Search Results (537)

Diamond coring bits exhibit stable rock-breaking and coring processes as well as a long service life. However, when drilling in complex and challenging formations are characterized by high hardness, strong plasticity, and high abrasiveness, issues such as low rock-breaking efficiency, rapid failure, and shortened service life frequently occur. To prevent premature bit failure and enhance rock-breaking efficiency, this study investigated the effects of drilling pressure and rotational speed on rock-breaking performance through bench-scale experiments using typical rock samples. A total of 15 experimental groups were included in this study, with one independent trial performed for each group. ROP is calculated as the ratio of effective drilling depth to time consumed, and MSE is derived based on axial force, torque, and rock-breaking volume. The experimental results indicated that (1) sandstone is more sensitive to rotational speed, whereas limestone and dolomite are more sensitive to drilling pressure; (2) the minimum mechanical specific energy (MSE) of sandstone was achieved at a drilling pressure of 15 kN and rotational speed of 50 r/min; (3) limestone exhibited the lowest MSE at 10 kN drilling pressure and 50 r/min rotational speed; and (4) dolomite showed the minimum energy consumption at 10 kN drilling pressure and 25 r/min rotational speed. On this basis, this paper establishes a cutting mechanics model for single-crystal diamond and a working load calculation model for the entire bit, respectively. The cutting mechanics model for single-crystal diamond is re-established based on Hertzian contact theory and elastic-plastic deformation theory. The findings of this study are expected to provide a working load calculation method for diamond coring bits in typical complex and challenging drilling formations and offer technical support for the design of coring bit cutting structures and the development of customized new products. It should be noted that the conclusions of this study are limited to the experimental parameter range (drilling pressure: 5–15 kN; rotational speed: 25–80 r/min), and their applicability under higher load conditions requires further verification. Full article

This paper investigates the cold rolling (CR) deformation behavior of electrolytic nickel at room temperature. While the microstructural evolution across deformation levels ranging from 5% to 98% is systematically characterized. The deposited electrolytic nickel exhibits numerous growth twins of various lengths and thicknesses, accounting for over 70% of the microstructure. The average grain size is 0.56 μm, and the grain size distribution is relatively broad. The plastic deformation of electrolytic nickel in the early stage is governed by the interaction between high-density dislocations and abundant twins. The primary mechanism accommodating deformation is detwinning. At 70% deformation, under high strain, complete detwinning occurs. When the CR reaches 90%, the average short-axis grain size is refined to 113 nm, indicating the deformation-induced refinement limit of electrolytic nickel. The microstructure at this stage exhibits a typical lamellar morphology. At 98% deformation, the average microhardness peaks at 240.3 HV, representing a cumulative increase of 46.88%. Dynamic recovery and recrystallization are observed at both 70% and 98% deformation levels, accompanied by the formation of Σ3 {120} type incoherent twins within recrystallized grains. Under large strain, the dominant cold plastic deformation mechanism transitions to a synergistic effect of dislocation slip and stratification. Full article

The CoCrMo alloys are progressively utilized as biomaterials. This research is dedicated to studying the consequence of (1, 3, and 5) wt% nano-TiO₂ addition on the porosity, microstructure, microhardness, and wear behavior of pre-alloyed CoCrMo powder produced by powder metallurgy (PM). Microstructural features were examined using SEM, SEM mapping, and XRD. Wear behavior was assessed through pin-on-disk tests performed under dry sliding conditions at varying loads and durations. Porosity increased with the addition of nano-TiO₂, from 15.26 at 0 wt% reaching 25.12% at 5 wt%, while density decreased from 7.16 to 6.33 g/cm³. Microhardness exhibited a slight improvement, attaining 348 HV at 5 wt%. SEM and XRD analyses confirmed partial particle separation after sintering and identified the TiO₂ reinforcement as rutile. Wear tests revealed that adding 1 wt% nano-TiO₂ enhanced wear resistance, whereas extended sliding durations resulted in increased wear rates. Adhesive wear was the predominant mechanism, accompanied by limited abrasive wear, oxidation, and plastic deformation. Full article

