Search Results (386)

This study investigates the mechanical properties of titanium (Titanflex®) and cobalt-chromium (Co-Cr) alloys for potential use in removable denture bases. Titanium alloys have gained attention due to their biocompatibility and regulatory concerns surrounding Co-Cr, which has been classified as a carcinogenic, mutagenic, and toxic to reproduction (CMR) substance under EU MDR (2017/745). Using selective laser melting (SLM), test specimens of Titanflex® and Co-Cr alloys were 3D-printed at different angles (0°, 45°, 90°) and compared to conventionally cast Co-Cr samples. Tensile testing was conducted to assess modulus of elasticity (E), proof stress (Rp_0.2), ultimate tensile strength (Rm), elongation parameters (Ag, Agt, At), and maximum load (Fm). Results showed that Titanflex® printed at 45° (Ti45) exhibited the highest Rp_0.2, Rm, and Fm, indicating superior strength and plastic resistance. Ti0 displayed the greatest elongation properties, highlighting titanium’s ductility. Co-Cr alloys demonstrated higher stiffness but lower ductility. Printing orientation significantly influenced mechanical properties, particularly in 3D-printed samples. Overall, Ti45 presented a balanced profile of strength and flexibility, making it a promising candidate for denture bases, while Co-Cr remains a rigid alternative with established clinical use. Future research should explore long-term performance under functional and biological conditions to guide clinical application. Full article

To apply 3D printing-based continuous fiber composites in shipbuilding and marine applications, the pin-bearing fastening method with notch holes can be considered as an effective method. In this study, pin-bearing strength tests were performed on a 3D-printed composite consisting of carbon fiber and Onyx to evaluate the effect of hole notches fabricated through pre- and post-processing. The experimental results showed the difference in the mechanical fastening strength of the specimens, depending on the method used to fabricate the hole notch. As the width-to-diameter ratio (W/D) decreased, ultimate bearing strength, strain, and toughness decreased. The post-treated specimens exhibited higher initial stiffness than the pre-treated specimens, and their bearing stress was up to 23% higher at smaller hole diameters (≤6 mm). In particular, for specimens with 0° fiber orientation, the post-processed specimens showed markedly higher toughness than the pre-processed ones, with increases at 5 mm and 6 mm hole diameters, respectively, thereby demonstrating superior performance in both strength and energy absorption. The damage modes of the circular notches were also found to depend on the pre- and post-processing conditions. These results suggest that fiber orientation, W/D ratio, and processing method should be considered when designing mechanical fasteners for 3D-printed composites in marine structures. Full article

The recycling of polymer composites remains a significant challenge due to both technical and economic obstacles. This study investigates the recycling potential of acrylonitrile butadiene styrene (ABS) composites filled with carbon powder (CP), employing injection moulding and fused filament fabrication (FFF) technologies. Laboratory-based experiments were conducted using ABS reinforced with 0.5, 1.0, and 1.5 wt.% CP to explore the tensile properties of mechanically recycled ABS+CP composites. The results indicate that CP addition positively influences tensile behaviour and that the ABS+CP composite maintains both tensile strength and stiffness after repeated processing. A concentration of 1.5 wt.% CP proved to be the optimal filler amount. The results for re-injection-moulded ABS + 1.5 wt.% CP demonstrate enhancements in tensile strength of approximately 3% and elastic modulus of approximately 15%, relative to virgin ABS. Similarly, such specimens reprocessed via FFF showed an average increase of 12% in tensile strength and of 27% in elastic modulus relative to virgin ABS across all three printing orientations (X, Y, and Z). These findings suggest improved interfacial adhesion and filler dispersion upon recycling. The study confirms the practical feasibility of ABS composite recycling and highlights their potential for structural and decorative use due to their appealing granite-like appearance. Full article

Background/Objectives: Adolescent Idiopathic Scoliosis persisting into adulthood (AAIS) presents progressive stiffening and degenerative changes that are not fully captured by existing classifications. This heterogeneity complicates clinical decision-making and surgical planning. The aim of this study was to propose a novel, treatment-oriented classification system for AAIS. Methods: A retrospective review was performed on patients with AAIS who underwent surgical correction between 2018 and 2022. Pre- and postoperative radiographs, CT scans, and MRI were analyzed to define curve characteristics and evaluate surgical outcomes. Subgroups were identified according to age and deformity features, and corresponding surgical strategies were outlined. Results: AAIS was stratified into Young Adult Idiopathic Scoliosis (YAdIS, 19–30 years) and Adult Idiopathic Scoliosis (AdIS, >30 years). YAdIS was divided into mild, flexible curves (YAdIS 1) and severe/stiff curves (YAdIS 2). AdIS was classified into three categories: AdIS 1 (isolated coronal deformity), AdIS 2 (combined coronal and sagittal deformity), and AdIS 3 (revision cases). Within AdIS 1, additional refinement by age (30–45, 45–60, >60 years) reflected increasing stiffness and degenerative changes. Tailored surgical strategies included selective fusions, posterior releases, high-density constructs, three-column osteotomies, and combined anterior–posterior approaches, depending on curve type and age group. Conclusions: This classification provides a comprehensive, treatment-oriented framework to support surgical decision-making in AAIS, enabling optimized planning and improved outcomes for adult patients with scoliosis of adolescent onset. Full article

