear rheometer and the force ductility method. Ultimately, through indirect tensile testing and semi-circular bending tests, and the introduction of the toughness index and fracture toughness, a comprehensive evaluation was conducted on how varying fiber types and content affect the crack resistance and toughness of bitumen mixtures. The results show that the density and dispersion of the bundle fibers are the key to the oil absorption capacity under similar internal and external structural conditions. The oil absorption rate of polypropylene fiber is the best, reaching 5.423. Fiber incorporation can significantly improve the high-temperature rheological properties of bitumen. At 4% dosage, G*/sinδ increased by about 107.04% on average at 76 °C. At low temperatures, the increase in fiber content leads to a decrease in bitumen elasticity, and the influence of glass fiber is more obvious. The area of toughness did not reach 2000 N·mm at 4% dosage. After adding fibers, the toughness index and fracture toughness of the mixture increased by more than 2% and 35%, respectively. The maximum increases in fracture energy and crack initiation energy of the mixture are 14.29% and 47.29%, respectively. It shows that the fiber enhances the toughness, crack resistance, and crack propagation resistance of the mixture. The research results can provide some reference for the application of fiber-reinforced bitumen mixtures. [ABSTRACT FROM AUTHOR]

This paper uses the finite-discrete element method (FDEM) to establish a fluid–solid coupling model for the propagation of multi-cluster hydraulic fractures. The validity of the proposed model is verified using the analytical solution and onsite microseismic data. The results show that with the approach angle increases, the propagation of hydraulic fracture transitions from a single capture mode to the mixed modes of capture, crossing and blocking. The total length of hydraulic fractures is negatively correlated with the approach angle and cohesion of natural fracture, and positively correlated with the distribution density and bandwidth of natural fracture. The length of shear fractures initially increases and then decreases with the increase in approach angle, showing negatively, positively, and positively correlated with cohesion, length, and bandwidth, respectively, while the trend of tensile fracture length is opposite to it. The tortuosity of hydraulic fractures (which is used to characterize the complexity of fracture morphology) initially decreases and then increases with the increase in the approach angle, negatively correlated with the cohesion of natural fracture, and positively correlated with the distribution density and bandwidth of natural fractures. Comparatively, the fracture propagation morphology is the most complex at the approach angle of 45°, which is more conducive to full reservoir enhancement. Conversely, under conditions of high cohesion, narrow width, and low-density distribution of natural fractures, the fracture morphology is relatively simple, all of which are unfavorable for reservoir enhancement in the target segment. [ABSTRACT FROM AUTHOR]

In this paper, a coupled hydro-mechanical field-enriched finite element method (HM-FE-FEM) is proposed to simulate hydraulic fracture propagation in poroelastic media. The governing equations of fluid flow and displacement are established based on the field variable and Biot's poroelastic theory. The unified field variable is introduced to characterize cracks and seepage channels in the poroelastic media. The coupled hydro-mechanical problems are solved by the staggered iterative scheme based on the Newton–Raphson iterative algorithm. The proposed method can be used to predict fluid pressure, fracture opening distribution, as well as crack initiation and propagation in hydraulic fracturing engineering. The accuracy and correctness of the proposed method HM-FE-FEM are validated by four benchmark examples. Subsequently, two classical hydraulic fracturing cases are investigated to showcase the potential and versatility of the proposed method. Finally, the performance of the proposed method is demonstrated by simulating hydraulically induced crack propagation in different types of complex natural networks. All the numerical results demonstrate the capability of HM-FE-FEM to predict and handle complex intersection behaviors in hydraulic fracturing engineering. Highlights: A coupled hydro-mechanical field-enriched finite element method is proposed to simulate the hydraulic fracture propagation in poroelastic media. The seepage channels and cracks in poroelastic media are characterized by the field variable. The accuracy and correctness of the proposed method are validated by four benchmark examples. The proposed method has the ability to simulate the complex coalescence behaviors in natural fracture networks. [ABSTRACT FROM AUTHOR]

