Fine Cracks Research Articles

Issue Information

Front cover: Fine cracks in the glaze on the surface of ceramics, known as crazing. The delicate crazing, created through the meticulous work of a skilled ceramic artist, resembles epithelial tissue. This piece was inspired by a microscopic image taken by Dr. Fumiko Matsukawa‐Usami and Professor Toshihiko Fujimori (National Institute for Basic Biology). Designed by TRAIS Co., Ltd. (Kobe, Japan). image

Studies on tribological behavior of aluminum hybrid composites strengthened with MoS2 and wheat husk ash

The current study examines the dry sliding wear characteristics of a hybrid aluminum matrix composite reinforced with wheat husk ash (WHA) and molybdenum disulfide (MoS2), produced through the squeeze casting technique. Experiments were conducted utilizing Taguchi's L27 (3)13 orthogonal array, with input parameters including applied load (20, 30, 40 N), sliding speed (1, 2, 3 m/s), reinforcement percentage (wt. 2.5, 5% and 7.5%), while wear and friction coefficient were observed as measurable responses. Analysis of variance (ANOVA) results highlighted that the reinforcement percentage had the most significant impact on the wear behavior of the hybrid composite. Notably, the (Al/5WHA/5MoS2) hybrid composite exhibited superior wear resistance (129 µm), accompanied by a 27% increase in hardness compared to the parent metal. Surface morphology analysis of worn-out specimens depicted the presence of fine grooves, delamination, and cracks.

Enhancing pixel-level crack segmentation with visual mamba and convolutional networks

Computer vision-based semantic segmentation methods are currently the most widely used for automated detection of structural cracks in buildings and pavements. However, these methods face persistent challenges in detecting fine cracks with small widths and in distinguishing cracks from background stains. This paper addresses these issues by introducing MambaCrackNet, a new network architecture for pixel-level crack segmentation. MambaCrackNet incorporates residual visual Mamba blocks and integrates visual Mamba and convolutional neural network-based segmentation techniques. This approach effectively enhances the detection of fine cracks, reduces misdetections of background stains, and remains robust to variations in patch size and training sample sizes, making it highly practical for engineering applications. On two open access crack datasets, MambaCrackNet outperformed mainstream crack segmentation models, achieving MIoU scores of 0.8939 and 0.8560 and F1-scores of 0.8817 and 0.8412.

Efficient Detection of Apparent Defects in Subway Tunnel Linings Based on Deep Learning Methods

High-precision and rapid detection of apparent defects in subway tunnel linings is crucial for ensuring the structural integrity of tunnels and the safety of train operations. However, current methods often do not adequately account for the spatial characteristics of these defects and perform poorly in detecting and extracting small-scale defects, which limits the accuracy of detection and geometric parameter extraction. To address these challenges, this paper proposes an efficient algorithm for detecting and extracting apparent defects in subway tunnels. Firstly, YOLOv8 was selected as the foundational architecture due to its comprehensive performance. The coordinate attention module and Bottleneck Transformer 3 were then integrated into the model’s backbone to enhance the focus on defect-prone areas and improve the learning of feature relationships between defects and other infrastructure. Subsequently, a high-resolution detection layer was added to the model’s head to further improve sensitivity to subtle defects. Additionally, a low-quality crack dataset was created using an open access dataset, and transfer learning combined with Real-ESRGAN was employed to enhance the detail and resolution of fine cracks. The results of the field experiments demonstrate that the proposed model significantly improves detection accuracy in high-incidence areas and for small-scale defects, achieving a mean average precision (mAP) of 87% in detecting cracks, leakage, exfoliation, and related infrastructure defects. Furthermore, the crack enhancement techniques substantially improve the representation of fine-crack details, increasing feature extraction accuracy by a factor of four. The findings of this paper could provide crucial technical support for the automated operation and maintenance of metro tunnels.

