Search Results (112)

This study aimed to develop experimental filler-reinforced resin composites for vat-photopolymerization 3D printing and to evaluate the effects of filler addition on their mechanical, physicochemical, and bonding properties for dental restorative applications. Silanized nano- and/or micro-fillers were incorporated into acrylic resin monomers to formulate photocurable resins suitable for vat-photopolymerization. The rheological behavior of these liquid-state resins was assessed through viscosity measurements. Printed resin composites were fabricated and characterized for mechanical properties—including flexural strength, flexural modulus, and Vickers hardness—both before and after 8 weeks of water immersion. Physicochemical properties, such as water sorption, water solubility, and degree of conversion, were also evaluated. Additionally, shear bond strength to a resin-based luting agent was measured before and after artificial aging via thermocycling. A commercial dental CAD-CAM resin composite served as a reference material. Filler incorporation significantly improved the mechanical properties of the printed composites. The highest performance was observed in the composite containing 60 wt% micro-fillers, with a flexural strength of 168 ± 10 MPa, flexural modulus of 6.3 ± 0.4 GPa, and Vickers hardness of 63 ± 1 VHN, while the commercial CAD-CAM composite showed values of 152 ± 8 MPa, 7.9 ± 0.3 GPa, and 66 ± 2 VHN, respectively. Filler addition did not adversely affect the degree of conversion, although the relatively low conversion led to the elution of unpolymerized monomers and increased water solubility. The shear bond strength of the optimal printed composite remained stable after aging without silanization, demonstrating superior bonding performance compared with the CAD-CAM composite. These findings suggest that the developed 3D-printed resin composite is a promising candidate for dental restorative materials. Full article

In this study, polymer matrix composites based on high-density polyethylene (HDPE) and recycled HDPE (HDPEr) were reinforced with zinc oxide nanoparticles (ZnO NPs). Four formulations (M1-M4) with HDPE/HDPEr/ZnO NP mass ratios of 50/50/0, 48/47/5, 45/45/10, and 43/42/15 were produced via melt injection molding. Disc-shaped samples (Ø30 ± 0.1 mm × 2 ± 0.1 mm) were evaluated in unaged and aged states (840 h at 100% humidity and 100 °C) using scanning electron microscopy, X-ray diffraction, ultraviolet–visible and Fourier-transform infrared spectroscopy, water absorption, thermal resistance, and mechanical and dielectric testing. Among all composites, M2 showed the best performance, with the highest aging resistance (estimated lifetime of 3891 h in humidity and 2361 h in heat). It also exhibited superior mechanical properties, with the highest indentation hardness, Vickers hardness, and elastic modulus before (0.042 GPa, 3.846 HV, and 0.732 GPa) and after aging under humidity (0.042 GPa, 3.932 HV, 0.706 GPa) and elevated temperature (0.085 GPa, 7.818 HV, 1.871 GPa). Although ZnO NPs slightly reduced electrical resistivity, M2 showed the most stable dielectric properties. In its unaged state, M2 had 22%, 30%, and 3% lower surface resistivity, volume resistivity, and dielectric strength, respectively, than M1 polymer. M2 was identified as the optimal formulation, combining mechanical strength, dielectric stability, and resistance to moisture and heat. Full article

It is vital to stabilize pillar dams in underground reservoirs in coal mine goafs to protect groundwater resources and quarry safety, practice green mining, and protect the ecological environment. Considering the actual occurrence of coal pillar dams in underground reservoirs, acoustic emission (AE) mechanical tests were performed on dry, naturally absorbed, and soaked coal samples. According to the mechanical analysis, Quantitative analysis revealed that dry samples exhibited the highest mechanical parameters (peak strength: 12.3 ± 0.8 MPa; elastic modulus: 1.45 ± 0.12 GPa), followed by natural absorption (peak strength: 9.7 ± 0.6 MPa; elastic modulus: 1.02 ± 0.09 GPa), and soaked absorption showed the lowest values (peak strength: 7.2 ± 0.5 MPa; elastic modulus: 0.78 ± 0.07 GPa). The rate of mechanical deterioration increased by ~25% per 1% increase in moisture content. It was identified that the internal crack development presented a macrofracture surface initiating at the sample center and expanding radially outward, and gradually expanding to the edges by adopting AE seismic source localization and the K-means clustering algorithm. Soaked absorption was easier to produce shear cracks than natural absorption, and a higher water content increased the likelihood. The b-value of the AE damage evaluation index based on crack development was negatively correlated with the rock damage state, and the S-value was positively correlated, and both effectively characterized it. The research results can offer reference and guidance for the support design, monitoring, and warning of coal pillar dams in underground reservoirs. (The samples were tested under two moisture conditions: (1) ‘Soaked absorption’—samples fully saturated by immersion in water for 24 h, and (2) ‘Natural absorption’—samples equilibrated at 50% relative humidity and 25 °C for 7 days). Full article