Extrusion of AlZnMgCu alloys is associated with a very high plastic resistance of the materials at forming temperatures and significant friction resistance, particularly at the contact surface between the ingots and the container. In technological practice, this translates into high maximum extrusion forces, often close to the capacity of hydraulic presses, and the occurrence of surface cracking of extruded profiles, resulting in a reduction in metal exit speed (production process efficiency). The accuracy of mathematical material models describing changes in the plastic stress of a material as a function of deformation, depending on the forming temperature and deformation speed, plays a very important role in the numerical modelling of extrusion processes using the finite element method (FEM). Therefore, three mathematical material models of the tested aluminium alloy were analysed in this study. In order to use the results of plastometric tests determined on the Gleeble device, they were approximated with varying degrees of accuracy using the Hnsel–Spittel equation and then implemented into the material database of the QForm-Extrusion^® programme. A series of numerical FEM calculations were performed for the extrusion of Ø50 × 3 mm tubes made of 7075 aluminium alloy using chamber dies for two different billet heating temperatures, 480 °C and 510 °C, and for three different material models. The metal flow was analysed in terms of geometric stability and dimensional deviations in the wall thickness of the extruded tube and its surface quality, as well as the maximum force in the extrusion process. Experimental studies of the industrial extrusion process of the tubes, using a press with a maximum force of 28 MN and a container diameter of 7 inches, confirmed the significant impact of the accuracy of the material model used on the results of the FEM numerical calculations. It was found that the developed material model of aluminium alloy 7075 number 1 allows for the most accurate representation of the actual conditions of deformation and quality of extruded tubes. Moreover, the material data obtained on the Gleeble simulator made it possible to determine the limit temperature of the extruded alloy, above which the material loses its cohesion and cracks appear on the surface of the extruded profiles. Full article

A weak-axis moment connection incorporating a double reduced beam section and a box-reinforced panel zone (WDRBS) is introduced for hot-rolled H-shaped columns. The configuration is intended to shift inelastic demand away from the column face and to constrain weak-axis panel-zone distortion. A series of finite element models is established and calibrated to examine the cyclic response of this connection type. By varying the geometric parameters of the second reduction zone, a closed-form expression for determining its cutting depth (c₂) is formulated, allowing both reduced regions to yield concurrently, i.e., the Optimum State. The numerical investigation demonstrates that connections designed according to this equation exhibit stable hysteresis, limited weld-adjacent plastic ll rightstrain, and sufficient deformation and energy-dissipation capacities. All specimens exhibit plastic rotations greater than 0.03 rad, ductility ratios greater than 3.0, and equivalent viscous damping ratios greater than 0.3. To facilitate engineering implementation using common hot-rolled sections, a simplified method is further proposed to approximate the admissible range of c₂ with practical accuracy. While the length of the second reduction region has only a modest influence on peak strength (approximately 1.5–6%), it markedly affects the failure mechanism and plastic-hinge distribution. A stepwise design procedure for WDRBS connections is accordingly recommended. The study does not consider composite-slab interaction or gravity-load effects, and the findings—based solely on finite element simulations—require future verification through full-scale experimental testing. Full article

Under cyclic loading, almost immediately after its onset, a surface layer forms where hardening and softening processes occur. The interaction of plastic deformation traces with each other, and with other structural elements, leads to the formation of a characteristic microstructure on the surface of a component subjected to cyclic loading. The set of factors (conditions) acting during cyclic loading determines the nature of slip band accumulation, the integral structurally sensitive fatigue parameter, expressed as the slope of the left side of the fatigue curve linearized in logarithmic coordinates, and the location of the breaking point on the fatigue curve in the high-cycle region. A combined review of numerous data on the fatigue of metals, obtained under various combinations of factors, and the generalization of these results through a normalization procedure for obtaining the relative (recalculated) parameters of fatigue, allows us to derive a universal method for “S-N” curve prediction. However, extensive generalization decreases the prediction accuracy for specific cases; therefore, it is proposed to form limited generalized dependencies corresponding to specific operating conditions. This paper evaluates the accuracy of fatigue limit prediction using generalized and limited-generalized relationships of fatigue recalculated parameters for various fatigue curves obtained from independent experimental data. Full article

