Cracking Characteristics Research Articles

Numerical study on fractal characteristic of blast-induced cracks in deep rock mass

The quantitative representation on the characteristics of blasting-induced cracks in rock mass is of great significance to guide the fine blasting design in practice. However, the quantitative relation between blasting-induced cracks of rock mass and in-situ stresses is currently lacking. To provide the reference for the fine blasting design to excavate rock mass with different in-situ stresses, the present study adopts the fractal theory to quantitatively represent the characteristics of blasting-induced cracks in rock mass. The effects of in-situ stress levels and lateral coefficients on the modes and fractal dimensions of blasting-induced cracks are investigated by numerical simulation combined with image processing. The results show that with the increase of in-situ stresses and lateral coefficients, the fractal dimensions of blast-induced cracks gradually decrease. In addition, quantitative relations between the fractal dimensions of blasting-induced cracks and in-situ stresses are established to provide the reference for the design of rock blasting.

Geotechnical and structural assessment on estimated bearing capacity of strip footing resting on silty sand incorporating moisture content effect

This paper aims to assess the ultimate bearing capacity of a strip footing on the ground surface of a silty sand soil layer. It considers structural failures and geotechnical changes, including the impact of moisture content, using numerical simulation in PLAXIS 3D V21. The structural damage assessments on a student center building located in the northern part of Peninsular Malaysia were performed by visual inspection, and thirty-six sub-points of rebound hammer tests were conducted on three selected different points (Point 1, 2, 3) of the building to evaluate concrete strength and record crack characteristics for severity classification. Subsequently, an extensive geotechnical laboratory tests were performed to investigate the effects of moisture content on physical and mechanical properties of silty sand including, soil compositions, Atterberg limits, compaction characteristics and unconfined compressive strength (UCS) from the building area which resulted to structural damage caused by differential settlement beneath the building. The visual inspection assessment has shown the student center building experienced severe damage category at Point 1 with crack width and length are 25 mm and 3 m respectively. At Point 2, there was minimal damage to the surface structure, with a crack measuring 1 mm in diameter and 0.1 m in length. Furthermore, crack width and length are 1 mm and 0.2 m respectively are recorded for Point 3. The study fills in a gap in the research by combining geotechnical and structural tests on the bearing capacity of silty sand with moisture content. The effect of soil saturation, matric suction, and the unsaturated strength of soil are affected by these factors in the analysis of the bearing capacity of the foundation. The exact solution gives us 568.213 kPa for a zero degree of saturation and 385.34 kPa for a 100 percent degree of saturation. The incorporation of geotechnical and structural assessments aims to find reliable strategies for failure remediations for instance patched and sealed with a concrete patching compound.

Experimental and Analytical Study of Directional Isothermal Fatigue in Additively Manufactured Ti-TiB Metal Matrix Composites

Additive manufacturing (AM) techniques are widely investigated for the cost-effective use of titanium (Ti) alloys in various aerospace applications. One of the AM techniques developed for such applications is plasma transferred arc solid free-form fabrication (PTA-SFFF). Materials manufactured through AM techniques often exhibit anisotropies in mechanical properties due to the layer-by-layer material build. In this regard, the present study investigates the isothermal directional fatigue of a Ti-TiB metal matrix composite (MMC) manufactured by PTA-SFFF. This investigation includes a rotating beam fatigue test in the fully reversed condition (stress ratio, R = −1), electron microscopy, and calculations for fatigue life predictions using Paris’ and modified Paris’ equations. The fatigue experiments were performed at 350 °C using specimen with the test axis oriented diagonally (45°) and parallel (90°) to the AM builds directions. The fatigue values from the current experiments along with literature data find that the Ti MMC manufactured via PTA-SFFF exhibit fatigue anisotropy reporting highest strength in 90° and lowest in perpendicular (0°) AM build directions. Furthermore, calculations were performed to evaluate the optimum values of the stress intensity modification factor (λ) for fatigue life prediction in 0°, 45°, and 90° AM build directions. It was found that for the specimens with 45°, and 90° AM build directions, the computed intensity modification factors were very similar. This suggests that the initial fatigue crack characteristics such as location, shape, and size were similar in both 45°, and 90° AM build directions. However, in 0° AM build direction, the computed stress intensity modification factor was different from that of the 45°, and 90° AM build directions. This indicates that the fatigue crack initiation at 0° AM build direction is different compared to the other two directions considered in this study. Moreover, the quality of fatigue life prediction was assessed by calculating R2 values for both Paris and modified Paris predictions. Using the R2 values, it was found that the fatigue life predictions made by the modified Paris equation resulted in improved prediction accuracy for all three builds, and the percentage improvement ranged from 30% to 60%. Additionally, electron microscopy investigations of 0°, 45°, and 90° AM build specimens revealed extensive damage to the TiB particle compared to the Ti matrix as well as frequent TiB clusters in all three AM build directions. These observations suggest that the spread of these TiB clusters plays a role in the fatigue anisotropy of Ti-TiB MMCs.

