Search Results (208)

Nitrogen vacancy (NV) diamonds are promising room temperature quantum sensors. As the technology moves towards application, efficient use of energy and cost become critical for miniaturization. This work focuses on microwave-based spin control using the short-circuited end of a slot line, analyzed by finite element method (FEM) for magnetic field amplitude and uniformity. A microstrip-to-slot-line converter with a $-10$ dB bandwidth of $3.2$ GHz was implemented. Rabi oscillation measurements with an NV microdiamond on a glass fiber show uniform excitation over $1.5$ MHz across the slot, allowing spin manipulation within the coherence time of the NV center. Full article

To meet the rapid maneuverability and lightweight demands of micro-nano satellites, a space micro solid thruster using 3D-printed short glass fiber reinforced polyamide 6 (PA6GF) composites was developed. Thruster shells with wall thicknesses of 4, 3, and 2.5 mm were designed, and ground ignition tests were conducted to monitor chamber pressure and shell temperature. Compared with conventional metallic thrusters, PA6GF composites have exhibited excellent thermal insulation and sufficient mechanical strength. Under 8 MPa and 2773 K ignition conditions, the shell thickness was reduced to 2.5 mm and could withstand pressures up to 10.37 MPa. These results indicate that PA6GF composites are well-suited for space micro solid thrusters with inner diameters of 15–70 mm, offering new possibilities for lightweight space propulsion system design. Full article

Prefabricated unidirectional carbon fiber reinforced polymer (CFRP) composite strips are extensively used as a means of infrastructure rehabilitation through adhesive bonding to the external surface of structural concrete elements. Most data to date are from laboratory tests ranging from a few months to 1–2 years providing an insufficient dataset for prediction of long-term durability. This investigation focuses on the assessment of the response of three different prefabricated CFRP systems exposed to water, seawater, and alkaline solutions for 5 years of immersion in deionized water conducted at three temperatures of 23, 37.8 and 60 °C, all well below the glass transition temperature levels. Overall response is characterized through tensile and short beam shear (SBS) testing at periodic intervals. It is noted that while the three systems are similar, with the dominant mechanisms of deterioration being related to matrix plasticization followed by fiber–matrix debonding with levels of matrix and interface deterioration being accelerated at elevated temperatures, their baseline characteristics and distributions are different emphasizing the need for greater standardization. While tensile modulus does not degrade appreciably over the 5-year period of exposure with final levels of deterioration being between 7.3 and 11.9%, both tensile strength and SBS strength degrade substantially with increasing levels based on temperature and time of immersion. Levels of tensile strength retention can be as low as 61.8–66.6% when immersed in deionized water at 60 °C, those for SBS strength can be 38.4–48.7% at the same immersion condition for the three FRP systems. Differences due to solution type are wider in the short-term and start approaching asymptotic levels within FRP systems at longer periods of exposure. The very high levels of deterioration in SBS strength indicate the breakdown of the materials at the fiber–matrix bond and interfacial levels. It is shown that the level of deterioration exceeds that presumed through design thresholds set by specific codes/standards and that new safety factors are warranted in addition to expanding the set of characteristics studied to include SBS or similar interface-level tests. Alkali solutions are also shown to have the highest deteriorative effects with deionized water having the least. Simple equations are developed to enable extrapolation of test data to predict long term durability and to develop design thresholds based on expectations of service life with an environmental factor of between 0.56 and 0.69 for a 50-year expected service life. Full article

Natural composites find application in various fields because of their low specific weight and low investment cost. But due to their inherent nature, natural composites have lower strength and tend to absorb moisture, which makes them weak. In this work, woven glass, mono-bi-filament polypropylene, and polyester fibers in an epoxy matrix were developed with four and five different stacking layers of texture utilizing the hand-layup procedure. However, understanding the directional dependence of material properties is necessary for the application of these new materials. Three distinctive plates were fabricated for the purpose of the investigation. The laminated plates were tested on a universal testing machine (UTM) and a flexible test setup to examine the mechanical properties of the polymer fiber. By adding short fibers such as polypropylene, polyester fibers in a random manner improved the mechanical strength of the polymer composite compared to the other fiber types such as woven glass fiber sheets and woven polypropylene sheets placed in the middle of the composite. This is because short polymer fibers bond well with epoxy resin and have very good bonding strength. Full article