Background: The compaction of formulation blends is a critical stage in pharmaceutical tablet manufacturing, particularly when drug substances or functional excipients exhibit limited flowability and tabletability. Objectives: This study systematically examined the mechanical behaviour of viscoelastic microcrystalline cellulose (MCC) and brittle anhydrous dibasic calcium phosphate (DCPA), as well as their mixtures, to check how deformation mechanisms influence powder handling and tablet performance. Methods: A compaction simulator, mimicking a small rotary tablet press, was used to evaluate tablet weight variability, densification profiles, die-filling height, force–displacement behaviour, and in-die Heckel analysis. Additional assessments included compression times, breaking force, tensile strength, elastic recovery, as well as in-die and out-of-die tablet thickness across various compositions and compaction pressures. Results/Conclusions: Bulk density values from the simulator showed strong correlation with pharmacopeial measurements (R² ≥ 0.997). Measurable differences in true density and cohesiveness led to poor flowability for MCC and good flow for DCPA, with mixtures containing higher DCPA concentration displaying markedly improved flow characteristic. Compaction analyses confirmed extensive plastic deformation for MCC and fragmentation for DCPA. Increasing MCC content elevated die-fill height, compaction energy, and tablet weight variability, whereas higher DCPA fractions decreased apparent density of tablets and reduced energy demand. Tabletability and compressibility profiles reflected that MCC generated hard tablets but exhibited higher elastic recovery, while DCPA formed softer tablets with closer to linear strength–pressure relationships. Energy profiling demonstrated that MCC stored more elastic energy and required higher overall compression work, whereas DCPA reduced elastic accumulation. Overall, blending viscoelastic and brittle excipients offers a robust strategy for optimizing manufacturability, mechanical strength, and energy efficiency in tablet production. Full article

The accurate modelling of material removal mechanisms in grinding processes requires precise constitutive equations describing dynamic material behaviour under extreme strain rates and large deformations. This study presents a novel methodology for optimising the Johnson–Cook (J–C) constitutive model parameters for micro-grinding applications, addressing the limitations of conventional mechanical testing at strain rates exceeding 10⁵ s⁻¹. The research employed single abrasive grain micro-cutting experiments using a diamond Vickers indenter on aluminium alloy 7075-T6 specimens. High-resolution topographic measurements (130 nm lateral resolution) were used to analyse the scratch geometry and lateral material displacement patterns. Ten modified J–C model variants (A1–A10) were systematically evaluated through finite element simulations, focusing on parameters governing plastic strengthening (B, n) and strain rate sensitivity (C). Quantitative non-conformity criteria assessed agreement between experimental and simulated results for cross-sectional areas and geometric shapes of material pile-ups and grooves. These criteria enable an objective evaluation by comparing the pile-up height (h), width (l), and horizontal distance to the peak (d). The results demonstrate that conventional J–C parameters from Hopkinson bar testing exhibit significant discrepancies in grinding conditions, with unrealistic stress values (17,000 MPa). The optimised model A3 (A = 473 MPa, B = 80 MPa, n = 0.5, C = 0.001) achieved superior convergence, reducing the non-conformity criteria to Σk_A = 0.46 and Σk_K = 1.16, compared to 0.88 and 1.67 for the baseline model. Strain mapping revealed deformation values from ε = 0.8 to ε = 11 in lateral pile-up regions, confirming the necessity of constitutive models describing material behaviour across wide strain ranges. The methodology successfully identified optimal parameter combinations, with convergence errors of 1–14% and 7–60% on the left and right scratch sides, respectively. The approach provides a cost-effective alternative to expensive dynamic testing methods, with applicability extending to other ductile materials in precision manufacturing. Full article

In cold regions, flexible pavements are vulnerable to frost-induced damage, necessitating effective insulation strategies. Foam glass aggregate (FGA) insulation layers, made from recycled glass, offer promising thermal insulation properties but are mechanically fragile and susceptible to permanent deformation under repeated loading. Manufacturers provide technical recommendations, particularly regarding load limits for installation and the dimensions of the thermal protection layer. These are considered insufficient to assist pavement designers in their work. The definition of critical criteria for permissible loads was deemed necessary to design mechanically durable structures using this alternative technology. This study investigates the critical stress conditions that FGA layers can tolerate within flexible pavement systems to ensure long-term structural integrity. Laboratory cyclic triaxial tests and full-scale accelerated pavement testing using a heavy vehicle simulator were conducted to evaluate the resilient modulus and permanent deformation behavior of FGA. The results show that FGA exhibits stress-dependent elastoplastic behavior, with resilient modulus values ranging from 70 to 200 MPa. Most samples exhibited plastic creep or incremental collapse behavior, underscoring the importance of careful stress management. A strain-hardening model was calibrated using both laboratory and full-scale data, incorporating a reliability level of 95%. This study identifies critical deviatoric stress thresholds (15–25 kPa) to maintain stable deformation behavior (Range A) under realistic confining pressures. FGA performs well as a lightweight, insulating, and draining layer, but design criteria remain to be defined for the design of multi-layer road structures adapted to local materials and traffic conditions. Establishing allowable critical stress levels would help designers mechanically validate the geometry, particularly the adequacy of the overlying layers. These findings support the development of mechanistic design criteria for FGA insulation layers, ensuring their durability and optimal performance in cold climate pavements. Full article

