Search Results (6)

To address the issues of low shear strength, susceptibility to eccentricity, and alignment difficulties in post-inserted core piles, a new type of steel tube concrete integrated mixing composite pile has been independently developed. This pile type replaces the conventional mixing pile shaft with a larger diameter steel tube equipped with mixing blades. After forming the external annular cement mixing pile, the steel tube is retained, and the hollow core is filled with concrete. To thoroughly explore the vertical compressive bearing characteristics of the steel tube concrete mixing composite pile and clarify its vertical compressive behavior, static load field tests and PLAXIS 3D finite element numerical simulations were conducted on four test piles of different sizes to analyze the vertical bearing performance of the steel tube concrete mixing composite pile. The research results indicate that for a composite pile with a length of 40 m, an outer diameter of 1000 mm, and a steel tube diameter of 273 mm, the ultimate bearing capacity of a single pile is 7200 kN, with the steel tube concrete core contributing approximately 81% of the vertical bearing capacity, while the cement mixing pile contributes around 19%. Based on the characteristic that the maximum axial force is concentrated in the upper half of the pile length, an innovative variable-diameter design with a reduced wall thickness of the steel pipe in the lower part of the pile was proposed. Practical verification has shown that, despite the reduced material usage, the load-bearing capacity remains largely unchanged. This effectively validates the feasibility of the “strong upper part and weak lower part” design concept and provides an effective way to reduce construction costs. Full article

Returning pruned branches into the field is a key procedure in kiwifruit cultivation. It utilizes discarded branches and aids in orchard management. Shearing and bending behaviors dominate the mechanized process of branch return; however, current research lacks appropriate modeling methods for these processes. In this study, we developed a discrete element method (DEM) model to simulate the shearing and bending behaviors of kiwifruit branches. Initially, laboratory experiments determined the shear strength and elastic modulus of branch samples to be 31.38 MPa and 1.21 GPa, respectively. An annular kiwifruit branch DEM model was constructed. A Plackett–Burman design test identified significant influencing factors: effective modulus of bond, bond cohesion, effective modulus between ball and wall, and the normal-to-shear stiffness ratio. Utilizing the response surface method, we derived relationships between DEM parameters and mechanical responses. Optimal parameter combinations were found: an effective modulus of bond at 2.2 × 10⁹ Pa, bond cohesion at 2.56 × 10⁸ Pa, effective modulus between ball and wall at 1.27 × 10⁸ Pa, and a normal-to-shear stiffness ratio of 1.16. Finally, simulations of the shearing and bending processes were conducted. The optimal parameter combination was verified with a relative error of 4.5%. Displacement–force curves showed general consistency, indicating reliability in the modeling approach. Full article

Utilization of agricultural waste can be done by converting it with conventional fuels to energy. For this purpose, it is necessary to understand the properties of waste and its mixture with the fossil fuels important for its storage and conversion. The objective of the work was to examine the influence of moisture content and the composition of agricultural waste with hard coal mixtures on the mechanical and rheological properties of the waste. The materials tested were powdered biomass: dried distillers grains with solubles (DDGS), meat and bone meal (MBM), and hard coal (HC). Mechanical properties were measured to investigate flowability with the Jenike shear tester. A technique with an annular powder rheometer was applied for rheological measurements. It was shown that an increased moisture content worsened the flowability of the mixtures, while an increased biomass content reduced the influence of moisture and stabilized the mechanical properties of the mixtures in quasi-static conditions. In dynamic conditions, moisture decreased the mechanical strength of the mixtures and increased their flowability. Full article

The cement sheath is an annular structure between casing and formation, which is crucial to the integrity of the wellbore system. Considering that the temperature and pressure environment is changing continuously with increasing burial depth, the micro-structure and macro=mechanical properties of the in-situ cement sheath will change accordingly. To investigate the variation of burial depth on the evolution of the tensile mechanical behavior of oil cement stone, five temperature-pressure curing and testing conditions (25 °C—0 MPa, 50 °C—10 MPa, 80 °C—20 MPa, 110 °C—30 MPa, and 140 °C—40 MPa) are set to approximately simulate an in situ temperature-pressure environment at five typical burial depths (0 m, 1000 m, 2000 m, 3000 m, and 4000 m). The in situ tensile behavior, micro-structure and pore size distribution of the cement stones at each condition are tested and comparatively analyzed. Results show that with increasing temperature and pressure, the brittleness of the cement stone reduces and its ductility strengthens accordingly. The tensile strength experiences rapid growth at first, then increases at a slower rate and finally decreases. The failure mode of the cement stone gradually transforms from tensile splitting to tensile-shear composite fracture, accompanied by increasing fracture surface roughness. Microscopically, with increasing curing temperature and pressure, the pore structure of cement stone gradually transforms from closely stacked laminated sheets to interconnected fiber networks. The dense structure of cement stone gradually becomes loose and porous. The porosity also increases from 15.96% to 29.46%. Full article

Diatomite is a powdering mineral mainly composed of diatom microfossils present in marine and lacustrine soils, which influences their physical and mechanical properties. Although many articles have been found in the literature concerning the influence of diatomite in the overall behavior of natural soils, few research efforts have been carried out to evaluate the influence of the diatom microfossil species on their shear resistance. Therefore, in this research, the influence of the diatomite species and the content in the peak and the residual shear strength of diatomite-fine grained soil mixtures was analyzed using the annular shear strength test. Scanning electron microscopy (SEM) and Atterberg limits were also carried out as additional tests to explain the interlocking effect between the microfossils and the soil. Overall, both diatomite species increased both peak and residual shear strength of the soil similar to dense sands. Nevertheless, the Mexican species reveal higher friction angle values compared with Colombian species. Full article

Annular channel angular extrusion has been recently developed as a new single-pass severe plastic deformation method suitable for producing large size cup-shaped parts from cylindrical billets. In this study, the novel technology was successfully applied to commercial AZ80 Mg alloy at 300 °C, and microstructure, texture evolution, and mechanical properties were investigated. Due to severe shear deformation, the initial microstructure, including the coarse grains and large eutectic β-phases, was greatly refined. The strong basal texture formed during the initial deformation stage was modified into a weak tilted dynamic texture. During the deformation process, fine β-particles separated from eutectic phases effectively hindered the grain boundary migration and rotation, enhancing the grain refinement and texture weakening. More than 63% of the microhardness increase was achieved in this extruded part. Also, tensile tests showed the yield strength and elongation in both directions (transverse and longitudinal) of extruded part were improved more than 2.5 times, and the ultimate tensile strength was improved more than 2 times, compared to the initial material state. The improved material properties were mainly attributed to microstructure (grain and phase) refinement and texture weakening. It was demonstrated that the annular channel angular extrusion process can be considered as a novel and effective single-pass severe plastic deformation method. Full article