Characteristics Of Microcracks Research Articles

Influence mechanism of initial mechanical damage on concrete permeability and tunnel lining leakage

The stress state is not effectively considered in existing studies when researching the permeability evolution of concrete with initial mechanical damages, causing ambiguity in the influence mechanism of initial mechanical damage on tunnel lining leakage. This deficiency can lead to significant uncertainty in predicting the probability and evaluating the consequences of tunnel leakage diseases, further affecting the formulation of relevant prevention strategies. Therefore, mechanical damage is induced to concrete specimens by subjecting them to certain stress levels, and triaxial compression seepage tests are subsequently conducted to study the influence of initial mechanical damage on permeability evolution and macrocracks. Furthermore, the relationship between microcrack characteristics and concrete permeability is studied, ultimately revealing the influence mechanism of initial mechanical damage on tunnel lining leakage. Research results indicate that the concrete permeability decreases first, becomes stable, and then continuously increases during testing, and is positively related to changes in horizontal deformation ratio. When the damage-inducing stress reaches 80% of the uniaxial compressive strength (UCS), the impact of initial mechanical damage on concrete permeability increases significantly. The increase in initial mechanical damage can lead to a significant rise in permeability, even when the crack volume is in a compacted state. Additionally, cracks on the surface of the specimen become clearly visible when the test terminates, once the damage-inducing stress reaches 85% UCS. Two factors contribute to the gradual increase in concrete permeability with the rise in initial damage-inducing stress. Firstly, microcracks inside the concrete gradually widen and propagate. Secondly, the microcracks resulting from the initial damage progressively enlarge due to water pressure during the triaxial compression seepage test. Influenced by the blockage of seepage channels, concrete permeability can occasionally decrease during testing. The accidental load induces the gradual propagation of microcracks inside the mechanically damaged concrete. Then, the rebound deformation of concrete after the removal of the accidental load causes the closed microcracks to reopen significantly, leading to an increase in permeability and subsequent tunnel lining water leakage.

Research on acoustic emission characteristics of metagabbros with different felsic development under splitting load

The acoustic emission (AE) characteristic signal can reveal the mechanical properties of rock materials and the development characteristics of internal microcracks. Rocks with different mineral development characteristics produce different AE signals during fracture. This study selected variable metagabbros with varying feldspathic development for AE tests under splitting load. The results demonstrated that the characteristics of AE ringing counts during the Brazilian fracture of metagabbro were closely correlated with the content of felsic minerals. The cumulative AE ringing count of metagabbros with feldspar nondevelopment exceeded 250 000, while those of metagabbros with feldspar development did not reach 200 000. As the feldspathic mineral content increases, the AE ringing counts of metagabbro exhibit an increasing trend in the high-energy (1e6–+∞ aJ) and high-amplitude (90–100 dB) intervals. With the development of feldspar minerals, the fracture mode of metagabbro gradually changed from shear failure to tensile failure. The higher the development of felsic minerals, the higher the stress level corresponding to the maximum fractal dimension, the greater the energy released by rock failure, and the more severe the damage. This study is of great significance for revealing the mechanism of rock rupture.

Microcrack characteristics of granite under circumferential strain-controlled uniaxial compression test using UDEC-GBM

Rockburst is one of the significant challenges for underground excavation stability. The post-peak behaviour of rock controls the way it fails, and the released energy is potentially involved in the rockburst. However, understanding of both microscopic and macroscopic behaviours of brittle rock in the post-peak stage is limited due to the lack of proper loading methods and quantitative microscopic analysis methods. This study proposes a circumferential strain-controlled loading algorithm in UDEC to control the failure process, which has been verified against previous literature. By employing the improved geometry generation method, the microcrack evolution is quantitatively assessed. Energy analysis reveals that up to 80% of the input energy is stored in the granite prior to complete failure, which could be released if the rock fails at this moment. Conversely, after the complete failure, intragranular cracks account for the majority of energy dissipation, indicating its importance in post-peak stability. A small portion of the peak stored strain energy needs to be extracted to achieve a controlled failure process. Furthermore, it is found that the significant increases in the formation of intergranular shear and low-angled microcracks potentially feature the complete failure of the specimen. The proposed model offers a complementary method to systematically investigate the post-peak behaviour of rock, including the evolution of microcracks and energy.

