Effect of frequency on the fatigue behavior of [±45]4s laminate of carbon fiber reinforced polyetheretherketone (PEEK) composites under tension-tension loading

Fatigue behavior of carbon fiber reinforced poly etheretherketone (PEEK) laminated composite was investigated. The [±45]_4s AS-4/PEEK laminated composites under static tensile measurement at various test temperatures were conducted. Three tension-tension fatigue loading frequencies, 1 Hz, 5 Hz and 10 Hz, were selected to study the effect of frequency on the fatigue behavior of [±45]_4s AS-4/PEEK laminate. The survival probability of experimental fatigue life data under different stress amplitude tests were estimated and analyzed by the median rank order-statistic cumulative-distribution function and the Weibull distribution function. The S-N curves at different fatigue loading frequencies exhibited a trend of two-segment straight line curves. The increase in surface temperature of specimens was found and the thermal stress history was also investigated by thermo-image techniques during fatigue life testing. The fatigue failure mechanism was investigated by X-ray radiography.     

Isothermal crystallization and melting behavior of short carbon fiber reinforced poly(ether ether ketone) composites

Films of short carbon fiber reinforced poly(ether ether ketone) (PEEK) composite were formed by compression molding pellets for 10 min at 380 °C under air. A heating stage was used to prepare isothermally treated PEEK composites before DSC scan. The dependence of degree of crystallinity on the heating rate (10–80 °C/min) was investigated for specimens crystallized at different temperatures. The results indicated that 50 °C/min was an optimum heating rate to suppress the reorganization and to avoid the superheating of high crystallinity specimens with the sample weight of 10 mg. The upper peak temperature of double-melting peaks continued to increase with crystallization temperature. This peak temperature was related to the transition from regime II to III. The phenomenon of lower crystallinity and higher melting temperature supports the interpretation that the upper melting peak corresponded to crystals growing during the earlier stage of isothermal crystallization.     

Fatigue behavior and oxidation resistance of carbon/ceramic composites reinforced with continuous carbon fibers

The aim of this work was to compare fatigue behavior and oxidation resistance of pitch-derived CC (carbon) composite with CC/ceramic (carbon/ceramic) composites obtained by impregnation of CC composite with polysiloxane-based preceram and their subsequent heat treatment. Two types of CC/ceramic composites were studied; CC/SiCO composite obtained at 1000 °C, and CC/SiC composite obtained at 1700 °C. Both types of composites show much better fatigue mechanical performance in comparison to pure CC composite. CC/SiCO composite had 3 times better fatigue properties, and CC/SiC composite 4.5 times better fatigue properties than the reference CC composite. After a fatigue test composites partially retain their mechanical properties, and normalized residual modulus in the direction perpendicular to laminates exceeds 50% for CC and CC/SiCO composites. In the other directions normalized residual modulus is higher than 80% for all composites. Oxidative tests led at 600 °C in air atmosphere indicated oxidation resistance of CC/SiC composites.     

Influence of oxidation on fatigue life of a carbon/silicon carbide composite in water vapor containing environments

The influence of oxidation on the fatigue life of two-dimensional carbon/silicon carbide composites in water vapor containing environments at 1300 °C was investigated. Tension–tension fatigue experiments were conducted at sinusoidal frequency of 3 Hz. Using a stress ratio (σ_min/σ_max) of 0.1, specimens were subjected to peak fatigue stresses of 90, 120 and 150 MPa. The mean residual strength of the specimens after survived 100,000 cycles with a peak stress of 90 MPa was 83.9% of that of the as-received composite. The mean fatigue lives of the specimens subjected to peak fatigue stresses of 120 and 150 MPa were 42,048 and 13,514 cycles, respectively. Oxidation was the dominant damage mechanism, which remarkably decreased the fatigue life. Oxidizing species diffusion within the composite defects was discussed. The higher the applied stresses, the larger the equivalent radius of the defect and the shorter the fatigue life.     