Cascade operation-enhanced high-resolution representation learning for meticulous segmentation of bridge cracks

High-resolution (HR) crack images have proven valuable for bridge inspection using unmanned aerial vehicles (UAVs), offering fine details crucial for accurate segmentation. Traditional deep learning (DL) struggles with HR images due to downsampling issues and limited computational resources. To address this, we propose Cascade-FcaHRNet, a HR representation learning-based multiscale architecture. It incorporates a frequency-channel attention mechanism to capture tiny crack features, a two-stage cascade operation for global and local refinement, and a region-sensitive loss to avoid ambiguous predictions. Ablation studies confirm the effectiveness of these modifications. Robustness experiments show improvements in performance metrics for crack segmentation. In a field test, the Cascade-FcaHRNet accurately segments bridge cracks wider than 0.5 mm from 4 K resolution images, enhancing safety and efficiency in UAV-based bridge inspection. The approach holds potential for developing scientifically sound maintenance and management strategies.

Efficacy of initiators on fuel conversion, heat sink, and coke propensity of hydrocarbon fuel under supercritical environment

The investigation includes the cracking characteristics of a multi-component hydrocarbon fuel with a boiling range of 149–224 °C under supercritical environments. The impact of reactor pressure and the influence of initiators on cracking characteristics, such as fuel conversion, coke deposition, gas and liquid product distribution pattern, and heat sink capacities, of the fuel are examined explicitly. The fuel conversion improved by 70.8% as the reactor pressure increased from 2.5 MPa to 5.5 MPa at 650 °C. However, the coke deposition also increased by 55% for the corresponding pressure range. A decrease in the olefin-to-alkane ratio with pressure signifies the possibility of a reduction in unimolecular decomposition reactions and an increase in bimolecular reactions. The efficacy of two initiators, namely triethylamine (TEA) and di-tert-butyl peroxide (DTBP), on heat sinks and coke deposition was also examined. Between the two initiators, the nitrogen-based TEA initiator showed better performance in terms of fuel conversion and coke deposition rate, and the oxygen-based DTBP offered better heat sink capacity. About 22% increment in endothermicity was obtained with 1 wt% DTBP loading at 650 °C under 5.5 MPa pressure.

Variation in preferential flow features induced by desiccation cracks in physical crusts

Studies have shown that preferential flow induced by cracks establishes multiple features such as morphology in different soil profiles. However, there has been little experimental evidence of the contribution of physical crust towards crack features and preferential flow. Essentially, this investigation focused on physical crusts (structural and deposition crust) of Lou soil, a loam and silt loam-textured soil, to demarcate the formation of cracks and preferential flow under artificial rainfall. The crack initiation and propagation processes were defined as the formation of primary cracks in the initial phase and narrow cracks around primary cracks, respectively. The cylindrical soil containers and cubical stainless-steel boxes were employed to trace preferential flow in the horizontal and vertical profile, respectively. The cracks in structural and deposition crusts were dominated by initiation and propagation cracks, respectively. The area, length, and width of the cracks in the structural crusts (5.7 cm2, 815, and 1.44 mm) were notably larger than deposition crusts (1.7 cm2, 604, and 0.96 mm). The maximum dyed depths of the structural and deposition crusts reached 35, 45, and 65 mm, and 35, 55, and 75 mm under the infiltration amounts of 10, 30, and 50 mm, respectively. The uniform infiltration depth, length index and PF-fr of structural crusts were in the ranges of 6.7 ∼ 25.5 mm, 19 ∼ 46 %, and 83 ∼ 111 %, respectively. Corresponding values for deposition crusts were 7.2 ∼ 26.2 mm, 10 ∼ 46 %, and 87 ∼ 103 %, respectively. The preferential flow in the soil profiles with structural crusts was superior to deposition crust. An assessment of the potential function of the physical crust for preferential flow is a supplement to study the effect of soil surface morphology on hydrological process.