Three-dimensional characteristic and evolution of creep cavity and microcrack of HR3C austenitic heat resistant steel after long-term creep at 650 °C

Three-dimensional characteristics of creep cavities and microcracks in HR3C austenitic steel after creep at 650 °C were investigated using high resolution X-ray computed tomography (CT) and three-dimensional atomic probe (3DAP). The variation of cavity volume fraction is related to the increasing fraction of cavities undergoing growth and coalescence. Irregular lamellar or “W” shaped microcrack along the grain boundary were observed by the CT and the number large sized microcracks decreased significantly with decreasing stress levels. 3DAP results show that the concentration of P elements was high at the M23C6/γ interface at the early stage of creep. With the increase of creep time, M23C6/γ interface have been found to not only contain high concentration of P element, but also be enriched with Si. The coarsening of the carbides at the grain boundary and the enrichment of P and Si elements at the interface creates the conditions for the nucleation of creep cavities and microcracks under stress. Thus, stress has an tremendous influence on the distribution of creep cavities and the propagation path of microcracks. Additionally, with the decrease of stress, the creep damage mode changes from intergranular/transgranular mixed cracks to creep cavity.

Influence of annealing temperature on microstructural evolution and tensile behavior of Ti−6Al−4V alloy manufactured by multi-directional forging

A range of annealing treatments were implemented to regulate the microstructure and mechanical properties of Ti−6Al−4V forging. The results show that both the as-forged and as-annealed microstructures exhibit a bimodal structure composed of equiaxed primary α phase (αp) and transformed β phase (βt). With the increase of annealing temperature, the secondary α (αs) phase precipitates from the β phase. There is no obvious texture and the crystal orientation is uniformly distributed. Meanwhile, strength initially increases and then decreases, whereas ductility remains largely unaffected. The alloy annealed at 860 °C has an excellent combination of strength and ductility, due to the larger content of the fine αs phase. All fracture surfaces contain massive dimples, which is a typical ductile fracture feature. The characteristics of microcracks, microvoids, and kinked αp/αl (equiaxed αp and lamellar α phase) phases are found near the fracture.

Effect of thermal treatment on microcracking characteristics of granite under tensile condition based on bonded-particle model and moment tensor

It is known that the heterogeneity caused by thermally induced micro-cracks and thermal stress can affect the mechanical behavior of granite. The laboratory-scale tests have the intrinsic limitation of non-repeatability and lack of effective methods to characterize the interaction effect between thermal micro-cracks and thermal stresses. In this study, we demonstrate how advancements in particle bonded model and moment tensor can help better understand the roles of high temperature in weakening granite and thermally induced cracking process in Brazilian test. Our results show that the types of micro-cracks (intergranular, intragranular, and transcrystalline ones) are related to their thermal expansion coefficients of mineralogical compositions. The intergranular tensile micro-cracks are predominant during the heating and heating–cooling processes. An obvious weakening of granite and non-central initiation is associated with the heterogeneity caused by the thermal damage and thermal stress. We also quantitatively evaluate the thermal damage based on orientation distribution, b-value, and nature of the sources, which gives a new microcracking perspective on tensile characteristics subjected to high temperature.

The impact of interfacial characteristics on the interfacial properties of 316 L/CuSn10 multi-material manufactured by laser powder bed fusion

Multi-material additive manufacturing (MMAM) enables the simultaneous creation of multi-material components in a single process, accomplishing customized different performances in specific regions of the same components. In particular, the copper-steel multi-material structure can provide considerable strength and high thermal conductivity, thus playing a crucial role in electronic components, heat exchangers and injection molds. However, few studies have explored the relationship between the microstructure and properties of the copper-steel fusion zone. Therefore, this study aims to reveal the heterogeneous evolution of the microstructure in the copper/steel fusion zone and its impact on the interfacial properties of 316 L/CuSn10 multi-material structure fabricated by laser powder bed fusion (L-PBF). We characterized the multi-layer specimens using laser confocal microscopy and SEM to obtain the macroscopic and microscopic microstructure, liquid metal embrittlement (LME) microcrack characteristics and precipitation evolution of the copper-steel fusion zone. The generation of liquid phase separation (LPS) was explored based on block specimens, and the textural characteristics of the fusion zone were analyzed using EBSD. As a result, because of multiple element precipitation and the high thermal conductivity of copper alloy, abrupt grain size changes occur in the fusion zone, affecting the fusion zone's corrosion resistance and nano-hardness. In tensile tests analyzing the anisotropy, the results show that LME microcracks have little impact on the interfacial bonding properties of the copper-steel bimetallic structure, among which the ultimate tensile strength of the specimens formed at 30° to the substrate reached a maximum of 562.9 MPa. These findings add substantially to our understanding of the relationship between the microstructure and properties of copper-steel bimetallic interface, and provide a theoretical reference for additive manufacturing copper-steel multi-material components.