Perforated materials are widely used in various fields, including in medicine, for example, in trays for placing and storing cutting tools and for sterilizing disposable materials. Currently, the effective elastic modulus of orthopedic plates is higher than the effective elastic modulus of human bone tissue (the effective elastic modulus of bone ranges between 10 and 30 GPa, depending on the type of bone). This difference in effective elastic modulus leads to the phenomenon known as the stress shielding effect, where the bone experiences insufficient mechanical loading. One potential approach to influence the effective elastic modulus of orthopedic plates is through perforations in their design. Stainless steel 316L has garnered significant interest among medical engineering specialists due to its lower weight, higher strength, and superior biocompatibility. The elastic properties of perforated constructions are influenced by their internal quality, dimensions, shapes, and the overall perforation area, making their study important. An experiment was conducted on perforated plates of 316L stainless steel with perforation areas ranging from 3% to 20%. Increasing the perforation area in perforated 316L stainless steel plates (perforated plates had dimensions of 50 mm in height, 20 mm in width, and 1 mm in thickness; hole diameter of 1 mm; and pitch between the holes of 2, 3, 4, and 5 mm) from 3% to 20% resulted in a decrease in Young’s modulus of the perforated plates from 199 GPa to 147.8 GPa, determined using a non-destructive method for determining resonant frequencies using a laser vibrometer. A three-point bending test on the perforated plates confirmed these findings, demonstrating a consistent trend of decreasing Young’s modulus with increasing perforation area, from 194.4 GPa at 3.14% to 142.6 GPa at 19.63%. The three-point bending method was also employed in this study to determine the Young’s modulus of the perforated plates in order to reinforce the obtained results on the elastic properties by determining the resonance frequencies with a laser vibrometer. It was discovered that the Young’s modulus of a perforated plate cannot be determined solely by the perforation area, as it depends on both the perforation diameter and the pitch between the perforations. In addition, finite element method (FEM) simulations were conducted, revealing that increasing perforation diameter and decreasing pitch significantly reduce the Young’s modulus—with values dropping from 201.5 GPa to 72.6 GPa across various configurations. Full article

The microstructure and tensile properties of 18Ni-300 maraging steel manufactured by selective laser melting (SLM) were investigated after different heat treatments and compared to the original samples. Heat treatment alters the microscopic morphology of the original sample, and the differences in the cross-sectional and longitudinal sectional morphology of the original sample become indistinguishable after heat treatment. Cellular and long strip structures can be observed in the original and aged samples. After solution aging, the cellular and long strip structures completely disappeared, being transformed into parallel and almost equal-length plate martensite. Additionally, inverted austenite and Ni₃(Ti, Al, Mo) precipitates were present. The microhardness increased from 310 HV to 710 HV, the nanohardness rose to 7.7 GPa, tensile strength reached 2068 MPa, and elongation to fracture improved to 4.5%. These optimal properties were achieved with solution treatment at 820 °C for 2 h and aging at 490 °C for 7 h. Full article

The development of lightweight construction is of crucial importance for the development of sustainable technologies and for the reduction in carbon dioxide emissions, especially in the automotive industry. This study aims to address the challenges associated with manufacturing plant fibre-based polymer composites. The investigation focused on two novel formulations of bio-based unsaturated polyester resins, assessing their viability as a matrix in plant fibre-reinforced composites within the context of automotive applications. The study addresses the challenges related to the preparation and processing of the system, leading to the necessity of diluting the resin with (hydroxymethyl)methacrylate (HEMA) to achieve an applicable viscosity. Two different flax fibre textiles, in the form of a short fibre mat and a woven fabric, were used as reinforcement. The composite panels were manufactured using the vacuum-assisted resin infusion (VARI) process. The most efficacious material combination, comprising Bcomp^® ampliTex™ 5040 and STRUKTOL^® POLYVERTEC^® 3831, with viscosity modified by 39% HEMA, exhibited a consistent fibre volume fraction of 40% and a glass transition temperature of 70 °C. In addition, the mechanical behaviour in the 0°-direction demonstrated tensile strength and modulus values of approximately 99 MPa and 9 GPa, respectively, accompanied by an elongation at break of 2%. The flexural modulus was found to be 7 GPa, and the flexural strength 94 MPa. Full article