The development of infill wells have gained significant traction in enhancing shale gas recovery in the Sichuan Basin. During the development of infill wells, the production of the parent wells leads to changes in in-situ stress, which in turn affects the fracture morphology of the infill well, resulting in frac-hits. These frac-hits are commonly considered a potential hazard to the adjacent infill well production and wellbore. In this study, a comprehensive flow-geomechanics coupling model has been developed to address this challenge. The model incorporates the processes of parent well fracturing and production, evolution of in-situ stress after production, and infill well fracturing and production. This study discusses four cases in the Sichuan Basin, each highlighting intriguing field phenomena. The first case focuses on an infill well situated in the same layer, while the second case pertains to a three-layers infill wells pad. The third case delves into the phenomenon of frac-hits in deep shale gas reservoirs (3800 m), while the final case explores the effect of high-steep structures in the fracturing process. By utilizing this integrated model and field data, the mechanisms underlying these phenomena are observed. The results indicate that: (i) The 'microseismic events barrier' (MSEB) effect caused by stress shadow has been reported and the main reasons have been analyzed. (ii) The range of stress shadow is critical to the deployment of multi-layers infill well pattern, the influence range in both horizontal and vertical directions is related to the size of hydraulic fractures. (iii) In deep shale gas reservoir, high stress and the development of natural fracture zones are the main reasons of frac-hit and the fracturing sequence can exacerbate this phenomenon. (iv) The high formation dip in the high-steep structural zone will restrict the propagation of hydraulic fractures in the horizontal direction. Through this research, valuable insights into the behavior of infill wells in the Sichuan Basin have been obtained, shedding light on the challenges and opportunities associated with maximizing shale gas recovery in this region. Highlights: In this study, a comprehensive flow-geomechanics coupling model has been developed to address the stress evolution caused by the depletion of parent well and then hydraulic fracturing of infill wells can be simulated based on the updated stress. Based on this method, we have conducted a large number of infill well case studies on shale gas fields across Sichuan Basin. The four case studies reported in this paper belong to different shale gas fields and have their own highlights and uniqueness. The 'microseismic events barrier' effect (MSEB effect) was reported in the first case which explained the reason for the sharp decrease in the number of microseismic (MS) events when the MS were close to the boundary of the parent well. Besides the phenomenon of parent well pressure regained through the enhanced permeable channel. The second case pertains to a three-layers infill wells pad which the infill wells were drilled both in upper, middle, and bottom layers. The stress influenced range in both horizontal and vertical directions analyzed. The third case delves into the inter-well interference in deep shale gas reservoirs. For the severe frac-hits having a negative effect on production and stimulation treatment, the influencing factors and types of frac-hits were summarized. The final case explores the effect of high-steep structures on the fracture propagation and explains why the hydraulic fracturing treatment in this area did not meet expectations [ABSTRACT FROM AUTHOR]

• The unified phase field model was used to study mixed mode fracture in three-point bending concrete beams. • The mechanical effect of multi-segment notches eccentricity was investigated. • The effect of size effects was studied on the P - CMOD curve, P - CMSD curve, and crack pattern. • The effect of material parameters was evaluated on the P - CMOD curve. Concrete, as a typical quasi-brittle material, generally experiences fracture failure, which is one of the most common forms of damage in engineering. This paper presents a simulation analysis of I-II mixed-mode fracture in three-point bending (TPB) concrete beams with a zigzag notch at the midspan, based on the unified phase field method (PFM). To analyze the applicability of the PFM, this paper verifies the insensitivity of the mixed-mode fracture of TPB beams to the PF length scale b and mesh size h. In addition, the P - CMOD (crack mouth opening displacement) curve, P - CMSD (crack mouth sliding displacement) curve and the propagation of cracks obtained from the simulation were compared with experimental results. The results indicate that the PF method effectively captures the crack propagation process in TPB beams under mixed-mode fracture conditions. A parametric analysis was conducted on the TPB beams regarding the zigzag notch width w , height ratio e , and material parameters G f-m , f t , and E. The results show that the notch width w has minimal influence on the mixed-mode fracture behavior of the TPB beams. With an increase in the crack height ratio e , there is a corresponding reduction in the peak load. As the fracture energy rises from 0.8 G f-m to 1.2 G f-m , the peak load only experiences a 7.9% increase. Higher fracture energy leads to a more gradual decrease in the curve, thereby resulting in a greater area between the curve and the horizontal axis. Increasing the tensile strength from 0.8 f t to 1.2 f t results in a 26.3% increase in the peak load with negligible effect on the area under the P - CMOD curve and the elastic stage of the concrete. When the elastic modulus increases from 0.8 E to 1.2 E , the peak load increases by only 10.3%. The impact of the elastic modulus on the curve's tail end is negligible. It is evident that the elastic modulus predominantly influences the curve's slope and peak. [ABSTRACT FROM AUTHOR]

