Search Results (344)

This study aimed to examine how downward load applied during instrumentation affects the stress generation and shaping properties in thermally treated and non-treated NiTi rotary instruments. ProTaper Universal (PTU; non-thermally treated) and ProTaper Gold (PTG; thermally treated) were used to prepare J-shaped canals in resin blocks. Load-controlled automated instrumentation and torque/force sensing devices were employed with preset downward loads of 1, 2, or 3 N (n = 10 each). The torque/force, instrumentation time, and canal-centering ratio were measured and analyzed using two-way or one-way analysis of variance with Tukey’s test (α = 0.05). In the PTU-1N group, instrumentation was not completed because a ledge was formed in all canals. The PTU-3N group showed significantly greater upward force (screw-in force) and clockwise torque, along with a significantly smaller canal-centering ratio (less deviation) at the apical 0 mm level, than the PTU-2N group (p < 0.05). The downward load did not influence the instrumentation time (p > 0.05). In the PTG groups, these effects of downward load on the force generation and canal-centering ratio were not significant (p > 0.05). In the non-thermally treated PTU instruments, greater downward loads enhanced screw-in force while decreasing apical canal deviation; however, these effects were abolished in the thermally treated PTG instruments. This study highlights the importance of adapting the instrumentation technique with instrument characteristics: thermally treated flexible instruments facilitate smoother use, while stiffer, non-thermally treated ones may require precise control of downward loads. Full article

Aiming at the multifunctional requirements of the limited space in high-end vehicle side-door latches, a double single-loop RRUPRR mechanism driven by a single motor for both electric releasing and cinching is proposed based on the POC set. The kinematical equations of the RRURR mechanism possess 2 × 2 analytical solutions. In order to apply the current motion/force transmission performance index of the parallel mechanisms to the transmission performance analysis of the serial mechanisms, matching methods for chain-driving transference and the moving/fixed platform inversion are proposed. The solution of the performance index of a single-degree-of-freedom single-loop mechanism is equivalent to the solution of the input motion/force transmission performance index of a parallel mechanism. The overall motion/force transmission performance index of a single-loop mechanism is constructed, and the corresponding calculation procedure is defined. Chain-driving transference can be obtained through forward and inverse solutions of the RRURR mechanism. In response to the extremely high requirements for motion/force transmission performance of electric release mechanisms, the proposed overall motion/force transmission performance index is used to calculate for the input motion screw and corresponding transmission-force screw of the single-loop RRURR mechanism and obtain the overall motion/force transmission performance of the mechanism. The performance atlas of the mechanism shows that it has excellent motion/force transmission characteristics within the workspace. Using ADAMS simulation software, the driving torque required for electric releasing and cinching of a vehicle side-door latch mechanism with a single motor is analyzed. The overall motion/force transmission performance index of a single-loop mechanism can be applied to single-loop overconstrained mechanisms and non-overconstrained mechanisms. Full article

Pedicle screw fixation is a common spinal surgery technique, but concerns remain about stability when screws are malpositioned. Traditional in vitro pull-out tests assess anchorage but lack physiological accuracy. This study examined the stability of correctly placed and intentionally malpositioned pedicle screws on forty vertebrae from five cadavers. Optimal screw paths were planned via CT scans and applied using 3D-printed guides. Four malposition types—medial, lateral, superior, and superior-lateral—were created by shifting the original trajectory. A custom setup applied three consecutive cycles of tensile and compressive load from 50 N to 200 N. Screw inclination under load was measured with a 3D optical system. The results showed increasing screw inclination with higher forces, reaching about 1° at 50 N and 2° at 100 N, similar in both load directions. Significant differences in inclination were only found at 100 N tensile load, where malpositioned screws showed a lower inclination. Overall, malpositioning had no major effect on screw loosening. These findings suggest that minor deviations in screw placement do not significantly compromise mechanical stability. Clinically, the main concern with malpositioning lies in the potential for injury to nearby structures rather than reduced screw fixation strength. Full article

