Search Results (78)

The brittle characteristics of fiber-reinforced concrete make it difficult to capture the time-varying properties during its flexural failure. This study employed high-speed imaging to investigate the effects of polypropylene fiber, polyvinyl alcohol fiber (PVA), and basalt fiber on the fracture behavior of concrete. The influence mechanisms of fibers on concrete fracture performance were thoroughly revealed by analyzing failure time, crack growth rate, fracture development process, and flexural strength. The results show that fibers significantly extend the time to flexural failure in concrete. At a fiber volume fraction (FVF) of 0.3%, the fracture times of PVA-reinforced concrete and basalt fiber-reinforced concrete increased by 23% and 17%, respectively, compared to plain concrete. Their average crack growth rates were 27.0 m/s and 28.6 m/s, respectively, which are lower than the 33.3 m/s observed in plain concrete. In the initial frame capturing crack initiation, the average crack growth rate was 35.7 m/s for fiber-reinforced concrete and 31.5 m/s for plain concrete. By the second frame, these rates increased to 67.8 m/s and 63.1 m/s, respectively. The cracking process in both plain and fiber-reinforced concrete specimens exhibited a “fast-to-slow” pattern. At approximately 1.5 ms, the crack shown in the second frame had propagated to about two-thirds of the specimen height. Compared to plain concrete, the flexural strengths of polypropylene fiber-reinforced concrete increased by 39.2%, 22.9%, and 26.2%; basalt fiber-reinforced concrete increased by 10.0%, 0.2%, and 9.3%; and PVA-reinforced concrete increased by 9.0%, 7.0%, and 10.6% at FVFs of 0.1%, 0.2%, and 0.3%, respectively. Full article

Welding repair of cracks in FSX-414 cobalt-based alloy, used in high-temperature components, poses significant challenges due to the presence of surface oxide films within the cracks. By comparing the formation of oxide films on the external surface and inside the narrow crevice of FSX-414 alloys preserved at 900 °C for up to 1000 h, we found that the oxide film growth rate on the external surface was slightly larger than that inside the narrow crevice, and the latter slowed down after 672 h. Additionally, the oxide films on both surfaces were mainly composed of O and Cr elements, providing excellent protection to the underlying metal and resulting in minimal internal oxidation. A compositional transition region formed between the oxide film and the base metal. The width of the transition region decreased with heating duration and was narrower in the external surface sample, leading to a steeper composition gradient between the oxide film and the inner metal. With prolonged exposure, increasing numbers of “pores” rich in W and O appeared near the oxide films, creating channels that connect the oxide layer with the internal metal and accelerate material degradation. “Pores” extended deeper into the metal within the narrow crevice compared to those on the surface. Prior to welding repair, channels composed of W and O near the oxide films must be cleaned along with the oxide layer itself, and the removal of oxide from narrow cracks poses greater difficulty. Full article

Ground fissures are widespread around the world and are particularly severe in the North China Plain. In order to investigate the crack propagation path and propagation mode of buried ground fissures from deep strata to the surface, physical simulation experiments and numerical simulation experiments were conducted based on the sand–clay interlayer strata in the Longyao area. The results show that during the settlement of the hanging wall strata, the propagation path of the cracks changes due to differences in soil properties. The crack propagation is interrupted in the sand layer and slowed down in the clay layer. The surface displacement is characterized by an alternating sequence of gradual and rapid growth phases. The process of crack propagation from depth to surface is divided into five stages, forming tensile cracks and causing the differential settlement of the surface. The strata are mainly under tensile stress, with the stress range of the hanging wall being 2.1 to 3.0 times that of the footwall. Under identical experimental conditions, buried ground fissures in the strata of sand–clay interlayers exhibit anti-dip crack propagation angles and surface deformation zone widths that are between those of homogeneous silty clay and sand. Based on the experimental results, an analytical formula for the hanging wall deformation zone was further proposed. The research results can provide an important reference and theoretical basis for the investigation and disaster prevention of buried ground fissures in the Longyao area of Hebei Province. Full article

