Fiber-reinforced Phenolic Resin Research Articles

Temperature-dependent creep damage mechanism and prediction model of fiber-reinforced phenolic resin composites

Carbon fiber-reinforced phenolic resin (CF/PF) and glass fiber-reinforced phenolic resin (GF/PF) composites are crucial for thermal insulation and load-bearing capabilities in the aerospace industry. Understanding their creep behavior at various temperatures is essential. This study investigates the impact of temperature on the bending creep properties of CF/PF and GF/PF composites, focusing on deformation response, damage mechanisms, and prediction models. Results reveal that the decrease in creep properties at elevated temperatures is mainly attributed to the increased viscoplastic strain. At room temperature, CF/PF composite demonstrates exceptional creep properties. CF/PF composite exhibits heightened sensitivity to elevated temperatures, undergoing creep rupture at 210 °C and 240 °C with failure strains of 0.48 % and 0.49 %, respectively. High-temperature damage mechanisms have been analyzed in depth using a combination of thermal stress finite element simulation and microscopic characterization. Thermal stress is directly related to the difference in thermal expansion between the fibers and the resin. The influence of fiber distribution and geometry results in the interface being subjected to both normal and shear stresses. The accumulation of interfacial damage increases the plastic deformation and degrades creep performance. Additionally, an advanced temperature-dependent Burgers model has been developed and effectively predicted the creep curves under different temperatures and loads. This model demonstrated great potential as a general predictive model.

Coupling effect of temperature and off-axis angle on the compressive properties of needled carbon/quartz fiber-reinforced phenolic resin composite

Studying high temperature off-axis compression of composites is key for advancing aerospace, optimizing designs, and developing innovative materials. For this objective, the impact of temperature and off-axis angle (denoted as θ) on the compressive properties of needled carbon/quartz fiber-reinforced phenolic resin (CF-QF/PF) composite has been explored. Initially, the thermal behavior of the materials was assessed through thermogravimetric (TG) analysis, followed by 25 sets of static compression tests across five off-axis angles at five temperatures. Subsequently, a model was applied to predict the strength and modulus under high temperature off-axis compression, with an average error of less than 1 %. The coupling failure mechanisms were then analyzed through various microscopic observations. The findings indicate that when T = 400 °C, temperature exposure reduces modulus and strength to 0.43 and 0.32 of their normalized values, respectively. Such findings suggest temperature has a more significant impact on strength. Meanwhile, TG results provide evidence for the significant property loss when T = 400 °C. A specific combination of temperature and off-axis angles will lead to a more pronounced reduction in strength and an increase in failure strain, while such an effect on modulus is less significant. Post-mortem analysis reveals that temperature contributes to matrix softening and weakening of the fiber-matrix interface. Compared to specimens with θ = 90°, others exhibit more frequent fiber bundle cracks and microcrack propagation along the fiber-matrix interface, adversely affecting their high temperature performance.

Facile Synthesis and Properties of Highly Porous Quartz Fiber-Reinforced Phenolic Resin Composites with High Strength.

Lightweight and high-strength insulation materials have important application prospects in the aerospace, metallurgical, and nuclear industries. In this study, a highly porous silica fiber reinforced phenolic resin matrix composite was prepared by vacuum impregnation and atmospheric drying using quartz fiber needled felt as reinforcement and anhydrous ethanol as a pore-making agent. The effects of curing agent content on the structure, composition, density, and thermal conductivity of the composite were studied. The mechanical properties of the composite in the xy direction and z direction were analyzed. The results showed that this process can also produce porous phenolic resin (PR) with a density as low as 0.291 g/cm3, where spherical phenolic resin particles are interconnected to form a porous network structure with a particle size of about 5.43 μm. The fiber-reinforced porous PR had low density (0.372~0.397 g/cm3) and low thermal conductivity (0.085~0.095 W/m·K). The spherical phenolic resin particles inside the composite were well combined with the fiber at the interface and uniformly distributed in the fiber lap network. The composite possessed enhanced mechanical properties with compressive strength of 3.5-5.1 MPa in the xy direction and appeared as gradual compaction rather than destruction as the strain reached 30% in the z direction. This research provides a lightweight and high-strength insulation material with a simple preparation process and excellent performance.

