Crack Propagation Characteristics Research Articles

Mechanical and acoustic characteristics of sandstone failure at different immersion heights under tailings water erosion conditions

To investigate the influence of tailings water immersion height on the failure process of rocks, intact yellow sandstone samples and yellow sandstone samples with prefabricated fissures were prepared. Uniaxial compression tests were conducted on these sandstone samples with varying immersion heights, and the failure processes were simultaneously monitored using a camera and an acoustic emission monitoring system. Based on the test results, the crack propagation and failure characteristics of the yellow sandstone samples under uniaxial loading at different immersion heights were determined. The relationships between the immersion height and peak strength and between the immersion height and elastic modulus were characterized. Additionally, the intrinsic connection between sandstone damage and acoustic emission signal parameters was revealed. The experimental results indicate that the uniaxial compressive strength and elastic modulus of the sandstone samples decrease continuously with increasing immersion height, but the rate of decrease gradually slows. The presence of water is the primary reason for the deterioration of mechanical properties, and the chemical components in the tailings water are significant factors that cannot be ignored. The initiation location and propagation of cracks in intact samples depend on the immersion height, while the fracture behaviour of fissured samples after immersion is mainly influenced by the prefabricated fissures. As the immersion height increases, the longitudinal wave velocity increases, while the number of acoustic emission events, peak frequency, and amplitude exhibit a decreasing trend that is initially rapid and then slows. A damage evolution model based on acoustic emission ringing counts at different immersion heights was established. It was also found that the acoustic emission signals of these yellow sandstone samples mainly show the characteristics of abrupt signals under any immersion water height.

Effect of aging state on low cycle fatigue performance of AA 2099 alloy

The evaluation of the fatigue performance is a crucial subject in the research of structural materials utilized in the field of aerospace engineering. In order to examine the influence of aging state on fatigue performance, low cycle fatigue (LCF) experiments were conducted on specimens made from AA2099 alloy in the under-aged (UA), peak-aged (PA), and over-aged (OA) states, with varying strain amplitudes (Δεt/2=0.3 %-0.5 %). In the UA and PA states, the grain boundary precipitates exhibit a small size, thereby prompting the crack to propagate through the grains. Certain grains in this region exhibit a crystallographic feature of crack propagation along the (111) slip plane, which is associated with the formation of the precipitation free bands (T1-PFB) within the grains. In contrast, in the OA state, the size of the grain boundary precipitates increases significantly, accompanied by a minimum precipitation free zones (PFZs) width increase to 75 nm, exacerbating the stress concentration at grain boundaries, with cracks primarily extending along the grain boundaries. Furthermore, the presence of coarse grain boundary precipitates and the widened PFZs promote the initiation and propagation of fatigue cracks, leading to a pronounced reduction in fatigue life.

Experimental study on dynamic crack growth and propagation characteristics of central hole double fracture shales under impact loading

Experimental study on dynamic crack growth and propagation characteristics of central hole double fracture shales under impact loading

Quasistatic progressive crack propagation behavior of crystalline rocks based on SCB tests

To explore the influence of mineral grains on the mechanical strength and crack propagation behavior of rocks, this study investigates the quasi-static crack propagation characteristics in four types of granular structured rocks (three varieties of granite and one type of diabase rock) through a semi-circular bend three-point bending test. The implementation of a servo-controlled crack-opening displacement mechanism facilitated the realization of quasistatic crack propagation. The entire experimental procedure was documented on a camera. Subsequently, the quasistatic propagation and development of cracks in crystalline rocks were examined using digital image correlation, whereas the distribution of mineral grains and their relationship with the pattern of crack evolution were investigated under optical microscopy. The paths of the cracks exhibited noticeable deviation, which were further influenced by the mineral grains. Specifically, cracks tended to circumvent harder minerals while gravitating towards softer ones, highlighting the significant role of mineralogical composition in determining the fracture behavior of granite.