The rapid growth of urban areas has increased the need for more efficient methods of pavement inspection and maintenance. However, conventional techniques remain slow, labor-intensive, and limited in spatial coverage, and their performance is strongly affected by traffic, weather conditions, and operational constraints. In response to these challenges, it is essential to synthesize the technological advances that improve inspection efficiency, coverage, and data quality compared to traditional approaches. Herein, we present a systematic review of the state of the art on the use of unmanned aerial vehicles (UAVs) for monitoring and assessing pavement deterioration, highlighting as a key contribution the comparative integration of sensors (photogrammetry, LiDAR, and thermography) with recent automatic damage-detection algorithms. A structured review methodology was applied, including the search, selection, and critical analysis of specialized studies on UAV-based pavement evaluation. The results indicate that UAV photogrammetry can achieve sub-centimeter accuracy (<1 cm) in 3D reconstructions, LiDAR systems can improve deformation detection by up to 35%, and AI-based algorithms can increase crack-identification accuracy by 10% to 25% compared with manual methods. Finally, the synthesis shows that multi-sensor integration and digital twins offer strong potential to enhance predictive maintenance and support the transition towards smarter and more sustainable urban infrastructure management strategies. Full article

The moisture content of wood components varies with changes in the external environment, which significantly affects the mechanical properties, moisture stress, decay, drying shrinkage, and cracking of wood components. Therefore, calculating the moisture content distribution of the cross-section of wood components is an important basis for in-depth research on wood components. First, a hygroscopicity test was performed on 45° sector-shaped Chinese fir thin-plate specimens. The specimens were treated to an absolutely dry state and placed in two different environments. The average moisture content and moisture content gradient on the cross-section of the specimens were measured, and the spatial distribution and temporal variation in the moisture content were studied. A theoretical model for the moisture content distribution of wood was then derived based on food drying theory. Finally, the applicability of the theoretical model was verified through experiments, and the effects of the root order μ_n of the characteristic equation of key parameters, the size of the component, and the position of the component on the moisture content distribution were discussed for the theoretical model. During the hygroscopic process, the average moisture content of wood components increased continuously, but the growth rate gradually slowed. The surface moisture content rapidly reached the level of the external moisture content first, followed by the equilibrium moisture content within a few hours. Hygroscopic hysteresis evidently occurred within the wood, which may take dozens or even hundreds of days. When calculating the average moisture content model of cylindrical components, as well as those of the models of the spatial and temporal variation in the moisture content, it is sufficient to take the first 3 orders of the root μ_n of the characteristic equation of the first Bessel function J. The rate of moisture release of cylindrical components is faster than that of laminates because the ratio of the surface area to the volume of a cylinder is greater than that of a plate, and the former is twice that of the latter. The results revealed that the theoretical model for the moisture content distribution of wood has good accuracy and applicability. Full article

To address the issue that the current research on TBM disc cutter rock breaking insufficiently considers actual stratified rock masses, this study constructs numerical models of stratified rock masses with different bedding dip angles and bedding spacings based on the discrete element method (DEM). The whole process of TBM disc cutter rock breaking is numerically simulated through the displacement loading mode. The research results show that the bedding dip angle has a significant impact on the crack propagation mode. When α = 45°, the bedding intersects with the contact point of the disc cutter, and cracks penetrate directly along the bedding without an obvious “crushed zone”, resulting in the minimum number of cracks. The bedding spacing regulates the rock-breaking effect in stages. When d = 45°, the “crushed zone” interacts with two beddings to form three branch cracks, reaching the peak number of cracks and achieving the optimal rock-breaking efficiency. The cracks generated by disc cutter rock breaking exhibit the characteristic of “slow initial growth and rapid later surge” with the increase in time steps, which is highly consistent with the actual mechanical process of rock breaking. This study reveals the influence mechanism of bedding properties on TBM disc cutter rock breaking, verifies the reliability of the DEM combined with PB and SJ models in the simulation of stratified rock mass breaking, and provides theoretical support and data references for the parameter optimization of TBM disc cutters and efficient tunneling under complex stratified geological conditions. Full article