Parameter design of continuous carbon fiber-reinforced phenolic resin composites via in situ-curing 3D printing technology

To improve the print quality and mechanical properties, the process parameters of the continuous carbon fiber-reinforced phenolic resin (CF/PF) composites were systematically investigated based on the in situ-curing 3D printing technology. The printing spacing and printing thickness affected the bonding between fiber bundles. Under the optimized parameters, the surface of the CF/PF composites was smooth and flat, without obvious gaps between the adjacent prepregs and printing layers. Especially, we optimized the resin impregnation temperature ( T i) and analyzed the influence mechanism on mechanical properties. With the increasing impregnation temperature, the resin content and the squeezing force applied to fiber bundles decrease, while the wettability between fiber and resin increases. The resin contents and the squeezing force play more important role on the mechanical properties of the CF/PF composites. With the combined influence of the above effects, the flexural strength of CF/PF composites reaches maximum value of 471.1 MPa under the impregnation temperature of 30°C, printing spacing of 0.80 mm, and printing thickness of 0.10 mm, with minimum defect volume, uniform distribution of fiber and resin, and appropriate fiber/resin interaction.

Lightweight, Flexible, and Covalent-Bonding Phenolic Fabric Reinforced Phenolic Ablator for Thermal Insulation and Conformal Infrared Stealth.

Fiber-reinforced phenolic resin aerogel (FRPRA) composite materials are seductive candidates for high-temperature thermal protection owing to their low density, excellent thermostability, and thermal insulation. However, the intrinsic stiffness restricts their further application for high efficiency. We report a homogeneous and chemical bonding strategy for fabricating lightweight and flexible FRPRA with good ablative thermal insulation performance. The compressible (cyclic strain of 60%) and bendable (cyclic strain of 30%) abilities as well as the structural stability during ablation all benefit from the compatibility between the phenolic resin aerogel matrix and the phenolic fiber reinforcement. Additionally, low bulk density and thermal conductivity of 0.20 g cm-3 and 0.043 W m-1 K-1, respectively, endow the composite with efficient thermal insulation capability. With an 8 mm-thick coupon, the temperature of 200 °C can be decreased to 70.6 °C and the temperature around 1200 °C can be camouflaged to 78 °C through combining with the Al panel. The material also enables a conformal stealth of 600 °C based on its bendability. Hence, the composite has potential in applications of both static and dynamic thermal insulation.

Characterization of friction and wear of phenolic resin matrix composites reinforced by bamboo fibers of alkaline and LaCl3 treatment

Mechanical and tribological properties of phenolic resin matrix composites reinforced by bamboo fibers, which were pre-treated with sodium hydroxide (NaOH) and post-treated with lanthanum chloride (LaCl3), were characterized by hardness, impact, microscratch tests, friction and wear testers, and thermogravimetric analysis. Bamboo fibers before and after modification were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Hemicellulose and lignin of bamboo fibers can be dissolved by alkaline or NaOH treatment, resulting in a rough surface. The high coordination number of rare earth atoms in LaCl3 solution enhanced the formation of chemical bonds between the hydroxyl groups of bamboo fibers and the oxygen-containing groups on the molecular chain of phenolic resin. The hardness and impact strength of the composites both firstly increased and then decreased with an increase in LaCl3 concentration or soaking duration in LaCl3 solution. Tribological performance (e.g. high-temperature friction coefficient, wear rate, thermogravimetric loss, crack propagation) of phenolic resin matrix composites was significantly improved by the treated bamboo fibers. The optimum mechanical and tribological properties of bamboo fiber-reinforced phenolic resin matrix composites were achieved under the conditions of LaCl3 concentration of 10% and soaking duration of 30 min.

Fabrication of a continuous carbon fiber-reinforced phenolic resin composites via in situ-curing 3D printing technology

An in situ-curing 3D printing technology was developed, which comprised resin impregnation, 3D printing/pre-curing and post-curing processes. Continuous carbon fiber-reinforced thermosetting phenolic resin (CF/PF) composites were fabricated based on that. The selection of pre-curing temperature was the key to successful printing. The deviation distances of prepregs during 3D printing, degrees of curing and defect volumes of the composites after 3D printing and post-curing were used to determine the pre-curing temperature. With the optimum pre-curing temperature of 260 °C, the deviation distance of the prepreg was 8.57 mm, defect volume of post-cured CF/PF composite was 12.1% and its mechanical properties were optimal. The degree of curing was 80.7% after 3D printing, which could maintain the structure integrity during the 3D printing and post-curing processes.