Characteristics of micron-scale pore-fracture modification in marine shale reservoirs with different combustion explosion energy

The combustion explosion fracturing of shale with in-situ methane is a revolutionary fracturing technique, but the modification characteristics of reservoir pores and fractures by combustion explosion energy level are still unclear. In order to study the transformation characteristics of micron-scale pore-fracture systems of marine shale reservoirs with different combustion explosion energies, this study selected a section of shale samples from the Longmaxi Formation in the Luzhou block in the southern Sichuan Basin to carry out different energy gradient combustion explosion test, named W1∼W5 (25–91 MPa). Based on micron CT scanning technology, the three-dimensional reconstruction of shale samples before and after combustion explosion was carried out to analyze the effect of combustion explosion energy on the transformation of the pore-fracture system characteristics. The results show that at the energy between 25 MPa and 45 MPa, the variation characteristics of cracks before and after explosion are not obvious. When the energy of the explosion is in the range of 61 MPa–91 MPa, the cracks gradually extend and become longer, and the distribution density of cracks becomes higher and more interconnected. After the explosion at 91 MPa, it can be seen that a number of annular cracks are generated at the edge of the sample, which are interconnected with radial cracks. Total porosity, connected porosity, pore number, and total pore volume of the shale increased after combustion explosion, where the total porosity at the combustion explosion energy of 91 MPa have the largest increment, while the connected porosity, pore number, and total pore volume in the combustion explosion energy of 71 MPa have the largest relative increments, indicating that there is a fracturing pressure value that strongly breaks through the bottleneck when the explosion pressure is between 61 MPa and 71 MPa. A comparison of different pore size sections before and after the combustion explosion pore volume share found that the explosion pressures of 25 MPa, 45 MPa and 91 MPa tend to expand from 100 to 200 μm pore size to form a larger volume share of >200 μm cracks, while at the explosion pressure of 71 MPa, more inclined to transform the 0–100 μm pores, so that the pores gradually transition to the 100–200 μm. Analysis shows that the gas explosion generates a large pressure, release a large amount of heat. Due to the high temperature and high pressure coupling effect, the pore-fracture in the shale changes significantly. Strong stress waves lead to stress concentration at the tip of shale and crack expansion and extension. At the same time, the local expansion force causes “pore expansion effect”. Various mineral particles in the shale undergo differential expansion, along the crystal rupture or through the crystal rupture. New pore fractures are also generated when the original pores keep expanding, which improves the shale pore connectivity. This understanding can provide a theoretical basis for the selection of the energy level of the in-situ methane combustion explosion in shale.

Experimental assessment on the dynamic mechanical characteristics and cracking mechanism of hybrid basalt-sisal fiber reinforced concrete

