Fracture Experiments Research Articles

From quasi-static to dynamic: Experimental study of mechanical and fracture behaviour of epoxy resin

Epoxy polymers are extensively used in various engineering applications such as aerospace, defence, sports, automotive etc. This article focuses on the in-depth mechanical characterisation of EPOFINE®-1564, a Bisphenol-A-based liquid epoxy resin under various loading conditions. To predict the tensile and compressive behaviour of the representative epoxy resin, quasi-static experiments were performed in the range of 10−4 to 10−2s−1 on Universal testing machine (UTM) while the dynamic experiments were conducted using Split Hopkinson Pressure Bar (SHPB) for high strain rates (1136–2833 s−1). In this study, 3D Digital Image Correlation (DIC) was also used to evaluate the specimen's full-field displacement profile over a wide range of strain rates. Analysis of various mechanical properties such as elastic modulus, yield strength, and ultimate strength, revealed that the epoxy polymer is strain rate dependent within the considered strain rate range. For understanding the fracture behaviour, three-point bend (TPB) experiments were also carried out for both quasi-static (1–10 mm/min) as well as dynamic (10–15 m s-1) regimes. Dynamic fracture experiments were performed using the modified Hopkinson Pressure Bar (MHPB). The fracture toughness was determined through load vs crack mouth opening displacement (CMOD). Fracture toughness was found to increase with the displacement rate due to the significant plastic deformation under quasi-static range. Conversely, it was found to decrease under dynamic loading because of absence of plastic deformation resulting in brittle fracture. The fracture surface of the specimen was examined through a high magnification digital microscope.

Analysis of near-well hydraulic fracture propagation behavior in inhomogeneous deep-sea hydrate-bearing-sediments

The hydrate reservoirs exhibit significant inhomogeneity due to the presence of various hydrate types, potentially impacting the effectiveness of hydraulic fracturing. The investigation of the relationship between hydraulic fracture extension patterns and pure hydrate blocks for varying conditions is highly valuable. The extended finite element method (XFEM) is applied to reveal the influence mechanism of hydrate heterogeneity on fracture propagation law. First, compared with the results of the fracturing experiments in hydrate-bearing clayey silt sediments, the accuracy of the method is verified. Subsequently, a model for fracturing near-well in deep-sea inhomogeneous hydrate-bearing-sediments is established, containing sedimentary matrix and pure hydrate blocks. The effects of disseminated hydrate saturation, injection rate, horizontal stress difference and the distribution location of pure hydrate blocks on the fracture extension path are investigated. Due to the pure hydrate is much more brittle, most hydraulic fractures, once encountered with it, choose to bypass. If the fracture is unable to bypass the pure hydrate block, the fracture appears to arrest and penetrate. The seafloor sediment matrix is characterized by its loose nature, and a continuous increase in the injection rate may result in the competing development of the fractures in both length and width directions.

Superior fracture resistance and topology-induced intrinsic toughening mechanism in 3D shell-based lattice metamaterials.

Lattice metamaterials have demonstrated remarkable mechanical properties at low densities. As these architected materials advance toward real-world applications, their tolerance for damage and defects becomes a limiting factor. However, a thorough understanding of the fracture resistance and fracture mechanisms in lattice metamaterials, particularly for the emerging shell-based lattices, has remained elusive. Here, using a combination of in situ fracture experiments and finite element simulations, we show that shell-based lattice metamaterials with Schwarz P minimal surface topology exhibit superior fracture resistance compared to conventional octet truss lattices, with average improvements in initiation toughness up to 150%. This superiority is attributed to the unique shell-based architecture that enables more efficient load transfer and higher energy dissipation through material damage, structural plasticity, and material plasticity. Our study reveals a topology-induced intrinsic toughening mechanism in shell-based lattices and highlights these architectures as a superior design route for creating lightweight and high-performance mechanical metamaterials.