To analyze the wear performance induced by rotor–stator rubbing in an aero-engine sealing structure under authentic operating conditions, a transonic rotor system with double bearing is constructed. This system incorporates the disk, shaft, blades, joint bolts, and auxiliary support structure. The system was evaluated in terms of its critical speed, vibration characteristics, component strength under operational conditions, and response characteristics in abnormal extreme scenarios. A ball screw-type feeding system is employed to achieve precise rotor–stator rubbing during rotation by controlling the coating feed. Additionally, a quartz lamp heating system is used to apply thermal loads to coating specimens, and the appropriate heat insulation and cooling measures are implemented. Furthermore, a high-frequency rubbing force test platform is developed to capture the key characteristics caused by rubbing. The test rig can conduct response tests of the system with rotor–stator rubbing and abrasion tests with tip speeds reaching 425 m/s, feed rates ranging from 2 to 2000 μm/s, and heating temperatures up to 1200 °C. Test debugging has confirmed these specifications and successfully executed rubbing tests, which demonstrate stability throughout the process and provide reliable rubbing force test results. This designed test rig and analysis methodology offers valuable insights for developing high-speed rotating machinery. Full article

This study investigates the deformation and fracture mechanisms of a Ti₆₁Al₁₆Cr₁₀Nb₈V₅ multi-principal element alloy (Ti61V5 alloy) under quasi-static and dynamic compression. The alloy comprises an equiaxed BCC matrix (~35 μm) with uniformly dispersed nano-sized B2 precipitates and a ~3.5% HCP phase along grain boundaries, exhibiting a density of 4.82 g/cm³, an ultimate tensile strength of 1260 MPa, 12.8% elongation, and a specific strength of 262 MPa·cm³/g. The Ti61V5 alloy exhibits a pronounced strain-rate-strengthening effect, with a strain rate sensitivity coefficient (m) of ~0.0088 at 0.001–10/s. Deformation activates abundant {011} and {112} slip bands in the BCC matrix, whose interactions generate jogs, dislocation dipoles, and loops, evolving into high-density forest dislocations and promoting screw-dominated mixed dislocations. The B2 phase strengthens the alloy via dislocation shearing, forming dislocation arrays, while the HCP phase enhances strength through a dislocation bypass mechanism. At higher strain rates (960–5020/s), m increases to ~0.0985. Besides {011} and {112}, the BCC matrix activates high-index slip planes {123}. Intensified slip band interactions generate dense jogs and forest dislocations, while planar dislocations combined with edge dislocation climb enable obstacle bypassing, increasing the fraction of edge-dominated mixed dislocations. The Ti61V5 alloy shows low sensitivity to adiabatic shear localization. Under forced shear, plastic-flow shear bands form first, followed by recrystallized shear bands formed through a rotational dynamic recrystallization mechanism. Microcracks initiate throughout the shear bands; during inward propagation, they may terminate upon encountering matrix microvoids or deflect and continue when linking with internal microcracks. Full article

Differential planetary roller lead screw (DPRS) serves as a quintessential actuating mechanism within the electromechanical braking (EMB) systems of vehicles, where its operational reliability is paramount to ensuring braking safety. Considering different braking intensities, how assembly errors affect the contact stress in DPRS was analyzed via the finite element method. Firstly, the braking force of the EMB system that employed DPRS was verified by the braking performance of legal provisions. Secondly, a rigid body dynamics model of DPRS was established to analyze the response time, braking clamping force, and axial contact force of DPRS under varied braking intensities. Finally, a finite element model of DPRS was constructed. The impact of assembly errors in the lead screw and rollers on the contact stress were investigated within the DPRS mechanism based on this model. The results indicate that as braking intensity increases, the deviation of the lead screw exerts a greater influence on the contact stress generated by the engagement between the lead screw and rollers compared to that between the nut and rollers. The skewness of the rollers also affects the contact stress generated by the engagement of both the lead screw with rollers and the nut with rollers. When assembly errors reach a certain threshold, the equivalent plastic strain is induced to exceed the critical value. This situation significantly impairing the normal operation of DPRS. This study provides guidance for setting the threshold of assembly errors in DPRS mechanisms. It also holds significant implications for the operational reliability of EMB systems. Full article