Currently, the main drivers for the production of phosphate glass fiber-reinforced composites are the growing demand for lightweight materials, reduced energy consumption, improved durability, and minimized environmental impact. This study aims to develop thermoset-based composites using chopped and continuous phosphate glass fibers (PGFs) combined with polyester and epoxy matrices, processed via contact molding. Physical, mechanical, thermal, and morphological characterizations were conducted. The addition of PGFs led to a steady increase in density and fiber volume fraction. For polyester composites with short PGFs, density rose from 1.60 g/cm³ (0 wt%) to 1.77 g/cm³ (22.8 wt%), with a corresponding volume fraction increase from 0% to 14.4%. Similarly, epoxy composites showed density values from 1.70 g/cm³ to 1.87 g/cm³ and volume fractions up to 15.2%. Thermogravimetric analysis (TGA) showed that as the fiber content increased, the thermal degradation of the resin was delayed, as evidenced by a rise in onset degradation temperature and greater residual mass—indicating improved thermal stability of the composites. Tensile strength increased from 20.8 MPa to 71.3 MPa (polyester) and from 26.8 MPa to 75.9 MPa (epoxy) with chopped fibers, reaching 145.7 MPa and 187.9 MPa, respectively, with continuous fibers. Flexural strength reached 167.9 MPa (polyester) and 218.0 MPa (epoxy) in continuous-fiber configurations. Young’s modulus values closely matched Hirsch model predictions. These findings confirm the potential of PGF-reinforced thermoset composites for high-performance and sustainable material applications. Full article

The work presented here describes an approach that separates the viscous stress from the quasi-static counterpart for polycarbonate (PC) and its short glass fiber composite (GF-PC), with the aim to characterize the influence of short glass fiber on the viscous behavior of PC as the matrix of GF-PC. A multi-relaxation (MR) test was used for the mechanical testing and a three-branch spring–dashpot model for the data analysis, using a genetic algorithm to establish 100 sets of fitting parameter values that enabled the three-branch model to regenerate the measured stress decay during relaxation. Using the spring modulus $\left(K_{v,s}\right)$ of the short-term branch in the three-branch model, two groups for these fitting parameter values were established as a function of specimen displacement (named stroke) of GF-PC, one of which shows a trend that is similar to the trend of the corresponding fitting parameters for the pure PC, and thus is believed to reflect the influence of glass fiber on the PC matrix of GF-PC. The study concludes that the short glass fiber increases the short-term viscous stress, but its role on the long-term viscous stress is marginal. Full article

The purpose of this study was to test the microhardness and compressive strength of mineral trioxide aggregate (MTA) modified by the addition of short glass fibers (SGFs) and shredded polyglycolic acid (PGA) sutures. Encapsulated MTA (MM-MTA, MicroMega, Besançon, France), modified using either SGF or shredded PGA sutures, was used for the experiment. Four experimental groups (n = 120) were as follows: control group (MTA) (n = 30), MM MTA + 5%SGF (n = 30), MM MTA + 10%SGF (n = 30), and MM MTA + 1%PGA (n = 30). For the modified materials, MM MTA powder was removed from the capsule by 1%, 5% and 10% of weight and 1% PGA, 5%, or 10% SGF were added, respectively. The microhardness of the samples (n = 20 per group) was measured using a Vickers microhardness testing machine, while compressive strength (n = 10 per group) was measured according to ISO 9917-1:2007. The highest microhardness value was measured for MTA + 10%SGF (14.73 ± 3.09) with a statistically significant difference in comparison to the other three groups (p < 0.05). Statistically significant higher compressive strength was measured in the groups with the addition of 5% and 10% SGF compared to MM MTA (p = 0.047 for both comparisons). There were no statistically significant differences between the groups (p = 0.784) regarding the compressive modulus. The addition of SGF significantly increased both the microhardness and compressive strength of MM MTA. Full article

Three-dimensional flexible solar fabrics based on hydrogenated amorphous silicon (a-Si:H) thin film solar cells were prepared and characterized. A glass fiber fabric with a polytetrafluoroethylene (PTFE) coating proved to be a suitable textile substrate. Interwoven metal wires enable an integrated electrical interconnection. An array of solar cells consisting of an a-Si:H layer stack with a highly p-type/intrinsic/highly n-type doping profile was deposited onto it. Silver was used as the back contact with indium tin oxide (ITO) as the front contact. The best solar cells show an efficiency of 3.9% with an open-circuit voltage of 876 mV and a short-circuit current density of 11.4 mA/cm². The high series resistance limits the fill factor to 39%. The potential of the textile solar cells is shown by the achieved pseudo fill factor of 79% when neglecting the series resistance, resulting in a pseudo efficiency of 7.6%. With four textile solar cells connected in a series, an open-circuit voltage of about 3 V is achieved. Full article