Fatigue behavior and damage evolution of SiC/SiC composites under high-temperature anaerobic cyclic loading

In the present study, the fatigue behavior and damage evolution of SiC/SiC minicomposites at elevated temperatures in oxygen-free environment are investigated which are important for their application and are still unclear. The high-temperature fatigue test platform is developed and the fatigue stress-life curve and the stress-strain response are obtained. The test result shows that the life of the material at elevated temperature is shorter than that at room temperature under the same stress level. Moreover, the hysteresis loop width and the residual strain increase with the increasing of the cycles while the hysteresis modulus decreases during the fatigue cycling. The evolution process of matrix cracks is observed using the real-time remote detection system. It is found that matrix cracking is insensitive to the cyclic loading which is similar to room temperature and is due to that the degeneration of the interfacial shear stress reduces the area of high stress in matrix. The fiber/matrix interfacial shear stress under different cycles is determined based on the fatigue modulus of each hysteresis loop. The result shows a fatigue enhancement phenomenon for the interface which is not observed at room temperature.     

Enhanced thermoelectric effect of carbon fiber reinforced cement composites by metallic oxide/cement interface

Thermoelectric power of carbon fiber reinforced cement composites was firstly enhanced efficiently by metallic oxide microparticles in the cement matrix. The absolute Seebeck coefficient of these composites increased steadily with increasing metallic oxide content and achieved 4–5 folds of the original one. The largest absolute thermoelectric power of +100.28 µV/°C was obtained for the composite with 5.0 wt% Bi₂O₃ microparticles. The carrier scattering of the interface between oxide microparticles and cement matrix is probably attributed to the Seebeck effect enhancement.     

Appropriate thickness of pyrolytic carbon coating on SiC fiber reinforcement to secure reasonable quasi-ductility on NITE SiC/SiC composites

Pyrolytic carbon (PyC) coating of silicon carbide (SiC) fibers is an important technology that creates quasi-ductility to SiC/SiC composites. Nano-infiltration and transient eutectic-phase (NITE) process is appealing for the fabrication of SiC/SiC composites for use in high temperature system structures. However, the appropriate conditions for the PyC coating of the composites have not been sufficiently tested. In this research, SiC fibers, with several thick PyC coatings prepared using a chemical vapor infiltration continuous furnace, were used in the fabrication of NITE SiC/SiC composites. Three point bending tests of the composites revealed that the thickness of the PyC coating affected the quasi-ductility of the composites. The composites reinforced by 300?nm thick coated SiC fibers showed a brittle fracture behavior; the composites reinforced 500 and 1200?nm thick PyC coated SiC fibers exhibited a better quasi-ductility. Transmission electron microscope research revealed that the surface of the as-coated PyC coating on a SiC fiber was almost smooth, but the interface between the PyC coating and SiC matrix in a NITE SiC/SiC composite was very rough. The thickness of the PyC coating was considered to be reduced maximum 400?nm during the composite fabrication procedure. The interface was possibly damaged during the composite fabrication procedure, and therefore, the thickness of the PyC coating on the SiC fibers should be thicker than 500?nm to ensure quasi-ductility of the NITE SiC/SiC composites.     

The influence of hygrothermal ageing on creep behavior of nanocomposite adhesive joints containing multi-walled carbon nanotubes and graphene oxide nanoplatelets

The effect of hygrothermal ageing on the creep behavior of multi-walled carbon nanotube (MWCNT) and graphene oxide nanoplatelet (GONP)-reinforced adhesive joints was investigated. The neat, MWCNT and GONP-reinforced adhesive single lap joints were manufactured and immersed in hot deionized water with three different temperatures for 24 h and then tested under creep loading. The results showed that the elastic and creep shear strain values of the neat adhesive joints increased by 14% and 25%, respectively, when the water temperature was increased from 30 to 50 °C. It was found out that 0.1 wt% MWCNTs had the maximum reinforcing effect against the creep behavior of adhesive joints pre-aged in hot water by 56% and 33% reductions in the elastic and creep strain values of the nanocomposite adhesive joints compared to the neat adhesive joints. Whereas, GONPs caused the maximum reductions of 45% and 20% in the elastic and creep strains of the nanocomposite adhesive joints compared to the neat joints. Furthermore, the Burgers rheological model was employed for simulating the creep response of adhesive joints. Semi-empirical models were proposed for the elastic and creep strains and the Burgers model parameters as functions of the water temperature and MWCNT/GONP weight percentage using the response surface methodology.     