Short carbon fiber-reinforced bio-based polyamide 11 (PA11) composites were developed in filament form for Additive Fusion Technology (AFT) 3D printing and benchmarked against injection-molded samples. Composites containing 15 and 25 weight percent (wt%) recycled carbon fibers (rCFs) were successfully extruded into 1.75 mm diameter filaments, whereas higher fiber contents (35 wt%) led to brittle filament failure. AFT printing with subsequent consolidation produced short fiber composites with highly aligned fibers, while injection molding generated more randomly oriented microstructures. Mechanical testing revealed that AFT-printed composites in the fiber direction achieved significantly higher stiffness and comparable tensile strength to injection-molded counterparts. At 25 wt% fiber content, AFT 0° specimens reached an axial tensile modulus of 14.5 GPa, about 32% higher than injection-molded samples (11.0 GPa), with similar axial tensile strength (~123 vs. 126 MPa). However, AFT specimens displayed pronounced anisotropy: transverse (90°) properties dropped to ~2.3 GPa for transverse modulus and ~46–50 MPa transverse tensile strength, near matrix-dominated levels. Impact testing showed orientation-dependent toughness, with AFT 90° samples at 15% fiber content achieving the highest impact energy (76 kJ·m⁻²), while AFT 0° samples were ~30% lower than injection-molded equivalents. Dynamic mechanical analysis confirmed that AFT 0° composites maintained higher stiffness up to ~80 °C. Overall, these results demonstrate that aligned short fiber filaments enable high stiffness and strength performance comparable to injection molding, with the trade-off of anisotropy that must be carefully considered in design. This study is the first to demonstrate the feasibility of combining bio-based PA11 with recycled short carbon fibers in AFT printing, thereby extending additive manufacturing to sustainable and high-stiffness short fiber composites. Full article

This study investigates the feasibility of kenaf fiber, which is a natural fiber, used as a polymer composite for use in quadcopter arm structures through finite element analysis. The research emphasizes the mechanical performance of various fiber orientations and cross-sectional configurations of the quadcopter arm, focusing on optimizing stress resistance, displacement, and strain characteristics. By relating the relationship between deflection and area moment of inertia of the quadcopter arm, a comparative analysis was conducted for circular hollow tubes, hollow rectangular tubes, and solid rectangular tubes, with the circular hollow tube configuration demonstrating the highest stiffness and minimal deflection. The result from the theoretical calculation and the simulation result of deflection are compared. The study also evaluates the influence of kenaf fiber orientations on the mechanical properties of the composite. Among the seven tested orientations, the sequence 0°, 30°, 45°, 30°, 0° yielded the highest maximum stress (0.3427 MPa), indicating optimal load distribution. Conversely, the 0°, 45°, 0°, 45°, 0° orientation provided the least displacement, making it ideal for high rigidity applications. These findings confirm the potential of kenaf fiber-reinforced polymer as an eco-friendly, lightweight alternative to synthetic fibers for UAV applications, offering a balance of strength, flexibility, and structural stability, and promoting sustainable value in the field of aerospace, as it proves the utilization of waste product into a high-value product. Full article

Special-shaped concrete-filled steel tube (CFST) frames can be embedded in partition walls to improve space utilization, but their frame-level seismic behavior across joint types remains under-documented. This study examines six two-story, single-bay frames with cruciform, T-, and L-shaped CFST columns and three joint configurations: external hoops with vertical ribs, fully bolted joints, and fully bolted joints with replaceable flange plates. Low-cycle reversed loading tests were combined with validated ABAQUS and OpenSees models to interpret mechanisms and conduct parametric analyses. All frames exhibited stable spindle-shaped hysteresis with minor pinching; equivalent viscous damping reached 0.13–0.25, ductility coefficients 3.03–3.69, and drift angles 0.088–0.126 rad. Hooped-and-ribbed joints showed the highest capacity and energy dissipation, while replaceable joints localized damage for rapid repair. Parametric results revealed that increasing the steel grade and steel ratio (≈5–20%) improved seismic indices more effectively than raising the concrete strength. Recommended design windows include axial load ratio < 0.4–0.5, slenderness ≤ 30, stiffness ratio ≈ 0.36, and flexural-capacity ratio ≈ 1.0. These findings provide symmetry-based, repair-oriented guidance for transportation buildings requiring rapid post-earthquake recovery. Full article