Evaluation of RPV closure head penetration integrity considering fitting and residual stresses

To ensure the structure integrity of the Reactor Pressure Vessel (RPV), the main challenge is the embrittlement of beltline material. However, the stress is more complex for the regions of Closure Head Penetration (CHP). Feedback of leakage at the CHP has been found during in-service inspection. Although the detailed mechanical evaluation of the RPV head and the CHP has been carried out by many international institutions, there are limited studies to concern structure integrity of CHP tube. The systematic analysis of the influence of material strength matching, assemble stress, the Welding Residual (WR) stress and work pressure load on the fracture is also limited. In this paper, the systematic influence of these factors is analyzed, and the distribution characteristics of Stress Intensity Factor (SIF) and the crack propagation characteristics are studied. The 2D model and accurate 3D model are carried out using the finite element method. The results show that the WR stress on the outer surface of the CHP and the area adjacent to the weld is larger than the yield strength of the material. There is a gap between the RPV and the upper part of the CHP. The attenuation rate of the WR stress in the outlet direction of RPV is lower than that in the inlet direction, so cracks are more likely to occur in the out of direction. The influence of WR stress on the circumferential stress distribution and fracture parameters in the wall thickness direction of CHP is bigger than the influence of assemble load and design condition load. However, the overall stress of CHP is low. The SIF values along the crack front have an asymmetric distribution, and the SIF value is very small. As the fatigue crack propagation life is much longer than the assumed limit in the design lifetime, the risk of fracture and crack fatigue propagation caused by mechanical stress is low.

Investigation of three-dimensional model reconstruction and fractal characteristics of crack propagation in jointed sandstone

The presence of random joints, cracks, and other defects significantly affects the meso-damage mechanism and macro-mechanical behavior of the rock. This study employed micro-CT scanning, digital image processing (DIP), and the rock failure process analysis system (RFPA3D) to reconstruct a genuine mesostructure, creating a three-dimensional (3D) numerical model of jointed sandstone. Under uniaxial stress, this model facilitated the meso-damage evolution process of prefabricated cracks in sandstone with varying dip angles. Additionally, the influence of jointed sandstone heterogeneity and prefabricated cracks with various dip angles on its failure mode and meso-damage mechanical properties were investigated. Utilizing the MATLAB platform, a 3D box dimension algorithm was developed to analyze the fractal characteristics of the mesodamage evolution in the sample. This algorithm enabled the quantitative characterization of the meso-damage evolution of sandstone. This study categorized three types of sandstone final failure modes: composite shear failure, shear failure along the joint surface, and tensile failure. Additionally, linear variations in the elastic modulus and compressive strength of the jointed sandstone were observed with increasing prefabricated fracture inclination, highlighting significant anisotropy. The presence of joints was found to induce and control the failure mode of sandstone. The meso-damage evolution process of sandstone was described in terms of the fractal dimension, indicating that more severe damage corresponded to a larger fractal dimension. This approach offers a novel statistical method for studying the progression of rock damage.

Dynamic impact experimental and global cohesive element method to shale fracture characterization

The fracture behavior and various of mechanical mechanisms of shale are greatly influenced by the bedding surface. To study the effects of bedding angles on the crack propagation patterns and dynamic fracture properties, the shale notched semi-circular bend (NSCB) specimens were studied by the modified split Hopkinson pressure bar (SHPB) device, three-dimensional digital image correlation (3D-DIC) system with the high-speed (HS) photography and ABAQUS finite element software. The research results showed that at the same impact velocity, the 30°, 45° and 60° beddings played an obvious deflexion effect on the shale crack propagation. However, the 0° and 90° bedding did not deflect the crack propagation. The dynamic fracture toughness of shale NSCB specimens increased with the increase of impact loading rate but the increase magnitude decreased with the higher impact rate. The kinetic energy during specimen fracture was calculated by the extracting displacement data from the 3D-DIC, and it was found that the kinetic energy accounted for less than 6% of the absorbed energy during the dynamic compression of the shale. The crack propagation characteristics of ABAQUS simulation was approximately consistent with the experimental results. It is conducive to the study of shale gas fracturing and the formation of complex seam networks in shale and it is of great research significance for the efficient extraction of shale gas.

The Review of Research on Fatigue Crack Propagation in Metallic Materials

In recent years, with the development of industry and scientific technology, the demand for materials has been increasing. Fatigue crack propagation is an important issue in the field of materials, and developing relevant theories and methods, understanding the mechanisms of fatigue cracks, and making scientific predictions on fatigue crack propagation are hot topics both domestically and internationally. Fracture mechanics, as a discipline studying the strength and propagation of cracks in materials, has developed a relatively complete theoretical system and engineering application methods over more than 100 years of continuous development. This article focuses on the effects of factors such as temperature, stress ratio, and load frequency on the fatigue crack propagation characteristics of metallic materials, and summarizes the common theories and methods of fatigue crack propagation.