The growing demand for electricity in developing countries has called attention and interest to renewable energy sources to mitigate the adverse environmental effects caused by energy generation through fossil fuels. Among different renewable energy sources, such as photovoltaic, wind, and biomass, hydraulic energy represents an attractive solution to address the demand for electricity in rural areas of Colombia that are not connected to the electrical grid. In the current paper, the fluid–structure interaction (FSI) of a recently designed Vertical-Axis Hydrokinetic Turbine (VAHT) Straight-Bladed (SB) Darrieus-type, modified with symmetric winglets, was studied by implementing the sliding mesh method (SMM). By coupling with Computational Fluid Dynamics (CFD) numerical simulations, the FSI study demonstrated that the hydrodynamic loads obtained can cause potential fatigue damage in the blades of the Straight-Bladed (SB) Darrieus VAHT. Fatigue life was assessed using the stress–life (S-N) approach, and materials such as structural steel, short glass fiber reinforced composites (SGFRC), and high-performance polymers (HPP), such as PEEK, were studied as potential materials for the construction of the blades. FSI results showed that the biaxiality index (BI) provides a good understanding of the dominant stresses in the blades as the azimuth angle changes. It was also shown that structural steel and PEEK are good materials for the manufacturing of the blades, both from a fatigue resistance and modal perspective. Full article

Short fiber-reinforced thermoplastic composites (SFRTPs) have excellent recyclability and processability, but their mechanical properties are weak compared to continuous fiber products. Various studies have reported that the addition of GNPs improves the mechanical properties of SFRTPs, but it is unclear what effect different types of reinforcing fibers have on a hybrid composite system. In this study, the effect of adding a small amount (1 wt%) of graphene nanoplatelets (GNPs) to fiber-reinforced polypropylene composites on their mechanical properties was investigated from a crystallinity perspective. GNPs were mixed with polypropylene (PP)/carbon fiber (CF) or PP/glass fiber (GF) using a melt blending process, and composites were molded by injection molding. The results of mechanical property characterization showed no significant effect when GNPs were added to PP/CF, but when GNPs were added to PP/GF, this increased the composite’s tensile strength and Young’s modulus by approximately 20% and 10%, respectively. The interfacial shear strength (IFSS) predicted using the modified Kelly–Tyson equation did not change much before and after the addition of GNPs to PP/CF. On the other hand, the IFSS increased from 10.8 MPa to 19.2 MPa with the addition of GNPs to PP/GF. The increase in IFSS led to an increase in the tensile strength of PP/GF with the incorporation of GNPs. Differential scanning calorimetry (DSC) indicated that GNPs accelerated the crystallization rate, and the X-ray diffraction (XRD) results confirmed that GNPs acted as a crystal nucleating agent. However, CF was also shown to be a nucleating agent, limiting the effect of GNP addition. In other words, it can be said that the addition of GNPs to PP/GF is more effective than their addition to PP/CF due to the differential crystallization effects of each fiber. Full article

Composite pipe fittings with an outer layer of 20% long glass fiber-reinforced polypropylene (LGFR-PP) and an inner layer of polypropylene (PP) were prepared via water-powered projectile-assisted co-injection molding short-shot (W-PACIM-S), water-powered projectile-assisted co-injection molding overflow (W-PACIM-O), gas-powered projectile-assisted co-injection molding short-shot (G-PACIM-S), and gas-powered projectile-assisted co-injection molding overflow (G-PACIM-O)techniques. The effects of different injection molding processes on the wall thickness, inner surface roughness, glass fiber orientation, and pressure resistance of pipe fittings were studied to evaluate the quality of the pipe fittings formed by each process. Compared with the short-shot method, the overflow method results in pipes with thinner walls in each layer, a more uniform distribution, smoother inner wall surfaces, and better orientation of glass fibers along the axial direction in the near boundary layer, resulting in better pressure resistance. Under the same injection method, the difference in fluid medium did not significantly change the trend of wall thickness variation in each layer. However, compared with gas, high-pressure water improves the uniformity of the pipe wall thickness and inner wall quality. In addition, the introduction of the warhead is more conducive to improving the degree of glass fiber orientation of the pipe fittings, and the thickness of the residual wall thickness of the pipe fittings has a great influence on the pressure resistance of the pipe fittings. Full article