Magnesium (Mg) alloys are the lightest metals used in engineering structures, making them highly valuable for lightweight designs in aerospace, automotives, and related industries. Their low density offers clear advantages for reducing product weight and improving energy efficiency–key priorities in modern manufacturing. However, their unique crystal structure leads to notable drawbacks: low plasticity at room temperature, uneven performance across different directions, and inconsistent strength under tension versus compression. These issues have severely limited their broader application beyond specialized use cases. Shear deformation methods address this challenge by creating high strain variations and complex stress conditions. This approach provides an effective way to regulate the internal structure of Mg alloys and enhance their overall performance, overcoming the inherent limitations of their crystal structure. This paper systematically summarizes current research on using shear deformation to process Mg alloys. It focuses on analyzing key structural changes induced by shear, including the formation and evolution of shear–related features, real–time grain reorganization, crystal twinning processes, the distribution of additional material phases, and reduced directional performance bias. The review also clarifies how these structural changes improve critical mechanical traits: strength, plasticity, formability, and the balance between tensile and compressive strength. Additionally, the paper introduces advanced shear–based processes and their derivative technologies, such as equal–channel angular extrusion, continuous shear extrusion, and ultrasonic vibration–assisted shearing. It also discusses strategies for constructing materials with gradient or mixed internal structures, which further expand the performance potential of Mg alloys. Finally, the review outlines future development directions to advance this field: developing shear processes that combine multiple physical fields, conducting real–time studies of microscale mechanisms, designing tailored shear paths for high–performance Mg alloys, and evaluating long–term service performance. These efforts aim to promote both theoretical innovation and industrial application of shear deformation technology for Mg alloys. Full article

This study proposes the insufficient prediction accuracy of load–displacement behavior for pile foundations in soft soil regions by proposing an elastoplastic load-transfer model applicable to axially loaded piles in soft clay, aiming to enhance the prediction capability of shaft resistance mobilization. The model systematically incorporates the elastoplastic shear deformation of the soil within the plastic zone adjacent to the pile shaft and the small-strain stiffness degradation of the soil in the elastic zone. The elastoplastic constitutive relationship in the plastic zone is formulated using critical state theory, plastic potential theory, and the associated flow rule, whereas the nonlinear elastic shear deformation in the elastic zone is described based on Hooke’s law combined with a small-strain stiffness degradation model. The developed load-transfer function is embedded into an iterative computational framework to obtain the load–displacement response of piles in multilayered soft soils. The model is validated using field pile test data from Louisiana and Shanghai. The results show that the proposed model can reasonably reproduce the elastoplastic $\tau -z$ evolution along the pile shaft and provides a theoretically robust and practically applicable method for predicting the settlement behavior of piles in clayey soils. This approach offers significant engineering value for optimizing pile design, evaluating bearing capacity, and developing cost-efficient foundation solutions in soft soil regions. Nevertheless, the current applicability of the model is primarily limited to short and medium-length piles in saturated normally consolidated clay. Future work will focus on incorporating strain-softening mechanisms and extending the model to a wider range of soil types. Full article

Commercially pure (CP) titanium is widely used for long-term biomedical implants due to its high biocompatibility and corrosion resistance. However, its relatively low strength limits its use in highly loaded applications. Ultrafine-grained (UFG) titanium obtained through severe plastic deformation offers enhanced mechanical performance while maintaining the stability of CP titanium. This study investigates how electrochemical surface modification by anodization affects the corrosion, biological performance, and technological behavior of UFG titanium. TiO₂ layers with nanotubular and nanoporous morphologies were produced at anodization voltages between 20 and 60 V. Corrosion tests in physiological solution confirmed stable passive behavior with corrosion rates below 4 µm year⁻¹, and surface wettability increased markedly with anodization. Osteoblast-like MG-63 cells exhibited good viability on all anodized surfaces, with improved adhesion and proliferation on samples anodized at 60 V. The porous TiO₂ layers were successfully intercalated with dimethyl sulfoxide and ibuprofen, demonstrating potential for local drug delivery. Implantation simulations on real Nanoimplant^® prototypes confirmed sufficient mechanical stability of the anodized layer. Overall, the optimized anodization of UFG titanium enhances its biological response while maintaining corrosion resistance, supporting its clinical use in long-term dental and orthopedic implants with integrated drug-release functionality. Full article