High-pressure hydrogen compatibility evaluations of alloys using hollow specimens were performed in accordance with ISO 7039. Hollow tensile specimens containing high-pressure hydrogen gas in a small-diameter hole along the axis can also be used to evaluate the influence of hydrogen gas without using high-pressure vessels. This method is not only simpler and less costly than the conventional approach, but it can also evaluate the instantaneous change in the environmental gas at specimen break. The following findings were obtained from slow-strain-rate tensile (SSRT) tests in a high-pressure hydrogen gas environment using hollow specimens of austenitic stainless steels: (1) the work hardening of the specimen in the SSRT tests stopped several minutes before the crack reached the outer surface owing to the influence of hydrogen; (2) the work hardening of the specimen resumed immediately after the hydrogen gas was released; (3) the crack growth took several minutes to reach the specimen’s surface; and (4) the fracture surface was not a cleavage fracture. These results indicate that materials are still ductile after exposure to the high-pressure hydrogen environment. This can be explained by the fact that hydrogen does not embrittle the material itself but inhibits the work hardening of the material. This phenomenon can be explained by the behavior of chemical bonds among atoms, and more discussion on strength from the perspective of chemical bonds is expected. Full article

This study investigates the microstructural evolution and damage mechanisms of the nickel-based single-crystal superalloy DD9-thermal barrier coating (TBC) system under 1050 °C high-temperature oxidation, while conducting a comparative analysis of oxidation behavior with the DD6-TBC system. Results show that both systems have similar oxidation mechanisms but face long-term oxidation drawbacks: as oxidation time increases, the thermally grown oxide (TGO) evolves into a mixed oxide layer and an Al₂O₃ layer, with initial rapid TGO growth consuming Al in the bond coat (BC) and subsequent Al depletion slowing growth, though long-term TGO accumulation raises cracking and spallation risks. DD9 and DD6 substrates significantly affect substrate-BC interfacial interdiffusion: the interdiffusion zone (IDZ) and secondary reaction zone (SRZ) grow continuously (SRZ growing faster), and linear topologically close-packed (TCP) phases precipitate in the SRZ, spreading throughout the substrate and impairing high-temperature mechanical properties. Specifically, DD9’s IDZ growth rate is faster than DD6’s in the first 800 h of oxidation but slows below DD6’s afterward, reflecting DD9’s superior long-term oxidation resistance due to better temperature resistance and high-temperature stability. This study clarifies key high-temperature service disadvantages of the two systems, providing experimental support for coated turbine blade life evaluation and a theoretical basis for optimizing third-generation single-crystal superalloy-TBC systems to enhance high-temperature service stability. Full article

This in vitro study aimed to evaluate the fatigue behavior of occlusal veneers (OVs) made of lithium disilicate and composition-gradient multilayered zirconia at different thicknesses, incorporating both experimental and theoretical analyses to predict long-term performance. Seventy-two OVs with ceramic layer thicknesses of 0.5 mm, 1.0 mm, and 1.5 mm were fabricated and adhesively bonded to dentin analog composite abutments. All specimens underwent thermomechanical fatigue testing, involving cyclic loading (49 N, 1.6 Hz, 1.2 million cycles) and thermocycling (5–55 °C), simulating five years of clinical function. Fracture patterns were analyzed using light microscopy and scanning electron microscopy. A fatigue lifetime model based on plate-on-foundation theory and slow crack growth was applied to estimate cycles to radial failure. No complete fractures or debonding occurred. However, 50% of 0.5 mm zirconia OVs developed flexural radial cracks from the intaglio surface, while all lithium disilicate and zirconia veneers ≥1.0 mm remained intact. Theoretical predictions closely matched the experimental outcomes, indicating that 0.5 mm zirconia performance aligned with the lower-bound fatigue estimates for 5Y-PSZ. Results suggest that lithium disilicate offers superior fatigue resistance at minimal thickness, while thin zirconia is prone to subsurface cracking. A minimum thickness of 0.7 mm is recommended for zirconia-based OVs. Full article