Strain rate and temperature‐dependent shear fracture mechanism of high‐energy propellant/liner interface zone

AbstractThe shear fracture of the high‐energy propellant/liner interface zone occurs in many application cases of solid rocket motors (SRMs). The shear fracture experiment development is thus a crucial issue. Here we aim to study the shear fracture mechanism of the interface zone under varying strain rates and temperatures. Shear experiments are carried out using self‐made specimens containing prefabricated cracks. Force‐displacement curves, experimental images, and fracture surface topographies are obtained at different strain rates and temperatures. The strain field of the specimen surface is analyzed using the digital image correlation (DIC) method. Additionally, the fracture surface topographies are analyzed using ImageJ software. The results show that the shear mechanical properties of the interface zone are strongly dependent on strain rates and temperatures. Specifically, the shear fracture strength and failure displacement exhibit a decrease with increasing temperature and an increase with increasing strain rate. The DIC analysis shows that the fracture strain of the interface zone typically ranges from 0.4 to 0.6. The analysis of the fracture surface topographies reveals that the shear fracture modes are predominantly mixed fractures, including propellant/liner interface fractures and propellant cohesive fractures. Since the propellant/liner interface is more sensitive to strain rate and the propellant is more sensitive to temperature, the propellant/liner interface fracture ratio increases from 1.99 % to 60.26 % with decreasing strain rate and temperature. The results show that the experimental method can effectively be used to study the shear fracture mechanism of the high‐energy propellant/liner interface zone.

Stimulation of tight basalt reservoirs using supercritical carbon dioxide: Implications for large-scale carbon sequestration

Although supercritical carbon dioxide (SC-CO2) fracturing shows tremendous potential for maximizing injection efficiency and enhancing storage volumes, few investigations have been reported on the SC-CO2 fracturing characteristics of tight basalts and the reactions between fractured basalt and SC-CO2. In this study, hydraulic fracturing experiments were conducted on cylindrical basalt specimens using water and SC-CO2 as fracturing fluids. Geometric parameters were proposed to characterize the fracture morphologies based on the three-dimensional (3D) reconstructions of fracture networks. The rock slices with induced fractures after SC-CO2 fracturing were then processed for fluid (deionized water/SC-CO2)-basalt reaction tests. The experimental results demonstrate that SC-CO2 fracturing can induce complex and tortuous fractures with spatially dispersed morphologies. Other fracturing behaviors accompanying the acoustic emission (AE) signals and pump pressure changes show that the AE activity responds almost simultaneously to variation in the pump pressure. The fractured basalt blocks exposed to both SC-CO2 and water exhibit rough and uneven surfaces, along with decreased intensities in the element peaks, indicating that solubility trapping predominantly occurs during the early injection stage. The above findings provide a laboratory research basis for understanding the fracturing and sequestration issues related to effective CO2 utilization.

Real-time monitoring of rock fracture by true triaxial test using fiber-optic strain monitoring in adjacent wells

The real-time monitoring of fracture propagation during hydraulic fracturing is crucial for obtaining a deeper understanding of fracture morphology and optimizing hydraulic fracture designs. Accurate measurements of key fracture parameters, such as the fracture height and width, are particularly important to ensure efficient oilfield development and precise fracture diagnosis. This study utilized the optical frequency domain reflectometer (OFDR) technique in physical simulation experiments to monitor fractures during indoor true triaxial hydraulic fracturing experiments. The results indicate that the distributed fiber optic strain monitoring technology can efficiently capture the initiation and expansion of fractures. In horizontal well monitoring, the fiber strain waterfall plot can be used to interpret the fracture width, initiation location, and expansion speed. The fiber response can be divided into three stages: strain contraction convergence, strain band formation, and postshutdown strain rate reversal. When the fracture does not contact the fiber, a dual peak strain phenomenon occurs in the fiber and gradually converges as the fracture approaches. During vertical well monitoring in adjacent wells, within the effective monitoring range of the fiber, the axial strain produced by the fiber can represent the fracture height with an accuracy of 95.6% relative to the actual fracture height. This study provides a new perspective on real-time fracture monitoring. The response patterns of fiber-induced strain due to fractures can help us better understand and assess the dynamic fracture behavior, offering significant value for the optimization of oilfield development and fracture diagnostic techniques.