Hybrid basalt-sisal fiber reinforced concrete (BSFRC) has good application prospects in construction engineering, while the research on its mechanical properties and impact resistance is rather limited. In this study, to systematically investigate the dynamic compressive behavior and cracking characteristics of BSFRC, 9 kinds of concrete specimens containing different fibers and contents were prepared and a series of dynamic compression tests under strain rates of 45–150 s−1 were conducted via the split Hopkinson pressure bar (SHPB) apparatus. For the 9 typical types of concrete prepared in this study, the B1SP2 (i.e., concrete containing 0.1 vol% basalt fibers, 0.1 vol% sisal fibers and 0.1 vol% polypropylene fibers) shows the highest dynamic compressive strength, and the B2S2 (i.e., concrete containing 0.2 vol% basalt fibers and 0.2 vol% sisal fibers) exhibits the highest energy dissipation density. By means of high-speed photography, digital image correlation (DIC) and scanning electron microscope (SEM) techniques, the progressive failure process and microscopic fracture mechanism of BSFRC were further revealed. Fibers in BSFRC effectively inhibit the expansion and penetration of microcracks, and thus delay the initiation and coalescence of macrocracks. Similar to basalt fibers, sisal fibers control cracking behavior of concrete mainly by cutting crack propagation path and exerting bridging effect, and its fiber action is more remarkable for larger cracks. Furthermore, the coupling effect of strain rate and fiber action on the dynamic mechanical behavior of BSFRC were discussed. High loading rate activates more fibers to exert the strength-enhancement and crack-inhibition effect, and the fiber action makes the strain rate dependance of compressive strength more pronounced in BSFRC than that in plain concrete.

Catalytic dehydrogenation cracking characteristics of vacuum residue over solid basic catalyst

The basic calcium aluminate with appropriate catalytic cracking activity, excellent anti-coking performance, and hydrothermal stability is of great potential for the utilization of heavy oil. However, there is a lack of systematic research on the catalytic dehydrogenation cracking characteristics of vacuum residue (VR) over solid basic catalyst. Thus, by combining the TG and Py-GC/MS methods, the dehydrogenation cracking behavior of S-VR was investigated. The results indicated that S-VR cracking on calcium aluminate leads to less coking and higher olefin content in liquid products compared with FCC catalyst and quartz sand. Then, the activation energy Ea is computed from the catalytic dehydrogenation cracking of S-VR on calcium aluminate. The results show that the Ea values from Friedman and OFW methods range from 68 to 143 kJ∙mol−1 and 114 to 192 kJ∙mol−1, respectively. After that, the molecular-level carbon number distributions of the products obtained from cracking S-VR on different reaction conditions are investigated, and the optimal reaction temperature and the heating rate are 650 °C and 1000 °C/s, respectively. Finally, the free radical regulation theory was constructed to explain the catalytic dehydrogenation cracking mechanism of basic calcium aluminate catalyst.

Ability of pre-cast strain-hardening cementitious composite plates to enhance the shear performance of RC haunched beams

The purpose of this paper is to test ten identical reinforced concrete haunched beams (RCHBs) to determine the effectiveness of pre-cast strain-hardening cementitious composite (PSHCC) plates for shear strengthening. For this purpose, the PSHCC plates have been manufactured in accordance with the test parameters, let to cure for roughly 30 days, and then dipped into the strengthened RCHBs' concrete cover at the critical shear span. The used PSHCC plates are rectangular in shape with a 20 mm thickness and a 100 mm width, and they are reinforced with a single layer of steel wire mesh. The considered key parameters were the effect of shear reinforcement in the test region, the PSHCC plate orientation angle (450, 600, or 900), and the spacing between PSHCC plates (200, 250, or 300 mm). In addition, it was interesting to observe how the strengthening plates, if they exist, are positioned in relation to the inner stirrups (aligned, un-aligned, or inclined). The application of PSHCC substantially enhanced the ultimate shear capacity of the strengthened beams, according to the results of experimental tests. Moreover, the inclined configuration of the PSHCC demonstrated higher shear performance than the vertical configuration, both in terms of the shear cracks characteristics and ultimate capacity. As well, the ductility and serviceability characteristics of the strengthened RCHBs were obviously affected by the application of PSHCC plates. Finally, a proposed analytical model was developed to estimate the shear capacity of the strengthened RCHBs using PSHCC plates.

Effect of PVA Fiber on the Mechanical Properties of Seawater Coral Sand Engineered Cementitious Composites.