High-strength and high-modulus epoxy resins are key elements for preparing carbon-fiber-reinforced polymer composites, which play an irreplaceable role in aerospace. In this study, five optimal epoxy systems were developed utilizing the reverse design strategy. The reverse design strategy was based on the ideal resin and curing agent structures offered by the AI polymer platform, and the rules were summarized to create an optimum resin formulation. The formulations used m-phenylenediamine (MPD) as the principal curing agent, which was modified with 10 wt% diethyltetramethylenediamine (DETDA), 10 wt% 4,4′-diaminodiphenylmethane (DDM), or 10 wt% triethylenetetramine (TETA) to establish multiple crosslinking networks. Systematic characterization using differential scanning calorimetry (DSC) and rheological analysis revealed that the optimized activation energy was 55.95–63.42 kJ/mol, and the processing viscosity was ≤500 mPa·s at 80 °C. A stepwise curing protocol (3 h@80 °C, 2 h@120 °C, and 3 h@180 °C) was established to achieve a complete crosslinking network. The results showed that the system with 10% DDM had a tensile strength of 132.6 MPa, a modulus of 5.0 GPa, and a glass transition temperature of 253.1 °C. This work advances the rational design of epoxy resins by bridging molecular architecture with macroscopic performance, offering a paradigm for developing a next-generation matrix tailored to accommodate extreme operational demands in high-end engineering sectors. Full article

This article discusses research on utilizing natural fibers and red mud waste as eco-friendly alternatives in the production of polymer matrix composites. In this study, composites of isophthalic unsaturated polyester matrix were produced by combining bamboo fibers (Bambusa vulgaris) and red mud waste. The red mud waste utilized had a particle size of 50–100 mesh, and the fibers measured 15 mm and 30 mm in length, distributed randomly throughout the matrix. Bamboo fibers were utilized in their raw form and underwent treatment with NaOH (5% for 2 h). The composites underwent mechanical assessment via flexural and tensile testing. The mechanical properties measured were analyzed using analysis of variance (ANOVA) and Tukey’s test. The fracture surfaces of the composites were examined using Scanning Electron Microscopy (SEM). Composites featuring 30 mm long treated fibers and 30% red mud exhibited improved flexural strength (124.71 MPa), along with a deformation of 2.16 mm and a flexural modulus of 15.79 GPa. Tensile tests revealed that incorporating red mud waste significantly enhanced the tensile strength by 68% (15BTRMW10) compared to neat polyester. ANOVA confirmed the dependability of the findings, emphasizing the viability of producing hybrid composites from red mud waste and bamboo fiber. Full article

To create an orthodontic bracket material combining the favourable properties of ceramic and polymer while minimising their limitations, graded porous ceramic scaffolds were created using unidirectional gelation-freeze casting, following which the pores were infiltrated with polymer. Two processing parameters were investigated: (1) sedimentation times of 0, 8, and 24 h, with ceramic solid loading of 20 vol.% and 2.5 wt.% gelatine concentration, and (2) ceramic solid loadings of 15, 20, and 25 vol.% with a fixed 2.5 wt.% gelatine concentration and an 8 h sedimentation time. The graded ceramic structures demonstrated porosity gradients ranging from 9.86 to 63.84 vol.%, except those with 25 vol.% ceramic solid loading at 8 h sedimentation. The Al₂O₃-UDMA/TEGDMA composites had compressive strengths of 60.25 to 120.92 MPa, modulus of elasticity of 19.84 to 35.29 GPa, and fracture toughness of 0.78 to 1.78 MPa·m^1/2. The values observed were between those of dense ceramic and pure polymer. Statistical analysis was conducted using Excel^® 2019 (Microsoft^®, Washington, DC, USA). Means, standard deviations, and 95% confidence intervals (CI) were calculated at a significance level of α = 0.05, alongside polynomial regression to evaluate relationships between variables. Composites with 20 vol.% ceramic solid loading at 8 h sedimentation displayed promising potential for further clinical validation. Full article