Investigation of Rock Mechanical Properties under Liquid Nitrogen Environment

In order to promote sustainable energy development and reduce the impact of fossil fuels on the environment, it is crucial to strengthen the development and utilization of clean and renewable geothermal energy. Liquid nitrogen fracturing, as an emerging waterless fracturing technology, has outstanding advantages in rock fracturing effect and thermal exchange ability with hot dry rock and is more environmentally friendly. In order to evaluate the influence of liquid nitrogen on the mechanical properties, acoustic emission characteristics, and cross-sectional crack propagation characteristics of granite at different initial temperatures, this paper carried out three-point bending tests and acoustic emission detection on granite treated by high-temperature heating and liquid nitrogen cooling. Finally, based on the cross-sectional scanning test, the expansion characteristics of microcracks in granite were analyzed. The results show that the higher the initial temperature of granite, the stronger the cold impact of liquid nitrogen on granite, and the faster the rock’s mechanical performance declines. The acoustic emission ringing count is closely related to the development of microcracks in granite, and as the initial temperature of granite increases, the more ringing counts there are, indicating that the huge temperature difference induces more microcracks inside the rock. In addition, the cold impact of liquid nitrogen can effectively promote the fracturing of granite. After liquid nitrogen treatment, the fractal dimension of the granite cross-section increases, the shape of the cross-section becomes rough, and many micropores appear. This study can provide a scientific basis for the engineering application of liquid nitrogen fracturing technology.

Macro-micro crack and damage evolution characteristics of concrete: After the action of acidic drying-saturation cycle

Repeated saturation and drying of acidic mine water have a major influence on the mechanical properties and stability monitoring of artificial dams (concrete walls) in underground reservoirs. A uniaxial compression acoustic emission (AE) monitoring test was conducted to quantify the evolution characteristics of micro cracks in concrete. In addition, the evolution characteristics of macro cracks during sample failure were quantitatively analyzed by fractal dimension theory and Image-Pro. Finally, the damage constitutive model was established and the damage evolution law was studied. The results of the study showed that the percentage of micro shear cracks in dry samples exhibited a decreasing and then increasing trend during the loading stage before the uniaxial compressive strength (UCS). However, after the acidic drying-saturation cycle (ADSC), this percentage of concrete showed an increasing trend. As the number of drying-saturation cycles increases or the pH decreases, the fractal dimension, total length, and area of the macro cracks also increase. The damage constitutive model, based on ADSC and loading conditions, works well. After the ADSC, the concrete sample will have three damage stages. Additionally, the strain at entry into each stage increases. Expansion and shrinkage of hydration products and chemical damage due to ion exchange are the mechanisms that change the mechanical properties and the macro-micro crack evolution pattern of concrete after ADSC.

Initial Microcrack Characteristics of Concrete Interfacial Transition Zone and Cement Paste

Initial Microcrack Characteristics of Concrete Interfacial Transition Zone and Cement Paste

Quantitative detection and evaluation of Rayleigh ultrasonic wave for fatigue crack on turbine blade surface

In this paper, different characteristics of micro-cracks on the surface of turbine blades have been successfully evaluated based on the detection of Rayleigh ultrasonic wave by numerical simulation and experimental study. The quantitative relationship between the maximum amplitude of Rayleigh ultrasonic wave and the features of cracks including width, depth, excitation position, and inclination angle was established. Numerical calculations of different curvature models show that curvature has no significant effect on the propagation of Rayleigh ultrasonic wave. According to the developed multi-functional ultrasonic equipment, cracks on complex surfaces can be detected by clamping two probes on the arc guide rail. The experimental results verify the validity of the numerical simulations. It gives an excellent basis for the effective automatic detection of cracks on the surface of turbine blades. This research provides a suitable method and new equipment for rapid quantitative inspection of turbine blades.