The physical and mechanical characteristics of seawater coral sand engineered cementitious composites (SCECC) were examined through uniaxial compression, three-point bending, and splitting tensile tests. The mechanical properties were scrutinized under varying fiber volume fraction conditions (V = 0%, 0.575%, 1.150%, 1.725%, and 2.300%). The experimental results indicated that the compressive strength, three-point bending strength, and split tensile strength of SCECC tended to increase with the rise in fiber volume fraction. The strengths attained their maximum values of 45.88, 12.56, and 3.03 MPa when the fiber volume fraction reached 2.300%. In the compression test, the compressive strength of the 7-day specimen can achieve more than 78.50% of that observed in the 28-day specimen. Three-point bending test has revealed that SCECC exhibits favorable strain-hardening and multi-crack cracking characteristics. Fracture patterns of SCECC exhibited variations corresponding to changes in fiber content, as illustrated by their load-deformation curves, the addition of PVA fibers can change the damage mode of cementitious composites from brittle to ductile. The fracture energy of SCECC further attests to its elevated toughness. This is due to the fact that the fibers delay the formation of microcracks and prevent crack expansion, thus significantly increasing the deformability of the material. By verifying its strength, deformability, fracture energy, and other key performance indicators, the feasibility of SCECC in coastal construction projects has been clarified. The successful development of SCECC provides an innovative and high-performance option for the construction of future island projects.

Based on an Overview of Crack Detection

This Crack detection, as an important part of concrete structural health monitoring, aims to reflect the stress state and damage degree of the structure. Traditional concrete crack detection mainly relies on manual visual identification, which has low detection efficiency and accuracy. In addition, manual visual detection has problems such as being greatly affected by lighting conditions, being unable to cover overhead locations such as bridge towers and high piers, and being highly subjective. In recent years, in order to solve the above problems, researchers at home and abroad have developed concrete crack detection equipment based on digital image technology, such as inspection vehicles equipped with high-resolution cameras, unmanned aerial vehicles, crawling robots, and so on. Meanwhile, efficient and accurate crack detection algorithms are the basis for realizing accurate crack identification. How to balance the detection speed and accuracy has been the focus of academic attention. This paper reviews the research progress of concrete crack detection equipment based on digital image technology at home and abroad in recent years, including camera platform, calibration method, preprocessing, traditional and deep learning algorithms, crack feature extraction, image stitching, and 3D representation and monitoring of cracks. In addition, the deficiencies in the research are summarized.

A multiscale enhanced pavement crack segmentation network coupling spectral and spatial information of UAV hyperspectral imagery

Road pavement cracks are a critical factor affecting the health conditions of road pavements. Accurate crack detection contributes to providing data support for road maintenance measures. Compared to conventional crack detection algorithms, deep learning based crack segmentation methods have practical significance for road maintenance and traffic safety management due to their high precision and automation. However, existing deep learning methods often suffer from segmentation accuracy loss due to the varying crack sizes and the presence of stains on the pavement with spatial characteristics similar to cracks, leading to the misclassification of cracks. Therefore, this study proposed a multiscale enhanced road pavement crack segmentation network (MS-CrackSeg) by coupling spectral and spatial information to detect pavement cracks from unmanned aerial vehicle (UAV) hyperspectral imagery. MS-CrackSeg can simultaneously learn the spatial and rich spectral features of cracks in the hyperspectral imagery, improving the discrimination of those targets with similar spatial features to cracks compared to previous approaches. Moreover, the Multiscale Self-Attention-like Feature Extraction Module (MSSA) is introduced to extract and fuse multiscale crack features to enhance the crack detection. Experiments on a dataset consisting of 1031 hyperspectral images demonstrated the superior crack segmentation of the proposed method compared to the comparative methods. In particular, the proposed method achieved the highest F1-score of 0.74 and mean Intersection over Union of 0.79, indicating an exceptional performance. The developed approach offers improved data support for road maintenance measures and has validated the advantages of UAV hyperspectral imagery in road crack segmentation. The annotated hyperspectral dataset and the code for MS-CrackSeg network are available at https://github.com/williamchen-x/MS-CrackSeg.

