Microcracking Mechanisms Research Articles

Experimental investigation on the influence of weak interlayers on sandstone rockburst and associated microcracking mechanism

Weak interlayers (WI) are common in sedimentary rock masses in deep coal mines. The qualitative effect of the WI on rockbursts is widely acknowledged; however, its influence mechanism still needs further investigation. In the present study, true triaxial unloading rockburst tests of sandstone with WI and calcite veins (CV) were conducted to explore their influence mechanisms. To explore the impact of WI, the rockburst stress, failure modes, acoustic emission (AE) parameters (energy, entropy, and b-value), and spatial energy characteristics of AE events were analyzed. The influence of the area ratio of WI and their distribution patterns (centralization and dispersion) on rockburst were further investigated. The results indicate that the rockburst stress (peak of maximum principal stress) decreased by 4 % for every 1 % increase in the sandstone's dispersion WI area ratio (1.9%–9.3 %). Namely, rockburst is more likely to occur when there is appropriate WI distributed in the sandstone because WI exacerbates the microcrack activities and energy release. The CV will reduce the weakening effect of WI on rockburst stress and can enhance the rockburst intensity, especially in samples with dispersion WI. Moreover, the more considerable AE energy is released around CV for the sandstone with dispersion WI. The interface between WI and matrix is prone to rockburst for the sandstone with centralized WI because of the concentrated energy release. The results of this paper can provide a reference for the prevention and control of rockbursts in mine sedimentary rocks containing WI and CV.

The relationships between tensile strength, mode I and mode II fracture toughness of rock: An empirical and microcracking perspective

The empirical relationships between tensile strength, mode I and mode II fracture toughness obtained by previous studies have the problem of a small amount of data for fitting, and more data are needed for further study. There is a discrepancy between the theoretical prediction and the experimental results of the relationship between mode II and mode I fracture toughness. Because of this, a review is conducted to determine the relationships among tensile strength, mode I fracture toughness, and mode II fracture toughness from the data gathered from the available literature. The results indicate that the mode I and mode II fracture toughness have linear relationships with tensile strength with the linear coefficient of 0.141 and 0.219, respectively. The linear coefficient between mode II and mode I fracture toughness is 2.389, indicating that the classical mixed mode criteria are mistaken the empirical relationship between mode II and mode I fracture toughness. The microcracking mechanism and failure model are quantified and compared in detail among tensile test, mode I and mode II fracture toughness tests based on moment tensor. It found that the nature of the source can be related to each other, which gives some light on the reason for the existence of certain relationships between these macroscopic parameters from a microcracking perspective.

Research about the microcrack mechanisms in molybdenum and corresponding suppression strategies during laser additive manufacturing process

In this study, the mechanism of microcracks in the laser powder bed fusion of molybdenum was analyzed, and the corresponding solutions were proposed. Through specially designed single-track experiment and finite element simulation analyses, we found that thermal stress was the main cause of cracking during the laser powder bed fusion process. The cracks were generated almost synchronously with the laser scanning process, and thus optimizing the process parameters alone could not inhibit the occurrence of cracks. Herein, alloying strategy was proposed and proved to be an effective way to solve the cracking problems. Specifically, by adding Cr and Ti elements, the high-temperature mechanical properties of Mo were improved through solid solution strengthening mechanism, hence the thermal stress induced cracking was suppressed effectively. In addition, according to the thermodynamic calculations, it was found that Cr and Ti had an inhibitory effect on the segregation of impurity at the grain boundaries and this conduce to improve the strength as well.

Lifetime study of uniform and non-uniform multi-crack fusion and extension in an approximate plane

The threat of cracks is very fatal for engineering structures. Usually, the main crack is fused by several secondary microcracks, so the investigation of the fusion mechanism and life of microcracks is crucial to improve the reliability of engineering structures. In this paper, firstly, the applicability and accuracy of linear elastic fracture mechanics are verified by comparing the test results and FEA results of small-scale yielding. Secondly, the fusion mechanism and life-solution of uniform and non-uniform multi-cracks are thoroughly investigated. It is also pointed out that the homogeneity of cracks is caused by the abrupt change of crack extension path by affecting the level of stress intensity factor (SIF). Finally, the effects of maximum load and stress ratio on crack fusion are explored. The results demonstrate that the maximum load has a positive effect on the ratio of the crack fusion life to the overall crack extension process life, but the effect of the stress ratio is essentially unchanged.

