Search Results (267)

Most components fail under complex states of stress and for this reason the study of materials failure under these conditions is an important topic. The article presents the experimental study of the failure of a CFRP material, with a 0/90° cross-ply configuration, subjected to both simple loading conditions (tension, compression, and shear) and combined loading (tension–shear), using a modified Arcan testing method. The Arcan device and specimen geometry were redesigned to reduce experimental errors and the dispersion of results. It was found that there are significant differences between the strength values obtained for simple loads performed by the standardized methods and by the Arcan method, respectively. For this reason, it is recommended to use the Arcan method only for mixed loading modes. Specimens with steel tabs were used to reduce both hole ovality during testing and the number of clamping screws to only four. It was found that the experimental results under complex stress states are well described by the Tsai–Hill failure criterion and the failure envelope for the material studied was plotted. Recommendations are provided regarding the appropriate use of the Arcan method in order to obtain precise results for CFRP composites under multiaxial loading. Full article

Currently, the packaging sector must continue developing more sustainable systems to reduce the high quantities of single-use plastic waste generated. This study evaluated the production and characterization of bio-based composite trays with antimicrobial activity. Different formulations of polybutylene adipate co-terephthalate (PBAT) and polylactic acid (PLA) with polyethylene glycol (PEG) as plasticizer and citric acid as a compatibilizer/crosslinker were evaluated, in addition to the inclusion of plantain microfibers (PFs), TiO₂, and menthol as reinforcing and antimicrobial agents, respectively. The mixtures were subjected to pellet extrusion (165/175/185/190 °C and 60 rpm) and then to flat sheet extrusion (at 185/190/195/205 °C and 60 rpm), besides calendering (at 3.5–6.0 rpm). A single-screw extruder was used in both cases. The obtained sheets (0.317 ± 0.040 mm thick and 17 cm wide) were molded into 12.5 × 11.0 × 3.5 cm trays in a thermoforming machine (at 325 °C and vacuum pressure). For the resulting composite sheets and trays, measurements of mechanical strength, moisture absorption, barrier (WVTR), transmittance, and color were performed. FT-IR, DSC, TGA, SEM, and in vitro antimicrobial tests were also conducted. Based on these tests, an initial formulation with an 85/15 (w/w) PLA/PBAT ratio was defined, which was then reinforced with 3% (w/w) PF. Furthermore, the inclusion of 5% (w/w) menthol in the composite led to fungistatic activity against Botrytis cinerea, also resulting in homogeneous sheets (tensile strength 24.137 ± 1.439 MPa) and trays (compressive strength 0.113 ± 0.010 MPa). These findings can be applied to the packaging and preservation of perishable produce. Full article

Background/Objectives: Rigid interfragmentary compression is essential for primary bone healing following fractures, osteotomies, and arthrodeses of the foot and ankle. Evidence on the clinical performance of the MAX Variable Pitch Compression (VPC) Screw System (Zimmer Biomet, Warsaw, IN, USA) remains limited. This post-market, retrospective cohort study evaluated its safety, performance, and patient-reported outcomes. Methods: A single-center, consecutive series of patients treated with the MAX VPC Screw System for foot or ankle fractures, osteotomies, or arthrodeses between March 2018 and October 2023 was analyzed. The primary endpoint was radiographic and clinical bone union or joint fusion at 6–8 weeks and ≥18 months. Secondary endpoints included adverse events and functional outcomes using the Foot and Ankle Ability Measure (FAAM). Results: A total of 214 procedures were included (27 fractures, 80 osteotomies, 107 arthrodeses). Union was assessed in 209 procedures (97.7%) at 6–8 weeks and in 82 procedures (38.3%) at ≥18 months. Union rates were 86.1% at 6–8 weeks and 98.8% at ≥18 months. Early union was higher in arthrodeses (91.5%) than in fractures/osteotomies (80.6%). Adverse events occurred in 13.1% of procedures, 67.9% of which were device-related; no recurrent mechanical failures were observed. Mean FAAM scores were 92.3 (ADL) and 78.8 (Sports) for arthrodeses and 94.3 and 85.8, respectively, for fractures/osteotomies, at a mean FAAM follow-up of 2.9 years. Conclusions: The MAX VPC Screw System demonstrated high bone-union rates, favorable functional outcomes, and a moderate number of device-related complications. These results support its clinical use in foot and ankle surgery. However, the retrospective, single-center design limits generalizability, and prospective multicenter trials are warranted to confirm these findings. Full article