Background/Objectives: Limb malalignment disrupts physiological joint forces and predisposes individuals to the development of osteoarthritis. Surgical interventions such as distal femur or high tibial osteotomy aim to restore mechanical balance on weight-bearing joints, thereby reducing long-term morbidity. Accurate alignment is crucial since it cannot be adjusted after stabilization with plates and screws. Recent advances in personalized medicine offer the opportunity to tailor surgical corrections to each patient’s unique anatomy and biomechanical profile. This study evaluates the benefits of 3D planning and patient-specific cutting guides over traditional 2D planning with standard implants for alignment correction procedures. Methods: We assessed limb alignment parameters pre- and postoperatively in patients with varus and valgus lower limb malalignment undergoing acute realignment surgery. The cohort included 23 opening-wedge high tibial osteotomies and 28 opening-wedge distal femur osteotomies. We compared the accuracy of postoperative alignment parameters between patients undergoing traditional 2D preoperative X-ray planning and those using 3D reconstructions of CT data. Outcome measures included mechanical axis deviation and tibiofemoral angles. Results: 3D reconstructions of computerized tomography data and patient-specific cutting guides significantly reduced the variation in postoperative limb alignment parameters relative to preoperative goals. In contrast, traditional 2D planning with standard non-custom implants resulted in higher deviations from the targeted alignment. Conclusions: Utilizing 3D CT reconstructions and patient-specific cutting guides enhances the accuracy of postoperative limb realignment compared to traditional 2D X-ray planning with standard non-custom implants. Patient-specific instrumentation and personalized approaches represent a key step toward precision orthopedic surgery, tailoring correction strategies to individual patient anatomy and potentially improving long-term joint health. This improvement may reduce the morbidity associated with lower limb malalignment and delay the onset of osteoarthritis. Level of Evidence: Therapeutic Level III. Full article

The existing scientific literature lacks comprehensive information regarding the influence of zirconia crown height on debonding and fracture of the ceramic restorations on titanium base abutments. Additionally, there is a lack of comparative studies evaluating different types of zirconia as restorative options for screw-retained restorations. Purpose: The purpose of this study was to assess the fracture strength and the failure modes of the zirconia crown/titanium abutment complex by investigating the impact of increasing the height of zirconia crown and comparing different types of zirconia (3 mol% yttria-stabilized zirconia and translucent 5 mol% yttria-stabilized zirconia). Materials and Methods: Six groups of 10 specimens in each group were fabricated. Three groups of specimens (groups # 1, 2, and 3) were fabricated from 3Y zirconia in corresponding heights of 8, 10, and 12 mm. Three more groups (groups # 4, 5, and 6) were fabricated from 5Y zirconia in the same heights (8, 10 and 12 mm). All copings were bonded to 4 mm high titanium base abutments using dual-polymerization resin cement. The specimens underwent load cycling of 100,000 cycles with a force of 100 N. Subsequently, the specimens were loaded to compression until fracture and the failure mode was visually evaluated. Results: Statistically significant differences in fracture strength were noted among all tested groups. Conclusions: 3Y zirconia showed increased strength compared to 5Y in all heights. Ceramic copings with lower height showed increased strength compared to higher copings in both tested zirconia materials. Full article

Extrusion-based printers have attracted much attention for their simplified printing process and broader material compatibility. Carbon fibers (CF), known for their excellent mechanical properties, are incorporated into polypropylene (PP) printing materials. This study presents a shear screw printer (SSP) with a modified screw design. The SSP generates torsional shear forces, enabling helical orientation of CFs within PP/CF composites. The study also compares the SSP’s performance with that of a conventional screw printer (CSP). PP/CF composite specimens containing 15% CF were printed at four different layup angles: 0°, 45°, 90°, and ±45° (net). The results show that combining CFs’ helical orientation with a net printing arrangement can effectively enhance tensile properties while reducing anisotropy. Furthermore, this approach can significantly mitigate warping in printed parts. Full article

