Search Results (36)

Flat slab structures are extensively utilized in modern construction owing to their efficient load transfer mechanisms and optimized space utilization. Nevertheless, the persistent issue of brittle punching shear failure at connection zones continues to pose significant engineering challenges. This study proposes an innovative cross-shaped steel-reinforced concrete (SRC) column–slab connection. Through combining test and numerical analyses, the failure mechanisms and performance control principles are systematically analyzed. A refined finite element model incorporating material nonlinearity, geometric characteristics, and interface effects is developed, demonstrating less than 3% error upon test validation. Using the validated model, the influence of key parameters—including concrete strength (C30–C60), reinforcement ratio (ρ = 0.65–1.77%), shear span–depth ratio (λ = 3–6), and limb height-to-thickness ratio (c₁/c₂ = 2–4)—on the punching shear behavior is thoroughly investigated. The results demonstrate that increasing concrete strength synergistically improves both punching shear capacity (by up to 49%) and ductility (by 33%). A critical reinforcement ratio threshold (0.8–1.2%) is identified. When exceeding this range, the punching shear capacity increases by 12%, but reduces ductility by 34%. Additionally, adjusting the shear span–depth ratio enables controlled failure mode transitions and a 24% reduction in punching shear capacity, as well as a 133% increase in displacement capacity. These results offer theoretical support for the design and promotion of this novel structural system. Full article

Ultra-deep tight sandy conglomerate reservoirs in the Junggar Basin are characterized by vertically alternating lithologies that include mudstone, sandy conglomerate, and sandstone. High in situ stresses and formation temperatures contribute to a brittle–ductile transition process in the reservoir rocks. However, the brittle behavior and ductile hydraulic fracture propagation mechanisms under in situ conditions remain inadequately understood. In this study, ultra-deep core samples were subjected to triaxial compression tests under varying confining pressures and temperatures to simulate different burial depths and evaluate their brittleness. A three-dimensional hydraulic fracture propagation model was developed in ABAQUS 2023 finite element software, incorporating a cohesive zone ductile constitutive model. Numerical simulations were conducted, considering interlayer horizontal stress differences, injection rate, and fracturing fluid viscosity, to systematically analyze the influence of geological and engineering factors on ductile fracture propagation. A fracture length–height competition diagram was constructed to illustrate the propagation mechanisms. The results reveal that high temperatures significantly accelerate the brittle–ductile transition, which occurs at confining pressures between 55 and 65 MPa. Following this transition, failure modes shift from single-shear failure to a multi-localized fracture with bulging deformation. Interlayer horizontal stress differences were found to strongly influence fracture penetration, with larger stress differences hindering vertical growth. Increasing injection rates promoted the uniform distribution of lateral fractures and fracture tip development, while medium- to high-viscosity fracturing fluids enhanced fracture width and vertical stimulation uniformity. These findings provide important insights for optimizing fracturing strategies and expanding the effective stimulation volume in the ultra-deep tight sandy conglomerate reservoirs of the Junggar Basin. Full article

As mineral resource extraction progresses to greater depths, it has become imperative for geomechanical applications to understand the thermomechanical degradation mechanisms of rocks under thermal loading. To investigate the thermomechanical characteristics of granite subjected to thermal treatments ranging from ambient to 1000 °C, we conducted uniaxial compression tests integrating P-wave velocity measurements, digital image correlation (DIC), and acoustic emission (AE) monitoring. The key findings reveal the following: (1) the specimen volume exhibits thermal expansion while the mass loss and P-wave velocity reduction demonstrate a temperature dependence; (2) the uniaxial compressive strength (UCS) and elastic modulus display progressive thermal degradation, while the peak strain shows an inverse relationship with temperature; (3) acoustic emission signals exhibit a strong correlation with failure–time curves, progressing through three distinct phases: quiescent, progressive accumulation, and accelerated failure, and fracture mechanisms transition progressively from tensile-dominated brittle failure to shear-induced ductile failure with increasing thermal loading; and (4) the damage evolution parameter exhibits exponential growth beyond 600 °C, reaching 98.85% at 1000 °C, where specimens demonstrate a complete loss of load-bearing capacity. These findings provide critical insights for designing deep geological engineering systems involving thermomechanical rock interactions. Full article

