固体推进剂燃烧波结构研究

设计了一套分析燃烧波结构的数值计算方法,可以利用热偶数据有效地分析均质推进剂固相反应的细节,为了解固体推进剂机理提拱了一种重要的手段;提出了均质推进剂也没有明显的固气界面的观点,因而也无表面温度可言;设计了固相反应热计算模型,提出了固相反应机理的观点,并指出压力不同固相反应机理基本相同,但固相放热程度不同;提出Π型热偶不宜测量非均质推进剂燃烧波结构的观点。     

Influence of the elastic mismatch on the Hertzian cone crack path in ceramic bilayers

Contact damage is a key aspect in the structural integrity of ceramics, particularly ceramic coatings and multilayers that may have an elastic mismatch. An understanding of the critical load and trajectories of the crack produced by contact loads in such materials is valuable to characterize the damage tolerance and improve their reliability. In this work, the Hertzian cone crack initiation and propagation in brittle bilayers has been studied by FEM and verified by experimental observations. It was concluded that the elastic mismatch affects the crack initiation position and critical load for cone cracking. Critical loads are lower in bilayers than in monolithic materials. Cone crack trajectory and the corresponding fracture energy release rate are also affected by the elastic mismatch, which thus influences the damage tolerance of the system.     

固体推进剂高过载冲击动态力学性能研究

综述了近年来固体推进剂受过载冲击时动态学响应研究的各种方法,分析对比了各种研究方法的优劣,讨论了未来固体推进剂受冲击载荷时动态力学性能研究的方向。     

Microstructure and mechanical properties of Mo0.9Cr0.1AlB solid solution

In this study, Mo_0.9Cr_0.1AlB solid solution ceramic bulks were prepared from the element powder mixtures using hot pressing sintering method. Compared with MoAlB ceramics, the grains of as-prepared Mo_0.9Cr_0.1AlB were refined obviously. The lattice constants of Mo_0.9Cr_0.1AlB were confirmed to be a = 3.205 Å, b = 13.999 Å and c = 3.098 Å. The density of Mo_0.9Cr_0.1AlB was lower than that of MoAlB due to the incorporation of Cr element. In addition, the effect of doping Cr element on the comprehensive mechanical properties was studied as well. The hardness and compressive strength were improved significantly. In comparison with MoAlB ceramic, the improvement of mechanical properties could be attributed to solid solution strengthening and grain refinement.     

The effect of room temperature and high temperature exposure on the elastic modulus, hardness and fracture toughness of glass ceramic sealants for solid oxide fuel cells

The reliable operation of solid oxide fuel cell stacks (SOFCs) depends strongly on the structural integrity of the sealing material. Indentation testing is used to determine the mechanical properties of glass-ceramic sealants typically used for solid oxide fuel cell stacks, in particular for the evaluation of elastic modulus, hardness and fracture toughness. Different sealing materials partly with reinforcement by metallic or ceramic filler (particles or short fibers) are tested. The materials are tested after the joining procedure and after additional annealing at operation temperatures to test the effect of further crystallization that might take place. Furthermore, the effect of environmentally enhanced slow crack growth at low temperatures in water saturated atmosphere is investigated. Finally, self-healing effects of the glass ceramic materials with and without pre-annealing at typical operation temperatures are considered.     

Analyzing indentation behavior of LaGaO3 single crystals using sharp indenters

In this work, the mechanical properties of (1 0 0) and (0 0 1) oriented LaGaO₃ single crystals have been studied using sharp indenters. Vickers hardness values for both the (1 0 0) and (0 0 1) samples were found to be in the same range (8 GPa). The values for the indentation fracture toughness (K_R) from Vickers indentation on the (1 0 0) samples were determined to be 0.8 ± 0.2 MPa m^1/2. Different crack lengths, implying a strong anisotropy in the indentation fracture toughness values, were observed in the two mutually perpendicular directions in the indentations on the (0 0 1) samples. These measurements led to estimates of 0.5 ± 0.1 and 1.3 ± 0.3 MPa m^1/2 for the two different sets of cracks on the (0 0 1) samples. In situ nanoindentation inside the SEM using a cube-corner indenter has also been used for studying the indentation fracture response of these samples.     

