Quartz Fiber Research Articles

Multi-scale finite element simulation of needle-punched quartz fiber reinforced composites

Abstract To investigate the effects of different needling parameters on the mechanical properties of quartz needled felts and their composites, this paper proposes a multi-scale modeling approach to simulate and calculate the mechanical properties of needled quartz fiber-reinforced composites. Firstly, based on the characteristics of needle-punching technology, the morphology of needle-punched composites was analyzed at a microscopic scale, and the quartz fiber structure was divided into three typical representative regions. Then, a periodic single-cell model of needled composites was established. Meanwhile, this article also analyzes the influence of parameters such as needling density, needle type, and needling depth on the mechanical properties of needled composites.

The Shear Performance of an Aircraft off Pin Made of Quartz Fiber Reinforced Phenolics: The Effect of the Fiber Distribution Property

Emergency breakaway pins (EBPs) have been widely used in aircraft, especially in the suspension connection between the engine device and the airfoil. Currently, the existing EBPs, which are made of metal materials, barely satisfy the lightweight requirement of the airplane industry. Thus, the construction of a novel EBP with quartz fiber reinforced phenolics is proposed in this study, and the shear response is examined experimentally using a double-sided shear test. The effect of the fiber distribution characteristic on the shear strength is then assessed quantitatively. The failure patterns, including the damage morphology of the two types of samples were then reconstructed using scanning electron microscopy (SEM). Experimental results showed that the breakaway composite pin fabricated by the laminated composite had a superior shear response than its counterpart with randomly distributed fibers for its uniaxially distributed fiber yarns provided a longer put-out damage trace that contributed to a higher shear-loading bearing capacity for the entire composite EBP. In specific, the average values of the shear strength and the shear stiffness for the former samples were higher by 61% and 22%, respectively, than that for the latter samples. Additionally, the composite EBP also has an excellent combination of lightweight advantage and stronger shear-bearing capacity over competing pins, providing novel insight for more secure designs for civil and military aviation.

Wave absorption and mechanical properties of SiCf-SiO2f/SiC based on a Jaumann structure

The demand for materials with microwave absorption and mechanical properties in high-temperature harsh environments is increasing in military and civil applications, but their availability is limited. In this study, we present a SiCf-SiO2f/SiC based on a Jaumann structure, where quartz fibers serve as the dielectric layer and SiC fibers act as the lossy layer, with alternating stacking of these two types of fibers. The composite exhibits remarkable characteristics including low density (2.1 g/cm3), high strength (flexural strength of 378 MPa), and temperature insensitivity (reflection coefficient (RC) remains below -7 dB from 25°C to 600°C). Acoustic Emission (AE) monitoring was conducted to evaluate the damage before and after oxidation at 1100°C. Our findings indicate that failure prior to oxidation primarily occurs due to microcracks penetrating into the quartz fibers and crystallization of these fibers, while failure after oxidation mainly arises from BN interface failure. Additionally, both the real and imaginary components of the dielectric constants increase along with reflection coefficients from 25°C to 600°C for SiCf-SiO2f/SiC. The analysis of RC based on different thicknesses demonstrates that the SiCf-SiO2f/SiC can still ensure an RC value below -7dB in X-band. The simulated Radar Cross Section (RCS) values remain unchanged within the temperature range of 25°C-600°C, indicating the temperature insensitivity property possessed by these composites.

Anti-ablation and insulation integrated gradient quartz fiber needle felt reinforced SiO2 ceramic/aerogel composite for thermal protection

Anti-ablation and insulation integrated gradient quartz fiber needle felt reinforced SiO2 ceramic/aerogel composite for thermal protection

Heat transfer and electromagnetic property investigation on the hot air quartz fiber/PTFE capillary/epoxy resin anti/de‐icing composites

