Search Results (154)

The microstructural characteristics and fracture behavior of a magnetic pole screw were investigated here. The screw threads were produced by cold thread rolling. Microstructural analysis (OM, SEM, EBSD), mechanical testing (tensile, hardness, fastening), and fracture morphology observation were conducted. The results indicate that work hardening and microstructural deformation were introduced by the gradient plastic deformation in the screw thread. The elongated microstructure of ferrite and pearlite was obtained in the deformation zones, resulting in increased hardness and decreased plasticity. The thread root subsurface experienced severe localized indentation deformation and exhibited the highest hardness. The distinct forming stress states led to a notable difference in the hardened layer depth between the thread crest and root. The torsional overload fracture was initiated at the stress-concentrated thread root, where the work-hardened microstructure exhibited a limited capacity to accommodate large plastic deformation. The crack propagation was influenced by the gradient microstructure, following three primary propagation paths: transgranular through ferrite, along the ferrite–pearlite phase interface, and cracking through lamellar pearlite. The results provide theoretical support for material design and process optimization to achieve the production of high-performance screws with high strength and hardness at the thread surface and high plasticity in the center. Full article

Threaded component fatigue failure is a severe issue in cyclically loaded mechanical systems, and the service life in these systems is controlled primarily by stress concentration at the thread root, especially in loading regimes dominated by bending. Rounded thread profiles such as knuckle threads have been thought to improve fatigue performance, although this is mostly due to the assumption being made on the basis of axial loading, the numerical stress analysis, and/or isolated stress-concentration analyses. This paper presents an experimental study on the fatigue behavior of knuckle-thread and conventional screw-thread specimens manufactured from AISI 1045 steel under rotating bending loading to determine the effects of thread geometry on fatigue life and damage mechanisms. Fatigue testing was conducted at varying stress levels to develop comparative stress–life (S–N) curves, the analytical relation being used in determining the stress-concentration factor, and standard literature techniques have been used in the analysis of fracture-surface in order to investigate the behavior of crack initiation and propagation. Results indicate that knuckle threads exhibit a lower stress concentration factor (K_t ≈ 1.59) than screw threads (K_t ≈ 2.11), resulting in longer fatigue life at the same nominal stress level, particularly in the high-cycle life regime. Fractographic research also indicates that knuckle threads enhance delayed crack initiation and more evenly distributed circumferential crack propagation, but screw threads show highly localized crack initiation and rapid radial propagation of cracks, resulting in earlier unstable fracture. These findings provide new experimental evidence that the improved fatigue performance of knuckle threads during rotating bending is linked to fundamental change in fatigue damage mechanism rather than to stress alleviation alone, thereby offering quantitative supporting guidance in designing fatigue-sensitive threaded components to experience cyclic bending. Full article

Introduction: The fracturing of abutment screws is a recurrent technical complication in implant-supported prostheses that may compromise prosthetic maintenance. Although multiple retrieval approaches have been described, comparative data under controlled experimental conditions remain limited. Materials and Methods: This in vitro pilot study evaluated the retrievability of fractured abutment screws when using three commonly applied instruments: an ultrasonic scaler, a fissure bur, and a screw removal kit. Eighteen implants from a single implant system were embedded in epoxy resin, and abutment screws were fractured under clockwise monotonic torque either with (w/A) or without (w/oA) abutments (n= 3 per retrieval method). Retrieval success and procedure time were recorded. Scanning electron microscopy (SEM) was performed to qualitatively assess deformation of the implant internal hex and screw thread morphology. Results: Fracture torque values were higher in specimens fractured with abutments compared with those without abutments. Fractures induced without abutments appeared to extend deeper within the screw channel, engaging a greater number of internal threads. In this pilot study, a shorter retrieval time was observed with the screw removal kit and fissure bur compared with the ultrasonic scaler, although retrieval outcomes varied between specimens. SEM observations suggested differing patterns of internal hex deformation between the retrieval techniques. Conclusions: Within the limitations of this in vitro pilot study, different retrieval approaches demonstrated characteristic mechanical behaviors and deformation patterns in the implant internal connection. These preliminary findings provide descriptive insight into the retrievability of fractured screws and may serve as a basis for future studies with larger sample sizes and clinically relevant fracture models. Full article

