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The analysis of failure behaviors of continuous fiber-reinforced ceramic matrix composites (CMCs) requires the characterization of the damage evolution process. In service environments, CMCs exhibit complex damage mechanisms and failure modes, which are affected by constituent materials, meso architecture, inherent defects, and loading conditions. In this paper, the in-plane tensile mechanical behavior of a plain woven SiCf/SiC CMC was investigated, and damage evolution and failure process were studied in detail by digital image correlation (DIC) and acoustic emission (AE) methods. The results show that: the initiation of macro-matrix cracks have obvious local characteristic, and the propagation paths are periodically distributed on the material surface; different damage modes (matrix cracking and fiber fracture) would affect the AE energy signal and can be observed in real-time; the significant increase of AE accumulated energy indicates that serious damage occurs inside the material, and the macroscopic mechanical behavior exhibits nonlinear characteristic, which corresponds to the proportional limit stress (PLS) of the material.

In this paper, the 12k T-700

Carbon fiber-reinforced carbon matrix (C/C) composites were prepared by chemical vapor infiltration, and then they were subjected to silicon (Si) reactive melt infiltration to obtain C/C–SiC–Si composites. The ablation behavior of these two types of composites was evaluated by high-energy (500w) carbon dioxide laser irradiation under argon atmosphere. The depths and three-dimensional (3D) profiles of laser ablation holes were measured by laser confocal microscopy. The results showed that the depth of ablation hole of C/C composites gradually increased, and the ablation rate decreased with ablation time. The temperature distribution on C/C composite surface was simulated by 3D finite element analysis. The C/C–SiC–Si composites exhibited a rapid ablation rate during the ablation process within 7 s; however, no further ablation damage on carbon matrix was observed after 7 s. Si was found to dissipate energy through phase change, transpiration cooling, and smog attenuation. A laser ablation model was proposed based on the energy dissipation mechanism. C/C–SiC–Si composite showed better performance of laser ablation resistance in 100 s than pure C/C composite.

Recently, carbon fiber-reinforced silicon carbide (C/SiC) composites are considered important candidates for laser protection materials. In this paper, the ablation mechanism of C/SiC composites and their modified composites under laser irradiation was studied. ZrB2–MoSi2–SiC ternary-phase ceramic was successfully coated on C/SiC composites by using high velocity oxygen fuel (HVOF) technology, with Mo as transition layer. The evolution of phase and morphology of the composites was investigated by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ablation behavior of composites was investigated by laser confocal microscopy (LCM). The results showed that the ablation mechanism of composites was controlled by phase transformation, thermal reaction and thermal diffusion. The solid-liquid transition of ZrB2 and MoSi2 was the dominant factor. Thermal reaction and good thermal diffusivity of coatings were also important factors affecting the ablation performance. ZrB2–SiC– MoSi2/Mo coating failed when all phase transitions were completed and no continuous liquid phase was formed, followed by rapid damage of C/SiC substrate. The results of this work can provide theoretical guidance and research ideas for the design and application of laser protective materials.

A Ni(TFA)2-catalyzed ortho-trifluoromethylation of 8-aminoquinoline derivatives was developed by acyl-directed C–H functionalization. A series of 7-trifluoromethylquinolinamine derivatives were originally obtained with moderate to excellent yields by using TMSCF3 as the trifluoromethylation reagent under mild conditions. In addition, the reaction mechanism is proposed and proved by the related experiment.

A new protocol for the Cu(OAc)2-mediated cyanation of arenes using benzimidazole as the directing group with 2-(4-methylpiperazin-1-yl)acetonitrile as the cyano source was developed. A series of cyano derivatives were facilely and conveniently obtained in moderate to good yields by using this method. The C–H activation catalytic system was originally applied to the C(sp2)–H cyanation of the aryl/heteroaryl to synthesize 2-(1H-benzo[d]imidazol-2-yl)aryl nitriles. There were 19 new compounds in the synthesized 20 cyanide products. In this reaction, 2-(4-methylpiperazin-1-yl)acetonitrile as the cyano source was originally employed in the C(sp2)–H cyanation of the arenes. In addition, a fluorescent material 5a was obtained by derivative reactions of the obtained cyanide product 3.