Study on dynamic behavior and crack propagation mechanism of the tanks in one-step BLEVE accident

A boiling liquid expanding vapor explosion (BLEVE) is one of the most serious accidents which generates overpressure and ejected fragments with potential great impact on the safety of the tank area. Hence, it is important to reveal the dynamic characteristics of the axial crack propagation at the top of the horizontal tank in a BLEVE accident. The rupture behavior of tanks under one-step BLEVE accidents is investigated and the detailed dynamic characteristics of crack opening angle and crack propagation rate were assessed through the small-scale BLEVE experiments with variations in tank wall thickness and filling levels. An extended Gurson-Tvergaard-Needleman (GTN) model was proposed to calculate the dynamic damage of the tank during the rupture process. The dynamic stress-strain damage characteristics of the tank during the one-step BLEVE process and the circumferential transformation mechanism of the axial crack were explored. Based on an analysis of the material damage and the size characteristics of the tank structure, criteria were proposed for judging whether the direction of crack growth will change.

Experimental study on crack propagation characteristics of unconventional reservoir rocks

This study investigates the fracture behaviour of three types of specimens (shale, sandstone, and coal), which are commonly found in unconventional reservoirs, based on mode Ⅰ single-edge notch beam (SENB) test. We employ the Digital Image Correlation technique to track the strain evolution and crack propagation paths of the three types of materials and compare their fracture characteristics. The experimental results show that both the surface roughness and crack initiation angle of the coal are larger comparing with that of sandstone and shale, which demonstrates the ductile property of coal and fracturing difficulty in coal seam. Moreover, the average velocity difference of crack propagation is obvious, which is 53.76 × 103, 453, and 0.33 mm/s in shale, sandstone, and coal, respectively. The elastoplastic J-R curves, which reflects the influence of the plastic zone, are presented to analyze the energy dissipation characteristics of three types of specimens during crack propagation. It is found that the J-integral of shale and sandstone does not increase with crack propagation, but the J-integral of coal shows obvious increasing trend with crack propagation due to the effect of plasticity. In addition, microscopic analysis is conducted using a petrographic microscope and scanning electron microscope (SEM) to explain the plastic zone differences at the notch tips of shale, sandstone, and coal. This study is a preliminary and significant step of hydraulic fracturing application in unconventional reservoirs for efficient recovery of the berried natural gas.

Study on rock-breaking mechanism and bit adaptive characteristics under the action of claw-toe impregnated diamond bit

In order to overcome the ingrained belief that the impregnated diamond bit primarily achieves rock-breaking via grinding and micro-cutting and to have a better understanding of the drilling mechanism of the bit, in this work, aiming at the inherent weakness of rock cracks, a claw-toe impregnated diamond bit (CTB) with a self-regenerative structure is innovatively designed. The concept is that the structure of the bit can actively induce the development of cracks inside the rock or create cracks in the dense rock. Through simulation, the differences in hole bottom morphology, drilling efficiency, rotational speed, torque and rock-breaking vibration between conventional bit (CB) and CTB (CTB with two sets of tooth units (CTB-2) and CTB with three sets of tooth units (CTB-3)) are analyzed, and the crack propagation and stress-strain field distribution characteristics of rock are compared when the tooth units of bit (TUBs) press into rock and cause initial damage to rock. Through field tests, the superiority of the claw-toe impregnated diamond bit (CTB) and its rock-breaking mechanism is verified. Compared with the conventional bit (CB), the simulation results show that the claw-toe impregnated diamond bit (CTB) can achieve efficient drilling with smaller rock-breaking torque, more stable rotational speed, and a more apparent shear effect on rock. The mean vibration reaction force of the claw-toe impregnated diamond bit with two sets of tooth units (CTB-2) and claw-toe impregnated diamond bit with three sets of tooth units (CTB-3) increases by 0.78 times and 0.43 times, respectively, and the mean rock-breaking torque decreases by 10.66% and 21.81%, respectively. The structure of the claw-toe impregnated diamond bit (CTB) can force rock to produce more tensile stress concentration areas, induce rock crack initiation, and accelerate rock failure. Field tests show that the service life of the claw-toe impregnated diamond bit with three sets of tooth units (CTB-3) is 1.9 times longer than the mean service life of the conventional bit (CB). Furthermore, the claw-toe impregnated diamond bit (CTB) has obvious structural advantages: it will self-sharpen its structure, maintain its best drilling structure in subsequent drilling, and tear up rock, resulting in better drilling performance.