DCNAM: Automatic detection of pixel level fine crack using a densely connected network with attention mechanism

Deep-learning-based crack identification has emerged as a prominent research area in structural health monitoring. Although the detection of common cracks has been the predominant focus in previous studies, the identification of tiny cracks has often been neglected. Efficiently managing thin cracks is vital, because they can threaten the overall structural integrity over time if left unaddressed. We address this gap by targeting thin cracks within a broad category of crack types. We introduce a fine-crack-detection algorithm that efficiently detects both common and tiny cracks. Owing to the limited availability of publicly accessible datasets specifically focused on thin cracks, we collect images of fine cracks to train and evaluate our algorithm. To validate the efficiency of our method, we conduct experiments on three publicly available crack datasets and our private dataset. Compared with the baseline neural network, our proposed approach demonstrates superior performance across all evaluation metrics. Furthermore, our model exhibits impressive generalization ability across the datasets, with the F1 score and mean intersection over union improving by 22.42% and 28.07%, respectively. Notably, our observations indicate that the advantages of the proposed method become more pronounced as the dataset size increases.

Flexural fatigue behavior of ultra-high performance fiber reinforced concrete

Even though UHPFRC has been extensively utilized in infrastructures owing to its excellent mechanical properties, its fatigue behavior remains unclear because related research is very limited. In this study, the fatigue characteristics of UHPFRC were investigated using a four-point bending experiment. In this study, the fatigue characteristics of UHPFRC were investigated using a four-point bending experiment. To determine the fatigue load conditions, static tests were conducted at different loading speeds and ages before, during, and after the fatigue tests. The obtained mechanical properties exhibited a clear dependence on loading rate and age duration. Consequently, a loading frequency of 3 Hz, which is close to that experienced in real infrastructures, was employed in the fatigue tests. A linear S-N relation with a 0.87 fatigue endurance limit was obtained on a semi-logarithmic scale. Additionally, the fatigue life showed a close relationship with the initial cycle deformation. Correspondingly, threshold values of deformation indicators were proposed for predicting the occurrence of fatigue failure. Furthermore, a linear positive relationship was found between the density of multiple fine cracks and fatigue life, based on post-fatigue crack measurements using a microscope. The relatively narrow crack width compared to other cementitious composites demonstrated UHPFRC's superior resistance to corrosion factors. Consistent with the linear S-N relation, the structural degradation appears to be governed by a fiber slippage-to-pull mechanism, as no fiber rupture was observed.

Experimental study on the mechanical characteristics of NPR anchored rock under kilometer-deep buried high geostress conditions

In this paper, a biaxial compression experimental study of NPR (Negative Poisson's Ratio) and PR (Poisson's Ratio) anchored rock under different burial depth conditions was conducted around a new type of constant resistance large deformation anchor cable, also known as NPR anchor cable. A comparative analysis was performed on mechanical characteristics of the two types of anchored rock. Furthermore, a concept of static toughness for anchored rock was established to evaluate the comprehensive mechanical performance. The results indicate that with increasing confining pressure, the elastic modulus of both types of anchored rock exhibits a gradual increase. The peak strength and residual strength initially decrease and then increase. The NPR anchored rock has higher elastic modulus, peak strength, and residual strength compared to PR, with increases of 17.5%, 26%, and 25%, respectively. As the confining pressure increases, the fine and short shear cracks within the lateral surfaces of the two types of anchored rock transform into wider and longer cracks. The final integrity of the NPR anchored rock is demonstrably superior to that of the PR. Compared to PR, the cumulative energy, cumulative count, and energy value per unit count of the NPR anchored rock throughout the experiment are significantly lower values. A calculated analysis revealed that the static toughness of the NPR anchored rock is considerably greater than that of PR.

Effect of different fibers and fiber contents on the mechanical properties and failure behavior of early age cemented lithium feldspar tailings backfill

The cemented lithium feldspar tailings backfill (CLFTB) samples with different fiber types and contents were prepared and subjected to uniaxial compression tests. The results show that glass fiber had the best improvement effect on UCS. With the increase in fiber content, the UCS showed a trend of first increasing and then decreasing, increasing from 1.138 MPa to 2.017 MPa and then decreasing to 1.907 MPa, with the optimal content being 0.6%. The relationship between the strength gain percentage (SGP) and the peak strain gain coefficient γ with fiber content was analyzed. As the fiber content increased, SGP first increased and then decreased while γ gradually increased. Fibers enhanced the ductility, peak load-bearing capacity, and dissipative energy required for the failure of CLFTB. Furthermore, showing greatly enhanced crack resistance in FRCLFTB, evidenced by an increase in the number of fine cracks and a decrease in fragment detachment.