Characteristics of bio-tar catalytic cracking by char’s inherent Fe2O3 and K2O for biomass gasification process

In this research, a newly-designed micro fluidized bed reaction analyzer (MFBRA) was used to evaluate the catalytic activity of char’s inherent Fe2O3 and K2O on bio-tar in Ar at temperatures of 1023 K, 1073 K, 1123 K, and 1173 K. The adopted samples of char and tar were obtained by biomass pyrolysis in Ar at 1273 K. Fe2O3- and K2O-loaded char were prepared by doping metal oxides on the demineralized char samples to simulate the inherent metal oxides in char. The real-time cracking properties of tar were examined and compared on the basis of the analyzer’s high heating rate, quick sample loading at the predetermined temperature, and online analysis of gas products. The results show that both Fe2O3 and K2O displayed obviously catalytic activity by improving tar conversion and reaction rate, and lowering activation energy (Ea). Compared to K2O at 1173 K, Fe2O3-loaded char promoted the generation of H2, CO, CO2, CH4, C3H6, and the total gas products with the conversion ratio (XFe2O3/K2O) of 2.04, 1.02, 1.24, 1.32, 1.56, and 1.12, respectively. However, it suppressed the formation of C2H6 with the XFe2O3/K2O of 0.43. Meanwhile, the maximum generation rates for CO, CO2, CH4, and the total gas products improved to different extent. During tar catalytic cracking, Fe2O3 suppressed carbon deposition on the char surface because of the larger specific area after experiments. Finally, the generation Ea of CH4, H2, CO, CO2, C3H6 and the total gas products by Fe2O3-loaded char further decreased drastically and that of C2H6 increased obviously. All of these indicated the catalytic activity of the inherent Fe2O3 in char was better than K2O.

MultiScaleCrackNet: A parallel multiscale deep CNN architecture for concrete crack classification

Structural health monitoring plays a crucial role in assessing the condition of civil structures and ensuring their safety and maintenance. One important aspect of structural assessment is the detection and analysis of cracks, which can occur in various structures such as bridges, buildings, tunnels, dams, monuments, and roadways. Recent advancements in crack classification and segmentation techniques have utilized convolutional neural network (CNN) variations. In this paper, we propose an end-to-end learning approach utilizing a deep hierarchical CNN for crack region identification. The proposed architecture leverages high pass kernels in the early convolutional layers to accurately capture the crack patterns, complemented by learnable filters to facilitate adaptive learning. Furthermore, parallel channels within the network enable the learning of cracks at multiple scales, accommodating the varying severity and characteristics of cracks. The model is trained using data at different scales and levels, ensuring comprehensive learning from the lowest to the highest convolutional layers. To validate the effectiveness of our approach, we conducted experimental evaluations using end-to-end training on the Concrete Crack Images for Classification dataset, Asphalt Crack Dataset, and SDNET2018 dataset for crack classification. The results demonstrate the robustness and efficacy of the proposed methodology in accurately identifying crack regions across different datasets.

Preparation and characterization of furfural residue derived char-based catalysts for biomass tar cracking

This study proposed an innovative strategy of catalytic cracking of tar during biomass pyrolysis/gasification using furfural residue derived biochar-based catalysts. Fe, Co, and Ni modified furfural residue char (FRC-Fe, FRC-Co, and FRC-Ni) were prepared by one-step impregnation method. The influences of cracking temperature and metal species on the tar cracking characteristics were investigated. The results showed that the tar conversion efficiency for all catalysts were improved with the cracking temperature increasing, the higher tar conversion efficiency achieved at 800 °C were 66.72 %, 89.58 %, 84.58 %, and 94.70 % for FRC, FRC-Fe, FRC-Co, and FRC-Ni respectively. FRC-Ni achieved the higher gas (H2, CO, CH4, CO2) yield 681.81 mL/g. At 800 °C, the catalyst (FRC-Ni) still reached a high tar conversion efficiency over 85.90 % after 5 cycles. SEM-EDS results showed that the distribution of Ni particles on the biochar support was uniform. TGA results demonstrated that FRC-Ni exhibited better thermal stability. XRD results indicated that there was no significant change in the grain size of Ni before and after the reaction. The FRC-Ni catalyst was reasonably stable due to its better anti-sintering and coke-resistant capabilities.