Effect of heat treatment on microcracking behaviors and Mode-I fracture characteristics of granite: An experimental and numerical investigation

Combining thermal stimulation and tensile fracture induced by cold water injection can synergistically enhance hydraulic fracturing, improving geothermal reservoir connectivity. To investigate the heat effect on the Mode-I fracture characteristics of granite, notched semi-circular bend (SCB) granite specimens were prepared and heat-treated at five temperatures ranging from 25 to 600 ℃. Mineralogical analysis and three-point bending tests were performed on the SCB specimens, and a grain-based model (GBM) incorporating four types of mineral particles was developed. The model was simulated for heat treatment and Mode-I loading and then validated against experimental results. The behavior and evolution of intra- and intergranular microcracks in the SCB specimens during heating, cooling, and mechanical loading were analyzed. Moreover, the fracture surface morphology and microcracking mechanisms observed in the SCB specimens at different heat-treatment temperatures were discussed. The results reveal a nonlinear trend in the Mode-I fracture toughness of the SCB specimens, initially increasing and then decreasing with heat-treatment temperature. The number of thermally induced cracks escalates with increasing heat-treatment temperature, predominantly as intergranular tensile cracks, followed by intragranular tensile cracks. Under Mode-I loading, the SCB specimens heat-treated below 450 ℃ predominantly exhibit intergranular cracks, while intragranular tensile cracks become more prevalent at 600 ℃. Thermally induced cracks can alter the propagation direction and path of mechanically induced cracks, causing macrocracks to deviate from the initial straight propagation path. Scanning electron microscope (SEM) analysis illustrates that at 300 ℃ and above, the fracture surface morphology becomes more fragmented and longer microcracks appear.

Study on the mechanism of energy evolution and bearing degradation in pre-cracked sandstone under non uniform cyclic loading

The engineering rock mass is affected by the original cracks, which increases the uncertainty of instability and failure mechanisms. Under the action of excavation unloading or other disturbance loads, its bearing properties are more complex and the deformation characteristics is more special, which has always been a difficult issue in the analysis of rock mechanics. In order to explore the propagation and failure mechanism of spatial micro cracks in fractured rock masses, acoustic emission (AE) experiment of sandstone was carried out under pre-static loading and low-frequency stepwise cyclic loading–unloading. The research results indicate that the peak strain and crack initiation stress of rocks with different pre-cracked positions have the highest differences of 12.62% and 18.65%, respectively. The difference between peak stress and crack initiation strain is within 4%. The pre-cracked position mainly affects the peak strain and crack initiation stress of pre-cracked rocks, and its effect on peak stress and crack initiation strain is limited. The crack initiation angle of prefabricated cracks is mainly distributed within the range of 45° − 90°, and it decreases with the increase of quantities of prefabricated cracks. The crack initiation angle of rocks with prefabricated three cracks is 30% lower than that of single crack. The research results have deepened the analysis of energy evolution and deformation damage of fractured rock masses.

Crack characteristics analysis and mechanisms in GH3536 alloy manufactured by laser powder bed fusion

The presence of cracks poses a significant challenge in the application of laser powder bed fusion (LPBF) for manufacturing high Ni-base superalloys. The crack characteristics of LPBF-fabricated GH3536 superalloy are investigated in this paper, with a focus on analyzing the generation and expansion mechanism of micro-cracks through an investigation into the evolution of the molten pool, thermal stress and micro-characteristics. The findings suggest that thermal stress serves as the primary driving force for both crack initiation and propagation, with a predominant concentration of thermal stress observed in the heat-affected zone located at the periphery of the molten pool. Grain disorientation is another crucial factor influencing both the initiation and propagation of cracks. The difference in orientation between adjacent grains at the crack exceeds 40°, with the crack primarily originating from large angle grain boundaries (LAGBs) and propagating along them. Furthermore, there exists inconsistency in terms of elastic modulus and deformation coordination between carbides (Mo2C, (Ni, Cr) Mo3C6) particles, and matrix. This inconsistency results in two normal partial stresses acting in different directions, leading to dislocation aggregation and crack nucleation.