EFEKTIVITAS PENAMBAHAN SERAT POLYPROPYLENE TERHADAP KUAT LENTUR BETON GEOPOLIMER dengan SUPERPLASTICIZER

Geopolymer concrete is concrete composed of a mixture of coarse and fine aggregate without Portland cement binder. Fly ash is used as a substitute, because it contains a lot of silica and alumina. Geopolymer concrete has good strength and durability, but concrete also has disadvantages, namely brittleness, workability and often cracking due to tensile loads. Superplasticizer (SP) is used at 2% of fly ash weight to improve workability. The SP used is Sika viscocrete 1003. The addition of polypropylene fiber is one way to overcome brittle properties and the appearance of fine cracks in concrete. In this paper using Sika fiberforce 48mm polypropylene fiber which has a tensile strength of 465N/mm2(MPa) at a dose of 0%, 0.5%, 1%, 1.5% and 2%. The alkaline activator used is a mixture of NaOH and Na2SiO3 solutions. The molarity of the NaOH solution used is 8M with a ratio of NaOH/Na2SiO3 2: 3. From the test results, it is known that the influence of polypropylene fiber is effective for increasing the bending strength of geopolymer concrete. The bending strength value of geopolymer concrete with the addition of polypropylene fibers increased by 60.19%. The polypropylene fiber content will be maximum at a percentage of 0.5% of the total volume of the mixture.Keywords: Fiber, Flexural Strength, Fly Ash Geopolymer Concrete, Polypropylene, Superplasticizer

EVALUATION OF WOOD DAMAGE AND FRACTURE BEHAVIOR BASED ON ENERGY ENTROPY OF ACOUSTIC EMISSION SIGNALS

In order to assess the damage and fracture behavior of wood under continuous loading, an energy entropy and b-value associated with the acoustic emission (AE) signal were defined to quantitatively describe the release of strain energy during loading. Firstly, the acoustic emission signals of the wood in the three-point bending test were collected. This paper presents the concept of energy entropy according to the definition of information entropy. In order to further evaluate the strain energy intensity released by the damage behavior of the wood specimen, the acoustic emission b-value was defined. Finally, by jointly analysing the dynamics of these two parameters, the test process can be divided into three phases. The results show that even in the elastic phase, micro-destructive behavior occur inside the wood specimen; in the plastic phase, the wood specimen is not only subjected to macroscopic damage, but also often accompanied by fine cracks inside.

Crack Behavior of Eccentrically Braced Frame Type-V with Ground Granulated Blast Furnace Slag

To make the structure stronger and stiffer, which is more susceptible to earthquake forces, a special mechanism is required to improve the structure's lateral stability. EBF-V with a horizontal link beam is a brace that can enhance structural performance by providing good stiffness and ductility. On the other hand, GGBFS, as a partial OPC replacement material, was applied to contribute to using more environmentally friendly materials. Besides offering a smaller carbon footprint, GGBFS also positively improves the mechanical properties of concrete. Thus, this study focuses on investigating the crack propagation pattern of reinforced concrete braced frames combined with 20% GGBFS in EBF-V with three variations of link beam element lengths of 0 cm (CBF), 15 cm (EBF-V-) and 25 cm (EBF-V-25). As a result, the CBF specimen showed the best seismic performance. In EBF specimens, there is an increase in the collapse mechanism to be more ductile. The link beam plays a role in making the crack pattern more focused. EBF-V-15 performs well under seismic loading with large lateral capacity and ductility. The cracks in the frame are evenly distributed, dominated by fine cracks, and symmetrical on both sides. This validates that GGBFS plays a good role in improving the frame performance with its pore-filling effect and pozzolanic reaction.