AbstractTo achieve the wave‐transparent and anti/de‐icing requirements of electromagnetic functional structural components on the windward surface of the aircraft, the PTFE capillary hot air tubes were pre‐buried inside the quartz fiber cloth and the hot air anti/de‐icing quartz fiber/PTFE capillary/epoxy resin (QF/PTFE/EP) composite components was prepared to that met the wave‐transparent performance. A multi‐field coupled numerical finite element simulation model was established, and the anti/de‐icing performance of the QF/PTFE/EP composite with different built‐in tube diameters were investigated by combining experiments and simulations under different hot air temperatures and pressures. The feasibility of hot air anti/de‐icing was verified through anti/de‐icing experiments and numerical simulation. The electromagnetic transmittance of the prepared hot air anti/de‐icing QF/PTFE/EP composite components was tested to characterize the effect on the stealth performance of the aircraft under the service environment. The experimental results demonstrated that with 5 mm tube pitch and hot air of 60°C ± 1°C, the surface temperature of the component with three tube diameters could reach more than 10°C. Furthermore, the decrease in the transmittance of the hot air anti/de‐icing QF/PTFE/EP composite components caused by different incidence angles and two polarization modes was less than 3%.Highlights The hot air QF/PTFE/EP anti/de‐icing composite components were fabricated. The heat transfer, anti/de‐icing, and electromagnetic transmittance performance of the hot air QF/PTFE/EP anti/de‐icing QF/PTFE/EP components were investigated. The experimental and simulation results verified the hot air anti/de‐icing QF/PTFE/EP components met the requirement of aircraft anti/de‐icing and wave transmission.

Mechanical properties and microstructure of quartz fiber-reinforced silica matrix composite with a single layer pyrocarbon interphase

Silica matrix composites (SiO2f/SiO2), reinforced with pyrolytic carbon (PyC) interfacial layers, were synthesized using the precursor impregnation and pyrolysis (PIP) method, mechanical properties and microstructure of these composites were thoroughly investigated. The flexural strength of SiO2f/PyC/SiO2 composites exceeded 55 MPa after treatment at 450°C. Notably, at medium and high temperatures, strength of SiO2f/SiO2 composites was significantly enhanced compared to that of uncoated PyC composites. The experimental resulted indicate that PyC temporary interfacial layer effectively mitigated the strong interfacial reaction between quartz fibers and matrix. Furthermore, fiber pull-out phenomenon observed at the fracture of SiO2f/PyC/SiO2 composites suggested that interfacial bonding was weak, which contributed to the high mechanical strength of these composites.

Wave-transparent and eco-friendly flame-retardant phosphorus-based phthalonitrile/quartz composites by a synchronized self-curing strategy with cyano and alkynyl groups

The robust human–machine interaction systems of the aerospace industry necessitate the development of thermal resistant wave-transparent composites, with a pivotal focus on organic resin matrix. However, enhancing the heat resistance of such materials while preserving other critical attributes has been a formidable challenge. In this study, a novel designed strategy of a dual-curing functional phosphorus-based phthalonitrile monomer (P-ALK-PN) has been proposed. The optimized curing temperatures for intra- or intermolecular Diels-Alder reactions of alkynyl groups and polyaddition reaction of cyano groups resulted in a homogeneous and highly crosslinked N-enriched phthalonitrile system. After curing at 450 °C, the resin, namely P-ALK-PN-450 °C, demonstrated exceptional thermal stability (T5% = 644 °C), thermo-oxidative stability (T5% = 554 °C), and char yield at 800 °C (90.7 % in N2 and 67.5 % in air). Their quartz fiber reinforced composites (P-ALK-PN/QFs) were subsequently fabricated by the hot-pressing process. Upon post-curing at 420 °C, P-ALK-PN-420 °C/QF displayed elevated glass transition temperature (550 °C), flexural strength (319 MPa), and relatively low dielectric properties with a dielectric constant (Dk) of approximately 4.2 and a dissipation factor (Df) less than 0.02 across a wide temperature ranging from 25 °C to 600 °C. Especially, it exhibited excellent flame retardancy (only a 6.7 % weight loss at ambient temperatures exceeding 1300 °C for 200 s) as well, stemming from release of eco-friendly inert gases (NH3) and formation of a graphitized protective layer during pyrolysis. These promising results highlight the potential applications of P-ALK-PN resins in aerospace and high-performance engineering fields.