Variable cross-section rotors demonstrate significant potential for enhancing screw vacuum pump performance. This study proposes a variable-radius and variable-pitch screw rotor with a seven-segment fully smooth profile, accompanied by its parametric design methodology. Corresponding clearance design methods are provided, resulting in optimized clearance distribution. A thermodynamic model incorporating four leakage channels was developed. This model effectively simulates screw vacuum pump performance and has been experimentally validated. Systematic analysis was conducted on the effects of key parameters on pump geometric characteristics and performance, with comparative studies against two traditional constant cross-section rotors. Results demonstrate that the proposed design method enables rapid and precise generation of new 3D rotor models. The clearance optimization results validate the design expectations. The variable-radius design achieves cross-sectional variation, and its combination with variable pitch produces a dual internal compression effect, to which the variable radius contributes more significantly. With an increasing cone angle, the internal volume ratio rises significantly. Compared with conventional constant cross-section rotors, the rotor demonstrates superior performance in internal volume ratio, sealing characteristics, and structural integrity, notably cutting shaft power by 52.9% versus equal-pitch rotors. These findings provide an effective solution for developing high-performance screw vacuum pumps. Full article

Background and Objectives: The management of periprosthetic tibial fractures distal to revision Total Knee Arthroplasty (TKA) presents a biomechanical challenge, often requiring extramedullary locking plates when long stems preclude nailing. While in femoral fractures the gap between the stem and plate is a well-documented stress riser, requiring implant overlap to prevent an inter-implant fracture, this specific biomechanical scenario has not been studied in the tibia, and it remains unclear if the femoral dogma of mandatory overlap applies to the straight, centrically loaded tibial anatomy. This study utilized Finite Element Analysis (FEA) to evaluate stress distribution in the tibial inter-implant gap. Materials and Methods: A comparative FEA was performed using a validated standardized tibia model simulating a healed distal fracture. Two cemented revision TKA constructs (50 mm and 80 mm stems) were modeled. These were paired with medial locking plates of varying lengths (10, 12, and 14 holes) to create different inter-implant distances. Eight distinct configurations, including non-plated controls, were subjected to physiological axial compression and three-point bending. Outcome measures included von Mises stress and total displacement. Results: The analysis revealed no significant stress concentration in the bone within the inter-implant zone across all plated models, regardless of the gap size. Instead, the addition of plates universally reduced bone stress compared to controls, effectively transferring load to the fixation hardware. Peak stresses were consistently observed in the proximal locking screws rather than the bone gap. The longest plates (14 holes) offered superior construct rigidity and stress distribution. Conclusions: Under the conditions evaluated in this preclinical finite element model, the tibia does not exhibit a biomechanical requirement for implant overlap to prevent stress risers. Our findings suggest that extramedullary fixation with the longest available anatomical locking plate represents a biomechanically plausible strategy for these fractures, even if an inter-implant gap remains. Full article

Screw-drive in-pipe robots are widely used for inspection and maintenance of pipeline infrastructure because their tilted-wheel locomotion enables continuous traversal of horizontal, vertical, and curved pipes. However, most existing designs rely on passive spring mechanisms to generate wall-contact forces, making traction performance highly sensitive to pipe-diameter variations, friction changes, and manufacturing tolerances. This paper presents an adaptive screw-drive in-pipe robot that integrates adjustable radial geometry, embedded Hall-effect force sensing, and closed-loop gripping-force control. A unified mechanical–geometric model is developed to describe the coupling between actuator displacement, spring compression, wheel-tilt geometry, and pipe-diameter variation. Based on this model, a minimum safe gripping-force condition is derived and used to define a reference force for real-time control. A proportional–derivative controller regulates the gripping force of the front traction module, while a rear stabilizing module ensures axial alignment and suppresses body rotation. Simulation results under realistic diameter transitions and external disturbances demonstrate stable force regulation, preservation of a positive traction margin, and reduced unnecessary actuator effort. The proposed approach enables robust and energy-aware screw-drive locomotion in variable-diameter pipelines. A physical prototype of the robot has been fabricated to support the forthcoming experimental campaign; however, the validation presented in this study is limited to modeling and simulation, with experimental evaluation planned for future work. Full article