• A novel cohesive zone modeling for simulation of mixed mode I/II delamination. • The effects of the fracture process zone are taken into account. • Linear and torsional springs with variable stiffness with traction-separation curves are used. • Analytical relationship presented to estimate the changes in crack growth resistance. In this paper, a novel cohesive zone modeling (CZM) approach is presented to simulate the crack initiation and propagation of mixed mode I/II delamination in laminated composites, with a focus on the effects of the fracture process zone. The CZ model employs a novel approach that combines linear and torsional spring elements to calculate the material's residual strength within the fracture process zone along the delamination growth path. In this model, the stiffness of springs changes based on the normal and tangential traction-separation curves. Unlike previous models, this approach considers the effect of all toughening mechanisms in the fracture process zone and softening behavior of the material's traction-separation curve. Also, the application of this model to estimate the R-curve behavior is demonstrated. In this way, an analytical relationship has been presented for changes in crack growth resistance with crack length increase for mode I and mode II loadings. This relationship calculates the fracture initiation toughness, the energy dissipation from toughening mechanisms in the fracture process zone, and the steady-state fracture toughness using only the potential energy of the linear and torsional elements of spring. Comparison of the obtained R-curve with experimental data highlights the efficacy of this new model. [ABSTRACT FROM AUTHOR]

• Different plastic deformations cause varied crack growth rates at same Δ K (K max). • A multi-parameter approach is utilized to predict the rate of fatigue crack growth. • The contribution of various parameters to crack propagation stages is investigated. • A method for predicting FCG rates considering the load ratio effect is presented. The development of digital image correlation (DIC) has led to a growing interest in the use of DIC methods for crack tip plastic zone size assessment and non-linear parametric characterization of fatigue crack growth rate (FCGR). This paper presents a study of the stress and strain evolution at the crack tip, employing the use of DIC to monitor the plastic deformation at the crack tip during fatigue crack growth (FCG) under varying load ratios. Furthermore, the dimensions of the plastic zone at varying crack lengths are quantified by combining DIC with theoretical methods. A methodology for forecasting the FCGR is presented, based on the measured dimensions of the plastic zone. In comparison with preceding methodologies, the proposed approach incorporates the effects of load ratio and fracture toughness, and characterizes FCGR by normalizing the equivalent plastic zone size through the analysis of the contribution of multiple parameters to the distinct phases of FCG. And ultimately obtains a FCGR prediction model with a correlation coefficient R CORR 2 of 0.966, demonstrates a superior fit to the FCGR in comparison to the stress intensity factor. Finally, the fracture morphology evolution of TC4ELI alloys under different loading conditions was analyzed by electron microscopy, and the results showed that the observations of fracture morphology at different loading ratios and FCG stages were consistent with the macroscopic results of monotonic cyclic plastic deformation analyzed by DIC. [ABSTRACT FROM AUTHOR]

• Crack morphology shows crack elongation, widening, and branching as the indentation velocity increases. • The limit speed of crack propagation is about 0.52 times the Rayleigh wave speed. • Crack bifurcation occurs when the stress intensity factor exceeds 2.3 times the fracture toughness. • Cracks preferentially propagate in a way that allows the energy to be released more quickly. The mechanisms of crack initiation, propagation and bifurcation in hard and brittle materials are the foundamental for planning their processing and conducting applied research. There are significant differences between crack propagation under dynamic loading and static crack propagation, and the complex propagation and bifurcation behaviors require further investigation. In this paper, the basic characteristics of crack initiation, crack bifurcation, propagation rate and stress distribution and their interrelationships, are investigated by peridynamic simulations of dynamic indentation in brittle materials with varying indenter and indentation speeds. The results show that as the indentation speed increases, greater tensile stress is generated at the crack initiation location, and the crack morphology shows a tendency to elongate, widen and bifurcate, which facilitates the acceleration of tensile stress release. Larger indenter angles and changing from a uniform motion to a harmonic motion indentation result in increased impact energy, which results in cracks widening and bifurcation at lower indentation velocities. In addition, the crack propagation velocity initially increase as the indentation velocity increases until reaching the limiting velocity, which is about 0.52 times the Rayleigh wave velocity. By calculating the stress intensity factor at the crack tip, it was found that the crack will start to bifurcate after the stress intensity factor exceeds 2.3 times the fracture toughness. Integrating the results of crack propagation analyses in different cases, the fastest way of releasing energy from the crack tip determines the crack propagation rate and morphology. The study provides valuable insights into the understanding of crack initiation and bifurcation during machining of brittle materials. [ABSTRACT FROM AUTHOR]