Effect of Fiber Characteristics on the Structure and Properties of Quartz Fiber Felt Reinforced Silica-Polybenzoxazine Aerogel Composites.

Fiber-reinforced aerogel composites are widely used for thermal protection. The properties of the fibers play a critical role in determining the structure and properties of the final aerogel composite. However, the effects of the fiber's characteristics on the structure and properties of the aerogel composite have rarely been studied. Herein, we prepared quartz fiber felt-reinforced silica-polybenzoxazine aerogel composite (QF/PBSAs) with different fiber diameters using a simple copolymerization process with the ambient pressure drying method. The reasons for the effects of fiber diameter on the structure and properties of the aerogel composites were investigated. The results showed that the pore structure of the aerogel composites was affected by the fiber diameter, which led to significant changes in the mechanical behavior and thermal insulation performance. At room temperature, pore structure and density were found to be the main factors influencing the thermal conductivity of the composites. At elevated temperatures, the radiative thermal conductivity (λr) plays a dominant role, and reducing the fiber diameter suppressed λr, thus decreasing the thermal conductivity. When the QF/PBSAs were exposed to a 1200 °C butane flame, the PBS aerogel was pyrolyzed, and the pyrolysis gas carried away a large amount of heat and formed a thermal barrier in the interfacial layer, at which time λr and the pyrolysis of the PBS aerogel jointly determined the backside temperature of the composites. The results of this study can provide valuable guidance for the application of polybenzoxazine aerogel composites in the field of thermal protection.

Experiments and Theory on Droplet Ignition with Spark Discharges

ABSTRACT Ignition experiments were performed with individual n-decane droplets, initially, about 1 mm in diameter, which were suspended in quartz fibers and subjected to electrical discharges (sparks) of controlled power and duration. Experiments were performed with glow and arc discharges in air at 1 atm and approximately 300 K . Theory is developed to predict the probability of ignition of a fuel droplet as a function of time when it is exposed to an ignition spark. The theory considers the effect of random spark-to-spark fluctuations in the heat flux into the liquid on the time for the droplet surface temperature to be high enough to enable ignition. A Bayesian analysis is also performed to evaluate confidence intervals for parameters related to droplet ignition. Reasonable agreement between theory and experiment is demonstrated, suggesting that spark-to-spark fluctuations of the heat flux into a droplet may lead to a sigmoidal variation of the probability of ignition with respect to time.

Determination of tetramethylammonium hydroxide in air using ion chromatography or ultra-performance liquid chromatography - high-resolution mass spectrometry

Tetramethylammonium hydroxide (TMAH) is extensively utilized in the semiconductor and optoelectronic industries, serving as either a developer or an etchant. TMAH possesses acute toxicity and alkaline corrosiveness, having caused several fatal and injurious accidents in Taiwan. However, there is currently a lack of methods available for assessing TMAH exposure. This study developed a method involving sampling with quartz fiber filters followed by ultrasonic agitation in 10 mL mobile phase, filtering, and analysis using either ion chromatography (IC) or ultra-performance liquid chromatography - high-resolution mass spectrometry (UPLC-HRMS). Utilizing the characteristics of HRMS, the compound analyzed was identified as tetramethylammonium ion (TMA+) through mass spectrometry analysis. The method exhibits excellent trapping capacity and recovery rate. The linear range of TMA+ for IC is 0.3 to 100 μg/mL, with a correlation coefficient of R = 0.9998. The linear range of TMA+ for UPLC-HRMS is 0.002 to 1 μg/mL, with a correlation coefficient of R = 0.996. The recovery rates for IC and HRMS were 116.6% and 90.6%, with corresponding coefficient of variation (CV) of 2.25% and 3.53%, respectively. Samples can be stored at room temperature for 28 days. Verification of this method was conducted at the TMAH factory, and the air concentrations measured in the TMAH filling area were 3.29 and 4.75 μg/m3 from IC and UPLC-HRMS, respectively. This method will be applied in the on-site analysis of occupational hazards for operators in chemical plants, technology factories, and recycling plants, aiming to evaluate risk values to protect the safety and health of workers and prevent occupational diseases.