Enhancing concrete crack healing: Revealing the synergistic impacts of multicomponent microbial repair systems

Small cracks in concrete can develop into larger cracks, reducing the service life of concrete structures. Therefore, the early prevention of fine crack progression is crucial. In this study, a multimicrobial system composed of Bacillus megaterium and Saccharomyces cerevisiae was used to repair concrete cracks, and its repair efficiency was evaluated through fracture healing observations, permeability tests, acoustic time value detection, and unconfined compressive strength tests. Additionally, scanning electron microscopy, energy dispersion spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy were used to analyze the concrete repair mechanism of the multicomponent microbial system. The results showed that when the ratio of S. cerevisiae to B. megaterium in the microbial system was 30 %:70 %, the calcium carbonate (CaCO3) yield increased by 10 %, and the mineralization deposition effect was optimal. Under the synergistic action of the two microorganisms, fracture healing proceeded quickly and the pore structure within the fracture became denser, significantly improving the permeability and strength repair rates of the sample and reducing the pulse velocity. For cracks 1.5 mm in width, the permeability and strength repair rates were 63 % and 35.12 %, respectively. The pulse velocity was reduced from 140 µs to 65 µs. The crack filler is mainly composed of CaCO3 crystals 5–10 µm in size, and the total calcium content of the multicomponent repair system was as high as 39.5 %, which was significantly higher than that of the single component repair system (36.1 %). The results indicate that the multicomponent microbial repair system maintains a higher calcium precipitation activity in a high-strength alkaline concrete environment and produces denser CaCO3 deposits, indicating good repair ability. These repair properties improve the overall performance of concrete. This study confirms the strong potential of multimicrobial systems for efficient, cost-effective, and environmentally-friendly concrete crack repair.

A Novel Load-Sharing System to Simulate the Creep of Strain-Hardening Cementitious Composites (SHCCs) in Practical Situations.

The ductility and exhibition of the multiple, fine, self-controlled cracking of strain-hardening cementitious composites (SHCCs) under tension has made them attractive for enhancing the durability of civil infrastructure. These fine cracks are key to preventing the ingress of water and harmful chemicals into the structure and thereby achieving steel reinforcement. However, several studies have suggested that the short-term fine cracks shown in the laboratory may end up exceeding the acceptable crack widths that are specified in design codes when SHCC members are subjected to sustained constant loads. In real structures, however, the load is also shared by the steel reinforcement in the member, so the SHCC within may not be under a constant load; therefore, the crack widening will not be as severe. This study focuses on the creep behaviour of SHCCs when they are applied as an external layer on reinforced concrete to enhance durability. A novel approach to simulate various stress-strain regimes in such systems is developed by using a fixture to share a sustained moment exclusively between a reinforcement member and SHCC. The developed load-sharing system allows stresses within the reinforcement and SHCC to be monitored against time during the imposed loading, while ensuring access to the SHCC layer for instrumentation and monitoring of strain/cracking. The time-dependent widening of cracks in the SHCC layer is found to be much less significant than that under constant loading, so resistance to water/chemical penetration can still be ensured in the long term. The obtained information on the variation in stress, strain, and crack opening with time will be useful for the development of a general model for the creep behaviour of SHCC members.

Compressive and Tensile Behavior of High-Ductility Alkali-Activated Composites with Polyethylene Terephthalate Powder