Underground coal gasification (UCG) enables the in situ clean conversion of coal seams, making it highly suitable for the development and utilization of deep coal seams. This study focused on the UCG of deep coal of the Xishanyao Formation in the Baikouquan area of Xinjiang, China. A multi-field coupled evolution model based on the finite element method was established for deep UCG to simulate the propagation of induced fractures and multi-physical fields during UCG. The following conclusions were obtained: (1) At burnout distances of 200, 500, and 1000 m, the maximum temperature influence ranges were 20, 23.75, and 25 m, respectively. (2) When the burnout distance reached 200 m, no natural fractures propagated due to the high stress of the deep overlying strata. However, when the burnout distances increased to 500 and 1000 m, the maximum heights of the propagated fractures reached 232.5 and 270 m, with average heights of 157.5 and 172.5 m, respectively. (3) At burnout distances of 200, 500, and 1000 m, the maximum subsidence displacements in the roof rock were 1.68, 5.60, and 17.40 m, respectively. (4) In the actual design process of UCG projects, excessively long gasification channels should be avoided to prevent interaction between aquifers and the UCG cavity, which could lead to the failure of the UCG project. Results of this paper contribute to controlling the scope of the temperature field in practical UCG projects, and predicting the propagation heights of induced fractures as well as the displacement characteristics of the overlying strata. With these as references, a more reasonable UCG scheme considering the scope of induced fractures and stress concentration can be designed, which helps avoid groundwater influx risks and improve the stability of UCG project. • A multi-field coupling evolution model for deep UCG was developed. • The extended range of multi-physics fields for UCG was determined. • The UCG induced fractures propagation law of overlying strata was investigated. • The guidance on the design and site selection of deep UCG projects was provided. [ABSTRACT FROM AUTHOR]

• A phase-field fracture model for QC reinforced composites is developed. • An equivalent critical ERR is introduced to reflect the interface effect. • Influence of interfaces on fracture behaviors is thoroughly investigated. • More fracture problems in QC composites can be studied based on the PFM. Quasicrystals (QCs) have been used as a particle reinforcement phase in polymer or metal matrix composites to enhance the material strength, hardness and wear resistance while maintaining the lightweight advantages of the composites. In this paper, a phase-field fracture model (PFM) is proposed to predict crack propagation and interfacial debonding in QC composites. The phase-field and interface-field variables are introduced to regularize the cracks and interfaces in the composites, respectively. An equivalent critical energy release rate is introduced to characterize the influence of the interface on crack propagation. The present model is numerically implemented in Comsol Multiphysics based on the W eak F orm PDE module. Several numerical examples are simulated to demonstrate the ability of the proposed model to predict crack propagation and interfacial failure of QC composites and to analyze the influence of QC reinforcement phase on fracture behaviors of QC composites. Numerical results indicate that the interface significantly influences the crack propagation paths, and the phason elastic field has a remarkable influence on the peak force and failure displacement in the fracture test of QC composites. The developed phase-field model and numeral implementation approach provide a convenient tool for predicting interfacial failure and assessing the safety of QC composites in engineering. [ABSTRACT FROM AUTHOR]

• A new configuration of specimen containing two holes was applied in a series of impact tests. • The strain field variation of the entire specimen under impact load was accurately calculated using 2D-DIC technology. • Analyzing the influence mechanism of non-uniform strain fields generated by holes on crack propagation behavior. Hole defects can lead to non-uniform strain distribution under the impact load, thereby influencing crack propagation behavior. In this paper, 2D-DIC technology was employed to examine the effects of holes of varying sizes and loading rates on crack dynamics in PMMA materials, aiming to elucidate detailed knowledge into the characteristics of crack propagation under complex strain fields. Through DIC analyses, the dynamic evolution of strain fields around the crack tip and hole periphery could be precisely captured, enabling tracking of crack propagation behavior including crack propagation velocity, crack propagation path, and crack deflection angle. It is concluded that the non-uniform strain zones generated by holes exert both inhibitory and attracting effects on crack growth. The influence of non-uniform strain zones on crack propagation increases with the elevation of loading rate and hole size. However, as the loading rate increases, the kinetic energy of the crack itself also increases, necessitating sufficiently large hole sizes to effectively influence crack propagation. Overall, this study provides a detailed experimental explanation of the effects of holes on cracks, which will aid engineers in maximizing the positive impact of holes on material performance and their application in the design of microstructure materials. [ABSTRACT FROM AUTHOR]

• Clarified the structural failure patterns and mechanisms of plain concrete linings under different loading paths. • Revealed the three-dimensional ultrasonic characteristics of lining structures in various damage states. • Developed a predictive method for bearing capacity across different crack propagation stages. The state of tunnel lining structures plays a crucial role in determining safety and service quality throughout their serving life. Therefore, establishing a quantitative method for evaluating the bearing capacity of linings is crucial. Understanding the process and status of crack propagation is key to ensuring structural safety. The three-dimensional development of lining damage cracks is closely related to structural safety. Unveiling the spatial growth of these cracks and the evolution of structural performance is vital for an accurate assessment of lining safety. Key factors in crack propagation, along with non-destructive detection methods, serve as primary approaches for evaluating the safety condition. This paper explores the evolution law and evaluation model of the bearing capacity of plain concrete linings under different loading paths. The distribution of structural stiffness changes significantly under different boundary settings. Therefore, full-scale loading tests of lining components were conducted, designing two types of linings: one intact and the other with initial defects, to simulate the failure of plain concrete linings under diverse loading conditions. The results show that: (1) The damage development of linings exhibits clear staged evolution characteristics; (2) The spatial development of lining cracks can be divided into three stages; (3) There are significant differences in ultrasonic parameters at different stages. Consequently, a method for evaluating the local bearing capacity state of linings based on the coupling of crack characteristics and ultrasonic parameters is proposed; (4) This method is also applicable to linings with initial damage, where damage evolution follows similar stages. The findings provide theoretical guidance for predicting and preventing crack propagation in operational tunnel linings. [ABSTRACT FROM AUTHOR]