To explore the influence of mine roof on the damage and failure of sandstone surrounding rock under different pressure rates, mechanical experiments with different strain rates were carried out on sandstone rock samples. The strength, deformation, failure, energy and damage characteristics of rock samples with different strain rates were also discussed. The research results show that with the increases in the strain rate, peak stress, and elastic modulus show a monotonically increasing trend, while the peak strain decreases in the reverse direction. At a low strain rate, the proportion of the mass fraction of complete rock blocks in the rock sample is relatively high, and the shape integrity is good, while rock samples with a high strain rate retain more small-sized fragmented rock blocks. This indicates that under high-rate loading, the bifurcation phenomenon of secondary cracks is obvious. The rock samples undergo a failure form dominated by small-sized fragments, with severe damage to the rock samples and significant fractal characteristics of the fragments. At the initial stage of loading, the primary fractures close, and the rock samples mainly dissipate energy in the forms of frictional slip and mineral fragmentation. In the middle stage of loading, the residual fractures are compacted, and the dissipative strain energy keeps increasing continuously. In the later stage of loading, secondary cracks accelerate their expansion, and elastic strain energy is released sharply, eventually leading to brittle failure of the rock sample. Under a low strain rate, secondary cracks slowly expand along the clay–quartz interface and cause intergranular failure of the rock sample. However, a high strain rate inhibits the stress relaxation of the clay, forces the energy to transfer to the quartz crystal, promotes the penetration of secondary cracks through the quartz crystal, and triggers transgranular failure. A constitutive model based on energy damage was further constructed, which can accurately characterize the nonlinear hardening characteristics and strength-deformation laws of rock samples with different strain rates. The evolution process of its energy damage can be divided into the unchanged stage, the slow growth stage, and the accelerated growth stage. The characteristics of this stage reveal the sudden change mechanism from the dissipation of elastic strain energy of rock samples to the unstable propagation of secondary cracks, clarify the cumulative influence of strain rate on damage, and provide a theoretical basis for the dynamic assessment of surrounding rock damage and disaster early warning when the mine roof comes under pressure. Full article

This study focuses on the ancient buildings in Cicheng Old Town, a typical architectural heritage area in the Jiangnan region of China. These buildings are famous for their well-preserved Tang Dynasty urban layout and Ming and Qing Dynasty roof tiles. However, the natural aging, weathering, and biological erosion of the roof tiles seriously threaten the integrity of heritage protection. Given that current detection methods mostly depend on manual checks, which are slow and cover only a small area, this study suggests using deep learning technology for heritage protection and creating a smart model to identify damage in flat tiles using the YOLOv8 architecture. During this research, the team used drone aerial photography to collect images of typical building roofs in Cicheng Old Town. Through preprocessing, unified annotation, and system training, a damage dataset containing 351 high-quality images was established, covering five types of damage: breakage, cracks, the accumulation of fallen leaves, lichen growth, and vegetation growth. The results show that (1) the model has an overall mAP of 73.44%, an F1 value of 0.75 in the vegetation growth category, and a recall rate of 0.70, showing stable and balanced detection performance for various damage types; (2) the model performs well in comparisons using confusion matrices and multidimensional indicators (including precision, recall, and log-average miss rate) and can effectively reduce the false detection and missed detection rates; and (3) the research team applied the model to drone images of the roof of Fengyue Painted Terrace Gate in Cicheng Old Town, Jiangbei District, Ningbo City, Zhejiang Province, and automatically detected and located multiple tile damage areas. The prediction results are highly consistent with field observations, verifying the feasibility and application potential of the model in actual heritage protection scenarios. Full article

The relationship between tearing energy and crack growth rates in elastomers is typically divided into three regions—slow crack growth, fast crack growth, and a transitional region—each described by separate power law relationships, requiring six variables to fully characterize the behavior. This study introduces a novel, unified equation that simplifies this relationship by combining two coexisting energy dissipation mechanisms into a single model with only four variables. The model consists of two terms, one for each energy dissipation mechanism: one term is dominant at slow crack growth rates and limited by a threshold energy, and the other is dominant at fast speeds. The transition region emerges naturally as the dominant mechanism shifts. The model’s simplicity enables new advances, such as predicting fast crack growth tearing and transition energies using only slow crack growth data. This capability is demonstrated across a wide range of non-strain crystallizing rubbers, including filled and unfilled compounds, tested at room temperature and elevated temperatures and in both swollen and unswollen states. This model offers a practical tool for material design, failure prediction, and reducing experimental effort in characterizing elastomer performance. Notably, this is the first model to unify slow, transition, and fast crack growth regimes into a single continuous equation requiring only four variables, enabling the prediction of high-speed behavior using only low-speed experimental data—a major advantage over existing six-parameter models. Full article