The development of lightweight, high-damping building materials is critical for enhancing the seismic resilience of civil infrastructure. This study introduces a novel approach to synergistically improve the damping and mechanical properties of cementitious composites by incorporating one-dimensional carbon nanotubes (CNTs) or two-dimensional graphene nanoplatelets (GNPs). The novelty lies in (1) a direct comparison of 1D versus 2D carbon nanomaterials efficacy within a vibration-relevant frequency range (0.5–2 Hz); (2) the use of the Ca(OH)₂ orientation index, derived from X-ray diffraction (XRD), to link microstructural texturing with macroscopic dynamic performance; and (3) establishing clear mechanistic link between carbon nanomaterials dispersion, pore structure evolution, and the resultant balance between stiffness and damping. Dynamic mechanical analysis identified an optimal dosage of 0.1% by weight for both nanomaterials. Comprehensive microstructural characterization (SEM, MIP, XRD, TGA/DTG) revealed that the carbon nanomaterials act as nucleation sites, promoting cement hydration and refining the pore structure. This structural enhancement concurrently improved mechanical strength and energy dissipation capacity. The primary damping mechanism was identified as interfacial friction and slippage at the nanofiller–matrix interface. These findings provide fundamental insights for the rational design of high-performance cementitious composites and offer an evidence-based pathway for creating advanced seismic-resistant materials. Full article

Background: With the progressive aging of the in institutionalized settings population, functional decline—manifested as reduced proprioception, joint stiffness, and muscle loss—poses a growing threat to the autonomy and quality of life of older adults. Occupational therapy plays a central role in addressing these challenges through targeted, evidence-based interventions. Objectives: This clinical trial evaluates the effectiveness of a multicomponent occupational therapy intervention that integrates balance and postural stability exercises, proprioceptive stimulation, and lower-limb strengthening with conventional gerontogymnastics. The program was designed to improve gait performance, reduce fall risk, and promote independence in institutionalized older adults. Methods: A total of 35 community-dwelling older adults were randomly assigned to three groups: gerontogymnastics intervention (n = 13), multicomponent intervention (n = 13), and control (n = 9). Participants underwent a 6-week intervention comprising two 45 min sessions per week. Pre- and post-intervention assessments focused on postural stability and balance-related functional outcomes. Results: The multicomponent group exhibited trends toward improvement in balance, proprioception, and functional mobility, although these did not reach statistical significance. Clinically meaningful improvements were defined using minimally clinically important differences (MCIDs) for functional measures such as Timed UP and Go (TUG) (>1.3 s) and Performance-Oriented Mobility Assessment (POMA) (≥3 points). The multicomponent group showed a 22.1% improvement in proprioceptive accuracy and a 13.9% improvement in mobility (TUG). Additionally, this trend may indicate a potential protective effect against age-related functional decline. Conclusions: These findings suggest that a multicomponent occupational therapy intervention may help maintain mobility and reduce functional decline in institutionalized older adults. Statistically significant gains were observed in lower-limb strength, while other improvements—such as proprioception and balance—did not reach significance but approached clinical relevance. These preliminary results support further investigation into balance-specific training within occupational therapy to promote independence and reduce fall risk. Interpretation should remain cautious due to the small sample size (n = 35) and short intervention duration, which limit statistical power and generalizability. Full article

This study examines the influence of printing parameters and filament composition on the mechanical properties of 3D printed parts, building upon prior research in fused deposition modeling. Two combinations of printing parameters, 75% infill, 0° orientation, four outer shells, with either gyroid and 3D Honeycomb infill patterns—were analyzed across eleven materials, including acrylonitrile butadiene styrene, polylactic acid, polylactic acid-based composites, polyethylene terephthalate glycol, and high-impact polystyrene. Tensile, compression, and bending tests were performed on the printed specimens to determine stiffness and elastic modulus. Each material demonstrated different levels of variability and sensitivity to printing parameters under the various loading conditions, emphasizing that no single configuration is optimal across all scenarios. For example, the gyroid pattern led to increases up to ~35% in bending modules for common thermoplastic filaments and ~30% for stone-filled polymers, while in tensile stiffness, variations between infill patterns remained below 5% for other conventional polymers. These findings underline the load-specific nature of optimal parameter combinations and the influence of material-specific characteristics, such as filler content or microstructural homogeneity. This study provides quantitative insights that can support application-driven parameter selection in additive manufacturing, offering a comparative dataset across widely used and emerging filaments. Full article