[Display omitted] • Experimental analysis of actual crack propagation paths reveals that cracks induce nonlinear vibrations in discs. • Reduced-order dynamic model developed for cracked discs, considering the breathing effect of cracks during vibration. • The maximum stress at the disc root gradually decreases, with the rate of decrease slowing down as the crack propagates. • The maximum stress at the crack tip decreases linearly as the crack propagates. Cracks in disc components can significantly reduce their service life. Most existing studies on cracked discs assume predefined crack paths (such as tangential or radial cracks) and rarely analyze the stress of the cracked disc during vibration. Additionally, dynamic models of the disc typically involve a significant number of degrees of freedom, resulting in substantial computational time when calculating the stress response. To address these issues, this paper conducts vibration experiments to determine the crack paths in discs and develops a reduced-order dynamic model of the disc with breathing crack based on shell theory. The proposed model in calculating stress is validated through comparison with the experimental results. Finally, the actual crack paths are introduced into the dynamic model, and the dynamic stress variation of the disc during crack propagation is studied by simulation and experiment. The results show that the crack in the disc exhibits the breathing effect during propagation, which induces nonlinear vibration of the disc. Moreover, as the crack propagates, the maximum stress at the disk root gradually decreases, and the decreasing rate becomes slower and slower. In contrast, the maximum stress at the crack tip decreases linearly. [ABSTRACT FROM AUTHOR]

Unexpected system failures are costly and preventing them is crucial to guarantee availability and reliability of complex assets. Prognostics help to increase the availability and reliability. However, existing methods have their limitations: physics-based methods have limited adaptivity to specific applications, while data-driven methods heavily rely on (scarcely available) historical data, which reduces their prognostic performance. Especially when operational conditions change over time, existing methods do not always perform well. As a solution, this paper proposes a new framework in which loads are explicitly incorporated in a prognostic method based on Bayesian filtering. This is accomplished by zooming in on the failure mechanism on the material level, thus establishing a quantitative relation between usage and degradation rates. This relation is updated using a Bayesian filter and measured loads, but also allows accurate degradation predictions by considering future (changing) loads. This enables decision support on either operational use or maintenance activities. The performance of the proposed load-controlled prognostic method is demonstrated in an atmospheric corrosion use case, based on a public real data set constructed from annual corrosion measurements on carbon steel specimens. The developed load-controlled particle filter (LCPF) is demonstrated to outperform a method based on a regular particle filter, a regression model and an ARIMA model for this specific scenario with changing operating conditions. The generalization of the framework is demonstrated by two additional conceptual case studies on crack propagation and seal wear. • A framework is proposed for maintenance decision-making in varying usage conditions. • The method showed good performance in a corrosion case study. • If load conditions change for longer periods, loads are essential prognostic input. • If load conditions vary frequently, loads are no required prognostic input. • Framework generalization is demonstrated on a crack growth and a wear case study. [ABSTRACT FROM AUTHOR]

Shattered rim, known as "wheel cancer", is a century-old problem that restricts the reliability of railway wheels. Crack propagation retardation of shattered rim in the railway wheel was investigated in this paper. First, a full-scale wheel-rail bench test rig was used to conduct wheel-rail tests on a wheelset with an interior rim crack taken from service. The interior rim crack did not propagate over the entire 50000 km distance. Cracks initiated from the two through-rim defects and propagated at a slow speed. Then, equivalent tests were conducted to investigate crack propagation behavior of the shattered rim. The crack growth rate increased with the increase of crack length for the specimen under tension–torsion loading, while that decreased with the increase of crack length for the specimens under pure-torsion and compression-tension loading. The crack propagation retardation is attributed to the compression and friction of the crack surfaces. Finally, a model was developed to describe crack propagation retardation in shattered rims. The effective stress intensity factor predicted by the model initially increases and then gradually decreases. The shattered rim has a critical size at different depths from the tread under constant amplitude load. The predicted critical size decreases with the increase of the depth. [ABSTRACT FROM AUTHOR]