Rate dependent C* fracture parameter using the optimized wedge-split test geometry and vision-based automated crack tip detection

Typical monotonic load-line displacement (LLD) control and crack mouth opening displacement (CMOD) control cracking tests are limited to singular loading rates and testing temperatures. These experimental protocols are not designed to derive a fundamental fracture parameter capable of relating to the viscoelastic property and cracking behavior of asphalt concrete (AC). On the other hand, a multi-rate LLD-control monotonic fracture experiment is capable of capturing the viscoelastic cracking behavior of AC by providing the rate-dependent fundamental C* fracture parameter as an output. Crack length and crack speed parameters are combined with reaction loads to calculate the rate-dependent C* parameter. The current C* experiment protocol implements manual processing of video images and exhibits high variability. The study aims to optimize the wedge-split geometry and improve the C* fracture parameter calculation protocol by applying an automated vision-based crack detection system and recording the crack growth path, considering the horizontal and vertical movement of the crack tip with higher accuracy. The three notch lengths (5, 15, and 30 mm) were evaluated. Plant and laboratory-produced mixes with varying stiffness and fracture characteristics were included in the testing program. An optimized notch length for the test geometry was determined based on the on-specimen strain field observed using the digital image correlation (DIC) technique and crack path analysis. The optimum notch length was found to be 15 mm due to consistent strain localization at the crack tip and less crack deviation in the horizontal direction. The main contribution of this paper is the proposed vision-based crack path detection method, which enables measuring the crack path's true crack length and maximum horizontal deviation. The developed protocol and optimization of the testing geometry led to a significant improvement of the existing C* testing protocol, resulting in higher data quality and consistent results. The proposed protocol was validated using three comparable and distinctively different lab-produced mixtures. The results show that the C* experiment effectively differentiated between the mixes based on crack speed and the C* parameter.

Stress transfer law in laboratory hydraulic fracturing experiments

During the true triaxial hydraulic fracturing experiments, the compression stress applied to the specimen surface cannot be transferred to the interior immediately, resulting in inconsistency with in-situ stress conditions. To quantitatively analyze the stress transfer process from the surface to the interior of the specimen, an experimental method for monitoring the inside stress was proposed based on Fiber Bragg Grating (FBG) sensing technique, based on which the true triaxial stress loading experiments were conducted on a concrete-like specimen of 30 cm × 30 cm × 30 cm. The results show that the stresses inside the specimen require a certain loading time to reach the uniform state. The loading time required for stress transfer from the surface to the interior of the specimen decreases with the increase of compression stresses. The stress transfer process in rock materials is determined by creep. The closure of microcracks results in stress redistribution inside the specimen during creep. Moreover, a 3-D Burgers model is modified to describe the stress transfer process. Finally, the stress transfer phenomenon during hydraulic fracturing was verified by coal fracturing experiments. This study can help to understand the stress transfer mechanism, providing guidance for standardizing the laboratory simulation of in-situ stress.

Intrinsic fracture toughness of a soft viscoelastic adhesive

The fracture toughness of inelastic materials consists of an intrinsic component associated with the crack tip fracture process and a dissipative component due to bulk dissipation. Experimental characterization of the intrinsic component of fracture toughness is important for understanding the fracture mechanism and predictive modeling of the fracture behavior. Here we present an experimental study on the intrinsic toughness of a soft viscoelastic adhesive. We first obtained full-field and full-history data of the displacement and deformation fields in pure shear fracture tests using a particle tracking method. By combining these data with a nonlinear constitutive model, we extracted the intrinsic toughness through an energy balance analysis. A two-stage crack propagation behavior was observed in our fracture experiments: under monotonic loading the crack first underwent a slow propagation stage and then suddenly entered a fast propagation stage. We found that the intrinsic toughness was highly scattered for the slow propagation stage, but remained consistent for the fast propagation stage. Further examination of the fracture surface and the onset of fast propagation revealed that transition from the slow to the fast propagation stage was governed by the applied stretch and was likely due to a change in the crack tip fracture process.