Researchers have been engaged in the study of high-ductility concrete (HDC) due to its excellent ductility and cracking control ability. This study combines the concepts of HDC and alkali-activated composites (AAC) to develop high-ductility alkali-activated composites (HDAAC) using polyethylene terephthalate (PET) powder. Experimental investigations were conducted to assess the compressive and tensile properties of HDAAC, focusing on the impact of varying PET powder content (0%, 15%, 30%, and 45%) and fly ash/slag ratios (FA/GGBS, 6:4, 7:3, and 8:2). The results indicated that the compressive strength of HDAAC ranged from approximately 30 MPa to about 100 MPa, with the specimens maintaining good integrity after axial compression failure due to the bridging action of PE fibers. The replacement of quartz powder (QP) with PET powder slightly decreased the compressive strength and elastic modulus of HDAAC, albeit mitigating its brittleness under compression. An increase in GGBS content enhanced the compressive strength and elastic modulus of HDAAC due to the increased formation of the C-A-S-H reaction products, leading to reduced porosity and a denser microstructure. Under axial tension, HDAAC exhibited typical multiple-cracking behavior with significant pseudo-strain hardening. Increases in the PET content and FA/GGBS ratio resulted in finer cracks, indicating excellent crack control and deformation capabilities. The initial cracking strength, tensile strength, and ultimate tensile strain ranged from 3.0 MPa to 4.6 MPa, 4.2 MPa to 8.2 MPa, and 4.1% to 7.2%, respectively. Despite a decrease in the initial cracking strength and tensile strength with higher PET content, the ultimate tensile strain of HDAAC slightly increased. Observations under a scanning electron microscope revealed a distinct interfacial transition zone near the PET powder, leading to poor bonding with the alkali-activated matrix. In contrast, QP dissolved on the surface in highly alkaline environments, forming better interface properties. These variations in interface properties can be used to interpret the variations in the mechanical performance of HDAAC.

Finite element and experimental analysis of surface integrity and surface roughness of precision machining SiCp/Al

The silicon carbide particle-reinforced matrix composites, or SiCp/Al, have excellent mechanical qualities, but producing them is quite difficult since the SiC particles’ and the Al matrix’s properties differ greatly from one another. During the cutting process, the Ra local oscillation phenomena takes place; that is, surface roughness seems to grow, decrease, and then increase as the cutting depth increases within a particular cutting depth range while maintaining the same cutting speed and feed. To find out why this behavior occurred, a cutting experiment and a simulation analysis of SiCp/Al composites were performed. Tests were conducted to find out how varied cutting depths affected surface roughness, and a finite element model for two-dimensional cutting was created. Based on the data, it can be concluded that Ra’s local oscillation phenomena is responsible for the surface quality at various cutting speeds. At 100 mm/s, 200 mm/s, 300 mm/s, and 400 mm/s, respectively, the mutation’s surface quality improved by 29.6%, 14.3%, 19.6%, and 30.7% prior to the cutting depth. The analysis is justified by the fact that the depth of cut is increasing, the way in which particles are removed has changed and the percentage of scratches appears to be decreasing. As aluminium is a plastic material, plastic deformation occurs during cutting by the sub-cutting edge of the extrusion, coating the machined surfaces and producing fine cracks rather than plough furrows. In a sense, increasing the cutting thickness results in larger chips, more force on the particles in the cutting path and easier removal. At the same time, it reduces the width of the chip in future cuts, improving the surface quality of the process.

A three-stage detection algorithm for automatic crack-width identification of fine concrete cracks

A three-stage detection algorithm for automatic crack-width identification of fine concrete cracks

Dynamic behaviors of nickel coated carbon nanotubes reinforced ultra-high performance cementitious composites under high strain rate impact loading

Understanding the dynamic mechanical behaviors of materials is a prerequisite for reliably analyzing and predicting the dynamic response of structures, which is of great significance for transportation infrastructure and military engineering subjected to extreme loads, particularly dynamic loads at high strain rates. Nickel coated multi-walled carbon nanotubes (Ni-MWCNTs) show promise as a reinforcement to modify the dynamic mechanical behaviors of ultra-high performance cementitious composites (UHPCC). Because Ni-MWCNTs combine the high tensile strength and large aspect ratio characteristics of fibers with the nano effect of nanomaterials, as well as have excellent dispersibility due to the nickel plating on the CNTs’ surface, they effectively improve the dynamic mechanical properties of UHPCC under impact loading at high strain rates of about 100 s−1/300 s−1/500 s−1 and reduce the brittle damage degree of composites. The maximal increase in dynamic compressive strength and energy absorption capacity of UHPCC reaches 47.9% and 68.2%, respectively. This enhancement effect arises from that Ni-MWCNTs improve the microstructure and form multiple fine cracks, resulting in an increased energy consumption required for crack formation, propagation and coalescence. Additionally, the dynamic mechanical properties of Ni-MWCNTs reinforced UHPCC exhibit noticeable strain rate effects. Consequently, a strain rate-dependent logarithmic functional dynamic increase factor model and dynamic constitutive model of UHPCC filled with Ni-MWCNTs are modified herein for predicting and modeling the dynamic mechanical behaviors of composites.