Simulation of Shear and Tensile Fractures Using Ductile Phase Field Modelling with the Calibration of P Wave Velocity Measurement and Moment Tensor Inversion

The appropriate understanding and formulation of rock discontinuities via FEM is still challenging for rock engineering, as continuous algorithms cannot handle the discontinuities in rock mass. Also, different failure modes of rock samples, containing tensile and shear failure, need to be computed separately. In this study, a novel double-phase field damage model was introduced with two independent phase field damage variables. The construction of the proposed model follows the thermodynamics framework from the overall Helmholtz free energy, with elastic, plastic and surface damage components. The proposed model is calibrated via traditional damage variables, based on ultrasonic wave velocity measurement and acoustic emission monitoring, and both show great consistency between simulation results and laboratory observations. Then the double-phase field damage model is applied to COMSOL software to simulate microcrack propagation in a pre-fractured rock sample. Both lateral and wing cracks are observed in this study, manifested as shear- and tensile-dominated cracks. We also observed different microcracking mechanisms in the proposed numerical models, such as tensile and shear cracking, the influence of plastic strain and the percolation between tensile and shear microcracks. Overall, this study provides valuable insights into the mechanics of microcracking in rocks, and the proposed model shows promising results in simulating crack propagation.

Experimental study on mode I fracture characteristics of heated granite subjected to water and liquid nitrogen cooling treatments

Liquid nitrogen (LN2) cryogenic fracturing, as a kind of waterless fracturing, is being considered for its potential to enhance the permeability of hot dry rock (HDR) reservoirs. The model I fracture behavior of HDR plays a pivotal role in the HDR fracturing. Therefore, this study focuses on the fracture behavior of the heated granite subjected to water cooling (WC) and liquid nitrogen cooling (LNC) under mode I load. The micro-cracking mechanism of the high-temperature granite under the rapid cooling treatment is analyzed based on the thermo-mechanical coupling grain-based model (GBM). The results indicate that the change in the fracture toughness with the granite temperature has obvious segmental characteristics and the temperature of 200 ℃ is a critical point. Before the critical temperature, the trend of fracture toughness is indistinct with the granite temperature for both cooling methods. However, beyond the critical temperature, the fracture toughness obviously decreases with the increase in the granite temperature, and the LNC is more effective at reducing fracture toughness compared to the WC. With increasing the granite temperature, shear cracks occur earlier during the three-point bending test. A higher proportion of tensile fractures after the LNC treatment is induced by mode I load than after the WC treatment, especially at high granite temperatures. Compared to the WC, the LNC can generate a greater number of microcracks inside the granite, which further results in smaller fracture damage of the LNC-treated granite during mode I load. Ultimately, this leads to improved stimulation performance in terms of reduced fracture resistance and decreased fracture energy requirements for the high-temperature granite cooled by LN2. The results can enhance the understanding of distinctions between LN2 cryogenic fracturing and hydraulic fracturing in geothermal exploitation.

Excellent combination of strength and elongation of TZM alloys achieved by c-ZrO2 and single cross rolling

In this study, new TZM-xZrO2 (x = 0, 0.5, 1, 1.5) (wt%) alloys were designed by powder metallurgy solid-solid mixing method combined with single cross rolling. The results show that c-ZrO2 in TZM alloys was mainly spherical, and the average size of c-ZrO2 particle increases gradually from 1.28 μm to 1.71 μm with the increase of its content. c-ZrO2 can effectively refine the molybdenum grain and adsorb the free brittle element O in grain boundaries in the form of TiO2 layer. The interface was composed of three phase: c-ZrO2, Y2O3 and TiO2, with the presence of [0−11] c-ZrO2 ǁ [−11−2] Y2O3 ǁ [−10−3] TiO2 crystal relationship. The rolled plates mainly exist 〈100〉//ND and 〈111〉//ND two kinds of grain orientation, the addition of c-ZrO2 particles promote <100>//ND orientation ratio, thus weakening the texture strength (maximum pole density value from 8.34 to 5.39), conducive to the improvement of plasticity. When the c-ZrO2 content was 0.5 wt%, the best performance was achieved, with good strength and elongation (ultimate tensile strength: 958 MPa; Elongation: 17.3%), showing excellent strength and elongation product (16.6 GPa·%), 31% higher than TZM alloy, better than most reported molybdenum alloys. With the further increase of c-ZrO2 content, the particles gradually coarsened, the hindering effect on dislocations was weakened, and it was easy to become the nucleation site of main cracks, resulting in the decrease of strength and plasticity. Fine grain strengthening and dislocation strengthening were important factors to improve the strength. The excellent ductility was mainly due to the deflection mechanism of microcracks and the blocking effect of grain boundary enrichment on crack propagation.