In this paper, the 12k T-700TM Multiaxial-Warp-Knitting–Needle (MWK–N) C/SiC composite and pin were designed and fabricated using the isothermal chemical vapor infiltration (ICVI) method. The composite’s microstructure and mechanical properties were examined by subjection to tensile and interlaminar shear tests. Three types of double-shear tests were conducted for C/SiC pins, including shear loading perpendicularly, along, and at 45° off-axial to the lamination. The fracture surface of the tensile and shear failure specimens was observed under scanning electronic microscope (SEM). The relationships between the composite’s microstructure, mechanical properties, and damage mechanisms were established. The composite’s average tensile strength was σuts = 68.3 MPa and the average interlaminar shear strength was τu = 38.7 MPa. For MWK–N–C/SiC pins, the double-shear strength was τu = 76.5 MPa, 99.7 MPa, and 79.6 MPa for test types I, II, and III, respectively. Compared with MWK–C/SiC pins, the double-shear strength of MWK–N–C/SiC pins all decreased, i.e., 26.7%, 50.8%, and 8% for test types I, II, and III, respectively. The MWK–N–C/SiC composite and pins possessed high interlaminar shear strength and double-shear strength, due to the needled fiber in the thickness direction, low porosity (10–15%), and high composite density (2.0 g/cm3).

We demonstrated an optical fiber sensor based on a cascaded fiber Fabry-Perot interferometer (FPI)-regenerated fiber Bragg grating (RFBG) for simultaneous measurement of temperature and strain under high temperature environments. The FPI is manufactured from a ∼74 µm long hollow core silica tube (HCST) sandwiched between two single mode fibers (SMFs). The RFBG is inscribed in one of the SMF arms which is embedded inside an alundum tube, making it insensitive to the applied strain on the entire fiber sensor, just in case the temperature and strain recovery process are described using the strain-free RFBG instead of a characteristic due-parameter matrix. This feature is intended for thermal compensation for the FPI structure that is sensitive to both temperature and strain. In the characterization tests, the proposed device has exhibited a temperature sensitivity ∼ 18.01 pm/°C in the range of 100 °C - 1000 °C and excellent linear response to strain in the range of 300 °C - 1000 °C. The measured strain sensitivity is as high as ∼ 2.17 pm/µɛ for a detection range from 0 µɛ to 450 µɛ at 800 °C, which is ∼ 1.5 times that of a FPI-RFBG without the alundum tube.

A series of π-conjugated molecules based on diimidazolepyridine derivatives were designed, synthesized by Suzuki coupling reaction and cyclization reaction and characterized. Diimidazolepyridine motif as the main structure could improve the thermal stability and optical property of the materials. All of the target compounds exhibited good thermal stabilities with T d values in the range of 416–490 °C. These compounds showed steady blue light emissions in the range of 424–478 nm and high quantum yields (0.33–0.69) in solution. Especially, compound 4f achieved appropriate energy gap (E g = 2.69 eV) and high fluorescence quantum yields (Φ f = 0.69) because of introducing electron-donating group, such energy gap was helpful to electronic transfer and transport. The materials have great potential for good electronic-transmission materials in OLEDs.

A visible-light-induced decarboxylation coupling/intramolecular cyclization is reported. The one-pot synthesis system provides mild, efficient, and atom economical access to the synthesis of 4-aryl-2-quinolinone derivatives. It is notable that the necessary oxidant in the traditional decarboxylation coupling is replaced by the visible-light irradiation in this paper. In addition, the HBV inhibitor is synthesized by the one-pot synthesis system in an atom economical manner.

A new protocol for Cu(TFA)2-catalyzed picolinamido-directed C8-H cyanation of naphthalene derivatives with benzoyl cyanide as cyano source was developed. A series of 8-cyano-1-(picolinamido)naphthalene derivatives were facilely and conveniently obtained in moderate to good yields by using this method. There were 10 new compounds in the synthesized 22 cyanide products. In this reaction, benzoyl cyanide as cyano source was originally employed to the C(sp2)-H cyanation of the arenes, and the picolinamide moiety as the directing group played a critical role in cyanation of naphthalenes.

A bidentate-chelation assistant palladium-catalyzed direct C-H cyanation of picolinamides with TMSCN is described. The reaction of various derivatives gave the corresponding cyanated products in moderate to good yields under mild conditions. In addition, the cyanated product could transform into some valuable functional groups in good yields. Copyright © 2016 John Wiley & Sons, Ltd.

In this work, a simple fiber Fabry-Perot air-cavity interferometer (FPI) is formed by splicing a 246 μm long hollow core silica tube (HCST) between two single mode fibers (SMFs). In the thermal characterization test, the FPI exhibits limited linear range up to 700 °C in the first cycle of isochronal annealing treatment from room temperature up to 1000 °C. However, after a series of repeated isochronal thermal annealing, the temperature response of the proposed FPI is extended further to 1000 °C with a good thermal repeatability. Meanwhile, the annealed FPI has linear axial strain sensitivities up to 1000 μe from room temperature up to 800 °C. The proposed fiber structure is a potential sensor for high-temperature or stress measurement in aeronautical or metallurgical fields.