Friction conditions, along with the flow behaviors of materials, significantly impact plastic deformation during metal forming. Extensive practical research on friction has thus been conducted, and industrial development has been remarkable. However, it has been continuously pointed out in academia that an in-depth analysis of friction laws and phenomena linked to the metal forming simulation (MFS) has not yet reached a sufficient state from an engineering perspective. Despite the significant impact of friction on the MFSs, its importance has been underestimated, and the related studies have been relatively limited. A few researchers on metal forming emphasized the inadequacy of the constant shear friction law (CSFL) and the constant friction coefficient for the Coulomb friction law (CFL). Yet, most researchers still use the CFL with a constant friction coefficient or the CSFL. Many researchers have related the friction coefficient to the yield criterion, and they believe that the friction coefficient cannot exceed a certain value (for example, 0.577). It has also been believed that the sticking condition is the same as the friction factor of unity, even though displacement and traction cannot be prescribed simultaneously in natural phenomena. Despite many researchers’ innovative academic and industrial contributions, friction phenomena in metal forming remain in an incomplete state of confusion. This study reviewed and synthesized research on friction phenomena during metal forming. The main review topics include friction phenomena, friction modeling and friction laws, friction-related issues, lubrication regime change (LRC), lubricants, and tribometers, with their application spaces limited to metal forming. This review synthesizes existing research related to friction in metal forming, proceeding in a problem-identifying and solution-oriented manner. Full article

To investigate the impact of subsurface karst cavities on the stability of pipe jacking construction, this study utilizes the Yunnan Central Water Diversion Project as a real-world case. Employing ABAQUS finite element software to establish a numerical model, it systematically analyzes construction stability under the specific condition of “karst cavities present ahead of the excavation direction” in karst formations. The research focuses on examining the effects of four key scenarios on the displacement and stress response of surrounding rock and pipe segments. These conditions specifically include the following: tunnel burial depth (10 m, 15 m, 20 m, 25 m), cavity diameter beneath the tunnel (1–4 m), cavity filling status, and distance between the cavity and the tunnel (1–4 m). The study reveals that in composite stratum tunnel construction, when cavities exist in the strata ahead, multi-area displacements increase progressively with cavity size. Displacement changes accelerate and magnify when the cutting face of the jacking machine approaches within approximately 2.5 m of the cavity. However, no significant difference is observed between soft plastic clay reinforcement and slurry reinforcement effects. When composite stratum tunnels traverse beneath karst caves, the maximum upward bulge at tunnel bases occurs at 1-meter diameter caves, reaching approximately 2.5 mm. When the diameter of the cave increases to 4 m, the arching settles to a maximum. As tunnel burial depth increases, the arch base rises while the crown sinks, with settlement magnitude exceeding bulge amount. The displacement and stress fields from the initial excavation phase become disturbed, intensify, and then stabilize. When the jacking machine reaches directly above the cavern, stress at the crown base increases while stress at the crown top decreases. The pipe bottom exhibits uplift, and the pipe top shows reduced settlement directly above the cavern. Cavern filling has a minor effect on pipe-segment displacement, with segments deforming into an approximate elliptical shape. At the completion stage of excavation, the maximum Mises stress occurs at the top of the launch-end pipe segment. While cavern-related factors have a limited influence on the pipe-segment Mises stress, this stress gradually increases as excavation progresses. Full article

Tungsten is a prime candidate material for the plasma-facing components of fusion reactors, thanks to its high melting point, high temperature strength, good thermal conductivity, high erosion resistance, etc. Yet, it has some limitations, mainly its brittle nature, difficulty of machining, and propensity to recrystallize at elevated temperatures. Among the approaches to the improvement of particular properties are alloying, dispersion strengthening, thermomechanical processing, and modifications to the sintering process. This study explores the possibility of combining fine powder size with ultra-high pressure to achieve significant densification at moderate temperatures during hot pressing. Two powder sizes and a range of temperatures from 1000 to 2000 °C were used, and their effects were observed. The resulting tungsten compacts were characterized for their microstructure, density, and mechanical and thermal properties. The high pressure enabled substantial densification already at relatively low temperatures, thanks to the plastic deformation of the powder particles. A significant degree of sintering, as manifested by the microstructural and property evolution, occurred however only at higher temperatures. The compacts exhibited brittleness, calling for further optimization of the method. Full article