Evolution mechanism and quantitative characterization of initial micro-cracks in marble under triaxial compression

Evolution mechanism and quantitative characterization of initial micro-cracks in marble under triaxial compression

Research on cracking and mechanical responses of semi-rigid base under falling weight impact

Disadvantages of semi-rigid materials bring a significant challenge to the maintenance of the semi-rigid base pavement. The micro-cracking treatment employs the falling weight to break the semi-rigid base into interlocking blocks to create a new base material to regenerate the old base. To study the micro-cracking mechanism, the cracking patterns and mechanical responses of the semi-rigid base under different types of falling weights and drop heights were obtained in field tests. The DEM-FDM coupling model was established to investigate the cracking distribution further. The results showed that as the impact contact area of the falling weight decreases, the depth of the groove progressively deepens, and the resilient modulus of the semi-rigid base decreases. Besides, the flat-bottomed falling weight produced the highest compressive stress, while the big convex points falling weight caused the most vertical displacement. Combined with simulation analysis, the flat-bottomed falling weight almost exclusively caused shear cracking on the contact edge. The small convex points falling weight mainly generated the shear cracking on the surface, and the big convex points falling weight induced more extensive tensile cracking within the semi-rigid base. Therefore, the big convex points falling weight is more recommended for micro-cracking treatment, which creates a greater cracking degree in semi-rigid base and is conducive to breaking the semi-rigid base into interlocking small blocks.

Microcracking of strawberry fruit cuticles: mechanism and factors

Microscopic cracks in the cuticle (microcracks) are the first symptom of the strawberry fruit disorder ‘water soaking’ in which the fruit surface appears watery, translucent, and pale. Water soaking severely impacts fruit quality. The objective was to investigate the factors and mechanisms of cuticular microcracking in strawberry. Fluorescence microscopy revealed numerous microcracks in the achene depressions, on the rims between depressions and at the bases of trichomes. Microcracks in the achene depressions and on the rims were either parallel or transversely oriented relative to a radius drawn from the rim to the point of attachment of the achene. In the achene depression, the frequency of microcracks with parallel orientation decreased from the calyx end of the fruit, towards the fruit tip, while the frequency of those with transverse orientation remained constant. Most microcracks occurred above the periclinal cell walls of the epidermal cells. The long axes of the epidermal cells were primarily parallel-oriented. Microcracking increased during fruit development. Cuticle mass per fruit remained constant as fruit surface area increased but cuticle thickness decreased. When fruit developed under high relative humidity (RH) conditions, the cuticle had more microcracks than under low RH conditions. Exposing the fruit surface to increasing RHs, increased microcracking, especially above 75% RH. Liquid-phase water on the fruit surface was markedly more effective in inducing microcracking than high vapor-phase water (high RH). The results demonstrate that a combination of surface area growth strain and water exposure is causal in inducing microcracking of the strawberry cuticle.

Influence of Layer Thickness Ratio on the Mechanical and Failure Properties of Soft-Hard Interbedded Rock-like Material

To figure out the influence of soft-hard layer thickness ratio on specimens' mechanical properties evolution and microcracking mechanism, combined with digital image correlation technology and acoustic emission facility, uniaxial compression tests were conducted on soft-hard interbedded rock-like materials considering seven bedding dip angles and two soft-hard layer thickness ratios. The results are as follows: 1) The failure mode and failure pattern of layered rock masses are mainly determined by the bedding dip angle α and are less related to the soft-hard thickness ratio. With the increase of dip angle, the failure strength curve of the specimen is approximately U-shaped, and the soft-hard layer thickness ratio affects the U-shaped. The decrease in soft-hard layer thickness ratio will reduce the uniaxial compressive strength of specimens with low dip angles (α≦30°), cause differences in the evolution path of local strain fields of layered rock masses and reduce the horizontal displacement of the main crack. 2) The increase of the proportion of soft layer in the soft-hard layer thickness ratio will reduce the proportion of tensile cracks in the tensile failure specimens and shear cracks in the shear failure specimens, complicating the process of cracks of the layer rock mass. 3) Increasing the proportion of soft layers in the soft-hard layers thickness ratio promotes the generation of secondary cracks in layered rock masses and further reduces the integrity of specimens. Finally, through the findings in this paper, it can provide a reference for analyzing the crack propagation behavior of layered rock.