Atomic oxygen (AO) is considered the most erosive particle to spacecraft materials in low earth orbit (LEO). Carbon fiber, carbon/carbon (C/C), and some modified C/C composites were exposed to a simulated AO environment to investigate their behaviors in LEO. Scanning electron microscopy (SEM), AO erosion rate calculation, and mechanical property testing were used to characterize the material properties. Results show that the carbon fiber and C/C specimens undergo significant degradation under the AO bombing. According to the effects of AO on C/C-SiC and CVD-SiC-coated C/C, a condensed CVD-SiC coat is a feasible approach to protect C/C composites from AO degradation.

The advanced high temperature composites have been considered as structural or functional material in complex and harsh environments, which usually comprise of various oxidizing particles such as molecular oxygen (MO), atomic oxygen (AO) and molecular water. This study aimed to investigate C/SiC behaviors in single factor or combination environments. In the MO oxidation, an inert surface is formed on SiC. At the AO oxidation, the Si of SiC is preferentially etched off leaving a certain depth of C layer on the sample. Two types of coupled oxidations defined as mode A (first MO and then AO oxidation), and mode B oxidation (first AO and then MO oxidation) were investigated systematically in this study, and found that the prior oxidative effect majorly determined the corresponding coupled oxidation behavior. From microscopic observation and fractural test, the mode B oxidation induced a more serious degradation upon the material than that of the mode A, which is illustrated by the proposed erosion mechanisms for the modes A and B.

A T300 carbon fiber and a SiC-coated C/SiC composite made from the same fiber were studied in atomic oxygen environment. The carbon fiber shows significant degradation while the erosion rate of SiC-coating of C/SiC is about 50 times lower. Evidence shows that Si is preferentially etched from the SiC surface. And XPS information showed that amorphous carbon and diamond-like carbonare periodically generated on the tested composite surface. Statistical analysis shows that the C/SiC specimens have no significant change in flexural properties after 1-year fluence AO treatment.

Tensile test was used upon a 3D-C/SiC composite under air or nitrogen atmosphere to characterize its mechanical behaviors and associated damage evolutions from room to cryogenic temperatures. The tensile strength relatively weakened most at −40 °C, however, that is recovered as temperature decreasing to −100 °C. The mismatch of coefficient of thermal expansions between carbon fiber and SiC matrix plays a role in this mechanical response. An interfacial damage model based on microscopic observation is proposed. Finite element method is used to analysis C/SiC deformations. Some generalizations were provided under the cryogenic environment.

We have experimentally demonstrated an optical fiber Mach-Zehnder interferometer (MZI) structure formed by a few-mode photonic crystal fiber (PCF) for curvature measurement and inscribed a fiber Bragg grating (FBG) in the PCF for the purpose of simultaneously measuring temperature. The structure consists of a PCF sandwiched between two multi-mode fibers (MMFs). Bending experimental results show that the proposed sensor has a sensitivity of −1.03 nm/m−1 at a curvature range from 10 m−1 to 22.4 m−1, and the curvature sensitivity of the embedded FBG was −0.003 nm/m−1. Temperature response experimental results showed that the MZI’s wavelength, λa, has a sensitivity of 60.3 pm/°C, and the FBG’s Bragg wavelength, λb, has sensitivity of 9.2 pm/°C in the temperature range of 8 to 100 °C. As such, it can be used for simultaneous measurement of curvature and temperature over ranges of 10 m−1 to 22.4 m−1 and 8 °C to 100 °C, respectively. The results show that the embedded FBG can be a good indicator to compensate the varying ambient temperature during a curvature measurement.

A kind of photoelectric detection method based on black-white bar code and modern photoelectric detection technology is put forward for measuring the displacement deviation of printing press cylinder surface in high-speed motion state. A high-precision noncontact photoelectric detection system is designed and implemented. The accurate testing bar code cooperates with the high-speed A/D mixed signal processing system, the position deviation of every point on the circumference of the printing press system in high-speed measurement state can be obtained, low measurement error which is in the range of ±10μm. The given experiment results indicate that: the system has stable working condition, high measurement speed, and the system provide a new kind of monitoring technology to effectively deal with the overprint deviation.