Background and Objectives: This biomechanical study aimed to compare the fixation stability of proximal fragments and assess the mechanical properties in models of unstable basicervical intertrochanteric fractures. Materials and Methods: Thirty-six synthetic femur models were utilized. After cephalomedullary nail insertion, unstable basicervical intertrochanteric fractures were created using an engraving machine. Specimens were divided into three groups based on the femoral head fixation method: Group 1 (n = 12, single 100 mm lag screw); Group 2 (n = 12, lag screw + 75 mm anti-rotation screw); and Group 3 (n = 12, lag screw + 95 mm anti-rotation screw). The anti-rotation screws were full-threaded locking screws positioned just below the lag screw. After applying 10,000 vertical cyclic loads, stereophotogrammetry was used to evaluate the proximal fragment rotation in three planes (coronal, sagittal, and axial), and screw-tip displacement was measured radiographically. Vertical load was then applied at a 10 mm/min rate until structural failure. Results: Rotational change in the sagittal plane was least in Group 3 (Group 1 = 1.7 ± 1.3°, Group 2 = 1.0 ± 0.8°, Group 3 = 0.6 ± 0.6°, p = 0.038). Varus (coronal plane) and retroversion (axial plane) collapse did not differ significantly among the three groups. While cranial migration showed no difference, axial migration was the significantly lowest in Group 3 (Group 1 = 1.07 ± 0.62 mm, Group 2 = 0.60 ± 0.57 mm, Group 3 = 0.50 ± 0.43 mm, p = 0.040). Failure load was slightly higher in Groups 2 and 3 than in Group 1, but without statistical significance. No significant differences were observed between Group 2 and Group 3 in any biomechanical outcomes. Conclusions: The novel cephalomedullary nail with a long inferior anti-rotation screw significantly reduced rotational instability and axial migration compared to a single-lag screw. There was no significant difference in the rotational stability between the 75 mm and 95 mm anti-rotation screw groups. This novel nail demonstrates superior biomechanical properties in this experimental model and warrants clinical evaluation for treating unstable basicervical intertrochanteric fractures. Full article

Product disassembly, critical in remanufacturing, often involves removing screws and bolts, which can be challenging due to degradation, such as rust or thread damage. Here, we develop a digital twin integrated with a Model Predictive Controller to optimise robotic screw unfastening. Using real-time force and torque data from a robot unscrewing an electric vehicle battery pack, the controller predicts and adjusts screwdriver position and spindle speed to minimise applied torque and force. Experimental results demonstrate that this approach improves unscrewing success rates and reduces torque variability compared to manual methods. These findings suggest that combining digital twin technology with MPC can enhance the efficiency and reliability of robotic disassembly processes, supporting sustainable remanufacturing efforts. Full article

Steel and prestressed concrete traction poles can be fixed to reinforced concrete pile foundations using typical bolted connections. The stainless steel fastening screw is connected to the ordinary steel foundation pile reinforcement by friction welding under specific friction welding process parameters. From the perspective of the structural strength of the connection between the traction pole and the foundation pile, regarding the transfer of tensile and shear forces through a single anchor bolt, the yield strength of stainless steel bolts should be R_e,min ≥ 345 MPa for M30 anchors, R_e,min ≥ 310 MPa for M36 anchors and R_e,min ≥ 300 MPa for M42 anchors. This requirement is reliably met by martensitic stainless steels, while other stainless steels have yield strengths below the required minimum. What truly determines the foundation pile’s load capacity is not the satisfactory mechanical strength of the stainless steel (here, the parameters are met), but the quality of the friction-welded end connection between the reinforcement and the threaded bars. Incorrect selection of the type of prestressing steel in the analyzed connection can have enormous consequences for foundation pile manufacturers. Annual production of foundation piles amounts to thousands of units, and an incorrect decision made by the pile designer at the design stage can result in significant financial losses and a high risk to human life. This article presents the results of studies on friction-welded connections of M30, M36, and M42 threaded bars made of austenitic 1.4301 (AISI 304) and martensitic 1.4021 (AISI 420) stainless steel with B500SP reinforcement bars. The tests yielded negative results for 1.4021 (AISI 420) steel, despite its yield strength exceeding R_e ≥ 360 MPa. Full article