Preferential distribution and oxidation inhibiting/catalytic effects of boron in carbon fiber reinforced carbon (CFRC) composites

Two different batches of CFRC composites were prepared in the absence/presence of B with the expectation of increasing oxidation stability and improving the processing compatibility of CFRC composites in commercial applications. The composites were examined to reveal the nature of substitutional B in oxidation, crystallinity and distribution preference in the composites. Substitutional B acts both a catalyst and an inhibitor in carbon oxidation, depending on the content and the extent of carbon burn-off reaction. Crystallinity increases with the incorporation of B, as expected; d₀₀₂ decreases, and L_c and L_a increase. Boron prefers to be distributed in the less ordered structure; non-graphitizable PAN-based carbon fibers have higher B contents than graphitizable coal-tar pitch, but processing conditions can change this preference. The incorporation of B in CFRC composites seems to be beneficial for improving the potential ability of the composites in applications by increasing crystallinity and oxidation stability.     

Effects of low-energy impact and thermal cycling loadings on fatigue behavior of the quasi-isotropic carbon/epoxy composites

Effects of low-energy impact loading and thermal cycling on fatigue behavior of carbon fiber reinforced epoxy (carbon/epoxy) laminates are examined. A low-energy of 0.62 Joules was adopted to impact carbon/epoxy laminates prior to thermal cycling exposure and fatigue test. The temperature ranged between 60 and −60 °C for thermal cycling and the stress ratio of 0.1 with a frequency of 3 Hz for fatigue loading were used. Impact performances were tested on the virgin specimens and the thermal-cycling exposure specimens. Residual tensile strength and fatigue tests were performed on the laminate composites after being subjected to thermal cycling. The relationship between tensile strength reduction and fatigue performance after thermal cycling was investigated. Stiffness degradation during fatigue testing was monitored; the differences in stiffness for these three composites (virgin specimens, low-energy impacted specimens, low-energy impacted and thermal-cycling exposure specimens) were compared and the coupling effects of low-energy impact and thermal fatigue were studied. Furthermore, the S-N curves were also plotted and the variation was compared on the aforementioned three composites. SEM was used to examine the difference in fracture morphologies on the composites with and without suffering low-energy impact and thermal fatigue.     

Recycled poly(ethylene terephthalate) and its short glass fibres composites: effects of hygrothermal aging on the thermo-mechanical behaviour

This paper reports on the effects of hygrothermal aging at 70 °C in water and at 80% relative humidity, on the thermo-mechanical properties, molar mass and microstructure of recycled poly(ethylene terephthalate) (rPET) and its short glass fibres composites.For all the investigated materials, the elastic mechanical properties (tensile and storage moduli) determined at low strain levels resulted practically unaffected by hygrothermal aging under the selected conditions. On the other hand, a marked reduction of the tensile strength and apparent fracture toughness has been observed for rPET matrix and its composites during hygrothermal aging, more markedly for materials immersed in water than for those aged at 80% RH. Both properties resulted to be related on the molar mass of the rPET matrix, that decreased during hygrothermal aging as a consequence of the hydrolysis process.The materials glass transition, evaluated as the temperature of the loss factor peak, increased during hygrothermal aging due to the progressively restricted mobility of the amorphous phase caused by a concurrent crystallinity increase. This crystallization process (chemicrystallization) is favoured by temperature, by the plasticizing effect of water and by the reduction of molar mass.Consistently with the mechanical measurements, the morphology of fracture surfaces exposed to hygrothermal aging in water revealed a reduction of plastic deformation of the rPET matrix and a weakening of the fibre-matrix interface for rPET composites.     

The effect of carbon nanotubes on the damage development in carbon fiber/epoxy composites

The aim of this study is to investigate the effect of carbon nanotubes (CNTs) on the initiation and development of damage in a woven carbon fiber/epoxy composite under quasi-static tensile loading. The composite is produced using resin transfer moulding and contains 0.25 wt.% of CNTs in the matrix. The results in the fiber direction report no improvement of the Young’s modulus and a slight improvement of the strength and strain-to-failure. The most important result of the study is a notion that CNTs have a hindering effect on the formation of transverse cracks. The conclusion is drawn from a combined analysis of the acoustic emission measurements (reporting a pronounced shift of all damage development thresholds towards higher strains by more than 30%) and X-ray/SEM observations (revealing a lower crack density in the CNT modified composite). The same analysis also indicates that the mechanism of energy dissipation through transverse microcracking is partially replaced by another mechanism that promotes (distributed) damage through fiber debonding.     