The 2195 Al–Li alloy is widely used in the aerospace field, where using friction stir welding technology can achieve lightweight and reduced wear designs for components. Fatigue failure, as one of the main modes of damage affecting the life and reliability of structural components, is particularly significant. This paper thoroughly explores the differences in microstructure and fatigue crack propagation behavior between the advancing side and retreating side of the friction stir welded joint in different sampling directions, providing a theoretical basis for enhancing the fatigue performance of friction stir welds. Characterization of the microstructure of the samples was performed using Electron Backscatter Diffraction (EBSD) and X-Ray Diffraction (XRD), and the fatigue properties were investigated using fatigue crack propagation rate curves and crack growth rate curves. The results indicate that the longitudinal base material grains tend to a fibrous structure, while the axial base material grains are distributed in a lamellar fashion. Compared to the advancing side of weld nugget zone, the retreating side of weld nugget zone has significantly reduced grain size and texture types. The fatigue performance of the retreating side of the weld nugget zone is superior to that of the advancing side, and the circumferential welds outperform the longitudinal welds in terms of fatigue performance. • Under the effects of dislocation strengthening and fine-grain strengthening, the yield strength increment in the advancing side of the friction stir weld nugget is smaller than that in the retreating side. The advancing side exhibits intense plastic deformation and more types of textures compared to the retreating side, but the texture strength is lower. • Under the same sampling direction and fatigue load conditions, the fatigue life of the retreating side of the weld nugget is longer than that of the advancing side. Under the same fatigue load conditions, the L-T fatigue life is longer than the T-L fatigue life. • The T-L oriented samples exhibit more pronounced transgranular fracture characteristics, while the L-T oriented samples show more pronounced intergranular fracture characteristics. [ABSTRACT FROM AUTHOR]

In this paper, ultrasonic impact treatment (UIT) and laser cladding TF550 alloy was combined to achieve the purpose of refining grains and improving oxidation performance. The results showed that after UIT, the porosity decreased from 8.47 % to 3.59 %, grain size of the equiaxed grain at the top area decreased to about 18 μm, but the width of the equiaxed grain region increased. The number of equiaxed grains at the bottom of the ultrasonic impact specimen increased, and the middle part was still columnar grain structure. The average size was about 88μm, which was about 66 % lower than that of the unimpacted specimen. In addition, compared with the sample without UIT, the ablation pit area of the sample with UIT decreased by 35.99 %, 31.58 % and 34.71 %, respectively. The content of O element decreased to about 50 %, and the content of Ti, V and Cr elements increased as a whole. The oxidation degree of the sample surface decreased and the ablation resistance increased. And the oxidation weight gain was lower after UIT, which was 7.5 % lower than that of the unimpacted sample. The thickness of the oxide film was reduced and the antioxidant properties were enhanced. • After UIT, the height of the cladding layer is reduced, the microstructure is refined. • After UIT, the ablation crack propagation of the sample is reduced, burn resistance performance is improved. • After UIT, the oxidation rate of the sample decreased, high temperature oxidation resistance was improved. [ABSTRACT FROM AUTHOR]

In this work we propose a novel peridynamic topology optimization formulation to improve fracture resistance. The main strength of peridynamics is based on the straightforwardness in which crack propagation can be predicted, as a natural part of a peridynamic numerical simulation. This property can be leveraged in a topology optimization framework, in order to obtain fracture resistance designs. Hence, we formulate a meshfree density-based nonlocal topology optimization framework using a bond-based peridynamic formulation. As it is demonstrated in this paper, the classical compliance based solutions are far from optimal in terms of fracture resistance and the designs obtained with the proposed formulation can provide fracture resistant solutions while only reducing slightly the structural stiffness. The proposed formulation is presented along with all the details of the sensitivity analysis and additional numerical aspects of the implementation. Moreover, the peridynamic material model used is presented along with its numerical implementation. Numerical examples demonstrate the accuracy of the computed sensitivities and illustrate the impact and effectiveness of the presented formulation. A thorough study of the optimization parameters is presented and various optimization convergence studies are taken in order to obtain a stable optimization process. All the results are compared to classical compliance minimization designs to illustrate the advantages and capabilities of the proposed framework. [ABSTRACT FROM AUTHOR]