This in vitro study evaluated short-fiber-reinforced composite materials and fiber-reinforced restorations of endodontically treated molars with furcal perforation. The endodontic treatment and mesio-occlusal–distal cavity preparation of 126 two-rooted mandibular third molars were performed. Eighteen non-perforated teeth were restored with resin composite as the control group. Furcal perforations and repair were performed on 108 teeth that were divided into six experimental groups: resin composite (RC), everX Flow (EXF), everX Posterior (EXP), Bioblock (BB), modified transfixed (MT), and horizontal glass-fiber (HGF) groups (n = 18). Fracture resistance tests were performed at an angle of 30◦ using a universal testing machine under static loading, and fracture patterns were classified. Welch’s analysis of variance, Pearson chi-square, and Tamhane post hoc tests (p = 0.05) were used to analyze the data (p = 0.05). The highest fracture resistance values were seen with the HGF (596.305 N), followed by MT (540.365 N), BB (477.906 N), EXP (476.647 N), EXF (414.462 N), control (413.811 N), and RC (335.325 N) groups (p < 0.001). There was no significant difference between the BB and EXP groups or between the EXF and control groups (p > 0.05). In terms of the dominant fracture pattern, the HGF and MT groups were repairable and possibly repairable, whereas the control, RC, and EXP groups were unrepairable. The EXF and BB groups were almost equally divided between possibly repairable and unrepairable. Restorations using horizontal fiber techniques and short-fiber-reinforced materials increased the fracture resistance of endodontically treated teeth with furcal perforation. Full article

The hygrothermal aging model, based on Fick’s second law of diffusion, characterizes the degradation of engineering constants in T700 carbon fiber/epoxy resin composites. It focuses on changes in the tensile modulus, shear modulus, and transverse Poisson’s ratio due to moisture absorption and temperature variations. The model validates through mass change observations before and after seawater immersion, along with surface morphology assessments and tensile experiments. The results reveal that the saturated moisture absorption rate for single-layer laminates in seawater immersion is 0.35%. Short-term seawater immersion at room temperature (≤60 days) does not induce cracks or defects (≥10 μm) on the composite’s surface. The composite’s modulus decreases as moisture absorption increases, with the longitudinal tensile modulus dropping by an order of 10⁻⁵%, while the other engineering constants decrease by an order of 10⁻³%. The modulus also decreases with rising temperature; the closer the temperature is to the matrix’s glass transition, the faster the modulus declines, with the longitudinal tensile modulus decreasing by 0.84%, and the other engineering constants decreasing by 100%. This research provides valuable insights for the engineering applications of composite materials in marine environments. Full article

Glass short fiber-reinforced thermoplastics (GSFRTPs) are a cost-effective alternative to other short fiber-reinforced thermoplastics (SFRTPs). Their excellent mechanical properties make them a suitable material for components that require rigidity and light weight in widely diverse fields, including transportation and office automation equipment. The melt-mixing process is used to shorten glass fibers. The notched impact strength of molded products is strongly affected by the fiber length. An important issue is how to conduct melt-molding processing while keeping the fibers long. In this regard, a survey of cases in which additives were used to increase the fiber length revealed no useful reports. However, a growing trend toward the reuse of plastic material wastes has emerged. When reusing GSFRTP wastes, the objective is to recycle the material as GSFRTPs. This promotion of the reuse of GSFRTPs necessitates the production of molded products with the fiber length maintained to the greatest extent feasible. Moreover, GSFRTPs should be recycled in a manner consistent with the original GSFRTPs. In recent years, there has also been a growing movement to reuse polyvinyl butyral (PVB) in accordance with Sustainable Development Goals (SDGs). It has been established that PVB can be extracted from the laminated glass state with high efficiency using mechanical methods. This study evaluated the mechanical properties of GSFRTPs with a PP matrix when PVB was added. The results show that the incorporation of PVB and maleic anhydride-modified PP in quantities of less than 1 wt% into GSFRTPs leads to sizing effects wherein the fibers are dispersed in bundles. Furthermore, this combination enhances the notched impact strength of the resulting molded product by 0.5 kJ/m² at the maximum. Full article

This paper presents a comparative analysis of fiber aspect ratios using scanning electron microscopy (SEM) and the mean field homogenization approach. The novelty of this work lies in an effective fiber length evaluation based on a comparative analysis of fiber aspect ratios using scanning electron microscopy (SEM) and the mean field homogenization approach. This makes it possible to use an electron microscope to image fiber samples corresponding to the sample size using microtomography. Molded samples and pellets of four polyamide-6 short-glass fiber-reinforced composites with mass fractions of 15%, 30%, and 50% were considered. The aspect ratio distribution measured by SEM for the investigated materials was 20.25 with a coefficient of variation of 5.1%. The fiber aspect ratio obtained based on mean field homogenization theory and the tensile curve approximation was underestimated at 13.698 with a coefficient of variation of 5.2%. The deviation between the micro- and macro-estimates can be represented as a mean effective aspect ratio of 68% with a coefficient of variation of 8.5%. The developed technology for preparing samples for SEM and automated image processing can be used to study other short-reinforced polymer composite materials. The obtained estimates can serve as a useful reference when calibrating other models of short-fiber-reinforced polymer materials. Full article