Effects of Notches on Breakdown Pressures and Fracture Evolution in Hydraulic Fracturing

AbstractSustainable ore extraction in cave mining heavily relies on the effective fragmentation or caveability of the orebody. Since cave mining offers substantial benefits, it has gained popularity after preconditioning was introduced to help improve caveability. Therefore, hydraulic fracturing serves as a vital technique for risk management and cave stimulation. The increased rock competency and high stress levels in the rock mass around the orebody significantly influence fracturing and, thus, cavability processes. In order to improve the çefficiency of preconditioning by hydraulic fracturing to specific parts of the non-caving or poorly caving formations, the use of notches as artificial flaws offers an influence on the directionality of fracture propagation; this approach also has the potential to decrease the necessary breakdown pressures, thereby lifting limitations on the design and mechanical capabilities of fracturing campaigns and reducing required breakdown pressures, which could improve hydraulic fracturing capabilities. In this study, we studied the effects of notches on hydraulic fracturing performance under varying stress conditions. A number of hydraulic fracturing experiments were conducted using different notch quantities and spacings. Notches were created parallel to the axis of confining stress, and specimens were then subjected to constant axial loads of 40 MPa under varying confining pressures ranging from 5 to 40 MPa. A supplementary 3-D discrete element method using 3DEC was performed, and the results were compared with the hydraulic fracturing experiment. The 3DEC models incorporated Darcy's Law to describe fluid flow through fractures, and the Mohr–Coulomb softening yield criterion was used to simulate failures on predefined surfaces, providing a thorough hydro-mechanical coupled solution. We found that introducing notches can effectively reduce the pressures needed for fracture initiation and growth. Moreover, with appropriate spacing, fracture direction can be controlled. This knowledge, combined with the use of numerical modelling, has advanced our understanding of fracture behaviour and the influence of notches on propagation paths under different stress regimes. These findings could potentially revolutionise the field of hydraulic fracturing, making it more efficient and sustainable.

A generalized Rivlin–Thomas theory for nucleation of cracks in viscoelastic materials

Recent fracture experiments using the Rivlin–Thomas pure-shear geometry in rubbery viscoelastic materials have suggested nucleation of cracks at a critical stretch, independent on loading rate. For linear material using the rate-independent cohesive model theory, the critical elongation between grips (in a quite general testing geometry) at nucleation is instead monotonically decreasing with rate of up to the square root of the ratio between the instantaneous and relaxed elastic modulus of the material. Shrimali & Lopez-Pamies have made the assumption of a constant critical stretch to develop a theory which contrasts therefore with classical models. However, we further generalize the Rivlin–Thomas theory by assuming an arbitrary relation between nucleation stretch and loading rate, which therefore includes both models as limit cases. We present a simple case of a Double Cantilever Beam (DCB) geometry with linear standard materials, to show an analytical example.

A Griffith description of fracture for non-monotonic loading with application to fatigue

With the fundamental objective of establishing the universality of the Griffith energy competition to describe the growth of large cracks in solids not just under monotonic but under general loading conditions, this paper puts forth a generalization of the classical Griffith energy competition in nominally elastic brittle materials to arbitrary non-monotonic quasistatic loading conditions, which include monotonic and cyclic loadings as special cases. Centered around experimental observations, the idea consists in: (i) viewing the critical energy release rate Gcnot as a material constant but rather as a material function of both space X and time t, (ii) one that decreases in value as the loading progresses, this solely within a small region Ωℓ(t) around crack fronts, with the characteristic size ℓ of such a region being material specific, and (iii) with the decrease in value of Gc being dependent on the history of the elastic fields in Ωℓ(t). By construction, the proposed Griffith formulation is able to describe any Paris-law behavior of the growth of large cracks in nominally elastic brittle materials for the limiting case when the loading is cyclic. For the opposite limiting case when the loading is monotonic, the formulation reduces to the classical Griffith formulation. Additional properties of the proposed formulation are illustrated via a parametric analysis and direct comparisons with representative fatigue fracture experiments on a ceramic, mortar, and PMMA.