Hierarchical Ceramic Nanofibrous Aerogels for Universal Passive Radiative Cooling

AbstractSolar‐induced thermal challenges in buildings, cold chain logistics, and spacecrafts may be overcome by integrating passive radiative cooling (PRC) with aerogels having thermal insulation (TI). Herein, a universal radiative cooling silica aerogel (UCSA) is prepared through the simple regeneration and freeze‐drying of commercial quartz fiber membranes. The optically engineered UCSA with a hybrid structure (silica nanofibers/microbeads) achieves remarkable solar reflectance (RS.E. = 98.1%) and atmospheric transparency window emittance (εATW = 92.1%) under Earth conditions, with a theoretical daytime cooling power of 103.3 W m−2. In the harsh space environment, it exhibits ultrahigh average solar reflectance (RS.E. = 99.1%) and broadband mid‐infrared emittance (εMIR = 90%), achieving a cooling power of 354.1 W m−2. Compared to single‐functional approaches, UCSA synergistically integrates the PRC and TI performance for excellent thermal management capability. Moreover, this ceramic aerogel can resist temperatures up to 830 °C, safeguarding building occupants and spacecraft electronics. Furthermore, UCSA passes environmental aging and thermal vacuum outgassing tests for long‐term viability both on Earth and in space. Finally, a USCA‐covered box achieves an average sub‐ambient cooling of 18.6 °C when exposed to sunlight. In summary, UCSA opens a path for energy‐efficient and sustainable cooling strategy with universal applications.

Fluorinated polyetherimide as the modifier for synergistically enhancing the mechanical, thermal and dielectric properties of bismaleimide resin and its composites

The aviation industry has a substantial demand for bismaleimide (BMI) resins that possess high toughness, excellent thermal stability, and low dielectric constant, which are critical for wave-transparent materials. This study presents the synthesis of a novel fluorinated polyetherimide (F-PEI) and its integration with BMI resin using an in situ pre-polymerization method. Upon blending 4 wt% F-PEI with bismaleimide resin, the resulting blending resin (BDP-4) demonstrated a significant enhancement in both impact strength (59.6 % increase) and flexural strength (13.9 % increase) compared to the unmodified BMI. Additionally, the glass transition temperature of BDP-4 was enhanced to 299.3 °C, representing a 5 °C increase, and the corresponding dielectric constant (k) and dielectric loss (tan δ) at 15.2 GHz were decreased from 3.02 to 2.96 and from 0.010 to 0.009, respectively. These improvements are attributed to the phase separation induced by the F-PEI content, which engendered a synergistic toughening mechanism beneficial for both thermal and dielectric attributes. Notably, the flexural strength (630.1 MPa), flexural modulus (26.5 GPa), and interlaminar shear strength (67.1 MPa) of quartz fiber reinforced F-PEI/BMI composites (QF/BDP-4) exceeded those of pure BMI composites. The findings indicate that F-PEI modification is an effective strategy for advancing BMI resin performance, with potential applications in high-performance industries such as aerospace and electronics.

Graphene-skinned alumina fiber fabricated through metalloid-catalytic graphene CVD growth on nonmetallic substrate and its mass production