This study investigates the reuse of mechanically recycled polyester–glass thermoset scraps (PS) as fillers in LDPE and HDPE matrices at 10–50 wt.% loading. Composites were produced through mechanical size reduction, single-screw extrusion, and compression molding without compatibilizers, and their mechanical and microstructural properties were systematically evaluated. LDPE composites exhibited a notable stiffness increase, with tensile modulus rising from 318.8 MPa (neat) to 1245.6 MPA (+291%) and tensile strength improving from 9.50 to 11.45 MPa (+20.5%). Flexural performance showed even stronger reinforcement: flexural modulus increased from 0.40 to 3.00 GPa (+650%) and flexural strength from 14.5 to 35.6 MPa (+145%). HDPE composites displayed similar behavior, with flexural modulus increasing from 1.2 to 3.1 GPa (+158%) and strength from 34.1 to 45.5 MPa (+33%). Surface-treated fillers provided additional stiffness gains (+36% in sPL4; +33% in sPH3). Impact strength decreased with loading (LDPE: −51%, HDPE: −61%), though surface treatment partially mitigated this (+14–19% in LDPE; +13% in HDPE). Density increased proportionally (PL: 0.95 → 1.20 g/cm³, PH: 0.99 → 1.23 g/cm³), while moisture uptake remained low (≤0.25%). Optical and SEM analyses indicated increasingly interconnected fiber networks at high loadings, driving stiffness and fracture behavior. Overall, PS-filled polyolefins offer a scalable route for converting thermoset waste into functional semi-structural materials. Full article

This research examines the feasibility of recovering and recycling condensate water, a waste byproduct generated by Atlas Copco ZR315 FF industrial air compressors utilizing oil-free rotary screw technology with integrated dryers. Given the growing severity of global water scarcity, finding alternative water sources is essential for sustainable industrial practices. This study specifically evaluates the potential of capturing and treating compressed air condensate as a viable method for water recovery. The investigation analyzes both the quantity and quality of condensate water produced by the ZR315 FF unit. It contrasts this recovery approach with traditional water production methods, such as desalination and atmospheric water generation (AWG) via dehumidification. The findings demonstrate that recovering condensate water from industrial air compressors is a cost-effective and energy-efficient substitute for conventional water production, especially in water-stressed areas like Morocco. The results show a significant opportunity to reduce industrial water usage and provide a sustainable source of process water. This research therefore supports the application of circular economy principles in industrial water management and offers practical solutions for overcoming water scarcity challenges within manufacturing environments. Full article

Al–Al₄C₃ composites exhibit promising mechanical properties including high specific strength, high specific stiffness. However, high reinforcement contents often promote brittle behavior, making it necessary to understand the mechanisms governing their limited toughness. In this work, a microstructural and mechanical study was carried out to evaluate the energy storage capacity in Al–Al₄C₃ composites fabricated by mechanical milling followed by heat treatment using X-ray diffraction (XRD) and Convolutional Multiple Whole Profile (CMWP) fitting method, the microstructural parameters governing the initial stored energy after fabrication were determined: dislocation density (ρ), dislocation character (q), and effective outer cut-off radius (R_e). Compression tests were carried out to quantify the elastic energy stored during loading (Es). The energy absorption efficiency (EAE) in the elastic region of the stress–strain curve was evaluated with respect to the elastic energy density per unit volume stored (Ee), obtained from microstructural parameters (ρ, q, and Re) present in the samples after fabrication and determined by XRD. A predictive model is proposed that expresses Es as a function of Ee and q, where the parameter q is critical for achieving quantitative agreement between both energy states. In general, samples with high EAE exhibited microstructures dominated by screw-character dislocations. High-resolution transmission electron microscopy (HRTEM) analyses revealed graphite regions near Al₄C₃ nanorods—formed during prolonged sintering—which, together with the thermal mismatch between Al and graphite during cooling, promote the formation of screw dislocations, their dissociation into extended partials, and the development of stacking faults. These mechanisms enhance the redistribution of stored energy and contribute to improved toughness of the composite. Full article