This finite element analysis compared a tissue-level implant with an engaging Ti-base to abutment-free, direct-to-implant, tissue-level configurations (3.7 mm and 4.5 mm platforms; short and long retention screws) to examine how platform width and screw length influence stresses under axial and oblique loads. Five configurations were modeled with identical materials and boundary conditions. Screw preload corresponding to a tightening torque of 35 N·cm was applied in the first step, followed by either a 400 N axial load or a 300 N at 30°. Oblique loading dominated the mechanical response, increasing stresses relative to axial loading and concentrating them at the implant neck and first thread, as well as at the crown screw-access and antirotation regions. Under oblique loads, the 3.7 mm platform implant showed the highest stresses, whereas the 4.5 mm platform implant was comparable to or slightly less stressed than the Ti-base configuration, whose peaks remained confined to a small internal recess. Crown stresses remained localized around the antirotation features, while the composite layer bore negligible load. Within the limitations of this numerical model, abutment-free, direct-to-implant workflows may achieve biomechanical performance comparable to Ti-base solutions if platform and screw selection are aligned with the occlusal scheme, but ISO-style fatigue testing and experimental or clinical validation are required. Full article

Fractures of the posterior malleolus are key determinants of ankle stability and long-term functional outcome in complex ankle injuries. The posterolateral rim fragment represents a bony avulsion of the posterior syndesmotic complex. Anatomical reduction of this fragment restores the fibular incisura, posterior tibiotalar stability, and syndesmotic integrity. Based on a geriatric case of a trimalleolar ankle fracture with a Bartoníček type 2 posterior malleolar component, this review describes a modified minimally invasive inside-out fixation technique performed under intraoperative three-dimensional imaging. The posterior malleolar fragment was stabilized using a posterior-to-anterior headless double-threaded compression screw. The medial malleolus was fixed with two parallel partially threaded cannulated cancellous screws, and the distal fibular fracture was stabilized using a reamed intramedullary locking nail. The surgical technique, potential complications, and postoperative management are described in detail. This approach combines the biomechanical advantages of direct posterior malleolar fixation with minimal soft-tissue disruption, providing a stable and reliable construct for the treatment of complex ankle fractures, particularly in geriatric patients and in those with compromised soft-tissue conditions. Full article

The SBPDN (Steel Bar Prestressed Deformed Normal relaxation) bar, which has ultra-high yield strength yet much lower bond resistance than conventional deformed bars, has been recently proposed to be used as the longitudinal rebar instead of a normal-strength deformed bar to simply realize strong earthquake-resilient concrete components. To facilitate and promote the application of concrete components reinforced with SBPDN rebars to the structures located in earthquake-prone regions, it is indispensable to develop reliable and effective anchoring means and clarify the bond strength of SBPDN bars embedded in concrete and/or grout mortar. This paper presents experimental information on the pull-out tests of fifteen SBPDN bars embedded in grout mortar, along with a discussion on the effective anchorage details and the bond strength of SBPDN bars. The tested SBPDN bars have a nominal diameter of 22.2 mm, the maximum diameter currently available on the market. All SBPDN bars were embedded in high-strength grout mortar with a targeted compressive strength of 60 MPa. The primary experimental variables included the end anchorage details, the diameter of sheath ducts, and the embedded length of the bars. Test results demonstrated that either screwing two nuts and a washer at the end of SBPDN bars or providing a rolling-threaded end region was effective in preventing them from premature slip from grout mortar. If the embedment length was 20 times the bar diameter or longer, the proposed two anchorages could ensure the SBPDN bar to fully develop its specific yielding strength as high as 1275 MPa. In addition, it has also been experimentally revealed that the bond strength of SBPDN bars embedded in grout mortar was much lower than that of conventional deformed bars and varied between 2.84 MPa and 3.98 MPa. Full article