Microstructural evolution and mechanical performances of SiC/SiC composites by polymer impregnation/microwave pyrolysis (PIMP) process

SiC/SiC composites were prepared by polymer impregnation/microwave pyrolysis (PIMP) process, and their microstructural evolution and the mechanical performances were characterized. Using non-coated Tyranno SA fiber preforms as reinforcement and impregnation with only allylperhydropolycarbosilane (AHPCS) into the preforms, Tyranno SA/SiC composite (TSA/SiC) with higher density was obtained. While using carbon-coated Tyranno SA fiber preforms, Tyranno SA/C/SiC composite (TSA/C/SiC) with lower density were also fabricated. In this composite, SiC particulate was loaded with polymer precursor (AHPCS) in the first cycle impregnation. Microstructural observation revealed that pore and crack formation was affected by processing conditions. Bending strength was also dependent on the microstructural evolution of the samples. In TSA/SiC composite, relatively strong interfaces contribute to effective load transfer so that higher bending strength could be reached. In the TSA/C/SiC composite, weak interfaces provide a relatively lower strength. Meanwhile, different microstructural evolution and interfacial properties of the composites lead to the variation of the fracture behaviors.     

Effect of fiber type on mechanical properties of short carbon fiber reinforced B4C composites

In order to enhance the mechanical properties of B₄C without density increase, the short carbon fibers M40, M55J and T700 reinforced B₄C ceramic composites were fabricated by hot-pressing process. The addition of the carbon fibers accelerates the densification of the B₄C, decreases their densities, and improves their strength and toughness. The enhancement effects of the three kinds of carbon fibers were studied by investigating the density, Vickers hardness and the mechanical properties such as flexural strength, flexural modulus and fracture toughness of the composites. The fiber type has a great influence on the mechanical properties and enhancement of the short carbon fiber reinforced B₄C composites. The flexible carbon fiber with high strength and low modulus such as T700 is appropriate to reinforce the B₄C matrix ceramic composites.     

Fabrication and piezoelectric properties of BaTiO3/BaTiO3-Bi(Mg1/2Ti1/2)O3-BiFeO3 composites

We fabricated xBaTiO₃ (BT)/(1-x)[BaTiO₃-Bi(Mg_1/2Ti_1/2)O₃-BiFeO₃] (BT-BMT-BF)?+?0.1?wt%MnCO₃ composites by spark plasma sintering and investigated the effect of BT content x, BT powder size, and BT-BMT-BF composition on piezoelectric properties. For xBT/(1-x)(0.3BT-0.1BMT-0.6BF) +?0.1?wt%MnCO₃ (x?=?0–0.75) composites with a 0.5-µm BT powder, the dielectric constant was increased with x, and the relative density was decreased at x?=?0.67 and 0.75, creating optimum BT content of x?=?0.50 with a piezoelectric constant d₃₃ of 107?pC/N. When a larger 1.5-µm BT powder was utilized for the composite with x?=?0.50, the d₃₃ value increased to 150?pC/N due to the grain size effect of the BT grains. To compensate for a compositional change from the optimum 0.3BT-0.1BMT-0.6BF due to partial diffusion between the BT and 0.3BT-0.1BMT-0.6BF grains, a 0.5BT/0.5(0.275BT-0.1BMT-0.625BF)?+?0.1?wt%MnCO₃ composite with the 1.5-µm BT powder was fabricated. We obtained an increased d₃₃ value of 166?pC/N. These results provided a useful composite design to enhance the piezoelectric properties.     

Influence of surface roughness and temperature on the oxidation behavior of ZrC/SiC samples

New composites were elaborated using ZrC and SiC powders and the Spark Plasma Sintering process. The samples were polished at 4 different levels in order to compare the influence of surface roughness and temperature (1400 and 1600 K) on the characteristics of the oxide layers. By XRD analysis, it was confirmed that polishing and temperature level provoked changes in the crystalline structure. SEM imaging coupled to EDS microanalysis showed that the oxide layer was made of zirconia grains with silica at the grain boundaries. Nano-indentation was used to analyze the influence of the initial surface roughness and temperature on the hardness of the oxide layer. At 1400 K, the initial polishing has favored the growth of a hard oxide layer, which could be probably correlated to the higher crystallinity of the oxide. At 1600 K, it seems that a rougher initial surface favors the hardness of the oxide layer, which could be correlated to a better adherence between the oxide layer and the substrate. Both phenomena (crystallinity and adherence) would be in competition to reduce the fragility of the oxide layer.     