Graphene growth on widely used dielectrics/insulators via chemical vapor deposition (CVD) is a strategy toward transfer-free applications of CVD graphene for the realization of advanced composite materials. Here, we develop graphene-skinned alumina fibers/fabrics (GAFs/GAFFs) through graphene CVD growth on commercial alumina fibers/fabrics (AFs/AFFs). We reveal a vapor-surface-solid growth model on a non-metallic substrate, which is distinct from the well-established vapor-solid model on conventional non-catalytic non-metallic substrates, but bears a closer resemblance to that observed on catalytic metallic substrates. The metalloid-catalytic growth of graphene on AFs/AFFs resulted in reduced growth temperature (~200 °C lower) and accelerated growth rate (~3.4 times faster) compared to that obtained on a representative non-metallic counterpart, quartz fiber. The fabricated GAFF features a wide-range tunable electrical conductivity (1-15000 Ω sq−1), high tensile strength (>1.5 GPa), lightweight, flexibility, and a hierarchical macrostructure. These attributes are inherited from both graphene and AFF, making GAFF promising for various applications including electrical heating and electromagnetic interference shielding. Beyond laboratory level preparation, the stable mass production of large-scale GAFF has been achieved through a home-made roll-to-roll system with capacity of 468-93600 m2/year depending on product specifications, providing foundations for the subsequent industrialization of this material, enabling its widespread adoption in various industries.

Porous Bismuth Vanadate Photoelectrodes for Solar Water Oxidation Reaction

Bismuth vanadate (BiVO4), a material known for its high visible light activity and good stability, is a promising candidate as a photoanode for overall water splitting [1]. Its performance is limited by its relatively short charge carrier diffusion length, which has recently been estimated to be ~15 nm [2]. For these kinds of photo-absorbers, commercial flat transparent conducting oxide (TCO) substrates are unsuitable since the thickness needed to absorb a sufficient amount of light far exceeds the carrier diffusion length. With this in mind, deposition of very thin semiconductor film onto the internal structure of (micro)porous, conducting substrates can ensure sufficient light absorption [3], whilst ensuring the individual film thickness is uniformly lower than the carrier diffusion length. Nanostructured TCO substrates can be fabricated using a convenient template-free technique called glancing angle deposition (GLAD). The glancing angle deposition method can be used to synthesize different variations of highly oriented submicron-sized pillars, ranging from vertical and tilted columns to zig-zag and helical structures with the help of shadowing effects and substrate rotation [4]. The optical and electrical properties of nanostructured TCO’s were found to depend on the type of material and the substrate temperature during deposition. We find that pillars made from tin-doped indium oxide show good conductivity (79 Ohm/sq) and are promising for the fabrication of nanostructured substrates for bismuth vanadate. A recently developed alternative approach is the use of transparent, porous, conducting substrates (TPCS) made from quartz felt, in which the quartz fibers are coated with F-doped SnO2 [5]. We found that a BiVO4 film thickness of 50 nm within these porous substrates is enough to absorb the same amount of light as a compact 400 nm bismuth vanadate film. We will discuss the deposition of BiVO4 into the TPCS substrates and the photoelectrochemical performance of these porous photoanodes.[1] K. Sivula and R. van de Krol, Nat. Rev. Mater. 1, 15010 (2016)[2] M. Schleuning, M. Kölbach, F. F. Abdi, K. Schwarzburg, M. Stolterfoht, R. Eichberger, R. van de Krol, D. Friedrich, H. Hempel, PRX Energy 1, 023008 (2022)[3] U. Björksten, J. Moser and M. Grätzel, Chem. Mater. 6, 858 (1994)[4] M. M. Hawkeye, M. T. Taschuk and M. J. Brett, “Glancing Angle Deposition of Thin Films”, John Wiley & Sons, Ltd., Chichester, UK (2014).[5] M. Caretti, E. Mensi, R.-A. Kessler, L. Lazouni, B. Goldman, L. Carbone, S. Nussbaum, R. A. Wells, H. Johnson, E. Rideau, J.-h. Yum, K. Sivula, Adv. Mater. 35, 2208740 (2023)

(Digital Presentation) Reactive Evaporation of Cr Vapors from Chromia-Alkaline Oxide Mixtures Generated in 800℃ Air and Subsequent Condensation Onto Aluminosilicate Fibers