Fatigue crack propagation characteristics of aluminum/steel laser-metal inert gas fusion-brazed joints in different micro-zones

Research on fatigue damage of aluminum/steel dissimilar joints is critical to ensure the reliability of multi-material lightweight structures. In this study, the fatigue crack propagation (FCP) characteristics of the interface, weld, and heat-affected zone (HAZ) of aluminum/steel laser-metal inert gas (MIG) fusion-brazed joints were investigated. Additionally, the influencing role of the microstructure of different micro-zones on the FCP behaviors was discussed. Single-edge notched tensile (SENT) specimens of the interface region exhibited a higher crack growth rate and crack threshold than SENT-weld and SENT- HAZ specimens due to the highly hard and brittle nature of the intermetallic compounds (IMC) at the aluminum/steel interface. Moreover, the fatigue fracture surface of SENT-interface specimens showed a brittle fracture pattern without fatigue striation characteristics, which was different from aluminum/steel solid-state and traditional aluminum alloy welded joints. Electron backscatter diffraction (EBSD) analysis results revealed that the synergistic effects of grain size, sub-grain boundaries, and micro-performance all contributed to the crack deflection of SENT-weld at a large angle to the HAZ, thereby resulting in more optimized crack resistance in the weld zone.

Analysis of the crack initiation and short crack propagation of laser cladding IN718 enduring fretting fatigue at 650 ℃

In order to reveal the behaviors of crack initiation and short fatigue crack propagation in laser cladding IN718 under high temperature conditions, very high cycle fretting fatigue (VHCFF) experiments were conducted at 650 ℃ with a transverse clamping force of P=400N and different axial stress loading conditions to obtain S_N data. The surface wear morphology and fracture morphology characteristics were analyzed by scanning electron microscope (SEM) and white light interferometer. Additionally, the microstructure characteristics of grains in the short fatigue crack region were examined through electron back scatter diffraction (EBSD). Parameters such as equivalent grain size, grain elastic modulus, Schmid factor, geometric compatibility factor, twist angle, and tilt angle were considered in the analysis of the characteristics of fatigue crack initiation and propagation. The results indicate that fretting fatigue cracks tend to initiate on grains with higher Schmid factors, larger equivalent grain size, and lower grain elastic modulus on the fretting contact surface. Moreover, the short fatigue cracks tend to propagate along the grains with the microstructural features of the high Schmid factor, the geometric compatibility factor of m′>0.4, the twist angle of α<50°, and the tilt angle of β<50°.

Study of crack propagation in multi-phase composites embedded with both stiff and compliant particles using phase field method

Abstract Crack propagation in two-phase particle-reinforced composites is extensively studied using&amp;#xD;the phase field method. Typically, the particle either has a higher stiffness(stiff) or a lower&amp;#xD;stiffness(compliant) than the matrix. However, the crack propagation in multi-phase composites&amp;#xD;with both the stiff and compliant particles is not yet understood well. In this work, we report&amp;#xD;on the crack propagation characteristics and the resulting enhanced effective fracture toughness&amp;#xD;in multi-phase composite materials with both stiff and compliant particles using the phase filed&amp;#xD;method. Three different geometric arrangements of particles are considered: a diagonal array,&amp;#xD;a cubic array, and a honeycomb array. The honeycomb configuration had the best combination&amp;#xD;of strength and effective fracture toughness. We show that apart from the local geometric&amp;#xD;arrangement of the individual particles, the ratio of the stiffness of the individual particles is&amp;#xD;an important factor in crack propagation. Furthermore, we show that the ratio of the critical&amp;#xD;energy release rate of the individual particles can be tuned to increase the effective fracture&amp;#xD;toughness.

Study on Acoustic Emission and Crack Propagation Characteristics of Single-Fissured Sandstone with Different Angles Under Uniaxial Compression

Study on Acoustic Emission and Crack Propagation Characteristics of Single-Fissured Sandstone with Different Angles Under Uniaxial Compression

Experimental study of precursory features of CO2 blasting-induced coal rock fracture based on grayscale and texture analysis.