Background: The use of prosthetic caps in screw-retained implant restorations aims to enhance passivity and protect abutment threads; however, these components may increase prosthetic volume and impair esthetics. Advances in high-strength zirconia have raised the question of whether such caps remain necessary. Methods: A retrospective clinical analysis was conducted on 20 partial screw-retained zirconia restorations comparing cases fabricated with and without a prosthetic cap. All restorations were followed for 3–5 years. Clinical outcomes included screw stability, marginal adaptation, esthetics (VAS), hygiene access, and biological response. A supplementary mechanical verification was performed on four standardized zirconia crowns fabricated through digital and conventional impression workflows to qualitatively assess their behavior under 30 N·cm torque and compressive loading above 1200 MPa. Results: Throughout follow-up, no mechanical or biological complications were recorded in either group. One restoration with a cap required screw re-tightening, while none failed in the cap-free group. Radiographic analysis showed smaller mean marginal gaps in cap-free restorations (0.183 mm) compared to those with caps (0.289 mm; p < 0.01). Esthetic satisfaction scores were higher in the cap-free group (VAS = 9.3 ± 0.1 vs. 8.2 ± 0.1; p < 0.001). Mechanical verification confirmed that all zirconia crowns tolerated torque and compressive loads without visible fracture or deformation. Conclusions: Within the study limitations, cap-free screw-retained zirconia restorations exhibited excellent 5-year clinical stability, improved esthetics, and better hygiene access compared with capped designs. The small-scale mechanical verification supported the clinical findings, indicating that cap omission does not compromise mechanical performance when accurate fit and digital workflow precision are ensured. Full article

In recent years, there has been a growing shift toward the use of screw extruders in the pitch modification process. To further improve the mixing efficiency of twin-screw extruders in pitch processing, this study focuses on redesigning the mixing elements of a co-rotating twin-screw extruder. By integrating the conventional kneading block assembly with PTA technology, three innovative screw mixing elements were developed. In this study, numerical simulations were performed using the finite element method (FEM) in the ANSYS Polyflow 2022 R1 software. The dynamic mesh technique was employed to model the screw rotation. The mixing performance of these novel screw elements was then evaluated in terms of distribution, mixing, and shear effects by utilizing the Particle Tracking Analy sis (PTA) technique within the Polyflow statistical module. The results demonstrate that the configuration and structural design of the mixing screw elements significantly influence the mixing effectiveness of spinnable pitch. Among the tested configurations, the slotted thread mixing element with six slots and a 30° slot angle (Model 2) was identified as the optimal design, exhibiting markedly superior mixing performance compared to the traditional kneading block (Model 4). Full article

FEA of orthodontic miniscrews has predominantly assumed isotropic, homogeneous bone, neglecting directional variations in mechanical properties. This study investigated the biomechanical behavior of miniscrews under different insertion angles and loading directions using both isotropic and orthotropic mandibular bone models. The results indicated that isotropic modeling may underestimate miniscrew displacement and associated instability, whereas orthotropic material properties better reflect the true mechanical response of bone. Oblique insertion at 60° (U60°) led to higher strain and greater variability, which may compromise osseointegration; aligning the loading direction parallel to the insertion plane is therefore recommended when oblique placement is unavoidable. Screw thread design had minimal influence on displacement, von Mises stress, or bone strain during vertical insertion. Stress and strain distributions exhibited symmetry, suggesting that analyzing partial loading directions can predict the overall biomechanical response. All predicted values remained below bone and material strength limits, confirming the mechanical safety of the current miniscrew design under a 2 N load. Implant failure is likely attributable to poor osseointegration or inflammation rather than structural limitations. Full article