Experimental study on the effect of anchors on the creep mechanical properties and acoustic emission characteristics of fractured sandstone under uniaxial compression

This study conducts laboratory tests to investigate the creep and acoustic emission (AE) of unanchored and anchored fractured sandstone samples under uniaxial compression by taking the Triassic fine sandstone collected from the Xiaolangdi Reservoir area as the research object and ensuring the same testing conditions using an RLJW-2000 rock rheometer and a PCI-Ⅱ AE instrument. Moreover, this study identified the effects of anchors on the creep mechanics and AE characteristics of fractured sandstone samples by analyzing the strain, long-term strength, AE event count, AE rate, AE energy rate, and rising angle – average frequency (RA-AF) characteristics of each sample before and after anchoring. According to the study results: (1) Under the same stress level, the anchored sample's instantaneous strain, creep strain, and total strain are smaller than those of the unanchored sample. Anchors exerted the largest inhibitory effect on creep strain, followed by the total strain, while anchors inhibited instantaneous strain to the smallest extent. (2) Compared to the unanchored sample, the anchored sample experienced a significant increase (as high as 50%) in long-term strength. Anchor reinforcement significantly improves the long-term strength of samples. (3) Under the same stress level, the AE event count and cumulative AE event count of the anchored sample are smaller than those of the unanchored sample. Anchors significantly inhibited microcracks initiation, propagation, overlapping, and penetration in samples. (4) The maximum AE rate of the anchored sample is only 69.30% of that of the unanchored sample, whereas the peak AE energy rate of the anchored sample is only 23.21% of that of the unanchored sample. Anchors reduce the AE event count generated and the AE energy released by samples per unit of time, exerting a significant crack-arrest effect on them. (5) The presence of anchors changes the type and number of microcracks in the samples' creep process. Anchors greatly inhibit the generation of high-RA and low-AF AE signals and generate low-RA and high-AF ones. As a result, more tensile microcracks occur in samples under stress levels close to the failure stress level (especially the last stress level), which inhibit the formation of shear microcracks in samples and causes samples to be more prone to macroscopic tensile-shear failure. (6) The microcrack characteristics of samples characterized by RA-AF values are consistent with the macrocrack characteristics of samples. Therefore, RA-AF values can satisfactorily characterize the microcracks' variation characteristics in the sandstone samples' creep process before and after anchoring.

A Coupled 3d Morphological Reconstruction Approach for Surface Microcrack in Si3 n4 Ceramic Bearing Roller Based on Adaptive Nano Feature Extraction & Multiscale Depth Fusion.

To extract the fuzzy contour features, tiny depth features of surface microcracks in the Si3 N4 ceramic bearings roller. An adaptive nano feature extraction and multiscale deep fusion coupling method is proposed, to sufficiently reconstruct the three-dimensional morphology characteristics of surface microcracks. Construct an adaptive nano feature extraction method, form the surface microcrack image scale space and the Gaussian difference pyramid function equation, realize the detection and matching of global feature points. The sparse point cloud is obtained. Through polar-line correction, depth estimation, and fusion of feature points on the surface microcracks image, a multiscale depth fusion matching cost pixel function is established to realize a dense point cloud reconstruction of surface microcracks. The reconstruction results show that the highest value of the local convex surface reconstructed by the dense point cloud reaches 1183nm, and the lowest local concave surface is accurate to 296nm. Compared with the measurement results of the confocal platform, the relative error of the reconstruction result is 24.6%. The overall feature-matching rate of the reconstruction reaches 93.3%. It provides a theoretical basis for the study of surface microcrack propagation mechanism and the prediction of bearing life.

The Influence of the Strain Rate and Prestatic Stress on the Dynamic Mechanical Properties of Sandstone-A Case Study from China.

A series of conventional dynamic uniaxial compressive (CDUC) tests and coupled static dynamic loading (CSDL) tests were performed using a split Hopkinson compression bar (SHPB) system to explore the variable dynamic mechanical behavior and fracture characteristics of medium siltstone at a microscopic scale in the laboratory. In the CDUC tests, the dynamic uniaxial strength of the medium sandstone is rate-dependent in the range of 17.5 to 96.8 s-1, while the dynamic elastic modulus is not dependent on the strain rate. Then, this paper proposes a generalized model to characterize the rate-dependent strength from 17.5 to 96.8 s-1. In the CSDL tests, with increasing initial prestatic stress, the dynamic elastic modulus and dynamic strength increase nonlinearly at first and then decrease. The results show that two classical morphological types (i.e., Type I and Type II) are observed in the dynamic stress-strain response from the CDUC and CSDL tests. By scanning electron microscopy (SEM), microscopic differences in the post-loading microcrack characteristics in the behavior of Type I and Type II are identified. In Class I behavior, intergranular fracture (IF) usually initiates at or near the grains, with most cracks deflected along the grain boundaries, resulting in a sharp angular edge, and then coalesces to the main fracture surface that splits the specimen along the direction of stress wave propagation. In contrast, Class II behavior results from the combined IF and transgranular fracture (TF).