Rockbolt is a common support method in underground tunnel engineering, used to enhance the strength of rock mass and improve the stability of surrounding rock. In this paper, the three-dimensional (3D) FDEM method is employed to study the influence of rockbolts on the deformation and crack evolution of surrounding rock in tunnel engineering. Firstly, the CUDA-based GPU parallel 3D FDEM algorithm is briefly described, and its calculation process is summarized. At the same time, the contact search grid partitioning algorithm is optimized to address the problem of program crashes caused by grid memory overflow. Subsequently, a new rockbolt characterization method suitable for 3D FDEM algorithm is proposed, and the calculation process and constitutive equation of the new rockbolt algorithm are described in detail. The accuracy and feasibility of the new rockbolt algorithm are successfully verified by the pull-out test model and the three-point test model. Next, the numerical simulation of TBM tunnel project is carried out to study the deformation behavior and crack evolution path of surrounding rock after tunnel excavation. The results show that the vertical displacement of surrounding rock at the top of rockbolt tunnel model is greatly reduced, the crack development process is slowed down and the number of cracks is reduced. Finally, the influence of rockbolt row spacing and length on the deformation and crack propagation of surrounding rock is discussed. It is found that as the spacing decreases or the rockbolt length increases, the number of cracks in the surrounding rock gradually decreases, and the vertical displacement at the top of the surrounding rock gradually reduces. This study is helpful to understand the influence of rockbolts on the stability of surrounding rock, especially in tunnel engineering, it is of great significance for adjusting the rockbolt scheme under adverse geological conditions. [ABSTRACT FROM AUTHOR]

Red clay is prone to cracking in desiccating environments, with criss-cross cracks compromising soil structures and inducing slope instability. Under natural hygrothermal conditions, a desiccation test of red clay slurry was performed with a self-made device and digital image correlation (DIC) technology to study the crack evolution and quantitatively analyse the relationships between moisture content, displacement, strain and cracks. The results showed that cracks were usually initiated by subdividing and intersecting with other cracks at right angles. The main cracks were initiated first and had the longest duration; the stabilised main cracks were longer and wider than secondary cracks. DIC technology was used to monitor crack evolution dynamically. Based on the areas of strain concentration, the locations of early-initiated cracks and propagation trends could be preliminarily predicted. The failure strain in cracking was related to the moisture content, while crack evolution was related to the Atterberg limits of the red clay. The soil shrinkage exhibited anisotropic behaviour, with greater vertical shrinkage at the soil clod centre compared with the edges. In contrast, the horizontal displacement and maximum principal strain at the soil clod centre were smaller than those at the edges. These findings contribute to providing guidance for formulating engineering geological hazard control measures. [ABSTRACT FROM AUTHOR]

This study primarily investigates the rock fracture mechanism of bottom cushion layer blasting and explores the effects of the bottom cushion layer on rock fragmentation. It involves analyses of the evolution patterns of blasting stress, characteristics of crack distribution, and rock fracture features in the specimens. First, blasting model experiments were carried out using the dynamic caustics principle to investigate the influence of bottom cushion layers and initiation methods on the integrity of the bottom rock mass. The experimental results indicate that the combined use of bottom cushion layers and inverse initiation effectively protects the integrity of the bottom rock mass. Subsequently, the process of stress wave propagation and dynamic crack propagation in rocks was simulated using the continuum–discontinuum element method (CDEM) and the Landau explosion source model, with varying thicknesses of bottom cushion layers. The numerical simulation results indicate that with increasing cushion thickness, the absorption of energy generated by the explosion becomes more pronounced, resulting in fewer cracks in the bottom rock mass. This illustrates the positive role of the cushion layer in protecting the integrity of the bottom rock mass. [ABSTRACT FROM AUTHOR]

Cyclic failure problems in layered ductile iron are evident in a wide range of elements in transportation and mining equipment and depend on production technology and operating conditions. The aim of this study was to analyze the effect of residual stresses on the behavior of cyclic and static failure. The stress intensity factor, crack initiation, propagation patterns, static tension diagrams, and fracture behavior of compact tension (CT) specimens were determined. The samples used in this study were made from base cast iron, some of which were subjected to a special localized heat treatment. Experimental and analytical methods were used to conduct this study. The experiments were performed using original testing methods that adhered to the American Society for Testing and Materials (ASTM) regulations. The deformations of the partially heat-treated specimens due to residual stresses were determined using the grid method. The limiting stress intensity coefficient and the failure threshold under cyclic loading were determined in accordance with ASTM recommendations for various crack depths and openings. The results show that the heat treatment process readily produces residual stresses of different magnitudes, stress redistribution, different structures, and layer positions. Residual stresses affect the crack initiation and propagation. The stress intensity factor depends on the depth of the crack, the position of the layers, and the magnitude of the residual stresses. [ABSTRACT FROM AUTHOR]