Coupled surface-volume pyrolysis effects of carbon-phenolic resin composites under hyperthermal non-equilibrium flows

The thermal protection system is essential for the safe and reliable flying of any high-speed aircraft. A carbon fiber-reinforced phenolic resin (PR) composite is one of the most important matrix candidates for ablative materials, and the microscopic understanding of the pyrolysis process of PR, however, still remains poor. The usual numerical approach is based on volumetric pyrolysis while neglecting the influence of external hyperthermal surroundings. A surface-volume coupled reactive molecular dynamics model is established in this work to simulate complicated heat/mechanics/chemistry multi-physical field coupled pyrolysis problems. The pyrolysis process of the carbon fiber-PR composite is investigated in the presence of vacuum and hyperthermal gas impacts and compared with the volumetric pyrolysis simulation only. The consideration of the surface–volume coupling reveals many unique features beyond the volumetric pyrolysis, which include the generation of different pyrolysis products and the dependence of the effective mass diffusivity of pyrolysis gases on impinging gases in the presence of the hyperthermal non-equilibrium environment. With the detailed revelation of the evolutions of PR solid phase and pyrolysis gaseous products, the work is of great help in improving the microscopic pyrolysis mechanisms, especially the “blowing gas effect,” a key phenomenon for improved understanding of the complicated hypersonic boundary layer flow.

Coefficient of thermal expansion and mechanical properties of modified fiber-reinforced boron phenolic composites

Abstract Boron phenolic resin is widely used in the aerospace field because of its excellent thermal properties. In this article, nitrile rubber powder was added to phenolic resin to modify fiber-reinforced phenolic resin composites. The results showed that the tensile strength continued to decrease; the elongation ratio increased from 20.01% to 32.04%; and flexural strength and flexural modulus reached the highest values of 188 and 9,401 MPa, respectively. Thermal analysis showed that rubber had little effect on the heat resistance at low temperatures, especially below 350°C. Furthermore, the coefficient of thermal expansion of the composites increased from 8.9 × 10−6 to 1.5 × 10−5 K−1, increasing by nearly 70%. The electron microscopy images showed a tortuous fracture path in modified composites, which indicated that rubber powder–modified phenolic composites had a ductile fracture.

Organic-inorganic composites for novel optical transformation induced by high-energy laser ablation

High-energy continuous-wave (CW) laser has been considered as a significant technology in recent decades. Such laser can destroy conventional materials in an extremely short time, necessitating their protection. In this study, zirconium carbide (ZrC) and silicon carbide (SiC) particle-modified short silicon carbide fiber-reinforced phenolic resin matrix composites (SiC/BPF-ZS) with significant anti-laser performance were designed and prepared. Our results showed that the ceramic particles and SiC fibers rapidly oxidized, leading to the formation of a ceramic coating composed of ZrO2 and SiO2. Owing to the formation of the ceramic coating, the reflectivity of the composites improved significantly from 15.8% to 73.2% after ablation at 500 W/cm2 for 30 s. Additionally, the SiC fibers played an important role in the formation of a high-reflectivity coating during laser ablation. Contrast experiments indicated that SiC fibers lead to better performance than the carbon fibers. The high reflectivity and low mass ablation rate are demonstrated to be the key factors improving the anti-laser ablation performance of the SiC/BPF-ZS composites.

Oxidation and ablation behaviors of carbon fiber/phenolic resin composites modified with borosilicate glass and polycarbosilane interface

In this work, modified carbon fiber-reinforced phenolic resin composites (CPR) were prepared. To improve the high temperature performance of CPR, borosilicate glass with different concentrations was incorporated and polycarbosilane (PCS) was added as an interface layer. The oxidation and ablation behaviors of the modified CPR composites were studied. It was found that the borosilicate glass filler changed the oxidation mechanism of composites at temperatures higher than 1000 °C, and caused the volatilization of borosilicate glass in addition to the oxidation of carbon. The strength of composites after oxidation was significantly improved via this modification. The thermal conductivities of composites decreased with the increase in content of fillers, leading to low back temperature during the ablation process and high heat-shielding performance. The ablation properties were improved via the formation of SiC with high melting point. The above results indicate that these modified composites are promising materials for application in thermal protection systems.