The phenomenon of tunnel erosion is quite common in the Loess Plateau. Tunnel erosion can cause disasters such as landslides, mudslides, and ground collapses, resulting in significant economic losses and posing a threat to people’s safety. Therefore, understanding the evolution mechanism of tunnel erosion not only helps to analyze and predict the development law of erosion but also has a certain guiding role in engineering activities. Many scholars (including our team) have conducted field investigations and statistical analysis on the phenomenon of tunnel erosion in loess; however, these studies still have shortcomings in visual quantitative analysis. The combination of the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) has significant advantages in studying soil seepage and erosion. Based on existing experimental research, this article combines the Discrete Element Method (DEM) with Computational Fluid Dynamics (CFD) to establish a CFD-DEM coupled model that can simulate tunnel erosion processes. In this model, by changing the working conditions (vertical cracks, horizontal cracks, and circular holes) and erosion water pressure conditions (200 Pa, 400 Pa, 600 Pa), the development process of tunnel erosion and changes in erosion rate are explored. The results indicate that during the process of fluid erosion, the original vertical crack, horizontal crack, and circular hole-shaped tunnels all become a circular cave. The increase in erosion water pressure accelerates the erosion rate of the model, and the attenuation rate of the particle contact force chain also increases, resulting in a decrease in the total erosion time. During the erosion process, the curve of the calculated erosion rate shows a pattern of slow growth at first, then rapid growth, before finally stabilizing. The variation law of the erosion rate curve combined with the process of tunnel erosion can roughly divide the process of tunnel erosion into three stages: the slow erosion stage, the rapid erosion stage, and the uniform erosion stage. Full article

Navigable waterways play a vital role in the efficient transportation of millions of tons of cargo annually. Inland traffic must pass through a lock, which consists of miter gates. Failures and closures of these gates can significantly disrupt waterborne commerce. Miter gates often experience fatigue cracking due to their loading and welded connections. Repairing every crack can lead to excessive miter gate downtime and serious economic impacts. However, if the rate of crack growth is shown to be sufficiently slow, e.g., using Paris’ law, immediate repairs may be deemed unnecessary, and this downtime can be avoided. Paris’ law is often obtained from laboratory testing with detailed crack measurements of specimens with relatively simple geometry. However, Paris’ law parameters for an in situ structure will likely deviate from those predicted from physical testing due to variations in loading and materials and a far more complicated geometry. To improve Paris’ law parameter prediction, this research proposes a framework that utilizes (1) convenient vision-based tracking of crack evolution both in the laboratory and the field and (2) numerical model estimation of stress intensity factors (SIFs). This study’s methodology provides an efficient tool for Paris’ law parameter prediction that can be updated as more data become available through vision-based monitoring and provide actionable information about the criticality of existing cracks. Full article

The particle size-dependent processes of structural relaxation and crystal growth in amorphous nifedipine were studied by means of non-isothermal differential scanning calorimetry (DSC) and Raman microscopy. The enthalpy relaxation was described in terms of the Tool–Narayanaswamy–Moynihan model, with the relaxation motions exhibiting the activation energy of 279 kJ·mol⁻¹ for the temperature shift, but with a significantly higher value of ~500 kJ·mol⁻¹ being obtained for the rapid transition from the glassy to the undercooled liquid state (the latter is in agreement with the activation energy of the viscous flow). This may suggest different types of relaxation kinetics manifesting during slow and rapid heating, with only a certain portion of the relaxation motions occurring that are dependent on the parameters of a given temperature range and time frame. The DSC-recorded crystallization was found to be complex, consisting of four sub-processes: primary crystal growth of α_p and β_p polymorphs, enantiotropic β_p → β_p′ transformation, and β_p/β_p′ → α_p recrystallization. Overall, nifedipine was found to be prone to the rapid glass-crystal growth that occurs below the glass transition temperature; a tendency of low-temperature degradation of the amorphous phase markedly increased with decreasing particle size (the main reason being the increased number of surface and bulk micro-cracks and mechanically induced defects). The activation energies of the DSC-monitored crystallization processes varied in the 100–125 kJ·mol⁻¹ range, which is in agreement with the microscopically measured activation energies of crystal growth. Considering the potential correlations between the structural relaxation and crystal growth processes interpreted within the Transition Zone Theory, a certain threshold in the complexity and magnitude of the cooperating regions (as determined from the structural relaxation) may exist, which can lead to a slow-down of the crystal growth if exceeded. Full article