Experimental investigation on damage evolution and failure mechanism of pre-corroded AA7075-T6 under multiaxial fatigue loading

To investigate the tension–torsion fatigue failure of pre-corroded AA7075-T6, fatigue damage accumulation, macro-crack formation and propagation are quantitatively characterized through 3D-DIC based strain maps and damage severity curves, micro-cracking characteristics are further examined by SEM, TEM, and EBSD observation. Experimental results show that corrosion pit induces fatigue macro-cracks formation, and the identified nucleation time, amount, and location are diverse for different loading conditions. Four dominated fatigue micro-crack initiation forms and corresponding mechanisms were analyzed, namely, pit bottom, sidewall dis-continuous surface, corrosion micro-feature (micro-pits/jut-ins), and pit subsurface, which depends on multi-factors involving corrosion macro-morphology, corrosion micro-morphology, loading condition and underlying microstructure.

Dynamic Propagation and Electro-Mechanical Characteristics of New Microcracks in Notched Coal Samples Studied by the Three-Point Bending Test System and AFM

This work extends research on the mechanism of electromagnetic radiation (EMR) induced by coal or rock fractures to the category of microscopic dynamic experimental research. A custom-made three-point bending test system and atomic force microscope (AFM) were integrated to obtain the microdynamic loading test system. The notched coal samples were prepared specially. The dynamic propagation of new microcracks in coal samples was measured, and the propagation velocity was calculated. The morphology and electro-mechanical characteristics of new microcracks were tested. More importantly, the causes of the changes in the electro-mechanical characteristics before and after fracture were analyzed, and the effects of these changes on the EMR were discussed. The results showed that the average propagation velocities during the same time interval are 9.5 μm/s, 12.1 μm/s, and 16.2 μm/s. The elastic modulus of the material at the microcrack edge is generally smaller than that of the material in other locations, while the adhesion and deformation are larger. Moreover, the closer the material is to the microcrack, the higher its surface potential. The electrons generated at the microcrack edge and emitted into the atmosphere, which made the greater potentials of the microcrack edge. Many electrons with different velocities and directions migrate in similar parallel-plate capacitors, which are formed by the relative microscale surface of the coal microcrack tip and have different field strengths, resulting in EMR with complex frequencies and different intensities. This study provides a micro-dynamic experimental basis for research on the electromagnetic radiation mechanism.

Microwave response characteristics and influencing factors of ores based on dielectric properties of synthetic samples

In order to understand the influence of different factors on the microwave response characteristics of ores, the effects of electrical conductivity, metal mineral content, compactness, metal mineral distribution, microwave frequency and temperature on the dielectric properties of synthetic ores (metal mineral and quartz) were studied. Microwave heating tests were carried out on three types of natural ores (Hongtoushan copper ore, Sishanling iron ore and Dandong gold ore) with significant differences in metal mineral contents. The test results showed that under microwave irradiation, the stronger the electrical conductivity of the metal minerals, the smaller the penetration depth in synthetic ore. For those metal minerals with lower electrical conductivity, the microwave absorption coefficient of the synthetic samples increases with increasing metal mineral content. For those metal minerals with higher electrical conductivity, the microwave absorption coefficient of the samples first increases and then decreases as the metal mineral content increases. When the metal minerals are distributed in layers, the penetration depth is much less than that given a uniform distribution. The penetration depth in the sample at microwave frequency of 915 MHz is greater than that at 2.45 GHz. The higher the electrical conductivity of metal minerals used in synthetic ores, the higher the high-temperature sensitivity of electromagnetic shielding coefficient (0 °C–500 °C). The Hongtoushan copper ore with high metal mineral content exhibits obvious size effect. The effects of ore structure and crystal particle size on the distribution characteristics of microcracks were discussed. Based on the test results, a quantitative prediction model of microwave sensitivity of ore was proposed, which provides guidance for the prediction of ore heating effect and the selection of microwave heating sequence of ore.

Evolutionary Analysis of Heterogeneous Granite Microcracks Based on Digital Image Processing in Grain-Block Model.

