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81.
《Journal of the European Ceramic Society》2017,37(2):523-529
Carbon/Carbon (C/C) composites derived from the thermoplastic polymer polyetherimide (PEI) were pyrolized up to 1000 °C, subsequently carbonized in inert atmosphere up to 2200 °C and afterwards infiltrated with liquid silicon. The investigation of fibers and matrix with Raman microspectroscopy revealed, that an increased carbonization temperature leads to an increased carbon order as well as an incipient stress-induced graphitization of the carbon matrix close to the fiber surfaces at 2200 °C. The derived C/C-SiC samples show a maximum flexural strength of 180 MPa with C/C composites treated at 2000 °C and monotonically increasing Young’s moduli ranging from 49 GPa with C/C preforms treated at 1600 °C up to 59 GPa after carbonization at 2200 °C. The carbon fiber strength was evaluated with a single fiber tensile test, which showed a monotonically increased Young’s modulus and a decrease of the strength after carbonization at 2200 °C. 相似文献
82.
Fanyu Kong Xiaodong He Qianqian Liu Xinxin Qi Yongting Zheng Rongguo Wang Yuelei Bai 《Ceramics International》2018,44(10):11591-11596
The presented work compared the etching behavior between combustion synthesized Ti3AlC2 (SHS-Ti3AlC2) and pressureless synthesized Ti3AlC2 (PLS-Ti3AlC2). Because the former had a more compact structure, it was harder to be etched than PLS-Ti3AlC2 under the same conditions. When served as anode material for Li-ion batteries, SHS-Ti3C2 showed much lower capacity than PLS-Ti3C2 at 1?C (52.7 and 87.4?mAh?g?1, respectively) due to the smaller d-spacing. Furthermore, Potentiostatic Intermittent Titration Technique (PITT) was used to determine the Li-ion chemical diffusion coefficient () of Ti3C2 in the range of 10?10 ??10?9 cm2 s?1, indicating that Ti3C2 could exhibit an excellent diffusion mobility for Li-ion. 相似文献
83.
《International Journal of Impact Engineering》1996,18(4):383-402
The dynamic plastic deformation of simply supported and clamped circular plates to a central pressure pulse is investigated theoretically. The plate material is assumed to be rigid-perfectly plastic and to obey a yield criterion which retains the transverse shear force as well as bending moments. Various patterns of deformation are obtained for a wide range of parameters which combine plastic bending and shear sliding. The dependence of the final central deflection and shear displacement on the relative shear strength, the load magnitude and the loaded area are discussed for a short duration pressure pulse. The influence of boundary conditions on shear and bending deformation is examined. 相似文献
84.
85.
《Journal of the European Ceramic Society》2000,20(14-15):2655-2659
The preparation and characterization of precursor derived Si–B–C–N ceramics with similar Si/C/N ratios but variable boron content are reported. The polymeric precursors were prepared via hydroboration of poly(methylvinylsilazane) using different BH3·SMe2/polymer stoichiometries. High temperature thermogravimetric analysis of as-pyrolysed ceramics as well as XRD studies of post-annealed samples display a retarding effect of boron on both crystallization of SiC and Si3N4 and stabilization of crystalline β-Si3N4. 相似文献
86.
《Composites Part A》2001,32(11):1603-1612
An investigation of the resistance welding between carbon fibre (CF)-reinforced polyetherimide (PEI) and CF-reinforced epoxy laminates is presented. A three-dimensional transient finite element model (FEM) featuring heat transfer, consolidation and thermal degradation was used for simulating the process. A hybrid interlayer made of a glass fibre (GF) fabric essentially impregnated with PEI on one side and with epoxy resin on the other side was produced to provide mechanical interlocking between the thermoplastic (TP) and the thermosetting (TS) systems. The ‘optimal’ resistance welding time based on the maximum lap shear strength (LSS) was determined for three power levels and correlated to the time required to achieve bonding predicted by the FEM. Consolidation quality and failure mechanisms were discussed in relation with processing parameters. Experimental and simulated processing windows were constructed and correlated to each other. However, thermal degradation as predicted by the model did not correlate to a reduction in performance of the joint. 相似文献
87.
