A first step toward a multi-scale and multi-physic model --a virtual material-- for self-healing ceramic matrix composites is presented. Each mechanism --mechanical, chemical-- that act on the material's lifetime at a given scale --fibre, yarn-- is introduced in a single modeling framework, aimed at providing powerful prediction tools.
CaCu_3Ti_4O_12/CaTiO_3 Composite Dielectrics: A Ba/Pb-free Ceramics with High Dielectric Constants
我们测量了Ca $_{1+x}$ Cu $_{3-x}$ Ti $_4$ O $_{12}$的介电性能（$x$ = 0、0.1、0.5、1、1.5、2、2.9和3），并发现Ca $_2$ Cu $_2$ Ti $_4$ O $_{12}$（CaCu $_3$ Ti $_4$ O $_{12}$和CaTiO $_3$的复合物）在220 - 300 K范围内，在100 kHz以下，具有1800的高介电常数和0.02的低耗散因子。这些是可比的（或甚至优于）的Pb/Ba基陶瓷，这可能是由于CaCu $_3$ Ti $_4$ O $_{12}$颗粒的表面上的CaTiO $_3$的阻挡层。本文报道的复合介电陶瓷是环境友好的，因为它们不含Ba/Pb。
Multiferroic composites with the composition (1-x) BaTi0.8Sn0.2O3 - (x) La0.5Ca0.5MnO3 (x =0, 0.3, 0.5, 0.7, 0.9 and 1) were prepared by sol-gel techniques. Rietveld refinements of the composites with 0-3 and 3-0 type connectivities exhibit the formation of pure phases and confirm the fraction of the composite samples. It was found that the composites grain size decreases slightly with increasing the La0.5Ca0.5MnO3 content. Magnetic measurements of the composite ceramics exhibit a gradual increase in saturation and remanent magnetization with increasing La0.5Ca0.5MnO3 content. Dielectric data …
This study of highly accelerated lifetime tests of SrTiO$_3$, a model semiconducting oxide, is motivated by the interest in reliable multilayer ceramic capacitors and resistance-switching thin-film devices. Our analytical solution to oxygen-vacancy migration under a DC voltage -- the cause of resistance degradation in SrTiO$_3$ -- agrees with previous numerical solutions. However, all solutions fail to explain why degradation kinetics feature a very strong voltage dependence, which we attribute to the nucleation and growth of cathode-initiated fast-conducting needles. While they have no color …
The diamond-SiC composite has a low density and the highest possible speed of sound among existing materials except for the diamond. The composite is synthesized by a complex exothermic chemical reaction between diamond powder and liquid Si. This makes it an ideal material for protection against impact loading. Experiments show that a system of patterns is formed at the diamond-SiC interface. Modeling of reaction-diffusion processes of composite synthesis proves a formation of ceramic materials with a regular (periodic) interconnected microstructure in a given system. Composite material with i…
The increasing demand for more efficient and environmental-friendly gas turbines has driven the development of new strategies for material development. SiC/SiC ceramic matrix composites (CMCs) can fulfil the stringent requirements; however, they require protection from the operating environment and debris ingested during operation. Environmental barrier coatings (EBCs) are a protective measure to enable the CMCs to operate under harsh conditions. EBC-coated CMCs will enable an increased efficiency and reduced pollutant and CO2 emissions. In this review, the fundamentals of SiC/SiC ceramic matr…
Self-organization of current channels percolation in polymer composite films with thermal nonlinearity of conductivity: comparison of experimental data and computer simulations
Soft materials capable of large inelastic deformation play an essential role in high-performance nacre-inspired architectured materials with a combination of stiffness, strength and toughness. The rigid "building blocks" made from glass or ceramic in these architectured materials lack inelastic deformation capabilities and thus rely on the soft interface material that bonds together these building blocks to achieve large deformation and high toughness. Here, we demonstrate the concept of achieving large inelastic deformation and high energy dissipation in soft materials by embedding microstruc…
We investigate the role of microstructural bridging on the fracture toughness of composite materials. To achieve this, a new computational framework is presented that integrates phase field fracture and cohesive zone models to simulate fibre breakage, matrix cracking and fibre-matrix debonding. The composite microstructure is represented by an embedded cell at the vicinity of the crack tip, whilst the rest of the sample is modelled as an anisotropic elastic solid. The model is first validated against experimental data of transverse matrix cracking from single-notched three-point bending tests.…