Hip joint implants are among the most prevalent types of medical implants utilized for the replacement of damaged joints. The utilization of modern implant materials, such as cobalt–chromium alloys, stainless steel, titanium, and other titanium alloys, is accompanied by challenges, including the toxicity of certain elements (e.g., aluminum, vanadium, nickel) and excessive Young’s modulus, which adversely impact biomechanical compatibility. A mismatch between the stiffness of the implant material and the bone tissue, known as stress shielding, can lead to adverse outcomes such as bone resorption and implant loosening. Recent studies have shifted the focus to β-titanium alloys due to their exceptional biocompatibility, corrosion resistance, and low Young’s modulus, which is close to the Young’s modulus of bone tissue (10–30 GPa). In this study, the microstructure, mechanical properties, and phase stability of the Ti-38Zr-11Nb alloy were investigated. Energy dispersion spectrometry was employed to confirm the homogeneous distribution of Ti, Zr, and Nb in the alloy. A subsequent microstructural analysis revealed the presence of elongated β-grains subsequent to rolling and quenching. Furthermore, grinding contributed to the process of recrystallization and the formation of subgrains. X-ray diffraction analysis confirmed the presence of a stable β-phase under any heat treatment conditions, which can be explained by the use of Nb as a β-stabilizer and Zr as a neutral element with a weak β-stabilizing effect in the presence of other β-stabilizers. Furthermore, the modulus of elasticity, as determined by tensile testing, exhibited a decline from 85 GPa to 81 GPa after annealing. Mechanical tests demonstrated a substantial enhancement in tensile strength (from 529 MPa to 628 MPa) concurrent with a 32% reduction in elongation to fracture of the samples. These alterations are attributed to microstructural transformations, including the formation of subgrains and the rearrangement of dislocations. This study’s findings suggest that the Ti-38Zr-11Nb alloy has potential as a material of choice due to its lower Young’s modulus compared to traditional materials and its stable β-phase, which enhances the implant’s durability and reduces the risk of brittle phases forming over time. This study demonstrates that the corrosion resistance of titanium grade 2 and Ti-38Zr-11Nb is comparable. The material in question exhibited no evidence of cytotoxic activity in the context of mammalian cells. Full article

Chitosan–silica aerogel nanocomposites are lightweight materials with a highly porous structure that have a wide range of applications, including drug delivery systems, tissue engineering, and insulation. These materials may be strengthened using tricalcium phosphate in chitosan–silica aerogel nanocomposites. Thus, in the present research projects, the influence of different atomic percentages of TCP (2%, 3%, and 5%) on mechanical parameters such as stress-strain, ultimate strength, and Young’s modulus of chitosan–silica aerogel NCs was evaluated using molecular dynamics modeling and LAMMPS software. The findings demonstrate that the addition of tricalcium phosphate (1–3%) enhanced the ultimate strength and Young’s modulus of the simulated nanocomposite from 26.968 to 43.468 GPa and from 681.145 to 1053.183 MPa, respectively. The ultimate strength and Young’s modulus of the silica aerogel/chitosan nanocomposites, however, decreased to 1021.418 MPa and 42.008 GPa, respectively, with the addition more than 5% TCP. Full article

Interlayered composites with three types of cores were fabricated and tested. Quasi-static penetration tests (QSPTs), bending tests, and impact tests were conducted on the fabricated composites with carbon fiber epoxy laminate facings. Penetration test procedures were carried out until the composite was perforated and completely punctured. A 9 mm diameter rounded-tip punch was used; the diameter of the support hole was 45 mm. To determine the mechanical properties in the bending tests, three-point bending was carried out at a speed of 2 mm/min. Impact tests were also carried out using a Charpy impact test and a hammer with an energy of 2 J. Our findings indicate that the core material plays a crucial role in determining a composite’s mechanical behavior. Balsa cores offer the best properties in the QSPT test and bending strength and stiffness (57 MPa and 7.4 GPa, respectively), while Rohacell^® cores provide excellent impact resistance (12 kJ/m²). Nomex^® cores demonstrate high bending stiffness (5.3 GPa) but perform worse than Balsa. The choice of core material is application-dependent; Balsa cores are optimal for bending and point loads, and Rohacell^® cores are optimal for impact-dominated scenarios. Full article