Friction stir spot welding (FSSW) technology relies on the generation of frictional heat during the rotation of the welding tool in contact with the workpiece as well as the stirring effect of the tool pin to produce solid-state spot joints, especially for lightweight materials. Although FSSW offers significant advantages over traditional fusion welding, the oxidation of the interfacial bond line remains one of the most challenging issues, affecting the quality and strength of the joint under both static and cyclic loading conditions. In this experimental study, inert argon gas was employed to surround the joint, aiming to prevent or minimize the formation of the interfacial oxides. Two welding processes were conducted with identical welding process parameters and welding tool geometry: the conventional process and another that employs an inert gas cover. Micrographs of as-welded specimens were analyzed using a computerized optical microscope to characterize the interfacial bond lines and an energy-dispersive spectroscope (EDS) was used to quantify the interfacial oxides. Specimens from both welding conditions were tested under static and cyclic loads to investigate the static and fatigue behaviors, respectively. The fatigue tested specimens were examined under different load levels to investigate the fatigue crack behavior and the modes of failure at low-cycle and high-cycle fatigue conditions. The optical micrographs showed significant improvement in bond line morphologies (33% enlarged fully bonded area) and both static and fatigue strengths (35% reduced partially bonded area) when the inert gas cover was used. The EDS analysis revealed a maximum reduction of the interfacial oxide of 41% in the bond line achieved in the argon-surrounded joints compared to specimens of the conventional welding process. Accordingly, an improvement of 14% in the static strength was reached, along with 60% and 26% in the fatigue strengths at low- and high-cycle fatigue conditions, respectively. [ABSTRACT FROM AUTHOR]

The purpose of this study is to clarify the effect of deformation during crack growth on the residual stress of sheared edges. By measuring the residual stress in the thickness direction of the sheared edge, the residual stress of the sheared edge on the scrap side was found to be larger than that on the product side. It was also found that this residual stress difference depends on the shearing clearance, and the difference becomes smaller with greater clearance. By experiments and numerical analysis, it was clarified that the difference in residual stress between the two sheared edges is due to the deformation caused by the Mode II growth of cracks. When the clearance is large, the growth of Mode I cracks increases and that of Mode II decreases, so it is considered that the stress difference between both edges becomes smaller. [ABSTRACT FROM AUTHOR]

To circumvent the numerous deficiencies inherent to water-based fracturing fluids and the associated greenhouse effect, CO2 fracturing fluids are employed as a novel reservoir working fluid for reservoir reconstruction in unconventional oil fields. Herein, a mathematical model of CO2 fracturing crack propagation based on seepage–stress–damage coupling was constructed for analysing the effects of different drilling fluid components and reservoir parameters on the crack propagation behaviour of low permeability reservoirs. Additionally, the fracture expansion mechanism of CO2 fracturing fluid on low permeability reservoirs was elucidated through mechanical and chemical analysis. The findings demonstrated that CO2 fracturing fluid can effectively facilitate the expansion of cracks in low-permeability reservoirs, and thickener content, reservoir pressure, and reservoir parameters were identified as influencing factors in the expansion of reservoir cracks and the evolution of rock damage. The 5% CO2 thickener can increase the apparent viscosity and fracture length of CO2 fracturing fluid to 5.12 mPa·s and 58 m, respectively, which are significantly higher than the fluid viscosity (0.04 mPa·s) and expansion capacity (13 m) of pure CO2 fracturing fluid. Furthermore, various other factors significantly influence the fracture expansion capacity of CO2 fracturing fluid, thereby offering technical support for fracture propagation in low-permeability reservoirs and enhancing oil recovery. [ABSTRACT FROM AUTHOR]

Abstract The deck-charge structure, also known as axially decoupled charge structure, has been widely applied in open-pit rock excavation to improve blasting performance. However, the relationships between blast-induced fragmentation and deck-charge structures remain not well understood. This paper aims to experimentally investigate the influences of deck ratio, deck position and deck material on blast-induced fragmentation. Concrete specimens with dimension of 400 × 400 × 200 mm3 were used for small-scale single-hole blasting experiments. The dynamic fracturing process under blast loading was recorded with a high-speed camera. Displacement and strain fields were analyzed employing a 3D digital image correlation (DIC) system, and the fragment size distribution (FSD) was quantified through ImageJ, an advanced image-processing tool. The borehole wall pressure (BWP) was monitored through the embedded PVDF gauges within the test specimens. The results indicate that during deck charge blasting, the host concrete undergoes three phases: crushing, further crushing and fracturing, and radial crack development. Fragmentation performance improves within an optimal air-deck ratio range, while excessive ratios lead to poorer fragmentation compared to fully coupled charge blasting. The center deck charge yields the superior fragmentation, followed by double-ends and top deck charges. Water-deck charge generates finer fragmentation than air deck and polyethylene (PE) deck charges. Expanded polystyrene (EPS) deck charge does not facilitate fragmentation but may reduce vibration and limit damage to the remaining rock mass. Based on experiment results, production blasts with fully coupled charge, center air-deck charge and center water-deck charge were performed in an open-pit mine. These field tests revealed that the proposed center deck charge blasting reduced median fragment size by at least 15%, with the center water-deck charge demonstrating superior fragmentation by maximizing explosive energy utilization for rock fracturing.