For the purpose of precisely depicting the failure and deformation of mudstone at varying burial depths under engineering activities, a statistical meso-damage constitutive model of mudstone was established on the basis of continuum damage mechanics, with the adoption of the compound power function and the Mohr–Coulomb yield criterion. Through triaxial compression tests under diverse confining pressures, the validity of this constitutive model was verified, and the macroscopic effects of mudstone damage evolution induced by internal defects and alterations in meso-structures were analyzed. The results reveal that an increase in confining pressure can remarkably enhance both the peak strength and the residual strength of mudstone. The constitutive model demonstrates relatively high accuracy in predicting the stress–strain responses, as well as the residual strength of mudstone. Moreover, parameter ε0 is capable of reflecting the macroscopic deformation strength of mudstone. Specifically, the larger the value of parameter ε0 is, the greater the peak deviatoric stress of mudstone will be, accompanied by a stronger bearing capacity. Parameter m, on the other hand, governs the brittle-to-ductile transition characteristics under failure. It also demonstrates that the macroscopic brittle failure characteristics of mudstone will become more noticeable as the value of parameter m increases. Full article

Polycrystalline ZnS is a typical infrared optical material. It is widely used in advanced optical systems due to its excellent optical properties. The machining accuracy of polycrystalline ZnS optical elements must satisfy the requirements of high-performance system development. However, the soft and brittle nature of the material poses a challenge for high-quality and efficient machining. In recent years, in situ laser-assisted diamond cutting has been proven to be an effective method for ultra-precision cutting of brittle materials. In this study, the mechanism of in situ laser-assisted cutting on ultra-precision cutting machinability enhancement of ZnS was investigated. Firstly, the physical properties of ZnS were characterized by high-temperature nanoindentation experiments. The result revealed an increase in ductile machinability of ZnS due to plastic deformation and a decrease in microhardness and Young’s modulus at high temperatures. It provided a fundamental theory for the ductile–brittle transition of ZnS. Subsequently, a series of diamond-cutting experiments were carried out to study the removal mechanism of ZnS during in situ laser-assisted cutting. It was found that the mass damage initiation depth groove generated by in situ laser-assisted cutting increased by 57.99% compared to the groove generated by ordinary cutting. It was found that micron-sized pits were suppressed under in situ laser-assisted cutting. The main damage form of HIP-ZnS was changed from flake spalling and pits to radial cleavage cracks. Additionally, the laser can suppress the removal mode difference of different grain crystallographic and ensure the ductile region processing. Finally, planning cutting experiments were carried out to verify that a smooth and uniform surface with Sa of 3.607 nm was achieved at a laser power of 20 W, which was 73.58% better than normal cutting. The main components of roughness were grain boundary steps and submicron pit. This study provides a promising method for ultra-precision cutting of ZnS. Full article

Exposure of metals to neutron irradiation results in an increase in the yield strength and a significant loss of ductility. Irradiation hardening is also closely related to the fracture toughness temperature shift or the ductile-to-brittle transition temperature (DBTT) shift in alloys with a body-centered cubic (bcc) crystal structure. Ion irradiation is an indispensable tool in the study of the radiation effects of materials for nuclear energy systems. Due to the shallow damage depth in ion-irradiated materials, the nanoindentation test is the most commonly used method for characterizing the changes in mechanical properties after ion irradiation. Issues that affect the analysis of irradiation hardening may arise due to changes in the surface morphology and mechanical properties, as well as the inherent complexities in nanoscale indentation. These issues, including changes in surface roughness, carbon contamination, the pile-up effect, and the indentation size effect, with corresponding measures, were reviewed. Modeling using the crystal plasticity finite element method of the nanoindentation of ion-irradiated materials was also reviewed. The challenges in extending the nanoindentation test to high temperatures and to multiscale simulation were addressed. Full article

The impact protection applications of polycarbonate (PC) products are gradually increasing. Due to the high sensitivity of PC to notches, research on notch impacts has become very important. In this paper, the impact performance of PC with two different molecular weights under different notch states was investigated. Three notch size factors, namely notch tip radius, notch angle, and notch center depth, were selected to design orthogonal experiments and research impact toughness. Subsequently, a single-factor study was conducted on the impact radius at the tip of the notch, which was the most important factor affecting the impact performance. Research shows that the brittle–ductile-transition tip radius of high-molecular-weight PC is 0.15 mm, and it has a higher impact toughness than low-molecular-weight PC during the brittle fracture process. The brittle–ductile-transition tip radius of lower molecular weight is 0.25 mm, while low-molecular-weight PC has a higher impact toughness during the ductile fracture process. The brittle and ductile fracture mechanisms of PC with different molecular weights were analyzed by observing the stress changes and cross-sectional morphology. Full article