This research aims to improve fundamental understanding of the reactive evaporation and condensation of Chromium (Cr) vapors, which are generated from Cr containing alloys used in many high-temperature (>500℃) process environments and can form potentially problematic condensed hexavalent (Cr(VI)) species downstream. This study focuses on the effects of alkaline oxides present in the Cr source on the resultant Cr evaporation and condensation. Vapor species were generated by flowing high-temperature (800℃) air containing 3% water vapor over chromia (Cr2O3) and mixtures of chromia with calcium oxide (CaO) or magnesium oxide (MgO) powders. Lab-grade quartz and alumina fiber samples were positioned downstream from the Cr-alkaline oxide source where the temperature decreases (<500℃) to collect condensed vapor species. Total condensed Cr and ratios of oxidation states were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES) and diphenyl carbazide (DPC) colorimetric/direct UV-VIS spectrophotometric analyses. Preliminary results indicate a decrease in partial pressures of generated Cr vapor species as well as a decrease in condensed Cr species on the aluminosilicate fibers when alkaline oxides are present in the Cr source compared to a pure Cr source. These results also indicate presence of hexavalent Cr (Cr(VI)) species condensed on all samples investigated. Computational thermodynamic equilibrium modelling corroborated the experimental results showing partial pressures of produced vapor species in the presence of alkaline oxides as well as stabilities of condensed Cr compounds on the fiber samples. Comparative results and analyses are presented and discussed to help inform mechanistic understanding and future related research and engineering efforts. Figure 1

Anti-oxidative quartz/carbon-braided fiber reinforced ceramizable composites modified with B4C and AlB2: Mechanical robustness, phase evolution and anti-oxidation mechanism

Carbon fiber reinforced ceramizable phenolic resin matrix composites (Cf/CPR) have been widely used in the field of thermal protection materials. However, the industrial application of the Cf/CPR is restricted by its easy oxidation failure under high temperature condition. In this work, a novel antioxidative ceramizable composites modified with AlB2 and B4C (Cf-Qf/CPR) were prepared by using quartz fiber-coated carbon fiber (Cf-Qf) as reinforcements via co-weaving technique. The thermal stability, mechanical properties, interfacial phase evolution and anti-oxidation mechanism of the composites were investigated. The residue yield and the flexural strength of the composites after treatment at 1200°C for 15 min were 93.4 % and 62.4 MPa, increased by 5.4 % and 67.3 % compared with those of Cf/CPR. Quartz fiber and ceramic protective layer showed synergistic effect to improve the oxidation resistance of carbon fiber and PyC, confirming good high temperature mechanical properties and oxidation resistance of as-received composites.

Numerical and experimental study on anisotropic heat transfer behaviors of quartz fabric composite preforms: Multiple micro‐scale models method

AbstractThis paper presents a comprehensive study on anisotropic heat transmission behaviors in quartz fiber fabrics. Considering the random distribution characteristic of fibers within the yarn, an innovative two‐scale finite element method (tFEM) is introduced, incorporating multiple micro‐scale fiber models (MMFM) based on scanning electron microscope (SEM) observations. MMFM are divided into 8 distinct models to capture intricate fiber arrangements. The macro‐scale fabric model is constructed based on the geometric structure analysis by Micro‐CT technology. Both micro‐ and macro‐scale models are assembled with the air matrix to form the two‐phase composite model. The Hot‐Disk thermal analysis instrument is applied to measure the anisotropic thermal conductivity (ATC). Numerical results from MMFM shows more excellent agreements with the experimental ones at 3D orthogonal directions of fabrics, i.e., the error rates of the thermal conductivity in the warp, weft and thickness directions between numerical and experimental methods are all less than 3%, which indicates the tFEM including MMFM in this paper is more accurate than the tFEM including OSMFM. In addition, the temperature distribution and heat transmission differences due to fiber arrangements are simulated and illustrated through the MMFM. Afterwards, temperature drop and isothermal characteristics are demonstrated in this study.Highlights Effects of fiber arrangements on steady heat transfer behaviors at micro‐scale are illustrated. Isothermal and temperature‐drop characteristics at micro‐ and macro‐scale are simulated and studied. The transverse isotropy of thermal conductivity at micro‐scale and the anisotropy of that at macro‐scale are revealed.