Rocks are natural materials with a heterogeneous microstructure, and the heterogeneity of the microstructure plays a crucial role in the evolution of microcracks during the compression process. A numerical model of a rock with a heterogeneous structure under compression is developed by digital image processing techniques and the discrete element method. On the grain scale, the damage mechanism and microcrack characteristics of a heterogeneous Biotite granite under compression fracture are investigated. First, the process of constructing a digital image-based heterogeneous grain model is described. The microscopic characteristics of geometric heterogeneity, elastic heterogeneity, and contact heterogeneity are all considered in the numerical model. Then, the model is calibrated according to the macroscopic properties of biotite granite obtained in the laboratory, and the numerically simulated microcrack cracking processes and damage modes are obtained with a high degree of agreement compared to the experiments. Numerical simulations have shown the following: (1) Microcracking occurs first at the weak side of the grain boundaries, and the appearance of intragranular shear cracks indicates that the rock has reached its peak strength. (2) The stress concentration caused by the heterogeneity of the microstructure is an essential factor that causes rock cracks and induces rupture. Intragranular cracks occur successively in quartz, feldspar (plagioclase), and biotite, with far more intragranular cracks in quartz and feldspar (plagioclase) than in biotite. (3) Microcracking in quartz occurs as clusters, fork and fracture features, and in feldspar (plagioclase) it tends to cause penetration microcracking, which usually surrounds or terminates at the biotite. (4) As the confining pressure increases, the tensile break between the grains is suppressed and the number of shear cracks increases. At the macro level, the rock failure mode of the numerical model changes from split damage to shear destruction, which is consistent with the law shown in laboratory experiments.

Progressive damage and fracture of biaxially-confined anisotropic coal under repeated impact loads

Coal masses in underground mines are in multiaxial stress states after excavation, and they are frequently subjected to dynamic loads particularly from continuous mining-induced seismic events. The changes of in-situ stress conditions and external dynamic loads may induce coal bursts, which involves the violent breaking of coal masses. Meanwhile, the coal bursting process may be influenced by bedding planes that are considered as unique structures in coal masses, which raises uncertainties of coal bursting mechanisms. This paper aims to reveal the progressive damage and burst proneness of anisotropic coal under coupled static stress and repeated dynamic loads. The tested coal specimens have five bedding plane orientations (β = 0°, 30°, 45°, 60°, and 90°), where β is the angle between the bedding plane and dynamic loading direction. A triaxial Hopkinson bar (Tri-HB) system is utilised to apply the biaxial static stress on the specimen and then followed by dynamic loading, and the stress and strain can be recorded by the system accordingly. After the loading test, ultrasonic wave velocity is measured to examine the degree of attenuation, and the quantification of microcrack characteristics is conducted by using the synchrotron-based X-ray computed tomography (CT). Then, the specimen is loaded again under the same biaxial static stress and dynamic load, and measured by ultrasonic sensors and X-ray CT. This process will be repeated until the final failure of the specimen. We found that both dynamic peak stress and P-wave velocity show a decreasing trend due to damage accumulation with increasing number of dynamic tests. The bearing capacities of anisotropic coal are mainly governed by bedding angles, for example, the specimen with β = 30° undergoes the lowest impact numbers, but the one with β = 90° can undergo the highest numbers. The crack initiation and propagation are progressively revealed by two-dimensional (2D) X-ray slices and 3D fracture network reconstructions. As impact number increases, both 2D and 3D fractal dimensions of cracks increase exponentially, whereas dynamic peak stress and P-wave velocity are negatively correlated with them.

Influence of Temperature on Quantification of Mesocracks: Implications for Physical Properties of Fine-Grained Granite

Abstract Thermally induced changes in mesocrack and the physical properties of fine-grained granite may influence their stability, transport characteristics, and performance related to various deep subsurface energy projects. In this study, granite was heat-treated at different temperatures (20°C, 100°C, 200°C, 300°C, 400°C, 500°C, and 600°C). The propagation and evolution of different types of cracks and the physical properties of the granite were quantitatively investigated, using optical observations of petrographic thin sections, P-wave velocity measurements, and permeability tests. The results show that as the temperature increased, the number and length of cracks increased, and the cracks were randomly distributed in all directions. This led to an increase in rock damage (λn) and an increase in permeability (K). In particular, when the temperature was ≥400°C, the damage rate significantly increased, and the number and length of intragranular cracks significantly exceeded the number and length of intergranular cracks. This led to changes in the permeation path, causing it to mainly travel through the interior of mineral particles. Using the inverse of P-wave velocity (VP), the dimensionless crack density (ρ) of granite was found to increase as the temperature increased, and this result was similar to the change of optical crack density (Pl). These analyses laid a reference for understanding the correlation between microcrack characteristics and macrophysical properties of granite.