Effect of pyrolysis temperature on the microstructure and capillary infiltration behavior of carbon/carbon composites

Carbon fiber fabric reinforced plastics were pyrolyzed at temperatures between 900?°C and 1600?°C to convert them into carbon/carbon (C/C) composites. The effects of pyrolysis temperatures on the microstructure, mechanical properties, and especially on the capillary infiltration behavior of C/C composites, suitable for liquid silicon infiltration (LSI), were investigated. The porosity of these C/C composites shows a decreasing trend with increasing pyrolysis temperature. The established model can explains the pyrolysis mechanism and the infiltration behaviors. Within the initial stage, the capillary infiltration rate of C/C composites with the model fluid water increases rapidly. In the second stage, where thermal imaging indicates that water has reached the top area of the plates at the initial stage. Capillary infiltration rate, based on water infiltration experiments mass increase, decreases because the shrinkage of micro-delamination take place at higher pyrolysis temperature. In combination with LSI results, a model for the capillary infiltration behavior of C/C is proposed.     

A study on the interfacial reaction and dielectric properties of Ba0.88(Nd1.40Bi0.42La0.30)Ti4O12/alkali-borosilicate glass composites

This study investigated the effects of sintering parameters and the addition of alkali-borosilicate glass into the Ba_0.88(Nd_1.40Bi_0.42La_0.30)Ti₄O₁₂ B(NBL)T ceramic. The microstructure evolution, ionic exchange phenomenon at phase interfaces and the dielectric properties variation of composites were examined by XRD, EPMA, TEM, RF impedance analyzer and network analyzer, respectively. XRD patterns revealed that interactions between B(NBL)T ceramic and glass during sintering could have caused the change in the preferred orientation as well as the shifting of the crystals’ diffraction angles. EPMA mapping showed that the concentrations of Ba, and Bi decreased along the edge of the B(NBL)T ceramic that is closest to the glass phase, while the opposite trend was seen for Na and Ca. TEM and EDS analyses confirm that an ionic exchange took place during sintering with the glass phase wetting the B(NBL)T ceramic and was responsible for the change in the crystal plane and the variation in lattice parameters. The ionic exchange that occurred between the B(NBL)T ceramic and the glass phase resulted in a decrease in the electrical resistivity of the glass phase, which in turn reduced the dielectric loss.     

A focused review on the tribological behavior of C/SiC composites: Present status and future prospects

Silicon carbide-based ceramic matrix composites have received extensive attention in recent years. Many excellent reviews have reported on the tribological behavior of carbon fiber-reinforced carbon and silicon carbide dual matrix (C/C-SiC) composites. However, a systematic overview of the tribological properties of carbon fiber-reinforced silicon carbide (C/SiC) composites does not exist. This review focuses on C/SiC composites and summarizes the key factors, including internal factors (constituent content, graphitization process, material structure and fiber direction), and various test conditions (pressure and speed, dry and wet, temperature, and counterparts) that affect their tribological behavior. Their wear mechanisms under different conditions are elaborated. Finally, some potential future development directions for improving the performance of C/SiC composites are proposed to provide high-quality ceramic matrix composites for engineering applications. These directions include structural modification, matrix modification, coating technology, laser surface texturing, and material genome method.     

Rheological behavior of (short) carbon fiber/thermoplastic composites. Part I: The influence of fiber type,processing conditions and level of incorporation

The aim of this work is to understand the influence of type of (short) carbon fibers, processing conditions and fiber incorporation level on the rheological behavior of carbon fiber/polypropylene (PP) composites. For this purpose, two types of fibers (sub‐micron Vapor Grown Carbon Fibers, VGCF, and ex‐PAN, PAN), three different extruder screw geometries and three different fiber incorporation contents were studied. The rheological characterization was performed by means of capillary and rotational rheometry, results being presented and discussed in terms of reinforcing capability in both shear (steady and oscillatory) and extensional flows. The results show that VGCF have a generally higher influence on the rheological behavior of the composites than the PAN fibers. However, because of their higher intrinsic rigidity, PAN fibers give rise to composites with better mechanical properties than the VGCF ones. It is also shown that the influence of the screw geometry on fiber damage and, consequently, on the behavior of the composites, is weak, fiber degradation occurring mainly in the compounding stage. The incorporation level has the expected influence, i.e., it produces gradual changes in all the properties considered in this study.