CO2 blasting has been identified as a potent method for enhancing the permeability of coal seams and improving gas drainage efficiency. This study is focused on elucidating the deformation and fracture mechanisms of coal and rock during CO2 blasting and on identifying the precursor characteristics of these processes. To this end, a CO2 blasting-induced coal rock fracture pressure model and a gas pressure distribution model were developed. The research utilized a self-developed CO2 blasting test platform along with a non-contact full-strain field measurement analysis system. Briquette samples were subjected to CO2 blasting tests under controlled experimental conditions, which included an axial pressure of 1.0 MPa and variable gas pressures of 0.5, 1.0, and 1.5 MPa. This methodology enabled the capture of the principal strain field on the surface of the samples. The Gray Level Co-occurrence Matrix (GLCM) was employed to extract and analyze the grayscale and texture features of the strain cloud maps, facilitating a quantitative assessment of their evolution. The aim was to pinpoint the precursor characteristics associated with coal rock cracking and crack propagation. The results revealed that: (1) During the cracking and subsequent propagation of samples, the strain field's grayscale histogram underwent a transformation from a "broad and low" to a "narrow and high" configuration, with a consistent increase in peak frequency. Specifically, at 3 ms, a primary crack was observed in the sample, evidenced by a grayscale peak frequency of 0.0846. By 9 ms, as the crack propagated, the grayscale peak frequency escalated to 0.1626. (2) The texture feature parameters experienced their initial abrupt change at 3ms. Correlation with the gas pressure distribution model indicated that this was the crack initiation moment in the sample. (3) A secondary abrupt shift in the texture feature parameters occurred at 9ms, in conjunction with experimental phenomena, was identified as the crack propagation phase. Monitoring the grayscale and texture features of the principal strain field on the coal rock surface proved effective in recognizing the precursor characteristics of crack initiation and propagation. This research has the potential to reduce blasting costs in coal mines, optimize blasting effects, and provided theoretical guidance for enhancing gas extraction efficiency from deep and low permeability coal seams.

Study on Crack Propagation Characteristics of Foam Concrete–Soil Composite with Different Height Ratios under Dynamic and Static Loading Conditions

Study on Crack Propagation Characteristics of Foam Concrete–Soil Composite with Different Height Ratios under Dynamic and Static Loading Conditions

Study of the crack propagation characteristics of brittle materials at low temperatures based on 3D-ILC

Study of the crack propagation characteristics of brittle materials at low temperatures based on 3D-ILC

Research on ultrasonic bone cutting mechanism based on extended finite element method.

The research on the crack propagation mechanism of bone has important research significance and clinical medical value for the selection of cutting parameters and the development of new surgical tools. In this paper, an extended finite element method (X-FEM) model of ultrasonic bone cutting considering microstructure was developed to further study the ultrasonic bone cutting mechanism and to quantitatively analyze the effects of cutting direction, ultrasonic parameters, and cutting parameters on the mechanism of ultrasonic bone cutting crack propagation. The results show that ultrasonic bone cutting is essentially a controlled crack propagation process, in which brittle crack and fatigue crack are the main crack propagation mechanisms. In order to improve the efficiency of ultrasonic bone cutting, large amplitude and high-frequency ultrasonic vibration are preferred. Compared with the other two cutting directions, the crack propagation deflection angle in the transverse cutting direction is the largest, resulting in the worst cutting surface. Therefore, in the path planning of orthopedic surgical robots, the transverse cutting direction should be avoided as much as possible. Frequency only has a significant effect on the crack propagation rate and has a positive correlation. There is a positive correlation between the deflection angle, propagation length, propagation rate, and amplitude, which provides the possibility to control the direction and length of crack propagation by controlling the amplitude of ultrasonic. The feed speed is much lower than the ultrasonic vibration speed, which makes the influence of ultrasonic vibration speed on the crack propagation characteristics dominant. The X-FEM model of ultrasonic bone cutting provides an effective method for selecting reasonable machining parameters of orthopedic robot and optimize the design of ultrasonic osteotome.

Effect of Heat Treatment on Fatigue Properties of TA15 Titanium Alloy Repaired by Laser Deposition

Laser‐deposition repair technology is employed to repair damaged TA15 titanium alloy forgings. Heat treatment is used to control the microstructure, strength, and plasticity of these repaired forgings. The fatigue properties and crack initiation and propagation characteristics of the repaired parts are studied. Optical microscopy and electron microscopy are used to analyze the microstructure, fatigue fracture, and longitudinal section near initiation. In the results, it is indicated that the tensile and fatigue properties of repaired parts after 900 °C heat treatment are superior to those treated at other temperatures. This is attributed to the strong tissue sensitivity of the repaired specimens’ performance. With increasing heat‐treatment temperature, the secondary α phase in the dimorphic structure tissue thickens. Additionally, the restoration zone develops in layered α phases and becomes truncated, leading to shortening and thickening. The heat‐affected zone undergoes a transformation from a transitional structure to a basket organization. After heat treatment at 1000 °C, the microstructure becomes relatively slender, cracks propagate readily, and the resistance is weakened.