Effect of High-Intensity Microwave Treatment on Structural and Chemical Characteristics of Chinese Fir

High-intensity microwave (HIMW) treatment is a time-saving and environmentally friendly method widely applied in the wood processing industry. It enhances wood permeability, making it suitable for drying and impregnation modification. This study aimed to investigate the effects of HIMW on macroscopic and microscopic cracks, tracheid cell wall damage, and the chemical structure of Chinese fir [Cunninghamia lanceolata (Lamb.) Hook] wood. Through the use of a camera, optical microscope, scanning electron microscope, transmission electron microscope, Fourier-transform infrared spectroscopy, and X-ray diffraction, the morphology of cracks, cell wall damage, the chemical composition of the cell wall, and the crystalline structure of cellulose treated with HIMW were examined and analyzed. The results revealed that the initial moisture content (MC) and microwave energy density (MWED) significantly influenced the crack characteristics and cell wall structure and slightly influenced the chemical composition and crystalline structure of cellulose of the Chinese fir cell wall. HIMW treatment can produce different characteristics of wood cracks. The size and number of cracks were significantly increased with the increase in MWED, and more cracks were found in low MC. Microcracks caused by HIMW treatment tended to initiate at the ray parenchyma, resulting in the stripping of ray cells along its radial direction. Meanwhile, the cracking of adjacent cell junctions, the rupturing of the pit margo and pit torus, and cell wall parts tearing along the direction of microfibers occurred as a result of the HIMW treatment. The most severe damage to the cell walls occurred at the interface of S1/S2, S1, and ML layers, and the cell walls were torn in the S2 layer. There were no significant changes in the FTIR spectra of the HIMW treatment samples. Hemicellulose degradation occurred first, which increased with the increase in MWED. The recrystallization of cellulose and the lignin content increased because of the change in the aromatic C=O groups. As MWED increased, both the crystallinity index (CI) and cellulose crystal width (D200) of the samples that underwent HIMW treatment increased accordingly, and the number of low-MC samples was greater than that of the high-MC samples. The findings contribute to understanding the crack characteristics and damage mechanism induced by HIMW treatment on wood. This study provides valuable insights into regulating the effects of HIMW treatment and expanding its application in wood processing, such as wood drying and functionalized impregnation, according to the specific end-use requirements.

A Fractal-Based Quantitative Method for the Study of Fracture Evolution of Coal under Different Confining Pressures

To study the dynamic crack evolution process of loaded coal from the perspective of fractals, we carried out in situ industrial CT scanning tests of loaded coal under different confining pressures, visualizing loaded coal fracturing. Combined with fractal theory, the temporal and spatial evolution law of coal cracks is described quantitatively. The results provide two findings: (1) from the perspective of two-dimensional images and three-dimensional space, the evolution characteristics of cracks in coal under different confining pressures were basically the same in each loading stage. During the loading stages, the cracks exhibited a change rule of a slow reduction, initiation/development, rapid increase, expansion, and penetration. (2) The fractal dimension of coal was calculated by introducing fractal theory, and its change law was in good agreement with the dynamic changes of the cracks, which can explain the influence of the confining pressure on the loaded coal. The fractal dimension showed three stages: a slight decrease, a stable increase, and then a significant increase. The larger the confining pressure, the more obvious the limiting effect. Thus, our approach provides a more accurate method for evaluating the spatial and temporal evolution of cracks in loaded coal. This study can be used to predict the instability failure of loaded coal samples.

Study on the effect of crack characteristics on radon exhalation from overburden of uranium tailings pond

Study on the effect of crack characteristics on radon exhalation from overburden of uranium tailings pond

An analysis of fatigue crack features at various crack lengths through mating fracture surface pairs

AbstractThis paper presents a novel high‐resolution direct analysis of mating AA7050‐T7451 fracture surfaces at crack lengths from 0.1 to 1.3 mm (Kmax of 4.51 to 16.39 MPa√m) for the purpose of analyzing the fatigue growth mechanisms. The various fractographic features observed at these crack lengths were then compared to the known accelerative effects of an applied loading sequence that contained underloads at regular intervals. A correlation was found between some of the observed features and the local fatigue crack growth rate. This study provides new insight into the prominent mechanisms that dictate crack growth rate and ultimately should assist with developing crack growth prediction methods that more accurately represent the physics of the fatigue crack growth mechanisms.