The resistance of screws to being pulled out of wood-based panels depends largely on the mechanical properties of the substrate. The properties of medium-density fibreboard (MDF) are locally reinforced in the area where the fastener is embedded. The aim of the study is to determine the effect of using polyurethane (PUR) adhesives as a reinforcing agent. The aim of the study is to determine the elastic properties of individual layers of MDF boards modified with a polyurethane agent (PUR 555.6) applied to the outer and inner layers of the material. Deformations during axial compression of multilayer samples were measured using a digital optical video extensometer with digital image correlation (DIC). The reinforced board showed a significant increase in stiffness in all main orthotropic directions. The stiffness of the inner layers increased by approximately 100%–160%, while that of the outer layers increased by 30%–60%. The shear modulus increased by 60%–70% in the inner layers and by up to 45% in the outer layers. The results confirm the effectiveness of the optical video extensometer method as a fast and reliable technique for determining the mechanical properties of modified layered wood composites. Full article

Background/Objectives: Symptomatic hardware removal remains the most frequent cause of reoperation after tibial tubercle osteotomy (TTO), with removal rates reported as high as 49%. Headless compression screws have been proposed as a low-profile alternative to conventional screws to reduce hardware-related morbidity, yet no study has directly compared their use with headed screws in TTO for patellofemoral instability. This study aimed to compare complication rates and the frequency of hardware removal between headless and headed screw fixation in TTO. Methods: A retrospective review was conducted on 84 patients (94 knees) who underwent TTO between 2014 and 2024. Patients were divided into two groups based on the type of fixation used: headless screws (56 knees) and headed screws (38 knees). Demographic characteristics, perioperative variables, functional outcomes (Kujala, Lysholm, and Tegner scores), complications, and reoperation rates were compared with a minimum one-year follow-up. Results: No significant differences were found between the groups in terms of baseline demographic and clinical characteristics. Symptomatic implant removal occurred in 13.2% of the headed screw group and in none of the patients in the headless screw group (p = 0.001). Reoperation for any reason was significantly lower in the headless group (3.6% vs. 26.3%, p = 0.002). Functional outcomes were similar between groups. Post-hoc power analysis confirmed sufficient statistical power (98.8%) to detect differences in implant removal rates. Conclusion: Headless screw fixation in TTO was associated with significantly lower rates of hardware-related reoperations and painful implant removal, while achieving functional outcomes similar to those with headed screws. Headless screws may represent a preferable fixation method for reducing implant-related complications in TTO. 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

This article addresses the problem of insufficient bearing capacity and stiffness in laminated timber beams during use and proposes a reinforcement method by increasing the cross-section. Twenty glued laminated timber beams with dimensions of 2850 mm × 120 mm × 50 mm were produced using Pinus sylvestris var. mongolica as the raw material. Douglas fir with good tensile properties and new self-tapping screws were selected as reinforcement materials. Through adhesive bonding and adhesive–nail combination methods, an enlarged section reinforcement beam was formed. The influence of section height, bonding process, and the arrangement of self-tapping screws on the bending performance of three groups of six adhesive-reinforced specimens and three groups of fourteen adhesive–nail reinforced specimens was examined through bending performance tests. The results showed that compared with specimens reinforced with single-layer panels, the ultimate load of specimens reinforced with double-layer panels increased by 22.82 to 29.49%, and bending stiffness increased by 17.26 to 48.17%. Within the same group, the ultimate load of specimens reinforced with standard compressive stress adhesive increased by 3.88 to 5.71% under bending. Compared with adhesive reinforcement specimens, adhesive–nail combined reinforcement specimens showed an 8.91 to 11.36% increase in ultimate load. In specimens with the same screw insertion angle, the ultimate bearing capacity of beams reinforced with longer screws and smaller spacing was actually lower. Moreover, the ultimate load of specimens reinforced with self-tapping screws inserted at 90° was 4.2% higher than that of specimens with screws inserted at 45°. 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