A CT image-driven computational framework for investigating complex 3D fracture in mesoscale concrete

Accurate prediction of fracture in concrete depends on the characterization of real meso-structures. Micro X-ray computed tomography (CT) can fulfil this task but is still too expensive and time-consuming to repetitively generate numerical models, also with massive degrees of freedom (DOFs) that prohibit nonlinear computations. To address such problems, we develop a novel computational framework driven by only one CT image for 3D fracture investigation of realistic mesoscale concrete models. The voxelized CT data of aggregates is first processed to obtain spatially continuous surfaces. A number of aggregates with real shapes from a created library are then randomly packed into containers through compaction and vibration simulated by a dynamic physics engine. In this way, realistic concrete models with various aggregate contents (up to 60%) can be achieved without performing extra CT tests and image processing. To capture potential micro-cracks, cohesive interface elements with zero-thickness are automatically inserted between solid elements. The proposed models with more than 15 million DOFs are well validated through typical uniaxial tension tests, elucidating complex formation mechanisms of micro-cracking, pre-peak nonlinearity, softening behaviour and 3D fracture networks. Quantitative analyses indicate that with the increase of aggregate content, the coupling effect of aggregate blocking and interfacial cracking becomes stronger to make the crack surfaces more tortuous with higher ITZ-mortar area ratios and lower load-carrying capacities, although more aggregates are often required to enhance overall elastic modulus and compressive strength, and reduce carbon footprints of concrete.

Modelling crack behavior of granite using multiscale grain-based model

Understanding the macroscopic and microscopic failure process of brittle rocks is helpful to predict the strength and deformation characteristics. However, the brittle rock is a typical heterogeneous material, and it is difficult to study the evolution mechanism of microcracks at the grain scale through laboratory tests. In this study, we propose a multiscale grain-based model based on FDEM, which can consider the actual grain size and the inter-grain and intra-grain contacts of diverse minerals. Most importantly, it can explicitly characterize local polycrystal inclusions and internal cleavage of some mineral grains. Based on the laboratory test data, a series of simulated tests were conducted, including uniaxial tensile tests, uniaxial compression tests, and conventional triaxial compression tests. The results reveal the importance of transgranular fracture capacity in the simulation of mesoscopic fracture. The failure mechanism of rock samples is controlled by the difference between inter-grain and intra-grain tensile strength under uniaxial compression condition. As the confining pressure increases, the tension failure mechanism is transformed into the shear failure mechanism, indicating a gradual change in rock properties from brittleness to ductility. The ability of mineral to absorb elastic strain energy will significantly affect the microcrack path. Under uniaxial tensile condition, the macroscopic failure results from multiple microcracks, and the intergranular tensile cracks are dominated. In addition, the cleavage planes will provide optimal paths for the propagation of microcracks. The results can help us to understand the mechanism of microcrack evolution in heterogeneous rock, and provide a method for comprehensive analysis of crack propagation and energy evolution.

Experimental investigation on the influence on mechanical properties and acoustic emission characteristics of granite after heating and water-cooling cycles

This study explores explore the failure characteristics of high temperature granite under different numbers of heating–cooling cycles. Combining a series of laboratory uniaxial compression tests with acoustic emission (AE) monitoring, it reveals the AE characteristics and damage behavior of high temperature granite in different damage stages. Increasing the number of heating–cooling cycles exponentially raised the mass-loss and volume-increase rates of the granite and exponentially decreased the P-wave velocity. These results indicate that multiple heating–cooling cycles irreversibly damaged the high temperature rock mass. Moreover, the variations in both the P-wave velocity and the stress threshold at each stage gradually plateaued after three thermal cycles. Under uniaxial compression, the evolution mechanism of microcracks in the rock was successfully described by the AE characteristic parameters and real-time spatial AE position. The cumulative AE counts and AE energy rates were consistent in different damage stages of the rock specimen. Both quantities began increasing after entering the unstable crack growth stage. As the number of heating–cooling cycles increased, the main fracture mechanism of rock rupture transitioned from mixed mode to shear mode, as evidenced by the distributions of rise angle and average frequency. Meanwhile, the gradually increasing b-value indicated that small-scale fracture events gradually dominated the rock damage. The present results can assist the design of deep geothermal-resource mining schemes and safe mining constructions.