A fine-grained WC-15wt%Al_0.5CoCrFeNi cemented carbide was prepared through a vacuum and gas pressure sintering. For achieving high surface integrity, diamond wheel grinding serves as the primary molding process for the machining of WC cemented carbide. To reveal the influence of grinding on the surface integrity of fine-grained WC-HEA cemented carbide, studies were conducted on grinding force, surface microstructure, surface roughness, residual stress, microhardness, and bending strength. The morphological analysis of the ground surface indicated a transition in the material removal mechanism of WC-HEA cemented carbide from ductile removal to brittle removal, with brittle removal becoming predominant as the depth of grinding increases. With the increasing depth of grinding, the grinding force increases, and the grinding force increases while the surface roughness decreases. Correspondingly, there is an improvement in both hardness and bending strength. Additionally, grinding induces high residual compressive stress on the surface, with a maximum compressive stress of 1795 MPa. The bending strength of the material is found to be dependent on the residual stress. Full article

Potassium dihydrogen phosphate (KDP) has garnered considerable attention due to its diverse applications across various scientific and engineering domains. Although promising machining performance enhancements have been achieved in ultra-precision diamond cutting, the brittle–ductile transition (BDT) depth for KDP crystals is essentially at the nanometer range and limits the further improvement of machining efficiency. In this paper, a novel ultra-precision diamond cutting process based on tool trapezoidal modulation is proposed for the first time to investigate the BDT characteristics of KDP crystals. By intentionally designing the tool modulation locus, the uncut chip thickness and cutting direction in the cutting duty cycle are kept constant, which provides a new strategy for probing the BDT mechanism and enhancing the machining performance. The BDT depth is significantly increased compared to the conventional ultra-precision diamond cutting owing to its unique modulation machining advantages. The significance of this paper lies not only in the improvement of the machining efficiency of KDP crystals through the proposed modulation cutting process, but also in the possibility of extending the relevant research methods and conclusions to the machining performance enhancement of other brittle optical crystals. Full article

Brittle intermetallic compounds, formed during the welding process of titanium/aluminum (Ti/Al), lead to a significant reduction in joint mechanical properties. The purpose of this study is to mitigate the formation of brittle phases during the laser welding of dissimilar Ti/Al metals, thereby enhancing the mechanical properties of the joints. In this investigation, an innovative approach is adopted, utilizing Nb foil as an interlayer to effectively minimize the formation of brittle intermetallic phases during dissimilar welding. A comprehensive analysis of the microstructure of the transition layer was conducted using material characterization methods, including scanning electron microscope equipped with an energy dispersive X-ray spectrometer. The mechanical performance of the welded joints was assessed using tensile testing. The results indicate that the effective welding width and joint penetration depth at the joint interface were reduced in Ti/Al dissimilar metals when Nb was added as an intermediate layer, under the same welding process parameters, when compared to unalloyed weld seams. Furthermore, the utilization of a 0.05 mm Nb foil as the intermediate layer results in a significant 25% increase in the average shear strength compared to the other condition, with the average shear strength of the joint reaching its peak value at 192 N/mm. The unalloyed Ti/Al weld joint usually fractured along the melting zone, displaying complete brittle fracture characteristics. After Nb microalloying, the joint typically fractures along the transition zone and interface, exhibiting both cleavage and ductile fracture characteristics, indicating the combination of a brittle and toughness fracture. This study provides experimental evidence and new insights for welding Ti/Al composite structures, with significant theoretical and practical applications. Full article

The application range of potassium dihydrogen phosphate (KDP) crystals can be expanded by enhancing their surface quality properties. Therefore, a method for controlling the surface-temperature field of various materials was developed to expand the plastic zone to overcome the difficulty in processing KDP crystals. The ductile/brittle transition depth of the KDP crystals was determined using a 38 nm nanoindentation experiment. The nanoscratch experiment revealed the rules of how the transformation depth of the KDP crystals changes with temperatures, and the effect of temperature on the microstructure of the KDP crystals was studied. Finally, KDP crystal surfaces were processed using a UPDFC machine at elevated temperatures. According to our experiments, the surface roughness of the KDP crystal reached 5.275 nm as temperature increased, thus enhancing its surface quality. This method could be applied to other brittle materials. Full article