Background/Objectives: The rate of periprosthetic joint infection (PJI) is expected to increase in the next years worldwide, mainly due to increasing volume of total joint replacement, longer prosthesis lifespans, and patients with multiple comorbidities. The aim of this study is to describe our personal technique, the modified Hofmann Articulated Spacer (mHAS), in which a CR femoral shield and a partially threaded cannulated screw are inserted into the liner replicating a tibial stem, and to evaluate the efficacy of the spacer as a definitive treatment option in selected patients with knee infections. Methods: A consecutive series of 132 patients were treated for orthopedic infection at the Orthopedic and Trauma Center, University of Turin, between November 2023 and May 2025. All patients included in the study had undergone knee prosthesis removal followed by the implantation of a modified Hofmann Articulated Spacer (mHAS). Functional recovery was evaluated through clinical examination, particularly knee range of motion, and patient-reported outcome measures (PROMs), including the Knee Society Score (KSS), Oxford Knee Score (OKS), and the EQ-5D-5L Visual Analogue Scale (VAS). Results: Nine patients were enrolled in the study, at a mean follow-up of 8.12 months (range: 3–13). The mean range of motion of the knee was 95 degrees (range: 80–120°, SD: 15°). The Knee Society Score (KSS) presented a mean value of 71.9 (SD: 18.11). The Oxford Knee Score (OKS) showed a mean value of 30.8 (SD: 8.5). The EuroQol-5 Dimension-5 Level Visual Analogue Scale (EQ-5D-5L VAS) scores demonstrated an excellent quality of life among the participants. Conclusions: The Modified Hofmann Articulated Spacer demonstrated good functional, qualitative outcomes and eradication rates in patients who underwent the first-stage revision TKA for PKI. This has led us to propose it as a definitive treatment option for more critical and low-demand patients and to postpone the second-stage surgery in the remaining cohort due to satisfactory spacer joint function without pain. Full article

Waste prevention is at the top of the EU Waste Framework directive hierarchy. With this in mind, this article considers the application of novel technologies in the Cultural Heritage Restoration and Conservation field through environmental and circular economy principles. While previous research has explored the use of wood waste for composite materials such as building insulation and concrete additives, the suitability of degraded historical wood waste for filament production and 3D printing has not yet been addressed. This article contributes to this topic by studying the PLA/wood composite, material composed of a polylactic acid (PLA) polymer matrix reinforced with wood particles, produced from degraded historical construction materials. The paper describes the process of producing filament from bio- and moisture-damaged pine beam and oak parquet, followed by the 3D printing of historical platband replica. Research methods include photogrammetry, filament machine construction, filament production and 3D printing. The machines settings used in the process: heater temperatures were set to 140 °C, 90 °C and 105 °C; servo speed was 33 s; spool tension was 12.5; winding speed was 24 RPM; and screw speed was 9.2 RPM. For material preparation, a mixture containing 25% pine and oak sawdust and PLA dust was processed to achieve particle sizes of 312 μm, 471 μm, and 432 μm, respectively. Filament production was carried out with diameters of 2.85 mm for the pine/PLA composite and 1.75 mm for the oak/PLA composite. Finally, replica samples were fabricated using 3D printing. The dual objective of this research was to develop the method of 3D printing from degraded historical materials and introduce it to restoration practice as a wood waste minimization technique. Perspectives for further study include the testing of 3D-printed construction materials in outdoor conditions, and pellet production to achieve a higher wood content, compared to the filament thread. The processes described are adaptable to a variety of materials and disciplines. Full article

The introduction of functional elements is essential for many industrial components which rely on elements such as bolts, screws, nuts, or clips that are integrated into the workpieces. In the field of cold joining technologies, double-sided self-pierce riveting (DS-SPR) presents itself as a proper alternative to produce the mechanical connection of those elements into sheet panels. For the purpose of this investigation, a tubular rivet with a machined thread to replicate a hollow bolt was joined to a sheet panel. Since this application will be subjected to torsion loads when a nut or other elements are fastened, tubular rivets with different numbers of semi-longitudinal rectangular openings at their ends (0, 2, 4, and 8) were investigated to identify the optimal design that ensures proper performance during its service life. The results show that rivets with four openings achieved a torsional resistance of more than 40 N·m, which is over double that of the original rivet without openings, while maintaining comparable shear strength (~10 kN). A functional hollow bolt with an outer thread was successfully produced, achieving a torque capacity of 35 N·m, equivalent to an M8 solid bolt, but with reduced weight. These findings highlight DS-SPR as a viable technology for manufacturing functional riveted elements that combine the permanent joints between sheets and removable connections with secondary components, offering both structural performance and lightweight advantages. Full article