Metal alloys continue to be, and are expected to remain, essential materials for fabricating prosthetic elements due to their unique properties, particularly their high strength, durability, and appropriate modulus of elasticity, which make them well-suited for such applications. However, commonly used non-precious metal alloys exhibit lower corrosion resistance compared to precious metal alloys. This reduced resistance leads to the release of metal ions from the alloy into the oral environment. Adverse biological responses to metal alloys can be mitigated through various surface modifications, most commonly by applying coatings. These coatings are typically ceramic, including oxides, nitrides, and carbides. In this study, the mechanical properties (hardness, modulus of elasticity, adhesion, and thickness) of complex Si(C,N) coatings applied to a prosthetic Ni-Cr alloy were investigated. Depending on the proportions of N, C, and Si in the coating, the hardness ranged from 12 to 15 GPa, while the modulus of elasticity varied between 130 and 170 GPa. Adhesion strength, measured via the scratch test method, was within an acceptable range. Microscopic analysis revealed that the coatings had a thickness of 2 to 2.5 μm, exhibiting a homogeneous, columnar structure. In conclusion, the properties of the fabricated Si(C,N) coatings are deemed satisfactory for their intended use as protective layers for prosthetic and orthodontic components. Full article

Using cold isostatic pressing and atmospheric pressure sintering, Ti-18Al-28Nb-xSn alloys were synthesized by incorporating 0.5 at.%, 1 at.%, 2 at.%, and 4 at.% Sn powder into Ti, Al, and Nb powders. This study investigated the effects of Sn concentration on the microstructure and mechanical properties of Ti₂AlNb-based alloys, with a particular focus on the underlying strengthening mechanisms. X-ray diffraction (XRD) analysis identified α₂, O, and B2 as the primary phases in the alloy and demonstrated that Sn addition significantly influenced the proportions of these phases, thus impacting the overall mechanical performance of Ti₂AlNb-based alloys. The optimal combination of elasticity, strength, and plasticity was achieved at a Sn concentration of 1 at.%; at this time, the elastic modulus of the alloy was 26.8 GPa, with a compressive strength of up to 1352 MPa and a fracture strain of 42.8%. However, further increases in Sn content beyond this level led to reductions in both strength and plasticity. At Sn concentrations above 2 at.%, increased porosity and the formation of micropores were observed, facilitating microcrack aggregation and fracture, which ultimately compromised the alloy’s mechanical integrity. By exploring the intrinsic strengthening mechanisms, this study tries to understand the influence of Sn on the strengthening effects and to optimize the content range of Sn addition to ensure the best strengthening effect and good density are shown in high-Nb-content TiAl alloy, providing a reference for future research in this field. Full article

This study investigates the impact of printing layer orientation on the mechanical properties of 3D-printed temporary prosthetic materials. Traditionally, temporary prostheses are fabricated using acrylic resin (polymethyl methacrylate), but advancements have introduced bis-acrylic resins, CAD/CAM-based acrylic resin (milled), and 3D printing technologies. In 3D printing, material is manufactured in overlapping layers, which can be oriented in different directions, directly affecting the material’s resistance. Specimens were designed as bars (2 mm × 2 mm × 25 mm) and grouped according to their printing orientation: BP0 (0 degrees), BP45 (45 degrees), and BP90 (90 degrees). The models were created using Fusion 360 software (version 2.0.12600) and printed on a 3D DLP printer with DLP Slicer software (Chitu DLP Slicer, CBD Tech, version v1.9.0). The bars were then subjected to 3-point bending tests using an Instron Universal Testing Machine to measure Flexural Strength (FS) and Flexural Modulus (FM). Results demonstrated that the BP90 group exhibited the highest Flexural Strength (114.71 ± 7.61 MPa), followed by BP45 (90.10 ± 8.45 MPa) and BP0 (80.90 ± 4.01 MPa). Flexural Modulus was also highest in the BP90 group (3.74 ± 3.64 GPa), followed by BP45 (2.85 ± 2.70 GPa) and BP0 (2.52 ± 2.44 GPa). Significant statistical differences (p < 0.05) were observed, indicating changes in the mechanical properties of the 3D-printed material. The study concludes that printing orientation significantly influences the mechanical properties of temporary prosthetic materials, making the selection of an optimal orientation essential to enhance material performance for its intended application. Full article