A comparative study of the ablation properties of carbon fiber-reinforced phenolic resin composites with a matrix modified with graphene oxide and graphitic carbon nitride

A comparative study of the ablation properties of carbon fiber-reinforced phenolic resin composites with a matrix modified with graphene oxide and graphitic carbon nitride

Effects of polycarbosilane interface on oxidation, mechanical, and ablation properties of carbon fiber-reinforced composites

Polycarbosilane (PCS) was introduced onto carbon fibers as an interface layer to meet requirements for using carbon fiber-reinforced phenolic resin composites (CPR) at high temperatures. Bending strength of as-received CPR with PCS (CPRS) was 541 ± 16 MPa, which is lower than that of pure CPR. However, because of protective PCS interlayer, the strength of CPRS after oxidation at 800 °C for 0.5 h was 112 ± 4.3 MPa, which is about 60% higher than residual strength of pure CPR after oxidation under the same conditions. Resulting protective interlayer of PCS at high temperatures leads to fracture toughness improvement of approximately 40% for CPRS. CPRS showed better ablation resistance under oxyacetylene flame than did pure CPR. Comprehensive protective effects from PCS interlayer and resulting improved thermal conductivity of CPRS account for enhanced ablation resistance.

Measurement and analysis of fiber-matrix interface strength of carbon fiber-reinforced phenolic resin matrix composites

Since fiber-matrix interface strength is critical to properties of carbon fiber-reinforced composites, measurement and analysis of interface strength are crucial steps in tailored design of composites. In the present work, the single fiber push-out test and the short-beam shear test were applied to measure the fiber-matrix interface strength in uni-directionally and two-directionally carbon fiber-reinforced phenolic resin matrix composites. The technical difficulties in processing the specimen and in realizing the fiber push-out were also discussed and clarified. For obtaining the successful test, typically, the thickness of the specimen should be smaller than 100 mm. During the fiber push-out, the de-bonding and fiber sliding at the interface were analyzed from the load-displacement curve features. The results indicated that both methods could be applied to determine the interface strength. The single fiber push-out and the short-beam shear tests resulted in a similar phenomenon in regard to the interface strength of uni-directionally and two-directionally carbon fiber-reinforced phenolic resin matrix composites, but expressed different values. The low interface strength measured from the short-beam shear test could be associated with multiple interlaminar shear failures. Furthermore, it was found that the interface strength of uni-directionally carbon fiber-reinforced phenolic resin matrix composites is somewhat higher than that of two-directionally carbon fiber-reinforced phenolic resin matrix composites. The difference in the interface strength could be attributed to the thermally induced residual stresses caused by the coefficient of thermal expansion mismatch of fiber and matrix. The approaches applied in the current work can be used for the evaluation of the interface strength of carbon fiber-reinforced phenolic resin matrix composites with different fiber-matrix bonding properties.

Processing and Properties of a Phenolic Composite System

Phenolic resin systems generate water as a reaction by-product via condensation reactions during curing at elevated temperatures. In the fabrication of fiber-reinforced phenolic resin matrix composites, volatile management is crucial in producing void-free quality laminates. A commercial vacuum-bag moldable phenolic prepreg system is selected for this study. The traditional single-vacuum-bag (SVB) process is unable to manage the volatiles effectively, resulting in inferior voidy laminates. However, a double-vacuum-bag (DVB) process is shown to afford superior volatile management and consistently yield void-free quality parts. The DVB process cure cycle (temperature/pressure profiles) for the selected composite system is designed, with the vacuum pressure application point carefully selected, to avoid excessive resin squeeze-outs and achieve the net shape and target resin content in the final consolidated laminate parts. Laminate consolidation quality is characterized by optical photomicrography for the cross sections and measurements of mechanical properties. A 40% increase in short beam shear strength, 30% greater flexural strength, 10% higher tensile and 18% higher compression strengths are obtained in composite laminates fabricated by the DVB process.