Prediction of concrete cracking behavior under different strain rates based on the boundary effects model

Predicting the cracking behavior of concrete under different strain rates through fracture parameters has been a longstanding topic of interest. In this study, the effect of concrete strength and strain rate on the fracture toughness and initial fracture energy for three-point bending notched beams is investigated by boundary effect model (BEM). With the help of BEM, only a series of basic parameters (such as tensile strength, maximum aggregate size and specimen size) are used in the process of calculating the fracture toughness and initial fracture energy. The cumbersome concrete fracture experiment is avoided in this model. The initial fracture toughness and unstable fracture toughness, predicted by BEM are agreed with the experimental results in the literature. The results demonstrate that BEM is valid for predicting the fracture toughness of different concrete strengths, even at increased strain rates. As the loading strain rate increases, the initial fracture toughness of different concrete strength shows a slight growth with increasing loading strain rate, which indicates that the concrete needs more energy to reach the cracking condition.

Experimental and simulation study on quasi-static and dynamic fracture toughness of 2A12-T4 aluminum alloy using CTS specimen

Based on the study of dynamic fracture toughness of mixed mode I/II fracture crack, using compact tensile shear (CTS) specimen and the method of split Hopkinson tensile bar (SHTB) combined with special fixture, which complete the experiments of complex fracture modes of 2A12-T4 aluminum alloy material under quasi-static and dynamic tensile tests. By combining the results of finite element simulation with experimental–numerical method, the feasibility of Richard’s theory formula in dynamic fracture experiment is discussed. The variation law of fracture toughness under quasi-static and dynamic complex fracture under mixed-mode was analyzed by finite element simulation and experiment. The results show that, in the process of quasi-static and dynamic fracture, the fracture toughness of CTS specimen under mixed mode I/II crack loading is the highest. The conclusion is proved by Richard theorical formula and experimental–numerical methods jointly. When the specimen is subjected to pure mode I fracture, the quasi-static fracture toughness is consistent with that is in condition of dynamic experiment. However, when the specimen is subjected to mode II and mixed mode I/II fracture, the dynamic fracture toughness changes greatly compared with the quasi-static fracture toughness. In addition, in the dynamic fracture experiment, the dynamic fracture toughness of mixed mode I/II depends on the initiation time, and the quasi-static fracture criterion is no longer applicable.

Influence of specimen configuration on mode I and mode II fracture toughness of sandstone

In order to investigate the impact of cracked specimen configurations on the apparent fracture toughness of the green sandstone, a series of fracture experiments were conducted utilizing four distinct types of specimens. The experimental results show that the cracked straight-through Brazilian disk (CSTBD) specimens observed the minimum mode I fracture toughness KIC and the maximum mode II fracture toughness KIIC. The KIC measured by notched semi-circular bending (NSCB) specimens is nearly twice that of CSTBD specimens, while the KIIC is only 77% of CSTBD specimens. It indicates that both the specimen configurations and loading conditions are significant factors influencing the apparent fracture toughness, which may be attributed to the different T-stress for different specimens. Furthermore, several fracture criteria were employed to evaluate the experimental results. Simultaneously, a theoretical framework based on the generalized maximum tangential strain (GMTSN) criterion was proposed to investigate the impact of T-stress on apparent fracture toughness. The results indicate that positive T-stress can improve the KIC, while negative T-stress can decrease the KIC. In addition, we also found that the dependence of KIIC on T-stress is exactly opposite to that of KIC. The study provides theoretical references for systematically evaluating experimental results and selecting specimens reasonably.