Reversed austenite is of vital importance in low-carbon martensitic stainless steel because it improves impact toughness. However, a proper amount of reversed austenite is obtained by tempering at a critical temperature, which reduces the strength of the steel. Therefore, how to improve strength–toughness matching is an important problem. Copper (Cu) is an effective strengthening element in steels. However, there is little in-depth discussion on the role of Cu on the microstructure and mechanical properties of low-carbon martensite steel. In this work, the effect of different Cu content on the reversed austenite formation, tensile strength, and impact toughness of a low-carbon martensitic stainless steel (0Cr13Ni4Mo) was systematically investigated through use of a transmission electron microscope (TEM), transmission Kikuchi diffraction (TKD), atom probe tomography (APT), and other characterization methods and mechanical property tests. The results showed that the addition of Cu decreased the phase transition temperatures of martensite and austenite and increased the volume fraction of the reversed austenite. APT results indicated that Cu-rich clusters first formed with alloying elements such as ferrum (Fe) and nickel (Ni) and then grew to be precipitates through rejection of the alloying elements. The Ni atoms diffused towards the interface between the precipitates and the martensite matrix, which provided heterogeneous nucleation sites for the reversed austenite. Cu precipitations strengthened tensile strength during tempering. However, it generated temper brittleness in the steel at a tempering temperature of 450 °C, resulting in the impact energy of the 3Cu-steel being only 7 J. A good combination with higher tensile strength (863 MPa) and ductility (192 J) was obtained when tempering at 600 °C in the presence of Cu-rich precipitates and a sufficient volume fraction of the reversed austenite. The results provide guidance for the design of steels with reversed austenite and Cu and promote the development of high-strength and high-toughness steels. Full article

Metamorphic core complexes are developed in crustal activity belts at the continental margins or within continents, and their main tectonic feature is that the ductile middle crust is exhumed at the surface. The deformation properties are closely related to the geodynamic process affecting the continental crust. However, the evolution of the metamorphic core complexes after their formation is still unclear. The Cretaceous Liaonan metamorphic core complex developed in the eastern North China craton provides an ideal environment to study its evolution. In this study, we estimate the paleo-temperature and paleo-stress at the time of formation of the metamorphic core complex dynamical recrystallization of quartz and calculate the thermo-rheological structure of the present Liaonan metamorphic core complex by one-dimensional steady-state heat conduction equation and power-creep law. The results show that compared with the Cretaceous period, the geothermal heat flow value of the present Liaonan metamorphic core complex decreases from 70–80 mW/m² to 49.4 mW/m², the thermal lithosphere thickness increases from 59–75 km to 173 km, and the brittle transition depth increases from 10–13 km to about 70 km, showing coupling of the crust–mantle rheological structure. We speculate that the evolution of the thermo-rheological structure of the Liaonan metamorphic core complex is possibly caused by rapid heat loss or lithospheric mantle flow in the Bohai Bay Basin. Full article

During cutting of foods, tensile stresses in front of the blade are responsible for the separation of the material. Therefore, tensile tests can be helpful to gain knowledge on deformation properties related to pre-fracture cutting behavior as well as on phenomena in the fracture zone, which are velocity-dependent in viscoelastic materials. The aim of this work was to apply a tensile test method for model caramels to investigate their behavior and to identify conditions where the ductile-brittle transition occurs. After executing pre-trials, tensile velocity, caramel moisture, and temperature were the parameters that were varied for this purpose. In general, increasing velocity, decreasing temperature, and decreasing moisture resulted in a stiffer response and caused a shift from a ductile to a more brittle behavior, attributable to reduced viscous contributions to the material and longer relaxation times. Fracture strain was notably lower than the maximum plastic elongation in the ductile case, but we observed equalization close to the ductile-brittle transition point for our material. This study serves as basis for an in-depth research on the complex deformation and fracture phenomena during cutting of viscoelastic food systems, including numerical modeling. Full article

Polyetheretherketone (PEEK) is a promising thermo-plastic polymer material due to its excellent mechanical properties. To further improve the mechanical properties of PEEK, different kinds of short fibers are added into the PEEK matrix. The grinding machinability of short-fiber-reinforced PEEK varies with the effect of fiber type and content. Therefore, it is crucial to investigate the surface quality and removal mechanism of fiber-reinforced PEEK in ultra-precision grinding. In this paper, different fiber types and mass fractions of short-fiber-reinforced PEEK, including carbon-fiber-reinforced PEEK (CF/PEEK) and glass-fiber-reinforced PEEK (GF/PEEK), are employed. The grinding machinability of short-fiber-reinforced PEEK was investigated using grinding experiments with grinding wheels of different grit sizes. The effects of the fiber type and mass fraction on the surface quality and removal mechanism during grinding were discussed. The results showed that the brittle–ductile transition depth of carbon fiber was much larger than that of glass fiber, so it was easier to achieve ductile removal in grinding with the carbon fiber. Therefore, the ground surface roughness of CF/PEEK was smaller than that of GF/PEEK under the same grinding conditions. With the increase in carbon fiber mass fraction, the ground surface roughness of CF/PEEK decreased due to the higher hardness. The brittle–ductile transition depth of glass fiber was small, and it was easy to achieve brittle removal when grinding. When the glass fiber removal mode was brittle removal, the GF/PEEK surface roughness increased with the increase in glass fiber content. Full article