This paper examines the impact of symmetry and asymmetry on the dynamic modeling and nonlinear control of a mobile robot with Ackermann steering geometry. A neural network-based residual model is incorporated as a novel control enhancement. This study presents a control-oriented formulation that addresses both idealized symmetric dynamics and real-world asymmetric behaviors caused by actuator imperfections, tire slip, and environmental variability. Using the Euler–Lagrange formalism, the robot’s dynamic equations are derived, and a modular simulation framework is implemented in MATLAB/Simulink R2022a, that incorporates distinct steering and propulsion subsystems. Symmetric elements, such as the structure of the inertia matrix and kinematic constraints, are contrasted with asymmetries introduced through actuator lag, unequal tire stiffness, and nonlinear friction. A residual neural network term is introduced to capture unmodeled dynamics and improve the robustness. The simulation results show that the control strategy, originally developed under symmetric assumptions, remains effective when adapted to systems exhibiting asymmetry, such as actuator delays and tire slip. Explicitly modeling these asymmetries enhances the precision of trajectory tracking and the overall system robustness, particularly in scenarios involving varied terrain and obstacle-rich environments. Full article

Aiming at the characteristics of limited actuation capability of the semi-active control system and strong nonlinearity of the hydro-pneumatic suspension, a constrained nonlinear control strategy of a semi-active hydro-pneumatic suspension system is proposed. According to the mathematical model of nonlinear hydro-pneumatic suspension, the static stiffness and linear damping coefficient based on the equivalent energy are calculated, and then the control-oriented dynamic equation whose expression minimizes the nonlinear term is constructed. Combined with actuation capacity constraints, an optimization model with constraints is established to minimize the deviation between the actual overall control force and the expected optimal control force, and the optimal approximation from nonlinear control to linear quadratic optimal control is realized. The control simulation results of various methods show that the nonlinear control with constraints of the semi-active hydro-pneumatic suspension system, which effectively combines the actuation capacity constraints and nonlinear characteristics of the system, achieves a good comprehensive control effect for the nonlinear suspension control with constraints. Full article

This paper presents an enhanced pseudo-rigid body model (PRBM) integrated with the LuGre friction law to analyze the dynamic behavior of flexure-hinge-based piezoelectric stick–slip actuators (PSSAs). The PRBM captures flexure compliance through Lagrangian dynamics, while Newtonian mechanics describe the piezoelectric stack and slider motion. Non-linear contact effects, including stick–slip transitions, are modeled using the LuGre formulation. A mass–spring–damper model (MSDM) is also implemented as a baseline for comparison. The models are solved in MATLAB Simulink version R2021a and validated against experimental data from a published prototype. The enhanced PRBM achieves strong agreement with experiments, with a root mean square error of 20.19%, compared to 51.65% for the MSDM. By reformulating the equations into closed-form expressions, it removes symbolic evaluations required in the standard PRBM, resulting in one to two orders of magnitude faster simulation time while preserving accuracy. Stable transient simulations are achieved at fine time steps ($\Delta t={10}^{-8}$ s). A systematic parametric study highlights preload force, flexure stiffness, friction coefficients, and tangential stiffness as dominant factors in extending the linear frequency–velocity regime. Overall, the PRBM–LuGre framework bridges the gap between computationally intensive finite element analysis and oversimplified lumped models, providing an accurate and efficient tool for design-oriented optimization of compliant piezoelectric actuators. Full article

In this paper, the overall mechanical response of composite laminates with different structural orientations in low-velocity impacts is discussed using a combination of finite element simulations and experiments. In this process, the crack dissipation energy combined with absorbed energy is proposed as the damage index to evaluate the degree of the plate’s impact damage. Both the impact energy and the crack energy calculated from the experimental primary damage energy are verified. The results show that with the increase in the impact energy, the primary damage mode changes, which changes the crack-absorbed energy accordingly as well as the stiffness and load-bearing capacity of the plate structure during the impact process. This index can not only be used to characterize the performance of cracks in the overall damage but can also predict the damage state of the plate and plain weave fabric. Full article

We present CFRCTop, a MATLAB implementation for topology optimization of continuous fiber-reinforced composite structures. The implementation includes density and fiber-orientation filtering, finite element analysis, sensitivity analysis, design variable updating, verification of optimality of fiber orientations, and visualization of results. This code is built upon the well-known topology optimization code top88. The template stiffness matrices (TSMs)-based method is employed for efficient finite element analysis and sensitivity analysis. The density and fiber-orientation variables are updated separately. Visualization of spatially varying fiber orientations is provided. Extensions to solving various problems are also discussed. Computational performance and scalability are studied to showcase the high efficiency of this implementation. CFRCTop is intended for students and newcomers in the field of topology optimization. Full article