《Synthetic Metals》1999,107(2):123-127
The (EDOEDT)4Hg3Br8 radical cation salt of 4,5-ethylenedioxy-4′,5′-ethylendithiotetrathiafulvalene has been synthesized as a mixture of two crystalline phases. Phase 1 is characterized by a semiconducting type of conductivity and the ESR peak-to-peak linewidth equal to 70–95 G. Phase 2 exhibits metal-like conductivity down to 105 K and the ESR peak-to-peak linewidth of 35–54 G. The X-ray crystal structure analysis of phase 1 reveals three crystallographically distinct donor molecule layers in the asymmetric part of the unit cell, one of them being composed of the stacks and the two others are built of mutually perpendicular tetramers. The polarized reflectance spectra of phase 1 are discussed. 相似文献
88.
Yehong Cheng Ping Hu Shanbao Zhou Xinghong Zhang Wenbo Han 《Journal of the European Ceramic Society》2018,38(11):3752-3758
Graphene is one of the important candidates in ceramic toughening due to its outstanding physical and chemical properties. For the weak interface toughening of large-diameter graphene sheet and alleviation of the interfacial reaction between ceramic precursors and graphene sheets during high-temperature pyrolysis, ZrC–SiC?Graphene composite was synthesized via a facile technology of infiltrating ceramic slurry instead of ceramic precursor into macroporous graphene network and spark plasma sintering. The incorporation of the graphene network improved fracture toughness, critical crack size, and fracture energy of ZrC–SiC ceramic. The multiple length-scale toughening mechanisms of ZrC–SiC?Graphene composite include the macroscopic toughening mechanism of crack deflection and bifurcation and the micro toughening mechanism of graphene bridging, ceramic micro zone tearing, graphene pull-out, graphene and ceramic brick slipping. 相似文献
89.
《International Journal of Hydrogen Energy》2019,44(33):18319-18329
The deposition of Cr on cathode materials in solid oxide fuel cells (SOFCs) is complex and impacted by multiple factors. In this report, a mathematical model based on electrochemical Cr-poisoning mechanism is developed to investigate the correlation between gas transport and Cr deposition in porous strontium doped lanthanum manganite/yttria stabilized zirconia (LSM/YSZ) cathode. Time evolution of cathode pore size and three phase boundaries (TPBs) in different cathode regions with Cr2O3 deposition is analyzed. The distribution of local current density in the cathode, the lifetime, the concentration polarization, the activation polarization and area specific resistance of SOFC cathodes are subsequently assessed quantitatively. Three types of LSM/YSZ cathode structures with uniform, ascending and descending gradient pore-size distributions are compared. The results show that uniform pore distribution contributes to the best performance when all the cathodes own TPBs with the same initial length. 相似文献
90.
《Ceramics International》2020,46(15):23760-23772
Predictive models are an important tool in the design and optimization of ballistic shields. Indeed, several authors in the literature have developed numerical models for simulating high-velocity impact on ceramic-based ballistic shields which are based on the finite element method. Element erosion is usually implemented in finite element models simulating impact to remove excessively distorted elements but, it leads to energy loss, which in turns may lead to the production of incorrect results. Due to the absence of a fixed mesh, the smoothed particle hydrodynamics method is well suited for large deformation problems, overcoming the limitations of the finite element method. On the other hand, the smoothed particle hydrodynamics method is computationally more expensive than the finite element method. Thus, a numerical model combining the lower computational cost of finite elements and the capability of smoothed particle hydrodynamics of dealing with crack formation and fracturing would be an interesting solution for the simulation of high-velocity impact on ceramics. The aim of this work is therefore to develop a finite element coupled to smoothed particle hydrodynamics numerical model for the simulation of high-velocity impact on ceramic-based ballistic shields. High-velocity impact tests were performed on Al2O3 tiles and the experimental results were used for the calibration of the numerical models; furthermore, high-velocity impact test were performed on multilayer targets with Al2O3 front layer and AA6061-T6 backing layer for the validation of the numerical models. This study proved that this approach is more appropriate for the simulation of the response of ceramic materials rather the common finite element model. 相似文献