Automatic crack detection on concrete and asphalt surfaces using semantic segmentation network with hierarchical Transformer

In recent studies, deep learning methodologies have shown significant promise in crack detection. However, their practical implementation faces challenges due to the intricate diversity of structural surfaces and the inherent narrowness of cracks. To mitigate these problems, this paper introduces SegFormer, an efficient semantic segmentation model with hierarchical Transformer, for crack detection on concrete and asphalt surfaces in multiple scenarios. The combination of Cross-Entropy (CE) and Dice loss functions is employed to enhance the detection of fine cracks. Additionally, the paper presents an evaluation framework and discusses metrics for assessing crack segmentation results to provide a more precise and comprehensive analysis of model performance. Experimental results indicate that SegFormer outperforms Convolutional Neural Networks (CNNs) such as FCN, U-Net, and DeepLabV3 utilizing different backbones. Notably, the integration of multiple loss functions contributes to a more stable training process, expedites convergence, and yields enhanced results compared to models utilizing individual loss functions.

Damage assessment of concrete beams repaired with basalt fiber-reinforced polymer sheets through digital image correlation and acoustic emission

Basalt fiber-reinforced polymer (BFRP) has high mechanical strengths as a repairing material but exhibits low ductility. This paper investigates the damage process of reinforced concrete beams repaired using BFRP sheets, aimed at understanding the underlying mechanisms of achieving structural ductility when BFRP sheets are used. The damage process was assessed using digital image correlation (DIC) and acoustic emission (AE) techniques applied to monitor surface and internal damages of three full-scale concrete beams subjected to four-point bending. A beam was first loaded to crack, then repaired with BFRP sheets, and finally reloaded to failure. Surface strain fields and cracks were monitored using a DIC method, and cracking events were monitored using AE sensors deployed at different positions of the beams. The AE signals were analyzed to assess the damage process. The test results indicated that (1) tensile cracks predominated throughout the loading process; (2) the BFRP sheets hindered the widening of cracks and promoted the generation of fine cracks; and (3) the development of concrete cracks promoted interfacial debonding at steel-concrete and BFRP-concrete interfaces. A combination of different types of cracks and interfacial debonding helped the repaired beam achieve ductile flexural behaviors.

Ductility Variation and Improvement of Strain-Hardening Cementitious Composites in Structural Utilization.

Strain-hardening cementitious composite (SHCC) has the obvious advantages of excellent material properties such as its high tensile and compressive strengths, high tensile strain capacity, and excellent durability against multi-cracking performance with very fine crack widths. In particular, the multi-cracking performance of SHCC during structural utilization is obviously reduced compared to that of SHCC in uniaxial tension tests using dumbbell-shaped specimens of small size. The corresponding tensile strain capacity of SHCC during structural utilization is, thus, significantly decreased compared to that of SHCC in uniaxial tension tests. However, the reduction in the ductility of SHCC during structural utilization has not been sufficiently understood, and further study is required. This paper presents an experimental investigation into the ductility variation of flexural-failed and shear-failed SHCC members as well as the ductility improvement of SHCC members with steel reinforcement compared with that of SHCC in uniaxial tension tests using small-sized specimens. This study focuses on not only the decrease in the crack elongation performance of the SHCC material during structural utilization but also the increase in the crack elongation performance of SHCC members with steel reinforcement. The results demonstrate that the crack elongation performance of flexural-failed and shear-failed SHCC members is significantly reduced compared to that of SHCC in the uniaxial tension tests. Moreover, it was confirmed that steel reinforcement can effectively improve the SHCC member, increasing the strain-hardening capacity and multi-cracking performance. The load-carrying capacity of the flexural-failed SHCC member with steel reinforcement seemed to increase linearly with an increase in the reinforcement ratio, accompanied by an increase in the distribution of multiple fine cracks in the flexural-failed SHCC member with steel reinforcement.