Background/Objectives: Proximal interphalangeal joint (PIJ) arthrodesis is a common surgical intervention for patients with PIJ osteoarthritis or trauma-related joint destruction. The objective of this study was to evaluate the biomechanical stability of various arthrodesis techniques under forces comparable to activities of daily living (ADL) to assess their suitability for early active movement protocols. Methods: In this in vitro study, composite cylinders simulating PIJ arthrodesis were subjected to standardized fusion angles of 40° using different fixation techniques, including crossed K-wires, compression screws, cerclage wires, tension band wiring, anatomical fixation plates, and locking grid plates. Forces representing ADLs such as typing, holding a pencil, carrying weight, and opening a jar were applied using a universal testing machine in a four-point bending setup. Micromotion and gap clearance were calculated and analyzed. Results: Techniques involving compression, such as compression screws, tension bands, and cerclage wires, exhibited lower micromotion and gap clearance under forces up to 17 N, suggesting potential suitability for early active movement protocols. In contrast, fixation plates demonstrated structural failure or excessive clearance during early active motion ADLs. K-wires showed intermediate results with moderate gap clearance and micromotion. Conclusions: Compression-based fixation techniques for PIJ arthrodesis may permit early active movement without external stabilization, while fixation plates are prone to failure under ADL forces. Further dynamic biomechanical testing and clinical studies are recommended to confirm these findings. Full article

The shallow, soft subsea formations, characterized by low strength and poor stability, lead to complex interactions between the screw motor drilling tool and the wellbore wall during directional drilling, complicating the accurate evaluation of the tool’s deflection capability. To address this issue, this paper proposes an integrated mechanical analysis method combining three-dimensional finite element analysis and transient dynamic analysis. By establishing a finite element model using 12-DOF (degree-of-freedom) spatial rigid-frame Euler–Bernoulli beam elements, coupled with well trajectory coordinate transformation and Rayleigh damping matrix, a precise description of drill string dynamic behavior is achieved. Furthermore, the introduction of pipe–soil dynamics and the p-y curve method improves the calculation of contact reaction forces between drilling tools and formation. Case studies demonstrate that increasing the tool face rotation angle intensifies lateral forces at the bit and stabilizer, with the predicted maximum dogleg severity within the first 10 m ahead of the bit progressively increasing. When the tool face rotation angle exceeds 2.5°, the maximum dogleg severity reaches 17.938°/30 m. With a gradual increase in the drilling pressure, the maximum bending stress on the drilling tool, maximum lateral cutting force, and stabilizer lateral forces progressively decrease, while vertical cutting forces and bit lateral forces gradually increase. However, the predicted maximum dogleg severity increases within the first 10 m ahead of the bit remain relatively moderate, suggesting the necessity for the multi-objective optimization of drilling pressure and related parameters prior to actual operations. Full article

Natural gas is one of the major sources of energy supply, where the measurement of natural gas is very crucial. The flowmeter fastening apparatus typically used tightened screw nuts for clamping. This study designed a clamping device for a DN300 specification gas pipe, which directly clamped the flowmeter with the flange by external force. This clamping method is more efficient compared to previous methods. Based on the fabricated flowmeter clamping experimental device, a simplified numerical model was established. A detailed analysis was conducted on several key components, including the screw nuts, flange, flowmeter, and pipe. The results indicate that the designed clamping devices can operate safely and reliably. The stress distribution is reasonable in the entire clamping device. The average stress in the flowmeter flange is significantly greater than the pressure of gas within the pipe. The stress distribution on the screw nuts generally shows a pattern of higher stress in the central area and lower stress in the surroundings. The maximum stress of the flowmeter clamping device is located on the flowmeter flange, reaching 146 MPa. The maximum stress value of the nut is the smallest, which is 117 MPa. Full article