Influence of activation temperature on adsorption characteristics of activated carbon fiber composites

In this work, the effect of activation temperature on adsorption properties of activated carbon fiber-reinforced phenolic resin matrix composites has been investigated. The composites were manufactured via a molding process with unwoven carbon fabrics and phenolic resin. The green body mold was heated at 125°C to cure the phenolic resin and they were carbonized in an inert environment at 1000°C for 2 h. They were then activated by CO 2 gas at 700, 800, 900 and 1000°C for 2 h, denoted as ACFC-700, ACFC-800, ACFC-900 and ACFC-1000. The specific surface area and the pore structure were evaluated from nitrogen adsorption data at 77 K, and the acid–base values on the surface were determined by titration methods. As a result, the activation temperatures had a major influence on adsorption characteristics and surface properties of the composites.

Interfacial Characteristics and Fracture Toughness of Electrolytically Ni-Plated Carbon Fiber-Reinforced Phenolic Resin Matrix Composites

The electrolytic plating of metallic nickel on a carbon fiber surface has been carried out in order to improve the interfacial adhesion and the mechanical properties in carbon fiber/phenolic matrix composite systems. The surface and the mechanical interfacial properties of composites are characterized by X-ray photoelectron spectrometry (XPS), surface free energy, and the critical stress intensity factor (KIC). From the experimental results, it is clearly revealed that the oxygen functional groups and the metallic nickel on fibers largely affect the mechanical interfacial behavior of the composites, resulting in increased surface polarity, whereas the nitrogen functional groups have no effect. Also, a good correlation between surface oxygen functional groups and mechanical interfacial properties and between wettability and KIC is established and it is found that a 10 A m−2 current density is the optimum condition for this system.

Simulated-stop tribological behavior of pitch—resin—CVI carbon—carbon composite

This work studies the braking (simulated-stop) behavior of a mesophase pitch fiber-reinforced phenolic resin plus chemical vapor infiltrated (CVI) hybrid matrix carbon—carbon (C-C) composite under different surface conditions. The results indicate that friction and wear behavior is sensitive to sliding surface condition, and the initial surface condition has a significant effect on tribological behavior of the composite. AP/1400, the only condition that does not experience a transition, shows much lower friction coefficient and wear than the other conditions. Under the same test conditions, BI specimens exhibit higher friction coefficients and wear than those of AP specimens. Of all the conditions, BI/2000 induces the highest temperature rise. Specimens braked from higher speed always suffer higher wear, but the stopping time is dependent more on the initial surface condition than the initial speed. As soon as a type I-to-type II transition occurs, the friction and wear rise abruptly. A V-shaped variation is exhibited in post-transitional friction coefficient of the composite. The severe structural damage during the final stage is responsible for the final increase in friction coefficient. Collection of large wear particles is consistent with the observed heavily delaminated surface film during this stage.

Thermal degradation of polymers. VIII. Ablation studies on a series of fiber‐reinforced phenolic resin composites

AbstractThe use of a laboratory ablation test rig for the assessment of tubular fiber‐reinforced composites is described. Ablation resistance, char depth, smoke, and flash measurements have been made on a series of composites based on a standard phenol–formaldehyde resin incorporating various fibrous reinforcing agents. The results have been compared with those obtained from a standard asbestos‐reinforced composite prepared from the same resin. Results are discussed in terms of the properties of the composite and of the fibrous reinforcing agent.

Phenolic resin char-formation during hyperthermal ablation

Ablation is a self-regulating heat and mass transfer process in which incident thermal energy is expended by sacrificial loss of material 1 1 ASTM (E 349)30. . The surface of a carbonaceous char is lost during the ablation of fiber-reinforced phenolic resin composites. The transient high temperatures penetrate deeply, resulting in an underlying pyrolysis zone with rapid pyrolysis rates and a high char interface temperature. Phenolic resin char-formation at high heating rates and high temperatures was studied using thermogravimetry (TG). The specialized thermobalance permitted runs in helium at rates of 3–430°C/min up to 1400°C. Computer code analysis provided rate parameters for an Arrhenius type correlation. The parameters represented well the parent TG run but were not independent of heating rate. A complex correlation was considered necessary for universal use. The attractive alternative was parameter evaluation at high heating rates using TG.