Experimental Investigation of Low-Frequency Distributed Acoustic Sensor Responses to Two Parallel Propagating Fractures.

Low-frequency distributed acoustic sensing (LF-DAS) is a diagnostic tool for hydraulic fracture propagation with far-field monitoring using fiber optic sensors. LF-DAS senses strain rate variation caused by stress field change due to fracture propagation. Fiber optic sensors are installed in the monitoring wells in the vicinity of a fractured well. From the strain responses, fracture propagation can be evaluated. To understand subsurface conditions with multiple propagating fractures, a laboratory-scale hydraulic fracture experiment was performed simulating the LF-DAS response to fracture propagation with embedded distributed optical fiber strain sensors under these conditions. The experiment was performed using a transparent cube of epoxy with two parallel radial initial flaws centered in the cube. Fluid was injected into the sample to generate fractures along the initial flaws. The experiment used distributed high-definition fiber optic strain sensors with tight spatial resolutions. The sensors were embedded at two different locations on opposite sides of the initial flaws, serving as observation/monitoring locations. We also employed finite element modeling to numerically solve the linear elastic equations of equilibrium continuity and stress-strain relationships. The measured strains from the experiment were compared to simulation results from the finite element model. The experimentally derived strain and strain-rate waterfall plots from this study show the responses to both fractures propagating, while the fracture at the lower position took most of the fluid during the experiment. Interestingly, a fracture first began propagating from the upper flaw of the two flaws, but once the lower fracture was initiated, it grew much faster than the upper fracture. Both fibers were intercepted by the lower fracture, further verifying the strain signature as a fracture is approaching and intersecting an offset fiber.

Onset of dynamic void coalescence in porous ductile solids

This paper investigates void growth and coalescence in porous ductile solids under dynamic loading condition. A physical definition for the onset of void coalescence in porous ductile solids under dynamic loading is proposed. The onset is deemed to occur when the third invariant of the tensorial form of the Hill–Mandel condition attains a zero value. The definition allows for systematic investigations on the effects of dimensionless stress rate κ and stress state, defined by the stress triaxiality T and Lode parameter L, on the onset of void coalescence via micromechanical analyses. The analyses reveal that the critical macroscopic effective strain for the onset of void coalescence displays an increasing–decreasing transition trend as the dimensionless stress rate increases, for all levels of T and L considered. The macroscopic effective strain at the transition is identified as the “ductile–brittle” transition strain. The dimensionless stress rate at which the transition strain occurs is found to be relatively constant. A mapping in the κ−T space for L=−1, representative of a generalized uniaxial tension typical in spall fracture experiments, is established which depicts regions where coalescence and non-coalescence can take place, as well as the ductile–brittle regions demarcated by a ductile–brittle transition curve. The results also show that the critical void volume fraction and macroscopic effective strain at the onset of void coalescence are insensitive to inertia at high stress triaxialities at L=−1.

Fracture propagation law of temporary plugging and diversion fracturing in shale reservoirs under completion experiments of horizontal well with multi-cluster sand jetting perforation

This study conducted temporary plugging and diversion fracturing (TPDF) experiments using a true triaxial fracturing simulation system within a laboratory setting that replicated a lab-based horizontal well completion with multi-cluster sand jetting perforation. The effects of temporary plugging agent (TPA) particle size, TPA concentration, single-cluster perforation number and cluster number on plugging pressure, multi-fracture diversion pattern and distribution of TPAs were investigated. A combination of TPAs with small particle sizes within the fracture and large particle sizes within the segment is conducive to increasing the plugging pressure and promoting the diversion of multi-fractures. The addition of fibers can quickly achieve ultra-high pressure, but it may lead to longitudinal fractures extending along the wellbore. The temporary plugging peak pressure increases with an increase in the concentration of the TPA, reaching a peak at a certain concentration, and further increases do not significantly improve the temporary plugging peak pressure. The breaking pressure and temporary plugging peak pressure show a decreasing trend with an increase in single-cluster perforation number. A lower number of single-cluster perforations is beneficial for increasing the breaking pressure and temporary plugging peak pressure, and it has a more significant control on the propagation of multi-cluster fractures. A lower number of clusters is not conducive to increasing the total number and complexity of artificial fractures, while a higher number of clusters makes it difficult to achieve effective plugging. The TPAs within the fracture is mainly concentrated in the complex fracture areas, especially at the intersections of fractures. Meanwhile, the TPAs within the segment are primarily distributed near the perforation cluster apertures which initiated complex fractures.