Slow-crack-growth and indentation damage in calcium magnesium aluminosilicate (CMAS) glass from desert sand

Desert sand from a Middle East country was melted into calcium magnesium aluminosilicate (CMAS) glass. Its chemical composition was analyzed to be 25.2CaO-2.6MgO-8.2Al₂O₃-59.8SiO₂-1.6Fe₂O₃-1.5K₂O weight % using inductively coupled plasma-atomic emission spectrometry. The CMAS glass powder was hot pressed into billets. Slow-crack-growth (SCG) and indentation deformation/fracture of the CMAS glass was investigated. The SCG susceptibility parameter (n) was found to be 25 ± 3 which is within a range of n = 15–35 that has been observed in many silicate glasses and glass ceramics. A similarity in indentation hardness and toughness was found between the CMAS glass and the low-silica content (50–70%) glasses. However, an exception was that significant lateral cracking was typified in the CMAS glass, as quantified via stress analysis in the vicinity of an indent.     

Analysis of spherical indentation of porous ceramic films

Spherical indentation of a porous brittle La_0.6Sr_0.4Co_0.2Fe_0.8O₃ ceramic film (porosity = 39.7%) on a stiffer elastic Ce_0.9Gd_0.1O_1.95 substrate is simulated by finite element modelling incorporating the Gurson model to account for densification. The simulated load-displacement curves, apparent elastic modulus E, indentation hardness H and densification profile are all in good agreement with experimental data for the film. The simulations show that E and H are not sensitive to film residual stress. However E is very sensitive to the indent depth-film thickness ratio f, although H is less so for f < 0.3. The simulated dependence of E and H on f are highly consistent with experimental data, supporting the extrapolation of E and H measured for 0.1 < f < 0.3, to zero depth for good estimates of the film-alone properties. The inclusion of densification in the simulation makes only a small difference to E, but has a large influence on H as a function of indentation depth.     

Preparation and characterization of novel nonstoichiometric magnesium aluminate spinels

Magnesium aluminate spinel is of great importance for nuclear industry, and its structure, showing a great impact on properties, is sensitive to the composition. In order to explore the stoichiometric effect on structure and properties of spinels, several different spinel compositions with MgO·nAl₂O₃ (n?=?0.5–2.4) were synthesized via solid state reaction. Synthetic samples were characterized by X-ray diffraction, scanning electron microscope and nanoindentation tests. The results of XRD and SEM indicate that the single-phase magnesia alumina spinels have been prepared successfully for the first time ranging from n?=?0.667 to n?=?1.5, which is beyond the previous reported ranges of n$\ge$ 0.91. The hardness and modulus decrease with increasing n, implying further that the nonstoichiometric spinel crystal structures are likely to exhibit superior mechanical properties.     

固体推进剂固相组分的混合研究

研究了含固体组分的两相体系固体推进剂混合过程的特点。用固体组分的浓度、粒径及其分布等参量研究分析了改性双基推进剂代料的混合特点。根据实验结果，认为改性双基推进剂的混合过程属分散混合。固体推进剂的性能将取决于分散混合后固体颗粒的尺寸。     

Mechanical properties of BaCe0.65Zr0.2Y0.15O3-δ – Ce0.85Gd0.15O2-δ dual-phase proton-conducting material with emphasis on micro-pillar splitting

BaCe_0.65Zr_0.2Y_0.15O_3-δ – Ce_0.85Gd_0.15O_2-δ (BCZ20Y15-GDC15) dual-phase material revealed potential for H₂ production technologies due to its exceptional H₂ permeation and chemical resistance. In this article, mechanical properties of BCZ20Y15-GDC15 dual-phase material were investigated to evaluate the mechanical behavior and develop strategies to warrant structural stability. Elastic modulus, hardness and fracture toughness values were studied using different indentation-based methods. The fracture experiments at different length-scales both revealed that the introduction of GDC15 makes the material tougher, facilitating the further design of robust and reliable components.     

Mechanical properties of BaCe0.65Zr0.2Y0.15O3-δ proton-conducting material determined using different nanoindentation methods

Proton-conducting membranes have great potential for applications in proton conducting membrane reactors for the production of commodity chemicals or synthetic fuels as well as for use in solid oxide fuel cells. However, to ensure the long-term structural stability under operation relevant conditions, the mechanical properties of the membrane materials need to be characterized. BaCe_0.65Zr_0.2Y_0.15O_3-δ is of particular interest due to its proven functional properties. In this research work, the mechanical properties of BaCe_0.65Zr_0.2Y_0.15O_3-δ were determined on different length scales using different methods including impulse excitation, indentation testing, and micro-pillar splitting. A detailed microstructural analysis of pillars revealed that irregular results are caused by pores causing crack deflection and complex crack patterns.