Effect of Polycarbosilane (PCS) on the High-Temperature Properties of Phenolic Resin (Phen) Films and Quartz Fiber/Phen-PCS Composites

In this study phenolic resin (Phen)-loaded PCS (Phen-PCS) films were prepared and quartz fiber/Phen-PCS composites based on the resin films were also prepared. The quartz fiber/Phen-PCS composites were prepared by impregnating 2.5 Dimension (2.5D was an arrangement of fibers) quartz fibers using the resin film infusion (RFI) process. The properties of the composites were investigated. The study demonstrated that the density of the composites, after curing gradually increased with the increase in PCS. The flexural strength of the composites exhibited a trend of increasing and then decreasing after curing and pyrolysis at 1100 °C under an N2 atmosphere. The flexural strength of the composites reached 13.73 MPa when the addition of PCS was 30% of the phenolic resin, representing an increase of 74.23% compared to that of the composites without PCS. The porosity was found to be as low as 2.3% after curing and 2.1% after pyrolysis. X-ray diffraction (XRD) analysis and infrared spectroscopy tests demonstrated that ceramicization products, such as SiO2 and SiC, were produced after pyrolysis of the composites containing PCS. This transformation significantly enhanced the ablation resistance of the composites. Butane flame tests were performed, and the lowest line and mass ablation rates were 0.026 mm/s and 0.196 mg/s after curing. The results of the study revealed the potential of PCS as a precursor to improve the mechanical properties and heat resistance of composites, which offers promising material options for high-temperature applications.

Experimental study on mechanical responses of 3D needle‐punched composite preforms at different needling densities: Failure structures, tensile and interlayer peeling strengths

AbstractIn this study, needle‐punched quartz fiber felt / fabrics preforms (NQFFPs) with a wide needling densities (NDs) range from 70 to 280 punches/cm2 were manufactured, then the inner correlation among the NDs, mechanical properties and structural failure modes were studied and revealed. Firstly, the effects of NDs on mechanical strengths, which included tensile and interlayer peeling strengths of NQFFPs, were analyzed through experimental methods. Moreover, MATLAB software was applied to fit the NDs‐mechanical strength curves, then best fitting equations were defined to characterize the change rules between NDs and mechanical strengths. Additionally, with NDs increment, tensile strengths decreased from 0.727 to 0.0925 MPa, whereas interlayer peeling strengths increased from 83.46 to 135.04 N/m. Afterwards, the 3D image technology was utilized to capture failure morphologies of NQFFPs at different NDs from tensile and interlayer peeling experiments, which furtherly revealed the failure mechanisms of NQFFPs at different NDs. This work is significant for the engineering manufacturing and application of needle‐punched preforms and the composites.Highlights Failure structure characteristics of NQFFPs at different NDs were captured. Change rules between NDs and strengths were characterized by math equations. The correlation among NDs, fracture morphologies and strengths was revealed.

Development of an optical fiber core sensor integrated with silver film for chloride ion measurement

This study introduced an optical fiber core sensor designed to measure chloride ions by removing the fiber's coating and cladding, allowing direct interaction between the fiber core and external solutions, thereby enhancing measurement sensitivity. Two types of fibers, plastic and quartz, were evaluated for their efficacy as sensors. Experimental results demonstrated that the fabricated plastic core fiber failed to accurately reflect alterations in external solutions onto the spectrum, making it unsuitable for sensor applications. Conversely, the quartz fiber core, when treated with chloroform to dissolve its cladding, exhibited superior performance due to its wider transmission wavelength range and higher durability. The integration of a silver film on the core further improved the sensor's sensitivity through surface plasmon resonance. The study also explored the impact of thin-film and thick-film formations on sensor performance, with the thin film providing rapid response times and the thick film offering enhanced durability. This advancement holds significant potential for applications in environmental monitoring and the early detection of chloride-induced corrosion in various structural materials.