Study on the Law of True Triaxial Hydraulic Fracturing by Acoustic Emission Monitoring.

Hydraulic fracturing generates fractures in a coal seam, which has been extensively used in coal mining and disaster management. To study the influences of water injection pressure and time on the propagation of hydraulic fracture, we conducted true triaxial hydraulic fracturing experiments under acoustic emission monitoring. Five briquette specimens were prepared by molding the mixture of coal powder, cement, river sand, and distilled water under 60 MPa to simulate the properties of coal seam. True triaxial loading was used to simulate the in situ stress environment of the coal seam. Hydraulic fracturing experiments on the test specimens were conducted under different water injection pressures and times. The following conclusions have been drawn. At the fixed injection time, increasing water injection pressure promotes the propagation of hydraulic fracture and the migration of water in the coal seam after the fractures are connected. The number of fractures increases from 3 to 8 as the water injected pressure increased from 3 to 9 MPa. Under the constant water injection pressure, the increase in longitudinal wave velocity in the test specimen decreases with the prolongation of water injection time. When the water reaches the action boundary of the water injection pressure, the water stops moving. At this moment, the water injection time has no effect on the longitudinal wave velocity anymore. The fracturing influence range can be increased by increasing the water injection pressure to produce a fracture network of a large radius with many fractures. Appropriately prolonging hydraulic fracturing time can ensure that the fracturing fluid fully moistens the coal seam and thus effectively reduces dust pollution.

Experimental investigation on macroscopic fracture and microstructural evolution of granite under high-temperature steam action

This study conducted simulated experiments on the thermal fracturing of granite under non-uniform stress conditions using the method of injecting high-temperature and high-pressure steam. Additionally, a comprehensive investigation was carried out on the thermal fracturing characteristics of granite after steam treatment, as well as the distribution patterns of cracks. The results show that: Firstly, the process of fracturing granite using high-temperature and high-pressure steam as a medium can be divided into five stages. The threshold temperature for thermal fracturing of granite is 260 ℃, at which point a large number of cracks develop or form interconnected networks. Secondly, under high-temperature conditions, the tensile strength of granite is greatly reduced. The temperature at which brittle fracture occurs in granite during the experiment was found to be 427 ℃ at a steam pressure of 10.6 MPa. Thirdly, under the influence of high-temperature and high-pressure steam, granite not only generates primary cracks along the direction perpendicular to the minimum principal stress but also produces a certain number of secondary cracks in other directions. The crack propagation direction can be determined from the velocity and permeability distribution maps of fractured granite. Finally, the fracture surface of granite exhibits significant brittle characteristics. The fracture morphology mainly includes transgranular and intergranular fractures. In the experiment, the fracture surface also showed fragmented and fatigue-induced fracture features. The fractal dimension of micro-morphological features can be used to assess the extent of thermal fracturing at different locations on the fracture surface. Through macroscopic fracturing experiments and comprehensive analysis of theory, wave velocity, and micro-morphology, the study obtained relevant crack propagation patterns and the formation of cracks in different directions. This is of practical significance in the formation of interconnected spatial fracture networks, thereby helping to increase the thermal exchange surface area of artificial reservoirs and improve the efficiency of geothermal exploitation.