Role of alloy composition on micro-cracking mechanisms in additively manufactured Ni-based superalloys

Inherent micro-cracking mechanisms in two contrasting high-gamma-prime (high-γ’) Ni-based superalloys processed by laser powder bed fusion (LPBF) were investigated. RENÉ 65 (R65) has a 42% γ’ volume fraction including Al, Ti, and Nb, while RENÉ 108 (R108) has a higher γ’ volume fraction (63%) including Al, Ta, and lesser Ti. Quantitative analysis showed R108 exhibits 329% higher micro-cracking density than R65. All micro-cracks propagate along high angle boundaries (HABs) and exhibit interdendritic morphologies suggesting solidification cracking is the dominant micro-cracking mechanism. Moreover, secondary phases detrimental for solid-state cracking are not observed at the HABs. Atom probe tomography (APT) showed preferential segregation of Hf, Mo, C, B at the R108 HAB and Zr, Ti, Mo, C, B at the R65 HAB. The Kou solidification cracking criterion showed that Hf and Zr partitioning along the grain boundaries increases micro-cracking susceptibility. Gamma prime did not form during the LPBF process and titanium has a higher tendency than tantalum to partition in the last liquid to solidify.

Tensile strength and failure behavior of rock-mortar interfaces: Direct and indirect measurements

The tensile strength at the rock-concrete interface is one of the crucial factors controlling the failure mechanisms of structures, such as concrete gravity dams. Despite the critical importance of the failure mechanism and tensile strength of rock-concrete interfaces, understanding of these factors remains very limited. This study investigated the tensile strength and fracturing processes at rock-mortar interfaces subjected to direct and indirect tensile loadings. Digital image correlation (DIC) and acoustic emission (AE) techniques were used to monitor the failure mechanisms of specimens subjected to direct tension and indirect loading (Brazilian tests). The results indicated that the direct tensile strength of the rock-mortar specimens was lower than their indirect tensile strength, with a direct/indirect tensile strength ratio of 65%. DIC strain field data and moment tensor inversions (MTI) of AE events indicated that a significant number of shear microcracks occurred in the specimens subjected to the Brazilian test. The presence of these shear microcracks, which require more energy to break, resulted in a higher tensile strength during the Brazilian tests. In contrast, microcracks were predominantly tensile in specimens subjected to direct tension, leading to a lower tensile strength. Spatiotemporal monitoring of the cracking processes in the rock-mortar interfaces revealed that they show AE precursors before failure under the Brazilian test, whereas they show a minimal number of AE events before failure under direct tension. Due to different microcracking mechanisms, specimens tested under Brazilian tests showed lower roughness with flatter fracture surfaces than those tested under direct tension with jagged and rough fracture surfaces. The results of this study shed light on better understanding the micromechanics of damage in the rock-concrete interfaces for a safer design of engineering structures.

Microcrack initiation and propagation in 3 C-SiC ceramic based on molecular dynamics nano-drilling

The evolutionary mechanism of microcracking has been the focus of research in materials processing. The experimental calculation and analysis of microcracking are inevitably difficult due to the limitations of the controllability of its emergence and expansion and the existing observation techniques. In this paper, an experimental model of nano-drilling of 3 C-SiC ceramic parts is constructed using molecular dynamics simulations to achieve real-time observation of the drilling process at the atomic scale, and the microcrack evolution behavior at different depths during the drilling process is discussed, and the microcrack initiation and propagation laws of 3 C-SiC ceramic drilling processing are proposed. The results show that when drilling reaches a certain depth, the compressive stress generated by drilling leads to a prominent region in the plastic deformation zone below the drill bit, where the atomic spacing becomes larger and the workpiece material splits, forming a microcrack eruption zone. The expansion direction of the microcrack is related to the dislocation slip direction, and it expands continuously with the continuous emission of dislocations at the crack tip. The influence of the special evolutionary behavior of the dislocation ring on the microcrack expansion during drilling is focused on, and it is found that the trend of microcrack expansion changed due to the creation of the dislocation ring, and the limit of microcrack expansion is significantly correlated with the dislocation ring evolutionary behavior. With the drilling simulation, the new microcrack expansion showed a periodic occurrence pattern with the special evolutionary behavior of dislocation rings.