Background: Ferrous metals are used extensively in the manufacturing of plates, pins, Kirschner wires (K-wires), and screws, and in the performance of partial and total joint replacement surgeries for the shoulder, elbow, and wrist joints. The primary surgical procedures commonly performed are hip and knee replacement surgeries. Metals possess a combination of high modulus, yield point, and ductility, rendering them well suited for load-bearing applications, as they can withstand significant loads without experiencing substantial deformations or permanent alterations in their dimensions. Application of metals and alloys is of prime importance in orthopedics as they lead the way to overcoming many issues encountered in implant use. In some instances, pure metals are used, but alloys consisting of two or more elements typically exhibit greater material characteristics, including corrosion resistance as well as toughness. The first item to address when selecting a metallic implant material is its biocompatibility. In this regard, three classes of materials are also commonly known as biomedical metals—316L stainless steel, pure titanium, and titanium alloys. Objective: The aim of this work is to create a model describing the material behavior and then simulate the metals under a load of 2300 N, which is equivalent to plastic loading. Methods: Under ten different case studies, a sub-routine was developed to combine the material characteristics of titanium and 316L stainless steel with the software. Results: The outcomes of the research were then investigated. A femur model was created using ANSYS software, and two materials, stainless steel and titanium, were used. The model was then exposed to a force of 2300 N. Full article

Rural domestic waste slag is often used to prepare organic fertilizer, thereby improving the environment and saving resources. The mixing of the raw materials and fermentation bacteria is key to the preparation of organic fertilizers. In the organic fertilizer continuous conveying device designed in this study, a paddle was substituted for a screw blade for transporting the material to improve the mixing performance. A discrete element method (DEM) model was established for the device. The influences of the paddle rotational speed n and paddle angle α were studied. The simulation results showed that mixing performance was improved when the paddle angle α was 45° and the paddle rotational speed n was 75 rpm, with an RSD of 15.96%. The larger the paddle rotational speed n, the larger the average normal contact force, and the smaller the influence of the paddle angle α. In addition, the paddle rotational speed n and paddle angle α could affect the speed of the particles in all directions in the device. The trajectory of a single particle in the device was analyzed, and it was found that changing the paddle parameters could improve the path length and improve the mixing performance. The research results lay the foundation for designing reasonable paddle parameters. Full article

Two-dimensional transition metal dichalcogenides have attracted considerable attention in electrocatalytic hydrogen evolution due to their unique layered structures and tunable electronic properties. However, prior research has predominantly focused on the intrinsic catalytic activity of planar few-layer structures, which offer limited exposure of edge-active sites due to their restricted two-dimensional geometry. Moreover, van der Waals interactions between layers impose substantial barriers to electron transport, significantly hindering charge transfer efficiency. To overcome these limitations, this study presents the innovative synthesis of high-quality single-screw WS₂ with a 5° dislocation angle via physical vapor deposition. Second harmonic generation measurements revealed a pronounced asymmetric polarization response, while the selected area electron diffractionand atomic force microscopy elucidated the material’s distinctive screwed dislocation configuration. In contrast to planar monolayer WS₂, the conical/screw-structured WS₂—formed through screw-dislocation-mediated growth—exhibits a higher density of exposed edge-active catalytic sites and enhanced electron transport capabilities. Electrochemical performance tests revealed that in an alkaline medium, the screwed WS₂ nanosheets exhibited an overpotential of 310 mV at a current density of −10 mA/cm², with a Tafel slope of 204 mV/dec. Additionally, under a current density of 18 mA/cm², the screwed WS₂ can sustain this current density for at least 30 h. These findings offer valuable insights into the design of low-cost, high-efficiency, non-precious metal catalysts for hydrogen evolution reactions. Full article